Title of Invention	TREATMENT METHOD FOR OPTICAL FIBER
Abstract	A treatment method for an optical fiber (2) including accommodating an optical fiber inside a treatment chamber (1a); introducing a deuterium containing gas into the treatment chamber (1a); and in a deuterium treatment step, exposing the optical fiber (2) to atmosphere of the deuterium containing gas. In the deuterium treatment step, a deuterium concentration D in the treatment chamber (1a) during the deuterium treatment is calculated from an initial value A of a deuterium concentration in the deuterium containing gas inside the treatment chamber (1a), a concentration B of oxygen in an ambient atmosphere of the treatment chamber (1a), and a concentration C of oxygen in the deuterium containing gas inside the treatment chamber (1a), and the deuterium concentration in the treatment chamber (1a) is controlled based on the deuterium concentration D calculated. Other gases such as hydrogen containing gas or nitrogen containing gas may also be used according to the invention.

Title of Invention

TREATMENT METHOD FOR OPTICAL FIBER

Abstract

A treatment method for an optical fiber (2) including accommodating an optical fiber inside a treatment chamber (1a); introducing a deuterium containing gas into the treatment chamber (1a); and in a deuterium treatment step, exposing the optical fiber (2) to atmosphere of the deuterium containing gas. In the deuterium treatment step, a deuterium concentration D in the treatment chamber (1a) during the deuterium treatment is calculated from an initial value A of a deuterium concentration in the deuterium containing gas inside the treatment chamber (1a), a concentration B of oxygen in an ambient atmosphere of the treatment chamber (1a), and a concentration C of oxygen in the deuterium containing gas inside the treatment chamber (1a), and the deuterium concentration in the treatment chamber (1a) is controlled based on the deuterium concentration D calculated. Other gases such as hydrogen containing gas or nitrogen containing gas may also be used according to the invention.

Full Text	TREATMENT METHOD FOR OPTICAL FIBER BACKGROUND OF THE INVENTION Field of the Invention The invention relates to a treatment method for an optical fiber. Description of Related Art After rendering optical fibers into a cable and laying the optical fiber cable, the transmission loss in a wavelength band of about 1400 nm of the optical fiber increases, and the transmission characteristics of the optical fiber degrade. In order to inhibit this degradation of the optical fiber transmission characteristics, a treatment method for optical fibers is applied in which an optical fiber is exposed to hydrogen or deuterium in advance. However, when carrying out a treatment method in which the optical fiber is exposed to hydrogen (hydrogen treatment), there is a problem in that the initial transmission loss of the optical fiber in a wavelength region of about 1383 nm increases. In contrast, when carrying out a treatment method in which the optical fiber is exposed to deuterium (deuterium treatment), no such problem occurs. Thus, the hydrogen treatment or the deuterium treatment must be selected and applied depending on the object Various methods have been proposed for applying a deuterium treatment to an optical fiber. In one method (see, for example, Japanese Unexamined Patent Application, First Publication No. 2003-137580), a gas that contains deuterium gas (hereinbelow, referred to as a "deuterium containing gas") continuously flows into a scalable treatment chamber, and the atmosphere in the treatment chamber is replaced by the deuterium containing gas. In another method (see, for example, Japanese Unexamined Patent Application, First Publication No. 2004-226979), after decreasing the pressure inside the treatment chamber, the inside of the treatment chamber is filled with the deuterium containing gas, and thereby the atmosphere inside the treatment chamber is replaced by the deuterium containing gas. In the latter method, recovery of the deuterium containing gas is possible. In addition, the hydrogen test method stipulated in IEC60793-2-50 is an example of a method for applying a hydrogen treatment to an optical fiber. In this hydrogen test method, an optical fiber is exposed to 1% hydrogen gas atmosphere or 100% hydrogen gas atmosphere at room temperature until the transmission loss at a wavelength of 1240 nm is equal to or greater than 0.03 dB/km. However, in this hydrogen test method, specific conditions of the treatment methods (treatment conditions) are not stipulated. In the case in which a deuterium treatment is applied to an optical fiber, when using the method in which the deuterium containing gas continuously flows into the treatment chamber, the treatment is applied while eliminating deuterium containing gas until the inside of the treatment chamber reaches a predetermined deuterium concentration. Thus, each time the deuterium treatment is applied, it is possible to maintain a predetermined deuterium concentration in the treatment chamber. However, in order to increase the production efficiency, the treatment must be applied at one time to an optical fiber having a long length, and accompanying this, the volume of the treatment chamber for applying the treatment to the optical fiber becomes large. Depending on how large the volume of the treatment chamber becomes, the amount of deuterium containing gas necessary for replacing the atmosphere in the treatment chamber increases, and thereby the cost also increases. In contrast, when using the method in which the treatment chamber is filled with deuterium containing gas after the pressure in the treatment chamber has been reduced, because creating a complete vacuum inside the treatment chamber is difficult, air that remains in the treatment chamber from each treatment mixes with the deuterium containing gas. As the number of treatments increases, the deuterium concentration in the recovered deuterium containing gas becomes low. When the deuterium concentration in the deuterium containing gas becomes low, there are also concerns in mat not only is a long time required until the deuterium has sufficiently permeated the optical fiber, but also that the deuterium treatment may become inadequate. Thus, in order to prevent defective deuterium treatments, it is necessary to monitor the deuterium concentration when applying the deuterium treatment to the optical fiber. An inflammable gas detector, an optical gas densitometer, or the like are examples of devices that measure the deuterium concentration. When using an air-based deuterium containing gas, it is possible to measure the deuterium concentration by such measuring devices. Note that here, any gas whose composition ratios are similar to those of the atmosphere is referred to as "air". However, when air is mixed into the deuterium containing gas and the composition ratios of the gas differ from those of the atmosphere, it becomes impossible to measure the deuterium concentration correctly by using the measuring devices described above. In a combustion densitometer such as an inflammable gas detector, deuterium is combusted, and the deuterium concentration is calculated from the amount of heat generated during the combustion. Thus, in the case in which, instead of air, an inert gas such as nitrogen, argon, helium, or the like serves as the base, the combustion becomes poor, and thus the concentration cannot be correctly measured. In addition, in an optical densitometer such as an optical gas densitometer, the deuterium concentration is calculated from the relative index of refraction of the deuterium containing gas. Thus, in the case in which the composition ratio of the gas that serves as the base fluctuates, it is not possible to measure the deuterium concentration correctly. In addition, it is possible to measure the deuterium concentration by analyzing the molecules of the deuterium gas included in the deuterium containing gas. However, this is not preferable because the measurement takes time, and thus the production costs drastically increase. SUMMARY OF THE INVENTION In consideration of the problems described above, an object of the invention is to provide a treatment method for an optical liber that can correctly control a deuterium concentration even when a gas that serves as abase of a deuterium containing gas is a gas other than air, and a composition ratio of a gas that serves as a base fluctuates. The invention provides a treatment method for an optical fiber, including: accommodating an optical fiber inside a treatment chamber, introducing a deuterium containing gas into the treatment chamber; and in the deuterium treatment step, exposing the optical fiber to atmosphere of the deuterium containing gas, wherein, in the deuterium treatment step, a deuterium concentration D in the treatment chamber during the deuterium treatment is calculated from an initial value A of a deuterium concentration in the deuterium containing gas inside the treatment chamber, a concentration B of oxygen in an ambient atmosphere of the treatment chamber, and a concentration C of oxygen in the deuterium containing gas inside the treatment chamber, and the deuterium concentration in the treatment chamber is controlled based on the deuterium concentration D calculated. In the treatment method for an optical fiber, the deuterium concentration D in the treatment chamber during the deuterium treatment step can be calculated using EQ. 1 below: D-Ax(l-C/B) EQ. 1 where A indicates the initial value of the deuterium concentration in the deuterium containing gas inside the treatment chamber, B indicates the concentration of oxygen in the ambient atmosphere (air) of the treatment chamber, and C indicates the concentration of oxygen in the deuterium containing gas inside the treatment chamber. The invention further provides a treatment method for an optical fiber, including: accommodating an optical fiber inside a treatment chamber; introducing a hydrogen containing gas into the treatment chamber, and in a hydrogen treatment step, exposing the optical fiber to atmosphere of the hydrogen containing gas, wherein, in the hydrogen treatment step, a hydrogen concentration 5 in the treatment chamber during the hydrogen treatment is calculated from an initial value a of a hydrogen concentration in the hydrogen containing gas inside the treatment chamber, a concentration β of oxygen in an ambient atmosphere of the treatment chamber, and a concentration γ of oxygen in the hydrogen containing gas inside the treatment chamber, and the hydrogen concentration in the treatment chamber is controlled based on the hydrogen concentration δ calculated. In the treatment method for an optical fiber, the hydrogen concentration 6 in the treatment chamber during the hydrogen treatment step is calculated using EQ. 2 below: δ-αx(i-γ/β) EQ. 2 where a indicates the initial value of the hydrogen concentration in the hydrogen containing gas inside the treatment chamber, β indicates the concentration of oxygen in the ambient atmosphere (air) of the treatment chamber, and y indicates the concentration of oxygen in the hydrogen containing gas inside the treatment chamber. In the treatment method for an optical fiber described above, preferably the treatment chamber is a sealed chamber. In the treatment memod for an optical fiber described above, a reduced pressure state may preferably be created inside the treatment chamber before the deuterium containing gas is introduced Preferably, but not necessarily, pressure in the treatment chamber during the reduced pressure state is set within a range of equal to or greater than 0.01 kPa to equal to or less than 75 kPa. In the treatment method for an optical fiber described above, partial pressure of deuterium during the deuterium treatment step may preferably be set within a range of equal to or greater than 0.1 kPa to equal to or less than 5 kPa, and partial pressure of hydrogen during the hydrogen treatment step may preferably be set within a range of equal to or greater than 0.1 kPa to equal to or less than 4 kPa. In the treatment memod for an optical fiber described above, pressure in the treatment chamber during the deuterium treatment step or the hydrogen treatment step may preferably, but not necessarily, be set within a range of equal to or greater than 10.1 kPa to equal to or less than 203 kPa. In the treatment memod for an optical fiber described above, temperature inside the treatment chamber may be maintained at a constant temperature within a range of equal to or greater man S'C to equal to or less than 40°C during the deuterium treatment step or the hydrogen treatment step. According to the treatment method for an optical fiber of the invention, in the case in which concentration control of the gas used in a treatment of an optical fiber is necessary, even in the case in which direct measurement of the concentration is not possible due to the capacity of the concentration measuring device, it is possible to measure the concentration of the oxygen mixed in the measured gas inside the treatment chamber and easily calculate the concentration of the measured gas from this oxygen concentration. Therefore, in order to determine the concentration of the measured gas, it is not necessary to extract the measured gas and analyze the measured gas by using a complicated analyzing apparatus such as gas chromatography. Thereby, it is possible to determine the concentration of the measured gas easily at that time. Thus, a treatment method for an optical fiber of the invention is an advantageous treatment method in terms of manufacture because it is possible to reduce cost and time. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS FIG. 1 is a schematic structural drawing showing an example of an optical fiber treatment apparatus of the invention. FIG. 2 is a graph showing the relationship between the annihilation delay time of the non-bridging oxygen hole centers (NBOHCs) and the pressure of the decreased pressure atmosphere in the first step. FIG. 3 is a schematic structural diagram showing an example of the optical fiber treatment apparatus of the invention. FIG. 4 is a graph showing the relationship between number of treatments and the retention rate of the partial pressure of the deuterium in the deuterium containing gas when the optical fiber has undergone deuterium treatment after the deuterium containing gas has been repeatedly used. FIG. 5 is a graph showing the results of the measurement of the deuterium concentration in the test samples of the invention. DETAILED DESCRIPTION OF THE INVENTION Below, a treatment method for an optical fiber mat applies embodiments of the invention will be explained in detail. In the treatment method for an optical fiber of the invention, first, during the fabrication step of the optical fiber, in order to annihilate non-bridging oxygen hole centers (hereinbelow, abbreviated "NBOHCs") generated in the optical fiber, a deuterium treatment or a hydrogen treatment is applied to the optical fiber (in the first embodiment to the fourth embodiment). FIG. 1 is a schematic structural drawing showing an example of the optical fiber treatment apparatus that is used in the treatment method for an optical fiber according to the invention. In FIG. 1, reference symbol 1 denotes the optical fiber treatment apparatus, reference symbol 1a denotes a reaction chamber, reference symbol lb denotes a gas inlet, reference symbol 1c denotes a gas inlet opening and closing valve, reference symbol 1d denotes a gas supply piping, reference symbol 1 e denotes an outlet, reference symbol 1f denotes a discharge opening and closing valve, 1g denotes a discharge pump, reference symbol 1h denotes a differential pressure gauge, reference symbol 2 denotes an optical fiber, and reference symbol 3 denotes a bobbin. This example of an optical fiber treatment apparatus 1 includes at least the reaction chamber 1a. The reaction chamber 1a is a scalable chamber that can accommodate therein the optical fiber 2, and has a vacuum state of about 0.1 kPa and a pressure resistance and sealing performance that can withstand a pressurized state from normal pressure to a pressure that is equal to or less than 250 kPa. The gas supply piping 1d is connected to the gas inlet lb of the reaction chamber la via the gas inlet opening and closing valve 1 c. The deuterium containing gas can be supplied into the reaction chamber 1a ffym the gas supply piping 1 d. Here, deuterium containing gas denotes deuterium gas alone or a mixed gas that contains deuterium gas. The discharge pump 1g is connected to the outlet 1e of the reaction chamber la via the discharge opening and closing vaqlve 1f. The deuterium containing gas or the like in the reaction chamber 1 a is discharged by this discharge pump 1 g. The differential pressure gauge1h is disposed in the reaction chamber la, and thereby the pressure inside the reaction chamber 1 a can be measured. Based on the values measured by the differential pressure gauge In, it is possible to adjust the supplied amount of deuterium containing gas and thereby create a deuterium containing gas atmosphere inside the reaction chamber 1a that has a predetermined pressure, or to start or stop the discharge pump 1g and thereby create a reduced pressure atmosphere inside the reaction chamber la that has a predetermined pressure. In addition, the reaction chamber 1a includes a temperature adjusting means (not shown) such as a heater or cooling mechanism, a thermometer (not shown), or a temperature adjusting portion (not shown). Thereby, by adjusting the internal temperature, it is possible to maintain a state of constant temperature within a range of 5°C to 40°C inside the reaction chamber 1a. Note that instead of the gas inlet opening and closing valve 1 c, the reaction chamber 1a may include a solenoid valve (not shown) that is capable of adjusting the amount of the gas flow. However, any device that can adjust the amount of deuterium containing gas supplied into the reaction chamber 1 a may be used. Next, a first embodiment of the treatment method (NBOHC annihi1ation) for an optica] fiber according to the invention will be exp1ained with reference to FIG. 1. In the treatment method for an optical fiber of this embodiment, in a first step, an optical fiber 2 is exposed to the reduced pressure atmosphere as exp1ained below. First, the optical fiber 2 having a predetermined length is wound around the bobbin 3. Next, the optical fiber 2 that has been wound around the bobbin 3 is p1aced in the reaction chamber 1 a of the treatment apparatus 1. The optical fiber 2 is not particu1arly limited as long as it is made of a silica g1ass or the like, and otherwise any type of optical fiber can be used. Next, after the discharge pump 1g, which is a vacuum pump, is activated, the discharge opening and closing valve 1f is opened, a reduced pressure atmosphere is created inside the reaction chamber 1a, that is, inside the space accommodating the optical fiber 2, is reduced by discharging the air inside the reaction chamber 1a, and thereby the optical fiber 2 is exposed to a reduced pressure atmosphere. Then, in a second step, following the first step, the optical fiber 2 is exposed to the deuterium containing gas atmosphere as described below. After the discharge opening and closing valve 1f is closed, the temperature inside the reaction chamber 1a is adjusted to provide a state of constant temperature within a range of 5°C to 40°C by using a temperature adjusting means (not shown), a thermometer (not shown), or a temperature adjusting portion (not shown). Next, the gas inlet opening and closing valve 1c is opened and the deuterium containing gas is supplied into the reduced pressure atmosphere inside the reaction chamber 1a. The deuterium containing gas is supplied until the inside of the reaction chamber 1a reaches a predetermined pressure and the atmosphere inside the space in the reaction chamber 1 a that accommodates the optical fiber 2 has been rep1aced by the deuterium containing gas. Then the inside of the reaction chamber 1a is sealed by closing the gas inlet opening and closing valve 1c. The optical fiber 2 is exposed to the deuterium obtaining gas atmosphere inside this reaction chamber 1a. Thereby, the optical fiber 2 is exposed to the deuterium containing gas atmosphere, and by reacting the NBOHCs in the silica g1ass that forms the optical fiber 2 with the deuterium (D2) to produce deuterated hydroxyl groups (-OD), it is possible to prevent the generation of hydroxyl groups (-OH). Thereby, it is possible to shift the absorption wavelength region of the optical fiber 2 from the 1.38 μm band, which is the absorption wavelength region of the hydroxyl group, to the 1.87 μm band, which is the absorption wavelength region of the deuterated hydroxyl group. That is to say, the wavelength absorption region is shifted outside of the optical communication wavelength region. Thus, it is possible to inhibit the degradation of the transmission characteristics of the optica] fiber 2 due to absorption loss caused by the hydroxyl groups in the silica g1ass. In addition, according to the treatment method for an optical fiber of this embodiment, the dispersion rate of the deuterium containing gas in the reaction chamber 1a can be increased by creating a reduced pressure atmosphere inside the reaction chamber 1 a that accommodates the optical fiber 2 and supplying the deuterium containing gat into the reaction chamber 1a in this reduced pressure atmosphere state. Thereby, even when the optical fiber 2 is wound around the bobbin 3, the deuterium containing gas passes through the minute gaps between the wound optical fiber 2 and spreads quickly into proximity to the coil core of the bobbin 3. Therefore, it is possible to increase the probability of contact between the optical fiber 2 in proximity to the coil core of the bobbin 3 and the deuterium gas. Thus, it is possible to apply a sufficient (uniform) deuterium treatment throughout the entire length of the optical fiber 2. Because the NBOHCs easily bond to the deuterium to form deuterated hydroxy] groups, the reaction in which the NBOHCs and the deuterium bind to form deuterated hydroxyl groups (i.e., the reaction that annihi1ates NBOHCs) is greatly influenced by the probability of contact between the NBOHCs and the deuterium gas. In the treatment method for an optical fiber of this embodiment, as described above, at the optical fiber in proximity to the coil core of the bobbin 3, it is possible to increase the probability of contact between the optical fiber 2 and the deuterium containing gas, and thereby it is possible to increase the reaction rate between the NBOHCs and the deuterium. Therefore, it is possible to increase the reaction rate between the NBOHCs and the deuterium throughout the entire optical fiber 2 that has been wound around the bobbin 3, and it is possible to annihi1ate NBOHCs throughout the entire optical fiber even if the exposure time is short by using the low concentration deuterium containing gas. Next, based on experimental results, the treatment method for an optical fiber of mis embodiment will be explained in detail. HO. 2 is a graph showing the re1ationship between the annihi1ation de1ay time of the NBOHCs of the optical fiber 2 that has been wound around the bobbin 3 and the pressure of the reduced pressure atmosphere in the first step described above. In FIG. 2, the rhombic symbols indicate the results of the case in which, in the second step, the partial pressure of the deuterium gas in the mixed gas atmosphere is 0.5 kPa and the circu1ar symbols indicate the result of the case in which, in the second step, the partial pressure of the deuterium gas in the mixed gas atmosphere is 1.0 kPa. The annihi1ation de1ay time of the NBOHCs denotes the difference between the annihi1ation time of the NBOHCs of the optical fiber 2 positioned in the innermost 1ayer and the annihi1ation time of the NBOHCs of the optical fiber 2 positioned in the outermost 1ayer, that is, the difference between the annihi1ation time of the NBOHCs of the optical fiber 2 positioned in the innermost 1ayer with respect to the annihi1ation time of the NBOHCs of the optical fiber 2 positioned in the outermost 1ayer. Among the portions of the optical fiber 2 that have been wound around the bobbin 3. the optical fiber 2 positioned in the innermost 1ayer denotes the portion (optical fiber 2) directly wound around the coil core of the bobbin 3. In contrast, among the portions of the optical fiber 2 that has been wound around the bobbin 3, the optical fiber 2 positioned in the outermost 1ayer denotes the portion (optical fiber 2) positioned in the outermost 1ayer. The shorter the annihi1ation de1ay time of the NBOHCs means that the annihi1ation time of the NBOHCs in the optical fiber 2 positioned in the innermost 1ayer is also shorter (the reaction in which the NBOHCs are annihi1ated is fast), The annihi1ation time of the innermost 1ayer becomes a value that is close to the annihi1ation time of the NBOHCs of the optical fiber 2 positioned in the outermost 1ayer. This means that the time necessary to annihi1ate the NBOHCs throughout the entire optical fiber 2 that has been wound around the bobbin 3 is short The annihi1ation time of the NBOHCs of the optical fiber 2 denotes the result of measurement by tile following method. The amount of absorption at 0.63 μm, which is the absorption wavelength of the NBOHCs, is measured in an optical fiber 2 that has been exposed to the deuterium gas for a predetermined time, and the remaining amount of NBOHCs is measured based on this absorption amount Then the change over time in the remaining amount of NBOHCs with respect to the exposure time of the optical fiber 2 to the deuterium containing gas is found, the exposure time to the deuterium containing gas necessary to annihi1ate the NBOHCs completely is estithated based on the change over time in the remaining amount of NBOHCs, and this estithation serves as the annihi1ation time of the NBOHCs. In the first step described above, the pressure of the reduced pressure atmosphere can be equal to or greater than 0.01 kPa and equal to or less than 75 kPa, and can also be equal to or greater than 0.01 kPa and equal to or less than 50kPa, By making the pressure of the reduced pressure atmosphere equal to or greater than 0.01 kPa and equal to or less than 75 kPa, it is possible to make the dispersion rate of the deuterium containing gas high, and it is possible to make the deuterium containing gas spread throughout the entire optical fiber 2 that has been wound around the bobbin 3 or the like. Thus, in the optical fiber 2 in proximity to the coil core of the bobbin 3, it is possible to make the probability of contact between the NBOHCs and the deuterium gas high, and thereby it is possible to accelerate the reaction between the NBOHCs and the deuterium gas (the reaction that annihi1ates the NBOHCs). According to the above, it is possible to make the annihi1ation time of the NBOHCs in the optical fiber 2 positioned in the innermost 1ayer short, and thereby, as shown in FIG. 2, the annihi1ation de1ay time of the NBOHCs can be greatly reduced In addition, because it is possible to make the probability of contact between the NBOHCs and the deuterium gas high, in the second step it is possible to annihi1ate NBOHCs throughout the entire optical fiber 2 even if a low concentration deuterium containing gas is used and the exposure time is made short In particu1ar, in the case in which the pressure of the reduced pressure atmosphere is equal to or greater than 0.01 kPa and equal to or less than SO kPa, the annihi1ation de1ay time of the NBOHCs becomes 0 or about 0, where the annihi1ation de1ay time is negligible. Thus, the NBOHCs react with the deuterium at the same reaction rate in both the optical fiber 2 positioned in the innermost 1ayer and the optical fiber 2 positioned in the outermost 1ayer, and thereby the NBOHCs can be annihi1ated. In addition, in the second step described above, preferably the optical fiber 2 is exposed to a deuterium containing gas in which the partial pressure of the deuterium gas is equal to or greater than 0.1 kPa and equal to or less than 5 kPa. Thereby, it is possible to spread deuterium gas having a concentration that is sufficient to annihi1ate NBOHCs throughout the entire optical fiber 2 that has been wound around the bobbin 3 or the like. A partial pressure of the deuterium gas less than 0.1 kPa is not preferable because the concentration of the deuterium is low, and thus it is difficult to annihi1ate NBOHCs throughout the entire optical fiber 2. In contrast, a partial pressure of the deuterium gas greater man 5 kPa is not preferable because a high concentration of deuterium is necessary, and thereby the fabrication cost becomes high. In addition, in the second step, preferably the deuterium containing gas is supplied into the reaction chamber 1 a that accommodates the optical fiber 2 to create a pressure inside the reaction chamber 1a equal to or greater than 10.1 kPa and equal to or less than 203 kPa, and the optical fiber 2 is exposed to the deuterium containing gas in this pressure range. Thereby, the diffusion rate of the deuterium containing gas inside the reaction chamber 1a becomes high, the deuterium containing gas can spread quickly into proximity to the coil core of the bobbin 3, and thereby it is possible to make the reaction rate between the NBOHCs and the deuterium high. The case in which the pressure of the deuterium containing gas in the reaction chamber 1 a in which the optical fiber 2 is exposed is less than 10.1 kPa is not preferable because the diffusion rate of the deuterium containing gas inside the reaction chamber 1 a is low and thus the reaction in which the NBOHCs are annihi1ated requires a long time. In addition, the case in which the pressure of the deuterium containing gas in the reaction chamber 1a in which me optical fiber 2 is exposed is greater than 203 kPa is not preferable because a reaction chamber 1a having a high pressure resistance must be used, and taking into consideration safety and the like, handling of the reaction chamber 1a becomes difficult In the second step, preferably, but not necessarily, the exposure time during which the optical fiber 2 is exposed to the deuterium containing gas is one day or less. Thereby, it is possible to annihi1ate the NBOHCs throughout the entire optical fiber 2 that has been wound around the bobbin 3. In the second step, preferably, but not necessarily, the optical fiber 2 is exposed to the deuterium containing gas in a state in which the temperature inside the reaction chamber 1a is adjusted so as to maintain a constant temperature within a range of equal to or greater man 5°C to equal to or less man 40°C. Thereby, it is possible to accelerate the reaction between the NBOHCs in the silica g1ass and the deuterium, and it is possible to annihi1ate the NBOHCs in a short period of time. The case in which the temperature inside the reaction chamber 1a is higher than 40 °C is not preferable because the surface covering resin 1ayer of the optical fiber 2 will change due to the heat FIG. 3 is a schethatic structural diagram showing another example of the optical fiber treatment apparatus used in the treatment method for an optical fiber according to the invention. The optical fiber treatment apparatus 4 in this example essentially includes a reaction chamber 4a, a deuterium storage tank 4b, and piping 4c by which the reaction chamber 4a communicates with the deuterium storage tank 4b. The reaction chamber 4a is a sca1able chamber that can accommodate an optical fiber 2 therein (first space), and has a vacuum state of about 0.1 kPa and a pressure resistance and sealing performance that can withstand a pressurized state from normal pressure to a pressure equal to or less than 250 kPa. The deuterium storage tank 4b is a tank that can store the deuterium containing gas therein (second space), and, like the reaction chamber 4a, has a vacuum state of about 0.1 kPa and a pressure resistance and sealing performance that can withstand a pressurized state from normal pressure to a pressure equal to or less than 250 kPa, The gas supply piping 4g is connected to the gas inlet 4d of the deuterium storage tank 4b via a gas inlet opening and closing valve 4f, and it is possible to supply the deuterium containing gas into the reaction chamber 4a from this gas supply piping 4g. Gas inlet and outlet openings 4h and 4i are included in the reaction chamber 4a and the deuterium storage tank 4b. The piping 4c connects to these gas inlet and outlet openings 4h and 4i via the opening and closing valves 4j and 4k, and the reaction chamber 4a and the deuterium storage tank 4b communicate via the one piping 4c. The inside of the piping 4c (third space) serves as the flow path, and the deuterium containing gas can flow to or from either the reaction chamber 4a or the deuterium storage tank 4b. A switching valve 4n is included along the course of the piping 4c, and a discharge pipe 4p and a gas venti1ation device 4q are connected to this switching valve 4n. Any valve that has connection portions that conduct in at least three directions and that can switch the path from the connection portion in one direction to the connection portions in any of the other two directions can be used as the switching valve 4n, A three-direction valve or a three-direction solenoid valve can be an example of the switching valve 4n. In addition, a combination pressurizing and depressurizing pump such as a scroll vacuum pump or a dry-vacuum diaphragm pump can be used as the gas venti1ation device 4q. In the description below, a portion of the path of the piping from the switching valve 4n to the gas inlet and outlet opening 4h of the reaction chamber 4a is referred to as the reaction chamber side piping 4r, and a portion of the path of the piping from the switching valve 4n to the gas inlet and outlet opening 4i of the deuterium storage tank 4b is referred to as the deuterium storage tank side piping 4s. In this embodiment, the switching valve 4n enables switching from one path among the reaction chamber side piping 4r, the deuterium storage tank side piping 4s, and the discharge pipe 4p to any one of the paths of the other two directions, and the gas ventilation device 4q enables venti1ating the gas from one direction to the other direction among the two switched paths. A differential pressure gauge 4t is disposed in the reaction chamber 4a, and thereby the pressurein the reaction chamber 4a can be measured. By using the gas venti1ation device 4q to adjust the supplied amount of deuterium containing gas based on this measured value, it is possible to provide the inside of the reaction chamber 4a with a deuterium containing gas atmosphere that has a predetermined pressure, or create a reduced pressure atmosphere that has a predetermined pressure inside of the reaction chamber 4a. In addition, the reaction chamber 4a includes a temperature adjusting means (not shown) such as a heater or cooling mechanism, a thermometer (not shown), or a temperature adjusting portion (not shown), and thereby it is possible to maintain a state of constant temperature within a range of 5°C to 40°C inside the reaction chamber 4a by adjusting the internal temperature. Next, a second embodiment of the treatment method for an optical fiber according to the invention will be exp1ained with reference to HO. 3. In the treatment method for an optical fiber of this embodiment, in a first step, the optical fiber 2 is exposed to a reduced pressure atmosphere as exp1ained below. First, an optical fiber 2 that has been wound around the bobbin 3 is p1aced inside the reaction chamber 4a. The temperature inside the reaction chamber 4a is adjusted to a constant temperature within a range of 5°C to 40°C. Then the switching valve 4n is switched so as to connect the reaction chamber side piping 4r and the discharge pipe 4p. Next, the opening and closing valve 4j of the reaction chamber side piping 4r is opened, the air in the reaction chamber 4a is discharged to the discharge pipe 4p by the gas venti1ation device 4q, a reduced pressure atmosphere is created inside of the reaction chamber 4a, that is, inside the first space that accommodates the optical fiber 2, and the optical fiber 2 is exposed to the reduced pressure atmosphere. Next, in the second step, following the first step, the optical fiber 2 is exposed to the deuterium containing gas as exp1ained below. The inside of the deuterium storage tank 4b is filled in advance with a deuterium containing gas that includes a predetermined concentration of deuterium gas at a predetermined pressure. Next, after closing the opening and closing valve 4j of the reaction chamber side piping 4r, the switching valve 4n is switched so that the reaction chamber side piping 4r and the deuterium storage tank side piping 4s are connected. Then the opening and closing valve 4j of the reaction chamber side piping 4r and the opening and closing valve 4k of the deuterium storage tank side piping 4s are opened, and the reaction chamber 4a and the deuterium storage tank 4b communicate via the piping 4c. In this manner, the inside of the piping 4c (third space) serves as a passage enabling the deuterium containing gas in the deuterium storage tank 4b to flow to the reaction chamber 4a, which has a reduced pressure atmosphere. Next, when the inside of the reaction chamber 4a reaches a predetermined pressure, the reaction chamber 4a is sealed by closing the opening and closing valve 4j of the reaction chamber side piping 4r and the opening and closing valve 4k of the deuterium storage tank side piping 4s. The optical fiber 2 is exposed to the deuterium containing gas inside this reaction chamber 4a. According to the above, the optical fiber 2 is exposed to the deuterium containing gas, the NBOHCs in the silica g1ass and the deuterium bind to form deuterated hydroxyl groups, and thereby it is possible to annihilate the NBOHCs. Next, the switching valve 4n is switched so that the reaction chamber side piping 4r and the deuterium storage tank side piping 4s communicate. The opening and closing valves 4j and 4k are opened, the reaction chamber 4a and the deuterium storage tank 4b communicate via the piping 4c, the gas venti1ation device 4q is activated, the deuterium containing gas inside the reaction chamber 4a is transferred to the deuterium storage tank 4b, and a vacuum is created in the inside of the reaction chamber 4a. Next, after the opening and closing valve 4j on the reaction chamber side piping 4r is closed and air is introduced into the reaction chamber 4a, the optical fiber 2 is extracted from the reaction chamber 4a. According to the above, without discharging the deuterium containing gas that has been used once, the deuterium containing gas is stored in the deuterium storage tank 4b and thus can be used in the deuterium treatment of another optical fiber 2. FIG. 4 is a graph showing the change in the partial pressure of the deuterium gas in the deuterium containing gas when, using the optical fiber treatment apparatus 4 of FIG. 3, optical fibers 2 have been treated by repeatedly using the deuterium containing gas. In the case in which the optical fiber treatment apparatus 4 of FIG. 3 is used, even after the deuterium treatment has been carried out 30 times, the retention rate of the partial pressure of the deuterium is equal to or greater than 70%. This concentration allows satisfactory deuterium treatment to be carried out In this manner, it is possible to use the deuterium containing gas repeatedly, so that it is possible to reduce the running costs associated with the deuterium gas significantly, thereby creating an inexpensive deuterium treatment. Next, a third embodiment of the treatment method for an optical fiber according to the invention will be exp1ained with reference to FIG. 1. The treatment method for an optical fiber in this embodiment, which annihi1ates the NBOHCs using a deuterium treatment, is for inhibiting an increase in the transmission loss in the optical fiber after being 1aid. In the treatment method for an optical fiber of this embodiment, first an optical fiber 2 having a predetermined length is wound around a bobbin 3. Next, the optical fiber 2 that has been wound around the bobbin 3 is p1aced inside the reaction chamber 1a of the treatment apparatus 1. Then, after closing the discharge opening and closing valve 1 f, the temperature inside the reaction chamber 1a is adjusted so as to maintain a state of constant temperature within a range of 5°C to 40°C by a temperature adjusting means (not shown), a thermometer (not shown), or a temperature adjusting portion (not shown). Next, the gas inlet opening and closing valve 1c is opened, the deuterium containing gas is supplied into the reaction chamber 1a, and while carrying out control such that the deuterium concentration in the deuterium containing gas inside this reaction chamber 1a is constant, the optical fiber 2 is exposed to the deuterium containing gas atmosphere inside the reaction chamber 1a- in this embodiment, in the deuterium treatment step described above, first the concentration B of the oxygen in the ambient atmosphere (air) of the reaction chamber 1a is measured Next, the concentration C of the oxygen in the deuterium containing gas inside the reaction chamber 1a is measured. The deuterium concentration D inside the reaction chamber 1a during the deuterium treatment is calcu1ated from the results of these measurements and the initial value A of the deuterium concentration in the deuterium containing gas inside the reaction chamber (treatment chamber) 1 a using the following BQ. 1. Based on the calcu1ated deuterium concentration D, the deuterium concentration inside the reaction chamber 1a is maintained at a concentration necessary for carrying out the deuterium treatment for the optical fiber 2 inside the reaction chamber 1 a sufficiently. Specifically, in the case in which the deuterium concentration inside the reaction chamber 1 a does not reach the concentration required for the deuterium treatment, the gas inlet opening and closing valve 1c is opened and deuterium containing gas is supplied into the reaction chamber 1a. In contrast, in the case in which the deuterium concentration inside the reaction chamber 1a exceeds the concentration required for the deuterium treatment, the gas inlet opening and closing valve 1c is closed and the supply of the deuterium containing gas into the reaction chamber 1a is stopped. D=Ax(l-C/B) EQ. 1 where D indicates a deuterium concentration inside the treatment chamber during the deuterium treatment, A indicates an initial value of the deuterium concentration in the deuterium containing gas inside the treatment chamber, B indicates concentration of oxygen in the ambient atmosphere (six) of the treatment chamber, and C indicates concentration of oxygen in the deuterium containing gas inside the treatment chamber. An oxygen densitometer (not shown) was used in order to measure the concentration B of the oxygen in the ambient atmosphere (air) of the reaction chamber 1a and the concentration C of the oxygen in the deuterium containing gas inside the reaction chamber 1a. Examples of oxygen densitometers that may be used are Toray's LC-750 and Yokogawa's oxygen densitometer 0X61. In this manner, by measuring the concentration B of the oxygen in the ambient atmosphere (air) of the reaction chamber 1a and the concentration C of the oxygen in the deuterium containing gas inside the reaction chamber 1a, it is possible to calcu1ate the amount of air mixed in the atmosphere inside the reaction chamber 1a, and based on this calcu1ated value, it is possible to calcu1ate the present deuterium concentration inside the reaction chamber 1 a. Because there are dangers such as explosions when the gas used in the treatment of the optical fiber is an inf1ammable gas (deuterium) as in the deuterium treatment, in terms of control, measurement of the deuterium concentration using a conventional combustion densitometer or an optical densitometer is not preferable. In addition, in the case in which a deuterium containing gas is used as the gas serving as the base, the present deuterium concentration inside the reaction chamber 1a is calcu1ated by measuring the concentration of the air, and in particu1ar the oxygen, mixed in the deuterium containing gas inside the reaction chamber 1a. The reason for this is that a cause of the deuterium concentration becoming low is the air mixed into the deuterium containing gas inside the reaction chamber 1a during the deuterium treatment Therefore, if the amount (concentration) of the air (oxygen) mixed into the deuterium containing gas inside the reaction chamber 1 a can be determined, then it is possible to determine the present deuterium concentration inside the reaction chamber 1a. Thus, according to the treatment method for an optical fiber in mis embodiment, there are no dangers such as explosions, and thereby it is possible to control the deuterium concentration correctly even when the composition ratios of the base gas (the deuterium containing gas) inside the reaction chamber 1 a fluctuate. In addition, in the treatment method for an optical fiber in this embodiment, preferably the reaction chamber 1a is a sealed container, If the reaction chamber 1a is a sealed container, before carrying out the deuterium treatment for the optical fiber 2 inside the reaction chamber 1a, a reduced pressure atmosphere can be created inside the reaction chamber 1a. Furthermore, in the treatment method for an optical fiber in this embodiment, preferably the deuterium treatment of the optical fiber 2 is carried out after a reduced pressure atmosphere has been created inside the reaction chamber 1 a. In this embodiment, a method will be exp1ained in which the deuterium treatment of the optical fiber 2 is carried out after a reduced pressure atmosphere has been created inside the reaction chamber 1a. After p1acing the optical fiber 2 inside the reaction chamber 1a of the treatment apparatus 1 and activating the discharge pump 1g, which is a vacuum pump, the discharge opening and closing valve 1f is opened, a reduced pressure atmosphere is created inside the reaction chamber 1a, that is, inside the space accommodating the optical fiber 2. by discharging the air inside the reaction chamber 1 a, and thereby the optical fiber 2 is exposed to the reduced pressure atmosphere. Next, after providing a state of constant temperature within a range of 5°C to 40°C by adjusting the temperature inside the reaction chamber 1 a, the gas inlet opening and closing valve 1c is opened and the deuterium containing gas is supplied into the reduced pressure atmosphere inside the reaction chamber 1 a. Subsequently, the deuterium containing gas is supplied until the inside of the reaction chamber 1a reaches a predetermined pressure and the atmosphere in the space inside the reaction chamber 1a that accommodates the optical fiber 2 is rep1aced by the deuterium containing gas. Then the inside of the reaction chamber 1a is sealed by closing the gas inlet opening and closing valve 1c, and the optical fiber 2 is exposed to the deuterium containing gas atmosphere in this reaction chamber 1 a. In this maimer, it is possible to make the dispersion rate of the deuterium containing gas inside the reaction chamber 1a high by creating a reduced pressure atmosphere inside the reaction chamber 1a that accommodates the optical fiber 2 and supplying the denterium containing gas inside the reaction chamber 1a in mis reduced pressure state. Thereby, even when the optical fiber 2 has been wound around a bobbin 3, the deuterium containing gas passes through minute gaps between the wound optical fiber 2 and spreads quickly into proximity to the coil core of the bobbin 3. Therefore, the probability of contact between the optical fiber 2 in proximity to the coil core of the bobbin 3 and the deuterium containing gas can be made high. Thus, it is possible to apply the deuterium treatment sufficiently (evenly) throughout the entire length of the optical fiber 2. In addition, this third embodiment of the treatment method for an optical fiber can be applied even when the measured gas is hydrogen other than deuterium or a gas other than oxygen, such as nitrogen. (Applicants may choose to list additional gases here for broader disclosure and possible subject thatter for additional dependent c1aim(s).J Next, a fourth embodiment of the treatment method for an optical fiber according to the invention will be exp1ained with reference to FIG. 1. The treatment method for an optical fiber in this embodiment, which annihi1ates the NBOHCs using a hydrogen treatment, is for inhibiting an increase in the transmission loss in the optical fiber after being laid. In the treatment method for an optical fiber of this embodiment, first, an optical fiber 2 having a predetermined length is wound around a bobbin 3. Next, the optical fiber 2 that has been wound around the bobbin 3 is p1aced inside the reaction chamber 1a of the treatment apparatus 1. Next, after closing the discharge opening and closing valve 1f, the temperature inside the reaction chamber 1a is maintained at a state of constant temperature within a range of 5°Cto 40°C by adjusting the temperature therein by using a temperature adjusting means (not shown), a thermometer (not shown), or a temperature adjusting portion (not shown). Next, the gas inlet opening and closing valve 1c is opened, the hydrogen containing gas is supplied into the reaction chamber 1a, and the optical fiber 2 is exposed to the hydrogen containing gas atmosphere in the reaction chamber 1a while control is carried out so that the hydrogen concentration in the hydrogen containing gas atmosphere in this reaction chamber 1 a remains constant. In this embodiment, in the hydrogen treatment step described above, first the concentration β of the oxygen in the ambient atmosphere (air) of the reaction chamber 1a is measured. Next, the concentration γ of the oxygen in the hydrogen containing gas inside the reaction chamber 1a is measured. The hydrogen concentration 5 in the reaction chamber 1a during the hydrogen treatment is calcu1ated from the results of these measurements and the initial value a of the hydrogen concentration in the hydrogen containing gas inside the reaction chamber 1a (treatment chamber) using the following EQ. 2. Based on the calcu1ated hydrogen concentration 5, the hydrogen concentration inside the reaction chamber 1a is maintained at a concentration necessary to carry out the hydrogen treatment of the optical fiber 2 inside the reaction chamber 1a sufficiently. Specifically, in the case in which the hydrogen concentration inside the reaction chamber 1a does not reaoh the concentration required for the hydrogen treatment, the gas inlet opening and closing valve 1c is opened and the hydrogen containing gas is supplied into the reaction chamber 1a. In contrast, in the case in which the hydrogen concentration inside the reaction chamber 1a exceeds the concentration required for the hydrogen treatment, the gas inlet opening and closing valve lc is closed and the supply of the hydrogen containing gas into the reaction chamber 1a is stopped. δ-α(1-γ/p) EQ.2 where 8 indicates a hydrogen concentration inside the treatment chamber during the hydrogen treatment, a indicates an initial value of the hydrogen concentration in the hydrogen containing gas inside the treatment chamber, (3 indicates concentration of oxygen in the ambient atmosphere (air) of the treatment chamber, and y indicates concentration of oxygen in the hydrogen containing gas inside the treatment chamber. An oxygen densitometer (not shown) was used to measure the concentration β of the oxygen in the ambient atmosphere (air) of the reaction chamber 1a and the concentration γ of the oxygen in the hydrogen containing gas in the reaction chamber 1 a. Examples of oxygen densitometers that can be used are Toray's LC-750 and Yokogawa's oxygen densitometer 0X61. In this manner, the amount of air mixed into the atmosphere of the reaction chamber 1 a is calcu1ated by measuring the concentration β of the oxygen in the ambient atmosphere (air) of the reaction chamber 1a and the concentration 7 of the oxygen in the hydrogen containing gas inside the reaction chamber 1a, and it is possible to calcu1ate the present hydrogen concentration inside the reaction chamber 1a from these calcu1ated values. Because there are dangers such as explosions and the like when the gas used in the treatment of the optical fiber is an inf1ammable gas (hydrogen) as in the hydrogen treatment, in terms of control, measurement of the hydrogen concentration using a conventional combustion densitometer or an optical densitometer is not preferable. Thus, in the case in which hydrogen containing gas is used as the gas that serves as the base, the present hydrogen concentration inside the reaction chamber 1 a is calcu1ated by measuring the concentration of the air, and in particu1ar, the oxygen, mixed in the hydrogen containing gas inside the reaction chamber 1 a. The reason for this is that a cause of the hydrogen concentration becoming low is the air mixed into the hydrogen containing gas inside the reaction chamber 1 a during the hydrogen treatment Therefore, it is possible to determine the amount (concentration) of air (oxygen) that has mixed into the hydrogen containing gas inside the reaction chamber 1 a, and thereby it is possible to determine the present hydrogen concentration inside the reaction chamber 1a. Thereby, according to the treatment method for an optical fiber in this embodiment, mere are no dangers such as explosions, and thereby it is possible to control the hydrogen concentration correctly even when the composition ratios of the gas serving as the base (the hydrogen containing gas) inside the reaction chamber 1 a fluctuate. In addition, in the treatment method for an optical fiber in this embodiment, preferably the reaction chamber 1 a is a sealed container. If the reaction chamber 1 a is a sealed container, before carrying out the hydrogen treatment of the optical fiber 2 inside the reaction chamber 1a, a reduced pressure atmosphere can be created inside the reaction chamber 1a. Furthermore, in the treatment method for an optical fiber in this embodiment, preferably the hydrogen treatment of the optical fiber 2 is carried out after a reduced pressure atmosphere has been created inside the reaction chamber 1a. In this embodiment, a method will be exp1ained in which the hydrogen treatment of the optical fiber 2 is carried out after a reduced pressure atmosphere has been created inside the reaction chamber 1 a. After p1acing the optical fiber 2 inside the reaction chamber 1a of the treatment apparatus 1 and activating the discharge pump 1g, which is a vacuum pump, the discharge opening and closing valve 1f is opened, and a reduced pressure atmosphere is created inside of the reaction chamber 1a, that is, inside the space accommodating the optica] fiber 2, by discharging the air inside the reaction chamber 1a, and the optical fiber 2 is exposed in the reduced pressure atmosphere. Next, after providing a state of constant temperature within a range of 5°C to 40°C by adjusting the temperature inside the reaction chamber 1 a, the gas inlet opening and closing valve 1 c is opened and the hydrogen containing gas is supplied into the reduced pressure atmosphere inside the reaction chamber 1 a. Subsequently, the hydrogen containing gas is supplied until the inside of the reaction chamber 1a reaches a predetermined pressure and the atmosphere in the space inside the reaction chamber 1a that accommodates the optical fiber 2 is rep1aced by the hydrogen containing gas. Then the inside of the reaction chamber 1a is sealed by closing the gas inlet opening and closing valve 1c, and in this reaction chamber 1a, the optical fiber 2 is exposed to the hydrogen containing gas atmosphere. In mis manner, it is possible to make the dispersion rate of the hydrogen containing gas inside the reaction ohamber 1 a high by creating a reduced pressure atmosphere inside the reaction chamber 1a that accommodates the optical fiber 2 and supplying the hydrogen containing gas into the reaction chamber 1a in this reduced pressure state. Thereby, even when the optical fiber 2 has been wound around the bobbin 3, the hydrogen containing gas passes through minute gaps between the wound optical fiber 2 and spreads quickly into proximity to the coil core of the bobbin 3. Therefore, the probability of contact between the optical fiber 2 in proximity to the coil core of the bobbin 3 and the hydrogen containing gas can be made high. Thus, it is possible to apply the hydrogen treatment sufficiently (evenly) throughout the entire length of the optical fiber 2. Below, the invention will be exp1ained in greater detail by using an experimental example. However, the invention is not limited by the following experimental example. Experimental Example An apparatus identical to the optical fiber optical fiber treatment apparatus shown in FIG. 1 was used to apply the deuterium treatment to an optical fiber. The deuterium treatment for an optical fiber was repeated; the deuterium concentration in the reaction chamber was measured each time by an optical densitometer (Riken Measuring Instruments, FI-21); the oxygen concentration in the reaction chamber was measured by using an oxygen densitometer (Toray, LO750H); and gas chrothatography of the deuterium inside the reaction chamber was carried out, The deuterium gas used a nitrogen gas as the base. The results of the measurements are shown in FIG, 5. In FIG. 5, the deuterium concentration (calcu1ated value, indicated by the rhombic symbols) denotes the value calcu1ated from the oxygen concentration inside the reaction chamber measured in this experimental example and EQ. 1 described above. In addition, the deuterium concentration (analytic value, indicated by the triangu1ar symbols) denotes the value obtained from the gas chrothatography analysis in the present experimental example. Furthermore, the oxygen concentration (measured value, indicated by the square symbols) denotes the value of the oxygen concentration inside the reaction chamber measured in the present experimental example, From the results shown in HO. 5, it has been confirmed that, like the case in which the deuterium inside the reaction chamber is analyzed by gas chrothatography, the deuterium concentration can be measured easily by finding the deuterium concentration in the reaction chamber from the values of the oxygen concentration in the reaction chamber measured by the oxygen densitometer using EQ. 1 described above. The treatment method for an optical fiber of the invention can be applied when using treatment gases other men deuterium or hydrogen It is contemp1ated that numerous modifications may be made to the exemp1ary embodiments of the invention without departing from the spirit and scope of the embodiments of the present invention as defined in the following c1aims. We c1aim : 1. A treatment method for an optical fiber, comprising: accommodating an optical fiber inside a treatment chamber; introducing a deuterium containing gas into the treatment chamber; and in a deuterium treatment step, exposing the optical fiber to atmosphere of the deuterium containing gas, wherein, in the deuterium treatment step, a deuterium concentration D in the treatment chamber during the deuterium treatment is calcu1ated from an initial value A of a deuterium concentration in the deuterium containing gas inside the treatment chamber, a concentration B of oxygen in an ambient atmosphere of the treatment chamber, and a concentration C of oxygen in the deuterium containing gas inside the treatment chamber using EQ. 1 below, and the deuterium concentration in the treatment chamber is controlled based on the deuterium concentration D calcu1ated. D=Ax(l-C/B) EQ. 1 2. A treatment method for an optical fiber according to c1aim 1, wherein the treatment chamber is a sealed chamber. 3. A treatment method for an optical fiber according to c1aim 1, wherein a reduced pressure state is created inside the treatment chamber before the deuterium containing gas is introduced. 4. A treatment method for an optical fiber according to c1aim 3, wherein pressure in the treatment chamber during the reduced pressure state is set within a range of equal to or greater than 0.01 kPa to equal to or less than 75 kPa. 5. A treatment method for an optical fiber according to c1aim 1, wherein partial pressure of deuterium during the deuterium treatment step is set within a range of equal to or greater than 0.1 kPa to equal to or less than 5 kPa. 6. A treatment method for an optical fiber according to c1aim 1, wherein pressure in the treatment chamber during the deuterium treatment step is set within a range of equal to or greater than 10.1 kPa to equal to or less than 203 kPa. 7. A treatment method for an optical fiber according to c1aim 1, wherein temperature inside the treatment chamber is maintained at a constant temperature within a range of equal to or greater than 5°C to equal to or less than 40° C during the deuterium treatment step. 8. A treatment method for an optical fiber, comprising: accommodating an optical fiber inside a treatment chamber; introducing a hydrogen containing gas into the treatment chamber; and in a hydrogen treatment step, exposing the optical fiber to atmosphere of the hydrogen containing gas, wherein, in the hydrogen treatment step, a hydrogen concentration 8 in the treatment chamber during the hydrogen treatment is calcu1ated from an initial value α of a hydrogen concentration in the hydrogen containing gas inside the treatment chamber, a concentration β of oxygen in an ambient atmosphere of the treatment chamber, and a concentration y of oxygen in the hydrogen containing gas inside the treatment chamber using EO. 2 below, and the hydrogen concentration in the treatment chamber is controlled based on the hydrogen concentration 8 calcu1ated, 9. A treatment method for an optical fiber according to c1aim 8, wherein the treatment chamber is a sealed chamber. 10. A treatment method for an optical fiber according to c1aim 8, wherein a reduced pressure state is created inside the treatment chamber before the hydrogen containing gas is introduced. 11. A treatment method for an optical fiber according to c1aim 10, wherein pressure in the treatment chamber during the reduced pressure state is set within a range of equal to or greater than 0.01 kPa to equal to or less than 75 kPa. 12. A treatment method for an optical fiber according to c1aim 8, wherein partial pressure of hydrogen during the hydrogen treatment step is set within a range of equal to or greater than 0.1 kPa to equal to or less than 4 kPa. 13. A treatment method for an optical fiber according to c1aim 8, wherein pressure in the treatment chamber during the hydrogen treatment step is set within a range of equal to or greater than 10.1 kPa to equal to or less than 203 kPa. 14. A treatment method for an optical fiber according to c1aim 8, wherein temperature inside the treatment chamber is maintained at a constant temperature within a range of equal to or greater than 5°C to equal to or less than 40° C during the hydrogen treatment step. 15. A treatment method for an optical fiber according to c1aim 1, wherein non- bridging oxygen hole centers or NBOHCs which are generated in the optical fiber react with the deuterium or are annihi1ated at the same reaction rate in both the optical fiber positioned in an innermost 1ayer and the optical fiber positioned in an outermost 1ayer, so that there is no annihi1ation de1ay time. 16. A treatment method for an optical fiber according to c1aim 1, wherein the absorption wavelength region of the optical fiber is shifted from the 1.38 μm band, which is the absorption wavelength region of the hydroxyl group, to the 1.87 μm band, which is the absorption wavelength region of the deuterated hydroxyl group. 17. A treatment method for an optical fiber according to c1aim 1, wherein absorption loss caused by the hydroxyl groups in the silica g1ass of the optical fiber inhibits degradation of the transmission characteristics of the optical fiber. 18. A treatment method for an optical fiber according to c1aim 1, wherein a dispersion rate of the deuterium containing gas in the reaction chamber is increased. 19. A treatment method for an optical fiber according to c1aim 1, wherein an optical fiber treatment apparatus comprises a reaction chamber, a deuterium storage tank and piping by which the reaction chamber communicates with the deuterium storage tank. 20. A treatment method for an optical fiber according to c1aim 19, wherein the deuterium containing gas stored in the deuterium storage tank is used in the deuterium treatment of at least one other optical fiber. 21. A treatment method for an optical fiber according to c1aim 1, wherein the deuterium gas used a nitrogen gas as a base. A treatment method for an optical fiber (2) including accommodating an optical fiber inside a treatment chamber (1a); introducing a deuterium containing gas into the treatment chamber (1a); and in a deuterium treatment step, exposing the optical fiber (2) to atmosphere of the deuterium containing gas. In the deuterium treatment step, a deuterium concentration D in the treatment chamber (1a) during the deuterium treatment is calculated from an initial value A of a deuterium concentration in the deuterium containing gas inside the treatment chamber (1a), a concentration B of oxygen in an ambient atmosphere of the treatment chamber (1a), and a concentration C of oxygen in the deuterium containing gas inside the treatment chamber (1a), and the deuterium concentration in the treatment chamber (1a) is controlled based on the deuterium concentration D calculated. Other gases such as hydrogen containing gas or nitrogen containing gas may also be used according to the invention.

Full Text

TREATMENT METHOD FOR OPTICAL FIBER
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a treatment method for an optical fiber.
Description of Related Art
After rendering optical fibers into a cable and laying the optical fiber cable, the
transmission loss in a wavelength band of about 1400 nm of the optical fiber increases,
and the transmission characteristics of the optical fiber degrade.
In order to inhibit this degradation of the optical fiber transmission
characteristics, a treatment method for optical fibers is applied in which an optical fiber is
exposed to hydrogen or deuterium in advance.
However, when carrying out a treatment method in which the optical fiber is
exposed to hydrogen (hydrogen treatment), there is a problem in that the initial
transmission loss of the optical fiber in a wavelength region of about 1383 nm increases.
In contrast, when carrying out a treatment method in which the optical fiber is exposed to
deuterium (deuterium treatment), no such problem occurs. Thus, the hydrogen
treatment or the deuterium treatment must be selected and applied depending on the
object
Various methods have been proposed for applying a deuterium treatment to an
optical fiber. In one method (see, for example, Japanese Unexamined Patent
Application, First Publication No. 2003-137580), a gas that contains deuterium gas
(hereinbelow, referred to as a "deuterium containing gas") continuously flows into a
scalable treatment chamber, and the atmosphere in the treatment chamber is replaced by
the deuterium containing gas. In another method (see, for example, Japanese
Unexamined Patent Application, First Publication No. 2004-226979), after decreasing
the pressure inside the treatment chamber, the inside of the treatment chamber is filled
with the deuterium containing gas, and thereby the atmosphere inside the treatment
chamber is replaced by the deuterium containing gas. In the latter method, recovery of
the deuterium containing gas is possible.
In addition, the hydrogen test method stipulated in IEC60793-2-50 is an
example of a method for applying a hydrogen treatment to an optical fiber. In this
hydrogen test method, an optical fiber is exposed to 1% hydrogen gas atmosphere or
100% hydrogen gas atmosphere at room temperature until the transmission loss at a
wavelength of 1240 nm is equal to or greater than 0.03 dB/km. However, in this
hydrogen test method, specific conditions of the treatment methods (treatment
conditions) are not stipulated.
In the case in which a deuterium treatment is applied to an optical fiber, when
using the method in which the deuterium containing gas continuously flows into the
treatment chamber, the treatment is applied while eliminating deuterium containing gas
until the inside of the treatment chamber reaches a predetermined deuterium
concentration. Thus, each time the deuterium treatment is applied, it is possible to
maintain a predetermined deuterium concentration in the treatment chamber.
However, in order to increase the production efficiency, the treatment must be
applied at one time to an optical fiber having a long length, and accompanying this, the
volume of the treatment chamber for applying the treatment to the optical fiber becomes
large. Depending on how large the volume of the treatment chamber becomes, the
amount of deuterium containing gas necessary for replacing the atmosphere in the
treatment chamber increases, and thereby the cost also increases.
In contrast, when using the method in which the treatment chamber is filled with
deuterium containing gas after the pressure in the treatment chamber has been reduced,
because creating a complete vacuum inside the treatment chamber is difficult, air that
remains in the treatment chamber from each treatment mixes with the deuterium
containing gas. As the number of treatments increases, the deuterium concentration in
the recovered deuterium containing gas becomes low.
When the deuterium concentration in the deuterium containing gas becomes low,
there are also concerns in mat not only is a long time required until the deuterium has
sufficiently permeated the optical fiber, but also that the deuterium treatment may
become inadequate. Thus, in order to prevent defective deuterium treatments, it is
necessary to monitor the deuterium concentration when applying the deuterium treatment
to the optical fiber.
An inflammable gas detector, an optical gas densitometer, or the like are
examples of devices that measure the deuterium concentration. When using an
air-based deuterium containing gas, it is possible to measure the deuterium concentration
by such measuring devices. Note that here, any gas whose composition ratios are
similar to those of the atmosphere is referred to as "air".
However, when air is mixed into the deuterium containing gas and the
composition ratios of the gas differ from those of the atmosphere, it becomes impossible
to measure the deuterium concentration correctly by using the measuring devices
described above. In a combustion densitometer such as an inflammable gas detector,
deuterium is combusted, and the deuterium concentration is calculated from the amount
of heat generated during the combustion. Thus, in the case in which, instead of air, an
inert gas such as nitrogen, argon, helium, or the like serves as the base, the combustion
becomes poor, and thus the concentration cannot be correctly measured.
In addition, in an optical densitometer such as an optical gas densitometer, the
deuterium concentration is calculated from the relative index of refraction of the
deuterium containing gas. Thus, in the case in which the composition ratio of the gas
that serves as the base fluctuates, it is not possible to measure the deuterium
concentration correctly.
In addition, it is possible to measure the deuterium concentration by analyzing
the molecules of the deuterium gas included in the deuterium containing gas. However,
this is not preferable because the measurement takes time, and thus the production costs
drastically increase.
SUMMARY OF THE INVENTION
In consideration of the problems described above, an object of the invention is to
provide a treatment method for an optical liber that can correctly control a deuterium
concentration even when a gas that serves as abase of a deuterium containing gas is a gas
other than air, and a composition ratio of a gas that serves as a base fluctuates.
The invention provides a treatment method for an optical fiber, including:
accommodating an optical fiber inside a treatment chamber, introducing a deuterium
containing gas into the treatment chamber; and in the deuterium treatment step, exposing
the optical fiber to atmosphere of the deuterium containing gas, wherein, in the deuterium
treatment step, a deuterium concentration D in the treatment chamber during the
deuterium treatment is calculated from an initial value A of a deuterium concentration in
the deuterium containing gas inside the treatment chamber, a concentration B of oxygen
in an ambient atmosphere of the treatment chamber, and a concentration C of oxygen in
the deuterium containing gas inside the treatment chamber, and the deuterium
concentration in the treatment chamber is controlled based on the deuterium
concentration D calculated.
In the treatment method for an optical fiber, the deuterium concentration D in
the treatment chamber during the deuterium treatment step can be calculated using EQ. 1
below:
D-Ax(l-C/B) EQ. 1
where A indicates the initial value of the deuterium concentration in the deuterium
containing gas inside the treatment chamber, B indicates the concentration of oxygen in
the ambient atmosphere (air) of the treatment chamber, and C indicates the concentration
of oxygen in the deuterium containing gas inside the treatment chamber.
The invention further provides a treatment method for an optical fiber,
including: accommodating an optical fiber inside a treatment chamber; introducing a
hydrogen containing gas into the treatment chamber, and in a hydrogen treatment step,
exposing the optical fiber to atmosphere of the hydrogen containing gas, wherein, in the
hydrogen treatment step, a hydrogen concentration 5 in the treatment chamber during the
hydrogen treatment is calculated from an initial value a of a hydrogen concentration in
the hydrogen containing gas inside the treatment chamber, a concentration β of oxygen in
an ambient atmosphere of the treatment chamber, and a concentration γ of oxygen in the
hydrogen containing gas inside the treatment chamber, and the hydrogen concentration in
the treatment chamber is controlled based on the hydrogen concentration δ calculated.
In the treatment method for an optical fiber, the hydrogen concentration 6 in the
treatment chamber during the hydrogen treatment step is calculated using EQ. 2 below:
δ-αx(i-γ/β) EQ. 2
where a indicates the initial value of the hydrogen concentration in the hydrogen
containing gas inside the treatment chamber, β indicates the concentration of oxygen in
the ambient atmosphere (air) of the treatment chamber, and y indicates the concentration
of oxygen in the hydrogen containing gas inside the treatment chamber.
In the treatment method for an optical fiber described above, preferably the
treatment chamber is a sealed chamber.
In the treatment memod for an optical fiber described above, a reduced pressure
state may preferably be created inside the treatment chamber before the deuterium
containing gas is introduced Preferably, but not necessarily, pressure in the treatment
chamber during the reduced pressure state is set within a range of equal to or greater than
0.01 kPa to equal to or less than 75 kPa.
In the treatment method for an optical fiber described above, partial pressure of
deuterium during the deuterium treatment step may preferably be set within a range of
equal to or greater than 0.1 kPa to equal to or less than 5 kPa, and partial pressure of
hydrogen during the hydrogen treatment step may preferably be set within a range of
equal to or greater than 0.1 kPa to equal to or less than 4 kPa.
In the treatment memod for an optical fiber described above, pressure in the
treatment chamber during the deuterium treatment step or the hydrogen treatment step
may preferably, but not necessarily, be set within a range of equal to or greater than 10.1
kPa to equal to or less than 203 kPa.
In the treatment memod for an optical fiber described above, temperature inside
the treatment chamber may be maintained at a constant temperature within a range of
equal to or greater man S'C to equal to or less than 40°C during the deuterium treatment
step or the hydrogen treatment step.
According to the treatment method for an optical fiber of the invention, in the
case in which concentration control of the gas used in a treatment of an optical fiber is
necessary, even in the case in which direct measurement of the concentration is not
possible due to the capacity of the concentration measuring device, it is possible to
measure the concentration of the oxygen mixed in the measured gas inside the treatment
chamber and easily calculate the concentration of the measured gas from this oxygen
concentration. Therefore, in order to determine the concentration of the measured gas,
it is not necessary to extract the measured gas and analyze the measured gas by using a
complicated analyzing apparatus such as gas chromatography. Thereby, it is possible to
determine the concentration of the measured gas easily at that time. Thus, a treatment
method for an optical fiber of the invention is an advantageous treatment method in terms
of manufacture because it is possible to reduce cost and time.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
FIG. 1 is a schematic structural drawing showing an example of an optical fiber
treatment apparatus of the invention.
FIG. 2 is a graph showing the relationship between the annihilation delay time
of the non-bridging oxygen hole centers (NBOHCs) and the pressure of the decreased
pressure atmosphere in the first step.
FIG. 3 is a schematic structural diagram showing an example of the optical fiber
treatment apparatus of the invention.
FIG. 4 is a graph showing the relationship between number of treatments and the
retention rate of the partial pressure of the deuterium in the deuterium containing gas
when the optical fiber has undergone deuterium treatment after the deuterium containing
gas has been repeatedly used.
FIG. 5 is a graph showing the results of the measurement of the deuterium
concentration in the test samples of the invention.
DETAILED DESCRIPTION OF THE INVENTION
Below, a treatment method for an optical fiber mat applies embodiments of the
invention will be explained in detail.
In the treatment method for an optical fiber of the invention, first, during the
fabrication step of the optical fiber, in order to annihilate non-bridging oxygen hole
centers (hereinbelow, abbreviated "NBOHCs") generated in the optical fiber, a deuterium
treatment or a hydrogen treatment is applied to the optical fiber (in the first embodiment
to the fourth embodiment).
FIG. 1 is a schematic structural drawing showing an example of the optical fiber
treatment apparatus that is used in the treatment method for an optical fiber according to
the invention.
In FIG. 1, reference symbol 1 denotes the optical fiber treatment apparatus,
reference symbol 1a denotes a reaction chamber, reference symbol lb denotes a gas inlet,
reference symbol 1c denotes a gas inlet opening and closing valve, reference symbol 1d
denotes a gas supply piping, reference symbol 1 e denotes an outlet, reference symbol 1f
denotes a discharge opening and closing valve, 1g denotes a discharge pump, reference
symbol 1h denotes a differential pressure gauge, reference symbol 2 denotes an optical
fiber, and reference symbol 3 denotes a bobbin. This example of an optical fiber
treatment apparatus 1 includes at least the reaction chamber 1a. The reaction chamber
1a is a scalable chamber that can accommodate therein the optical fiber 2, and has a
vacuum state of about 0.1 kPa and a pressure resistance and sealing performance that can
withstand a pressurized state from normal pressure to a pressure that is equal to or less
than 250 kPa.
The gas supply piping 1d is connected to the gas inlet lb of the reaction chamber
la via the gas inlet opening and closing valve 1 c. The deuterium containing gas can be
supplied into the reaction chamber 1a ffym the gas supply piping 1 d.
Here, deuterium containing gas denotes deuterium gas alone or a mixed gas that
contains deuterium gas.
The discharge pump 1g is connected to the outlet 1e of the reaction chamber la
via the discharge opening and closing vaqlve 1f. The deuterium containing gas or the
like in the reaction chamber 1 a is discharged by this discharge pump 1 g.
The differential pressure gauge1h is disposed in the reaction chamber la, and
thereby the pressure inside the reaction chamber 1 a can be measured. Based on the
values measured by the differential pressure gauge In, it is possible to adjust the supplied
amount of deuterium containing gas and thereby create a deuterium containing gas
atmosphere inside the reaction chamber 1a that has a predetermined pressure, or to start
or stop the discharge pump 1g and thereby create a reduced pressure atmosphere inside
the reaction chamber la that has a predetermined pressure.
In addition, the reaction chamber 1a includes a temperature adjusting means (not
shown) such as a heater or cooling mechanism, a thermometer (not shown), or a
temperature adjusting portion (not shown). Thereby, by adjusting the internal
temperature, it is possible to maintain a state of constant temperature within a range of
5°C to 40°C inside the reaction chamber 1a.
Note that instead of the gas inlet opening and closing valve 1 c, the reaction
chamber 1a may include a solenoid valve (not shown) that is capable of adjusting the
amount of the gas flow. However, any device that can adjust the amount of deuterium
containing gas supplied into the reaction chamber 1 a may be used.
Next, a first embodiment of the treatment method (NBOHC annihi1ation) for an
optica] fiber according to the invention will be exp1ained with reference to FIG. 1.
In the treatment method for an optical fiber of this embodiment, in a first step,
an optical fiber 2 is exposed to the reduced pressure atmosphere as exp1ained below.
First, the optical fiber 2 having a predetermined length is wound around the
bobbin 3.
Next, the optical fiber 2 that has been wound around the bobbin 3 is p1aced in
the reaction chamber 1 a of the treatment apparatus 1. The optical fiber 2 is not
particu1arly limited as long as it is made of a silica g1ass or the like, and otherwise any
type of optical fiber can be used.
Next, after the discharge pump 1g, which is a vacuum pump, is activated, the
discharge opening and closing valve 1f is opened, a reduced pressure atmosphere is
created inside the reaction chamber 1a, that is, inside the space accommodating the
optical fiber 2, is reduced by discharging the air inside the reaction chamber 1a, and
thereby the optical fiber 2 is exposed to a reduced pressure atmosphere.
Then, in a second step, following the first step, the optical fiber 2 is exposed to
the deuterium containing gas atmosphere as described below.
After the discharge opening and closing valve 1f is closed, the temperature
inside the reaction chamber 1a is adjusted to provide a state of constant temperature
within a range of 5°C to 40°C by using a temperature adjusting means (not shown), a
thermometer (not shown), or a temperature adjusting portion (not shown). Next, the gas
inlet opening and closing valve 1c is opened and the deuterium containing gas is supplied
into the reduced pressure atmosphere inside the reaction chamber 1a. The deuterium
containing gas is supplied until the inside of the reaction chamber 1a reaches a
predetermined pressure and the atmosphere inside the space in the reaction chamber 1 a
that accommodates the optical fiber 2 has been rep1aced by the deuterium containing gas.
Then the inside of the reaction chamber 1a is sealed by closing the gas inlet opening and
closing valve 1c. The optical fiber 2 is exposed to the deuterium obtaining gas
atmosphere inside this reaction chamber 1a. Thereby, the optical fiber 2 is exposed to
the deuterium containing gas atmosphere, and by reacting the NBOHCs in the silica g1ass
that forms the optical fiber 2 with the deuterium (D2) to produce deuterated hydroxyl
groups (-OD), it is possible to prevent the generation of hydroxyl groups (-OH).
Thereby, it is possible to shift the absorption wavelength region of the optical fiber 2
from the 1.38 μm band, which is the absorption wavelength region of the hydroxyl group,
to the 1.87 μm band, which is the absorption wavelength region of the deuterated
hydroxyl group. That is to say, the wavelength absorption region is shifted outside of
the optical communication wavelength region. Thus, it is possible to inhibit the
degradation of the transmission characteristics of the optica] fiber 2 due to absorption
loss caused by the hydroxyl groups in the silica g1ass.
In addition, according to the treatment method for an optical fiber of this
embodiment, the dispersion rate of the deuterium containing gas in the reaction chamber
1a can be increased by creating a reduced pressure atmosphere inside the reaction
chamber 1 a that accommodates the optical fiber 2 and supplying the deuterium
containing gat into the reaction chamber 1a in this reduced pressure atmosphere state.
Thereby, even when the optical fiber 2 is wound around the bobbin 3, the deuterium
containing gas passes through the minute gaps between the wound optical fiber 2 and
spreads quickly into proximity to the coil core of the bobbin 3. Therefore, it is possible
to increase the probability of contact between the optical fiber 2 in proximity to the coil
core of the bobbin 3 and the deuterium gas. Thus, it is possible to apply a sufficient
(uniform) deuterium treatment throughout the entire length of the optical fiber 2.
Because the NBOHCs easily bond to the deuterium to form deuterated hydroxy]
groups, the reaction in which the NBOHCs and the deuterium bind to form deuterated
hydroxyl groups (i.e., the reaction that annihi1ates NBOHCs) is greatly influenced by the
probability of contact between the NBOHCs and the deuterium gas.
In the treatment method for an optical fiber of this embodiment, as described
above, at the optical fiber in proximity to the coil core of the bobbin 3, it is possible to
increase the probability of contact between the optical fiber 2 and the deuterium
containing gas, and thereby it is possible to increase the reaction rate between the
NBOHCs and the deuterium.
Therefore, it is possible to increase the reaction rate between the NBOHCs and
the deuterium throughout the entire optical fiber 2 that has been wound around the
bobbin 3, and it is possible to annihi1ate NBOHCs throughout the entire optical fiber
even if the exposure time is short by using the low concentration deuterium containing
gas.
Next, based on experimental results, the treatment method for an optical fiber of
mis embodiment will be explained in detail.
HO. 2 is a graph showing the re1ationship between the annihi1ation de1ay time
of the NBOHCs of the optical fiber 2 that has been wound around the bobbin 3 and the
pressure of the reduced pressure atmosphere in the first step described above.
In FIG. 2, the rhombic symbols indicate the results of the case in which, in the
second step, the partial pressure of the deuterium gas in the mixed gas atmosphere is 0.5
kPa and the circu1ar symbols indicate the result of the case in which, in the second step,
the partial pressure of the deuterium gas in the mixed gas atmosphere is 1.0 kPa.
The annihi1ation de1ay time of the NBOHCs denotes the difference between the
annihi1ation time of the NBOHCs of the optical fiber 2 positioned in the innermost 1ayer
and the annihi1ation time of the NBOHCs of the optical fiber 2 positioned in the
outermost 1ayer, that is, the difference between the annihi1ation time of the NBOHCs of
the optical fiber 2 positioned in the innermost 1ayer with respect to the annihi1ation time
of the NBOHCs of the optical fiber 2 positioned in the outermost 1ayer.
Among the portions of the optical fiber 2 that have been wound around the
bobbin 3. the optical fiber 2 positioned in the innermost 1ayer denotes the portion (optical
fiber 2) directly wound around the coil core of the bobbin 3. In contrast, among the
portions of the optical fiber 2 that has been wound around the bobbin 3, the optical fiber
2 positioned in the outermost 1ayer denotes the portion (optical fiber 2) positioned in the
outermost 1ayer.
The shorter the annihi1ation de1ay time of the NBOHCs means that the
annihi1ation time of the NBOHCs in the optical fiber 2 positioned in the innermost 1ayer
is also shorter (the reaction in which the NBOHCs are annihi1ated is fast), The
annihi1ation time of the innermost 1ayer becomes a value that is close to the annihi1ation
time of the NBOHCs of the optical fiber 2 positioned in the outermost 1ayer. This
means that the time necessary to annihi1ate the NBOHCs throughout the entire optical
fiber 2 that has been wound around the bobbin 3 is short
The annihi1ation time of the NBOHCs of the optical fiber 2 denotes the result of
measurement by tile following method.
The amount of absorption at 0.63 μm, which is the absorption wavelength of the
NBOHCs, is measured in an optical fiber 2 that has been exposed to the deuterium gas
for a predetermined time, and the remaining amount of NBOHCs is measured based on
this absorption amount
Then the change over time in the remaining amount of NBOHCs with respect to
the exposure time of the optical fiber 2 to the deuterium containing gas is found, the
exposure time to the deuterium containing gas necessary to annihi1ate the NBOHCs
completely is estithated based on the change over time in the remaining amount of
NBOHCs, and this estithation serves as the annihi1ation time of the NBOHCs.
In the first step described above, the pressure of the reduced pressure
atmosphere can be equal to or greater than 0.01 kPa and equal to or less than 75 kPa, and
can also be equal to or greater than 0.01 kPa and equal to or less than 50kPa, By
making the pressure of the reduced pressure atmosphere equal to or greater than 0.01 kPa
and equal to or less than 75 kPa, it is possible to make the dispersion rate of the
deuterium containing gas high, and it is possible to make the deuterium containing gas
spread throughout the entire optical fiber 2 that has been wound around the bobbin 3 or
the like. Thus, in the optical fiber 2 in proximity to the coil core of the bobbin 3, it is
possible to make the probability of contact between the NBOHCs and the deuterium gas
high, and thereby it is possible to accelerate the reaction between the NBOHCs and the
deuterium gas (the reaction that annihi1ates the NBOHCs). According to the above, it is
possible to make the annihi1ation time of the NBOHCs in the optical fiber 2 positioned in
the innermost 1ayer short, and thereby, as shown in FIG. 2, the annihi1ation de1ay time of
the NBOHCs can be greatly reduced
In addition, because it is possible to make the probability of contact between the
NBOHCs and the deuterium gas high, in the second step it is possible to annihi1ate
NBOHCs throughout the entire optical fiber 2 even if a low concentration deuterium
containing gas is used and the exposure time is made short
In particu1ar, in the case in which the pressure of the reduced pressure
atmosphere is equal to or greater than 0.01 kPa and equal to or less than SO kPa, the
annihi1ation de1ay time of the NBOHCs becomes 0 or about 0, where the annihi1ation
de1ay time is negligible. Thus, the NBOHCs react with the deuterium at the same
reaction rate in both the optical fiber 2 positioned in the innermost 1ayer and the optical
fiber 2 positioned in the outermost 1ayer, and thereby the NBOHCs can be annihi1ated.
In addition, in the second step described above, preferably the optical fiber 2 is
exposed to a deuterium containing gas in which the partial pressure of the deuterium gas
is equal to or greater than 0.1 kPa and equal to or less than 5 kPa. Thereby, it is
possible to spread deuterium gas having a concentration that is sufficient to annihi1ate
NBOHCs throughout the entire optical fiber 2 that has been wound around the bobbin 3
or the like.
A partial pressure of the deuterium gas less than 0.1 kPa is not preferable
because the concentration of the deuterium is low, and thus it is difficult to annihi1ate
NBOHCs throughout the entire optical fiber 2. In contrast, a partial pressure of the
deuterium gas greater man 5 kPa is not preferable because a high concentration of
deuterium is necessary, and thereby the fabrication cost becomes high.
In addition, in the second step, preferably the deuterium containing gas is
supplied into the reaction chamber 1 a that accommodates the optical fiber 2 to create a
pressure inside the reaction chamber 1a equal to or greater than 10.1 kPa and equal to or
less than 203 kPa, and the optical fiber 2 is exposed to the deuterium containing gas in
this pressure range.
Thereby, the diffusion rate of the deuterium containing gas inside the reaction
chamber 1a becomes high, the deuterium containing gas can spread quickly into
proximity to the coil core of the bobbin 3, and thereby it is possible to make the reaction
rate between the NBOHCs and the deuterium high.
The case in which the pressure of the deuterium containing gas in the reaction
chamber 1 a in which the optical fiber 2 is exposed is less than 10.1 kPa is not preferable
because the diffusion rate of the deuterium containing gas inside the reaction chamber 1 a
is low and thus the reaction in which the NBOHCs are annihi1ated requires a long time.
In addition, the case in which the pressure of the deuterium containing gas in the
reaction chamber 1a in which me optical fiber 2 is exposed is greater than 203 kPa is not
preferable because a reaction chamber 1a having a high pressure resistance must be used,
and taking into consideration safety and the like, handling of the reaction chamber 1a
becomes difficult
In the second step, preferably, but not necessarily, the exposure time during
which the optical fiber 2 is exposed to the deuterium containing gas is one day or less.
Thereby, it is possible to annihi1ate the NBOHCs throughout the entire optical fiber 2
that has been wound around the bobbin 3.
In the second step, preferably, but not necessarily, the optical fiber 2 is exposed
to the deuterium containing gas in a state in which the temperature inside the reaction
chamber 1a is adjusted so as to maintain a constant temperature within a range of equal
to or greater man 5°C to equal to or less man 40°C. Thereby, it is possible to accelerate
the reaction between the NBOHCs in the silica g1ass and the deuterium, and it is possible
to annihi1ate the NBOHCs in a short period of time.
The case in which the temperature inside the reaction chamber 1a is higher than
40 °C is not preferable because the surface covering resin 1ayer of the optical fiber 2 will
change due to the heat
FIG. 3 is a schethatic structural diagram showing another example of the optical
fiber treatment apparatus used in the treatment method for an optical fiber according to
the invention.
The optical fiber treatment apparatus 4 in this example essentially includes a
reaction chamber 4a, a deuterium storage tank 4b, and piping 4c by which the reaction
chamber 4a communicates with the deuterium storage tank 4b.
The reaction chamber 4a is a sca1able chamber that can accommodate an optical
fiber 2 therein (first space), and has a vacuum state of about 0.1 kPa and a pressure
resistance and sealing performance that can withstand a pressurized state from normal
pressure to a pressure equal to or less than 250 kPa.
The deuterium storage tank 4b is a tank that can store the deuterium containing
gas therein (second space), and, like the reaction chamber 4a, has a vacuum state of about
0.1 kPa and a pressure resistance and sealing performance that can withstand a
pressurized state from normal pressure to a pressure equal to or less than 250 kPa,
The gas supply piping 4g is connected to the gas inlet 4d of the deuterium
storage tank 4b via a gas inlet opening and closing valve 4f, and it is possible to supply
the deuterium containing gas into the reaction chamber 4a from this gas supply piping 4g.
Gas inlet and outlet openings 4h and 4i are included in the reaction chamber 4a
and the deuterium storage tank 4b. The piping 4c connects to these gas inlet and outlet
openings 4h and 4i via the opening and closing valves 4j and 4k, and the reaction
chamber 4a and the deuterium storage tank 4b communicate via the one piping 4c.
The inside of the piping 4c (third space) serves as the flow path, and the
deuterium containing gas can flow to or from either the reaction chamber 4a or the
deuterium storage tank 4b. A switching valve 4n is included along the course of the
piping 4c, and a discharge pipe 4p and a gas venti1ation device 4q are connected to this
switching valve 4n.
Any valve that has connection portions that conduct in at least three directions
and that can switch the path from the connection portion in one direction to the
connection portions in any of the other two directions can be used as the switching valve
4n, A three-direction valve or a three-direction solenoid valve can be an example of the
switching valve 4n.
In addition, a combination pressurizing and depressurizing pump such as a scroll
vacuum pump or a dry-vacuum diaphragm pump can be used as the gas venti1ation
device 4q.
In the description below, a portion of the path of the piping from the switching
valve 4n to the gas inlet and outlet opening 4h of the reaction chamber 4a is referred to as
the reaction chamber side piping 4r, and a portion of the path of the piping from the
switching valve 4n to the gas inlet and outlet opening 4i of the deuterium storage tank 4b
is referred to as the deuterium storage tank side piping 4s.
In this embodiment, the switching valve 4n enables switching from one path
among the reaction chamber side piping 4r, the deuterium storage tank side piping 4s,
and the discharge pipe 4p to any one of the paths of the other two directions, and the gas
ventilation device 4q enables venti1ating the gas from one direction to the other direction
among the two switched paths.
A differential pressure gauge 4t is disposed in the reaction chamber 4a, and
thereby the pressurein the reaction chamber 4a can be measured. By using the gas
venti1ation device 4q to adjust the supplied amount of deuterium containing gas based on
this measured value, it is possible to provide the inside of the reaction chamber 4a with a
deuterium containing gas atmosphere that has a predetermined pressure, or create a
reduced pressure atmosphere that has a predetermined pressure inside of the reaction
chamber 4a.
In addition, the reaction chamber 4a includes a temperature adjusting means
(not shown) such as a heater or cooling mechanism, a thermometer (not shown), or a
temperature adjusting portion (not shown), and thereby it is possible to maintain a state
of constant temperature within a range of 5°C to 40°C inside the reaction chamber 4a by
adjusting the internal temperature.
Next, a second embodiment of the treatment method for an optical fiber
according to the invention will be exp1ained with reference to HO. 3.
In the treatment method for an optical fiber of this embodiment, in a first step,
the optical fiber 2 is exposed to a reduced pressure atmosphere as exp1ained below.
First, an optical fiber 2 that has been wound around the bobbin 3 is p1aced inside
the reaction chamber 4a. The temperature inside the reaction chamber 4a is adjusted to
a constant temperature within a range of 5°C to 40°C. Then the switching valve 4n is
switched so as to connect the reaction chamber side piping 4r and the discharge pipe 4p.
Next, the opening and closing valve 4j of the reaction chamber side piping 4r is
opened, the air in the reaction chamber 4a is discharged to the discharge pipe 4p by the
gas venti1ation device 4q, a reduced pressure atmosphere is created inside of the reaction
chamber 4a, that is, inside the first space that accommodates the optical fiber 2, and the
optical fiber 2 is exposed to the reduced pressure atmosphere.
Next, in the second step, following the first step, the optical fiber 2 is exposed to
the deuterium containing gas as exp1ained below.
The inside of the deuterium storage tank 4b is filled in advance with a deuterium
containing gas that includes a predetermined concentration of deuterium gas at a
predetermined pressure.
Next, after closing the opening and closing valve 4j of the reaction chamber side
piping 4r, the switching valve 4n is switched so that the reaction chamber side piping 4r
and the deuterium storage tank side piping 4s are connected. Then the opening and
closing valve 4j of the reaction chamber side piping 4r and the opening and closing valve
4k of the deuterium storage tank side piping 4s are opened, and the reaction chamber 4a
and the deuterium storage tank 4b communicate via the piping 4c.
In this manner, the inside of the piping 4c (third space) serves as a passage
enabling the deuterium containing gas in the deuterium storage tank 4b to flow to the
reaction chamber 4a, which has a reduced pressure atmosphere.
Next, when the inside of the reaction chamber 4a reaches a predetermined
pressure, the reaction chamber 4a is sealed by closing the opening and closing valve 4j of
the reaction chamber side piping 4r and the opening and closing valve 4k of the
deuterium storage tank side piping 4s. The optical fiber 2 is exposed to the deuterium
containing gas inside this reaction chamber 4a.
According to the above, the optical fiber 2 is exposed to the deuterium
containing gas, the NBOHCs in the silica g1ass and the deuterium bind to form
deuterated hydroxyl groups, and thereby it is possible to annihilate the NBOHCs.
Next, the switching valve 4n is switched so that the reaction chamber side piping
4r and the deuterium storage tank side piping 4s communicate. The opening and
closing valves 4j and 4k are opened, the reaction chamber 4a and the deuterium storage
tank 4b communicate via the piping 4c, the gas venti1ation device 4q is activated, the
deuterium containing gas inside the reaction chamber 4a is transferred to the deuterium
storage tank 4b, and a vacuum is created in the inside of the reaction chamber 4a.
Next, after the opening and closing valve 4j on the reaction chamber side piping
4r is closed and air is introduced into the reaction chamber 4a, the optical fiber 2 is
extracted from the reaction chamber 4a.
According to the above, without discharging the deuterium containing gas that
has been used once, the deuterium containing gas is stored in the deuterium storage tank
4b and thus can be used in the deuterium treatment of another optical fiber 2.
FIG. 4 is a graph showing the change in the partial pressure of the deuterium gas
in the deuterium containing gas when, using the optical fiber treatment apparatus 4 of
FIG. 3, optical fibers 2 have been treated by repeatedly using the deuterium containing
gas.
In the case in which the optical fiber treatment apparatus 4 of FIG. 3 is used,
even after the deuterium treatment has been carried out 30 times, the retention rate of the
partial pressure of the deuterium is equal to or greater than 70%. This concentration
allows satisfactory deuterium treatment to be carried out
In this manner, it is possible to use the deuterium containing gas repeatedly, so
that it is possible to reduce the running costs associated with the deuterium gas
significantly, thereby creating an inexpensive deuterium treatment.
Next, a third embodiment of the treatment method for an optical fiber according
to the invention will be exp1ained with reference to FIG. 1.
The treatment method for an optical fiber in this embodiment, which annihi1ates
the NBOHCs using a deuterium treatment, is for inhibiting an increase in the
transmission loss in the optical fiber after being 1aid.
In the treatment method for an optical fiber of this embodiment, first an optical
fiber 2 having a predetermined length is wound around a bobbin 3.
Next, the optical fiber 2 that has been wound around the bobbin 3 is p1aced
inside the reaction chamber 1a of the treatment apparatus 1.
Then, after closing the discharge opening and closing valve 1 f, the temperature
inside the reaction chamber 1a is adjusted so as to maintain a state of constant
temperature within a range of 5°C to 40°C by a temperature adjusting means (not shown),
a thermometer (not shown), or a temperature adjusting portion (not shown).
Next, the gas inlet opening and closing valve 1c is opened, the deuterium
containing gas is supplied into the reaction chamber 1a, and while carrying out control
such that the deuterium concentration in the deuterium containing gas inside this reaction
chamber 1a is constant, the optical fiber 2 is exposed to the deuterium containing gas
atmosphere inside the reaction chamber 1a-
in this embodiment, in the deuterium treatment step described above, first the
concentration B of the oxygen in the ambient atmosphere (air) of the reaction chamber 1a
is measured Next, the concentration C of the oxygen in the deuterium containing gas
inside the reaction chamber 1a is measured. The deuterium concentration D inside the
reaction chamber 1a during the deuterium treatment is calcu1ated from the results of these
measurements and the initial value A of the deuterium concentration in the deuterium
containing gas inside the reaction chamber (treatment chamber) 1 a using the following
BQ. 1. Based on the calcu1ated deuterium concentration D, the deuterium concentration
inside the reaction chamber 1a is maintained at a concentration necessary for carrying out
the deuterium treatment for the optical fiber 2 inside the reaction chamber 1 a sufficiently.
Specifically, in the case in which the deuterium concentration inside the reaction
chamber 1 a does not reach the concentration required for the deuterium treatment, the
gas inlet opening and closing valve 1c is opened and deuterium containing gas is
supplied into the reaction chamber 1a. In contrast, in the case in which the deuterium
concentration inside the reaction chamber 1a exceeds the concentration required for the
deuterium treatment, the gas inlet opening and closing valve 1c is closed and the supply
of the deuterium containing gas into the reaction chamber 1a is stopped.
D=Ax(l-C/B) EQ. 1
where D indicates a deuterium concentration inside the treatment chamber during the
deuterium treatment, A indicates an initial value of the deuterium concentration in the
deuterium containing gas inside the treatment chamber, B indicates concentration of
oxygen in the ambient atmosphere (six) of the treatment chamber, and C indicates
concentration of oxygen in the deuterium containing gas inside the treatment chamber.
An oxygen densitometer (not shown) was used in order to measure the
concentration B of the oxygen in the ambient atmosphere (air) of the reaction chamber 1a
and the concentration C of the oxygen in the deuterium containing gas inside the reaction
chamber 1a. Examples of oxygen densitometers that may be used are Toray's LC-750
and Yokogawa's oxygen densitometer 0X61.
In this manner, by measuring the concentration B of the oxygen in the ambient
atmosphere (air) of the reaction chamber 1a and the concentration C of the oxygen in the
deuterium containing gas inside the reaction chamber 1a, it is possible to calcu1ate the
amount of air mixed in the atmosphere inside the reaction chamber 1a, and based on this
calcu1ated value, it is possible to calcu1ate the present deuterium concentration inside the
reaction chamber 1 a. Because there are dangers such as explosions when the gas used
in the treatment of the optical fiber is an inf1ammable gas (deuterium) as in the deuterium
treatment, in terms of control, measurement of the deuterium concentration using a
conventional combustion densitometer or an optical densitometer is not preferable. In
addition, in the case in which a deuterium containing gas is used as the gas serving as the
base, the present deuterium concentration inside the reaction chamber 1a is calcu1ated by
measuring the concentration of the air, and in particu1ar the oxygen, mixed in the
deuterium containing gas inside the reaction chamber 1a. The reason for this is that a
cause of the deuterium concentration becoming low is the air mixed into the deuterium
containing gas inside the reaction chamber 1a during the deuterium treatment
Therefore, if the amount (concentration) of the air (oxygen) mixed into the deuterium
containing gas inside the reaction chamber 1 a can be determined, then it is possible to
determine the present deuterium concentration inside the reaction chamber 1a.
Thus, according to the treatment method for an optical fiber in mis embodiment,
there are no dangers such as explosions, and thereby it is possible to control the
deuterium concentration correctly even when the composition ratios of the base gas (the
deuterium containing gas) inside the reaction chamber 1 a fluctuate.
In addition, in the treatment method for an optical fiber in this embodiment,
preferably the reaction chamber 1a is a sealed container, If the reaction chamber 1a is a
sealed container, before carrying out the deuterium treatment for the optical fiber 2 inside
the reaction chamber 1a, a reduced pressure atmosphere can be created inside the
reaction chamber 1a.
Furthermore, in the treatment method for an optical fiber in this embodiment,
preferably the deuterium treatment of the optical fiber 2 is carried out after a reduced
pressure atmosphere has been created inside the reaction chamber 1 a.
In this embodiment, a method will be exp1ained in which the deuterium
treatment of the optical fiber 2 is carried out after a reduced pressure atmosphere has
been created inside the reaction chamber 1a.
After p1acing the optical fiber 2 inside the reaction chamber 1a of the treatment
apparatus 1 and activating the discharge pump 1g, which is a vacuum pump, the
discharge opening and closing valve 1f is opened, a reduced pressure atmosphere is
created inside the reaction chamber 1a, that is, inside the space accommodating the
optical fiber 2. by discharging the air inside the reaction chamber 1 a, and thereby the
optical fiber 2 is exposed to the reduced pressure atmosphere.
Next, after providing a state of constant temperature within a range of 5°C to
40°C by adjusting the temperature inside the reaction chamber 1 a, the gas inlet opening
and closing valve 1c is opened and the deuterium containing gas is supplied into the
reduced pressure atmosphere inside the reaction chamber 1 a. Subsequently, the
deuterium containing gas is supplied until the inside of the reaction chamber 1a reaches a
predetermined pressure and the atmosphere in the space inside the reaction chamber 1a
that accommodates the optical fiber 2 is rep1aced by the deuterium containing gas.
Then the inside of the reaction chamber 1a is sealed by closing the gas inlet opening and
closing valve 1c, and the optical fiber 2 is exposed to the deuterium containing gas
atmosphere in this reaction chamber 1 a.
In this maimer, it is possible to make the dispersion rate of the deuterium
containing gas inside the reaction chamber 1a high by creating a reduced pressure
atmosphere inside the reaction chamber 1a that accommodates the optical fiber 2 and
supplying the denterium containing gas inside the reaction chamber 1a in mis reduced
pressure state. Thereby, even when the optical fiber 2 has been wound around a bobbin
3, the deuterium containing gas passes through minute gaps between the wound optical
fiber 2 and spreads quickly into proximity to the coil core of the bobbin 3. Therefore,
the probability of contact between the optical fiber 2 in proximity to the coil core of the
bobbin 3 and the deuterium containing gas can be made high. Thus, it is possible to
apply the deuterium treatment sufficiently (evenly) throughout the entire length of the
optical fiber 2.
In addition, this third embodiment of the treatment method for an optical fiber
can be applied even when the measured gas is hydrogen other than deuterium or a gas
other than oxygen, such as nitrogen. (Applicants may choose to list additional gases
here for broader disclosure and possible subject thatter for additional dependent
c1aim(s).J
Next, a fourth embodiment of the treatment method for an optical fiber
according to the invention will be exp1ained with reference to FIG. 1.
The treatment method for an optical fiber in this embodiment, which annihi1ates
the NBOHCs using a hydrogen treatment, is for inhibiting an increase in the transmission
loss in the optical fiber after being laid.
In the treatment method for an optical fiber of this embodiment, first, an optical
fiber 2 having a predetermined length is wound around a bobbin 3.
Next, the optical fiber 2 that has been wound around the bobbin 3 is p1aced
inside the reaction chamber 1a of the treatment apparatus 1.
Next, after closing the discharge opening and closing valve 1f, the temperature
inside the reaction chamber 1a is maintained at a state of constant temperature within a
range of 5°Cto 40°C by adjusting the temperature therein by using a temperature
adjusting means (not shown), a thermometer (not shown), or a temperature adjusting
portion (not shown).
Next, the gas inlet opening and closing valve 1c is opened, the hydrogen
containing gas is supplied into the reaction chamber 1a, and the optical fiber 2 is exposed
to the hydrogen containing gas atmosphere in the reaction chamber 1a while control is
carried out so that the hydrogen concentration in the hydrogen containing gas atmosphere
in this reaction chamber 1 a remains constant.
In this embodiment, in the hydrogen treatment step described above, first the
concentration β of the oxygen in the ambient atmosphere (air) of the reaction chamber 1a
is measured. Next, the concentration γ of the oxygen in the hydrogen containing gas
inside the reaction chamber 1a is measured. The hydrogen concentration 5 in the
reaction chamber 1a during the hydrogen treatment is calcu1ated from the results of these
measurements and the initial value a of the hydrogen concentration in the hydrogen
containing gas inside the reaction chamber 1a (treatment chamber) using the following
EQ. 2. Based on the calcu1ated hydrogen concentration 5, the hydrogen concentration
inside the reaction chamber 1a is maintained at a concentration necessary to carry out the
hydrogen treatment of the optical fiber 2 inside the reaction chamber 1a sufficiently.
Specifically, in the case in which the hydrogen concentration inside the reaction chamber
1a does not reaoh the concentration required for the hydrogen treatment, the gas inlet
opening and closing valve 1c is opened and the hydrogen containing gas is supplied into
the reaction chamber 1a. In contrast, in the case in which the hydrogen concentration
inside the reaction chamber 1a exceeds the concentration required for the hydrogen
treatment, the gas inlet opening and closing valve lc is closed and the supply of the
hydrogen containing gas into the reaction chamber 1a is stopped.
δ-α*(1-γ/p) EQ.2
where 8 indicates a hydrogen concentration inside the treatment chamber during the
hydrogen treatment, a indicates an initial value of the hydrogen concentration in the
hydrogen containing gas inside the treatment chamber, (3 indicates concentration of
oxygen in the ambient atmosphere (air) of the treatment chamber, and y indicates
concentration of oxygen in the hydrogen containing gas inside the treatment chamber.
An oxygen densitometer (not shown) was used to measure the concentration β
of the oxygen in the ambient atmosphere (air) of the reaction chamber 1a and the
concentration γ of the oxygen in the hydrogen containing gas in the reaction chamber 1 a.
Examples of oxygen densitometers that can be used are Toray's LC-750 and Yokogawa's
oxygen densitometer 0X61.
In this manner, the amount of air mixed into the atmosphere of the reaction
chamber 1 a is calcu1ated by measuring the concentration β of the oxygen in the ambient
atmosphere (air) of the reaction chamber 1a and the concentration 7 of the oxygen in the
hydrogen containing gas inside the reaction chamber 1a, and it is possible to calcu1ate the
present hydrogen concentration inside the reaction chamber 1a from these calcu1ated
values. Because there are dangers such as explosions and the like when the gas used in
the treatment of the optical fiber is an inf1ammable gas (hydrogen) as in the hydrogen
treatment, in terms of control, measurement of the hydrogen concentration using a
conventional combustion densitometer or an optical densitometer is not preferable.
Thus, in the case in which hydrogen containing gas is used as the gas that serves as the
base, the present hydrogen concentration inside the reaction chamber 1 a is calcu1ated by
measuring the concentration of the air, and in particu1ar, the oxygen, mixed in the
hydrogen containing gas inside the reaction chamber 1 a. The reason for this is that a
cause of the hydrogen concentration becoming low is the air mixed into the hydrogen
*
containing gas inside the reaction chamber 1 a during the hydrogen treatment Therefore,
it is possible to determine the amount (concentration) of air (oxygen) that has mixed into
the hydrogen containing gas inside the reaction chamber 1 a, and thereby it is possible to
determine the present hydrogen concentration inside the reaction chamber 1a.
Thereby, according to the treatment method for an optical fiber in this
embodiment, mere are no dangers such as explosions, and thereby it is possible to control
the hydrogen concentration correctly even when the composition ratios of the gas serving
as the base (the hydrogen containing gas) inside the reaction chamber 1 a fluctuate.
In addition, in the treatment method for an optical fiber in this embodiment,
preferably the reaction chamber 1 a is a sealed container. If the reaction chamber 1 a is a
sealed container, before carrying out the hydrogen treatment of the optical fiber 2 inside
the reaction chamber 1a, a reduced pressure atmosphere can be created inside the
reaction chamber 1a.
Furthermore, in the treatment method for an optical fiber in this embodiment,
preferably the hydrogen treatment of the optical fiber 2 is carried out after a reduced
pressure atmosphere has been created inside the reaction chamber 1a.
In this embodiment, a method will be exp1ained in which the hydrogen treatment
of the optical fiber 2 is carried out after a reduced pressure atmosphere has been created
inside the reaction chamber 1 a.
After p1acing the optical fiber 2 inside the reaction chamber 1a of the treatment
apparatus 1 and activating the discharge pump 1g, which is a vacuum pump, the
discharge opening and closing valve 1f is opened, and a reduced pressure atmosphere is
created inside of the reaction chamber 1a, that is, inside the space accommodating the
optica] fiber 2, by discharging the air inside the reaction chamber 1a, and the optical fiber
2 is exposed in the reduced pressure atmosphere.
Next, after providing a state of constant temperature within a range of 5°C to
40°C by adjusting the temperature inside the reaction chamber 1 a, the gas inlet opening
and closing valve 1 c is opened and the hydrogen containing gas is supplied into the
reduced pressure atmosphere inside the reaction chamber 1 a. Subsequently, the
hydrogen containing gas is supplied until the inside of the reaction chamber 1a reaches a
predetermined pressure and the atmosphere in the space inside the reaction chamber 1a
that accommodates the optical fiber 2 is rep1aced by the hydrogen containing gas. Then
the inside of the reaction chamber 1a is sealed by closing the gas inlet opening and
closing valve 1c, and in this reaction chamber 1a, the optical fiber 2 is exposed to the
hydrogen containing gas atmosphere.
In mis manner, it is possible to make the dispersion rate of the hydrogen
containing gas inside the reaction ohamber 1 a high by creating a reduced pressure
atmosphere inside the reaction chamber 1a that accommodates the optical fiber 2 and
supplying the hydrogen containing gas into the reaction chamber 1a in this reduced
pressure state. Thereby, even when the optical fiber 2 has been wound around the
bobbin 3, the hydrogen containing gas passes through minute gaps between the wound
optical fiber 2 and spreads quickly into proximity to the coil core of the bobbin 3.
Therefore, the probability of contact between the optical fiber 2 in proximity to the coil
core of the bobbin 3 and the hydrogen containing gas can be made high. Thus, it is
possible to apply the hydrogen treatment sufficiently (evenly) throughout the entire
length of the optical fiber 2.
Below, the invention will be exp1ained in greater detail by using an experimental
example. However, the invention is not limited by the following experimental example.
Experimental Example
An apparatus identical to the optical fiber optical fiber treatment apparatus
shown in FIG. 1 was used to apply the deuterium treatment to an optical fiber.
The deuterium treatment for an optical fiber was repeated; the deuterium
concentration in the reaction chamber was measured each time by an optical
densitometer (Riken Measuring Instruments, FI-21); the oxygen concentration in the
reaction chamber was measured by using an oxygen densitometer (Toray, LO750H); and
gas chrothatography of the deuterium inside the reaction chamber was carried out,
The deuterium gas used a nitrogen gas as the base.
The results of the measurements are shown in FIG, 5.
In FIG. 5, the deuterium concentration (calcu1ated value, indicated by the
rhombic symbols) denotes the value calcu1ated from the oxygen concentration inside the
reaction chamber measured in this experimental example and EQ. 1 described above. In
addition, the deuterium concentration (analytic value, indicated by the triangu1ar
symbols) denotes the value obtained from the gas chrothatography analysis in the present
experimental example. Furthermore, the oxygen concentration (measured value,
indicated by the square symbols) denotes the value of the oxygen concentration inside the
reaction chamber measured in the present experimental example,
From the results shown in HO. 5, it has been confirmed that, like the case in
which the deuterium inside the reaction chamber is analyzed by gas chrothatography, the
deuterium concentration can be measured easily by finding the deuterium concentration
in the reaction chamber from the values of the oxygen concentration in the reaction
chamber measured by the oxygen densitometer using EQ. 1 described above.
The treatment method for an optical fiber of the invention can be applied when
using treatment gases other men deuterium or hydrogen
It is contemp1ated that numerous modifications may be made to the exemp1ary
embodiments of the invention without departing from the spirit and scope of the
embodiments of the present invention as defined in the following c1aims.

We c1aim :
1. A treatment method for an optical fiber, comprising:
accommodating an optical fiber inside a treatment chamber;
introducing a deuterium containing gas into the treatment chamber; and
in a deuterium treatment step, exposing the optical fiber to atmosphere of the
deuterium containing gas,
wherein, in the deuterium treatment step, a deuterium concentration D in the
treatment chamber during the deuterium treatment is calcu1ated from an initial value
A of a deuterium concentration in the deuterium containing gas inside the treatment
chamber, a concentration B of oxygen in an ambient atmosphere of the treatment
chamber, and a concentration C of oxygen in the deuterium containing gas inside the
treatment chamber using EQ. 1 below, and the deuterium concentration in the
treatment chamber is controlled based on the deuterium concentration D calcu1ated.
D=Ax(l-C/B) EQ. 1
2. A treatment method for an optical fiber according to c1aim 1, wherein the treatment
chamber is a sealed chamber.
3. A treatment method for an optical fiber according to c1aim 1, wherein a reduced
pressure state is created inside the treatment chamber before the deuterium containing
gas is introduced.
4. A treatment method for an optical fiber according to c1aim 3, wherein pressure in
the treatment chamber during the reduced pressure state is set within a range of equal
to or greater than 0.01 kPa to equal to or less than 75 kPa.
5. A treatment method for an optical fiber according to c1aim 1, wherein partial
pressure of deuterium during the deuterium treatment step is set within a range of
equal to or greater than 0.1 kPa to equal to or less than 5 kPa.
6. A treatment method for an optical fiber according to c1aim 1, wherein pressure in
the treatment chamber during the deuterium treatment step is set within a range of
equal to or greater than 10.1 kPa to equal to or less than 203 kPa.
7. A treatment method for an optical fiber according to c1aim 1, wherein temperature
inside the treatment chamber is maintained at a constant temperature within a range of
equal to or greater than 5°C to equal to or less than 40° C during the deuterium
treatment step.
8. A treatment method for an optical fiber, comprising:
accommodating an optical fiber inside a treatment chamber;
introducing a hydrogen containing gas into the treatment chamber; and
in a hydrogen treatment step, exposing the optical fiber to atmosphere of the
hydrogen containing gas, wherein,
in the hydrogen treatment step, a hydrogen concentration 8 in the treatment
chamber during the hydrogen treatment is calcu1ated from an initial value α of a
hydrogen concentration in the hydrogen containing gas inside the treatment chamber,
a concentration β of oxygen in an ambient atmosphere of the treatment chamber, and a
concentration y of oxygen in the hydrogen containing gas inside the treatment
chamber using EO. 2 below, and the hydrogen concentration in the treatment chamber
is controlled based on the hydrogen concentration 8 calcu1ated,

9. A treatment method for an optical fiber according to c1aim 8, wherein the treatment
chamber is a sealed chamber.
10. A treatment method for an optical fiber according to c1aim 8, wherein a reduced
pressure state is created inside the treatment chamber before the hydrogen containing
gas is introduced.
11. A treatment method for an optical fiber according to c1aim 10, wherein pressure
in the treatment chamber during the reduced pressure state is set within a range of
equal to or greater than 0.01 kPa to equal to or less than 75 kPa.
12. A treatment method for an optical fiber according to c1aim 8, wherein partial
pressure of hydrogen during the hydrogen treatment step is set within a range of equal
to or greater than 0.1 kPa to equal to or less than 4 kPa.
13. A treatment method for an optical fiber according to c1aim 8, wherein pressure in
the treatment chamber during the hydrogen treatment step is set within a range of
equal to or greater than 10.1 kPa to equal to or less than 203 kPa.
14. A treatment method for an optical fiber according to c1aim 8, wherein temperature
inside the treatment chamber is maintained at a constant temperature within a range of
equal to or greater than 5°C to equal to or less than 40° C during the hydrogen
treatment step.
15. A treatment method for an optical fiber according to c1aim 1, wherein non-
bridging oxygen hole centers or NBOHCs which are generated in the optical fiber
react with the deuterium or are annihi1ated at the same reaction rate in both the optical
fiber positioned in an innermost 1ayer and the optical fiber positioned in an outermost
1ayer, so that there is no annihi1ation de1ay time.
16. A treatment method for an optical fiber according to c1aim 1, wherein the
absorption wavelength region of the optical fiber is shifted from the 1.38 μm band,
which is the absorption wavelength region of the hydroxyl group, to the 1.87 μm
band, which is the absorption wavelength region of the deuterated hydroxyl group.
17. A treatment method for an optical fiber according to c1aim 1, wherein absorption
loss caused by the hydroxyl groups in the silica g1ass of the optical fiber inhibits
degradation of the transmission characteristics of the optical fiber.
18. A treatment method for an optical fiber according to c1aim 1, wherein a
dispersion rate of the deuterium containing gas in the reaction chamber is increased.
19. A treatment method for an optical fiber according to c1aim 1, wherein an optical
fiber treatment apparatus comprises a reaction chamber, a deuterium storage tank and
piping by which the reaction chamber communicates with the deuterium storage tank.
20. A treatment method for an optical fiber according to c1aim 19, wherein the
deuterium containing gas stored in the deuterium storage tank is used in the deuterium
treatment of at least one other optical fiber.
21. A treatment method for an optical fiber according to c1aim 1, wherein the
deuterium gas used a nitrogen gas as a base.

A treatment method for an optical fiber (2) including accommodating an
optical fiber inside a treatment chamber (1a); introducing a deuterium containing gas
into the treatment chamber (1a); and in a deuterium treatment step, exposing the
optical fiber (2) to atmosphere of the deuterium containing gas. In the deuterium
treatment step, a deuterium concentration D in the treatment chamber (1a) during the
deuterium treatment is calculated from an initial value A of a deuterium concentration
in the deuterium containing gas inside the treatment chamber (1a), a concentration B
of oxygen in an ambient atmosphere of the treatment chamber (1a), and a
concentration C of oxygen in the deuterium containing gas inside the treatment
chamber (1a), and the deuterium concentration in the treatment chamber (1a) is
controlled based on the deuterium concentration D calculated. Other gases such as
hydrogen containing gas or nitrogen containing gas may also be used according to the
invention.

Documents:

1092-KOL-2005-CORRESPONDENCE.pdf

1092-KOL-2005-FORM 27.pdf

1092-KOL-2005-FORM-27.pdf

1092-kol-2005-granted-abstract.pdf

1092-kol-2005-granted-assignment.pdf

1092-kol-2005-granted-claims.pdf

1092-kol-2005-granted-correspondence.pdf

1092-kol-2005-granted-description (complete).pdf

1092-kol-2005-granted-drawings.pdf

1092-kol-2005-granted-examination report.pdf

1092-kol-2005-granted-form 1.pdf

1092-kol-2005-granted-form 13.pdf

1092-kol-2005-granted-form 18.pdf

1092-kol-2005-granted-form 2.pdf

1092-kol-2005-granted-form 3.pdf

1092-kol-2005-granted-form 5.pdf

1092-kol-2005-granted-gpa.pdf

1092-kol-2005-granted-priority document.pdf

1092-kol-2005-granted-reply to examination report.pdf

1092-kol-2005-granted-specification.pdf

1092-kol-2005-granted-translated copy of priority document.pdf

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Patent Number

229483

Indian Patent Application Number

1092/KOL/2005

PG Journal Number

08/2009

Publication Date

20-Feb-2009

Grant Date

18-Feb-2009

Date of Filing

30-Nov-2005

Name of Patentee

FUJIKURA LTD

Applicant Address

5-1, KIBA 1-CHOME, KOHTOH-KU

Inventors:

#	Inventor's Name	Inventor's Address
1	YAMASHIRO KENJI	C/O FUJIKURA LTD. SAKURA WORKS 1440, MUTSUZAKI SAKURA-SHI, CHIBA-KEN
2	HAMADA TAKAHIRO	C/O FUJIKURA LTD. SAKURA WORKS 1440, MUTSUZAKI SAKURA-SHI, CHIBA-KEN
3	FUJIMAKI MUNEHISA	C/O FUJIKURA LTD. SAKURA WORKS 1440, MUTSUZAKI SAKURA-SHI, CHIBA-KEN
4	HARADA KOICHI	C/O FUJIKURA LTD. SAKURA WORKS 1440, MUTSUZAKI SAKURA-SHI, CHIBA-KEN
5	SHIRAKO YUKINARI	C/O FUJIKURA LTD. SAKURA WORKS 1440, MUTSUZAKI SAKURA-SHI, CHIBA-KEN
6	SAWANO HIROYUKI	C/O FUJIKURA LTD. SAKURA WORKS 1440, MUTSUZAKI SAKURA-SHI, CHIBA-KEN
7	HIROFUNE SHUNICHIROU	C/O FUJIKURA LTD. SAKURA WORKS 1440, MUTSUZAKI SAKURA-SHI, CHIBA-KEN

PCT International Classification Number

C01B 4/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	2004-349938	2004-12-02	Japan