Title of Invention	AN APPARATUS FOR COOLING A QUARTZ TUBE
Abstract	Disclosed is an apparatus for cooling a quartz tube used in fabrication of an optical fiber preform by MCVD, which comprises a nozzle part supplied with a coolant consisting of at least two vent sections so as to be separated for detaching the quartz tube from a lathe mounting it during processing, and a plurality of vents formed along the inside of the vent sections for ejecting the coolant.

Full Text

-1A- The invention relates to an apparatus and method for cooling a quartz tube. Background of the Invention The present invention further concerns an apparatus for fabricating an optical fibre preform by modified chemical vapour deposition (MCVD) and more particularly an apparatus for cooling a quartz tube used in the fabrication of an optical fibre. Since the intensity of an optical signal is usually reduced when it is transmitted through a long distance or divided into several branches, it is necessary to amplify the optical signal using a semiconductor or light amplifier. The light amplifier is widely used in ultra high speed communication networks, generally employing an erbium (Er) doped optical fibre as a medium for amplifying the optical signal. The erbium doped optical fibre is fabricated using modified chemical vapour deposition (MCVD). The fabrication of an optical fibre preform for a light amplifier by using MCVD will now be described with reference to Fig. 1. A raw gas 8 0 composed of SiC14 or GeCl4 and a proper amount of an additional chemicals is made to flow through a quartz tube 50 fixedly attached to a chuck while the quartz tube 50 is rotated and heated by a burner 82 to produce a hot zone 78. The raw gas 80 undergoes a chemical reaction in the hot zone 78, producing particles. The reaction formula is SiCl4 + 02 -> SiO2 + 2C12 and GeCl4 + 02 -> GeO2 + 2C12. The particles are deposited onto the inside of the quartz tube 50 which has a lower temperature in the flow direction under thermophoresis.. The burner 82 is moved at a given speed in the gas flow direction, so that the chemical reaction to produce the particles is continuously carried out following the burner, as is the deposition of the particles along the inside of the quartz tube 50. 2 Meanwhile, the deposited particles are sintered by the heat of the moving burner 82 to form a glass phase coating. Thus, firstly a clad layer 72 is formed on the inside of the quartz tube 5 0 to prevent penetration of foreign matter. Then, the core layer 74 is formed to transmit light by flowing a raw gas 8 0 of different composition through the quartz tube. This quartz tube 5 0 is heated to over 2000°C, collapsed and closed to form a final optical fibre preform. To obtain an optical fibre preform for a light amplifier using MCVD, a process such as liquid penetration, gaseous state addition or sol-gel is used. The liquid penetration process is used with a porous layer formed over the core layer. A liquid of a given composition is caused to penetrate the porous layer to modify the properties of the optical fibre preform. In this case, the uniformity, density, particle size, thickness, adhesiveness, etc. of the porous layer greatly affect the property of the finally obtained optical fibre. Referring to Fig. 2, a cooling apparatus is provided behind the burner to form the porous layer. After forming the clad layer 72 and the core layer 74 as shown in Fig. 1, the burner 82 is moved in the direction opposite to the flowing direction of the raw gas 8 0 while the cooling apparatus 70 ejects a coolant 48 towards the upper outside surface of the quartz tube 50, whereby a porous layer 76 is gradually formed over the core layer 74 as shown in Fig. 2. However, such a cooling process results in non-uniform cooling of the inside of the quartz tube 50 because of the coolant being ejected in a single direction towards the quartz tube, and thus a nonuniform porous layer 76, so that the finally obtained optical fibre has a nonuniform distribution of refractive index, increasing the reflective loss. Another conventional cooling apparatus for achieving the 3 porous layer consists, as shown in Fig. 3, of a coolant supply tank 60 for supplying a coolant 48, a nozzle support annular tube 64, a connecting tube 62 for supplying the coolant 48 from the coolant supply tank 60 to the nozzle support annular tube 64, and a plurality of nozzles 66 radially mounted along the inner perimeter of the nozzle support annular tube 64 to eject the coolant towards the quartz tube 50. The nozzles 66 project towards the centre of the nozzle support annular tube 64. In operation, the coolant 48 is supplied from the coolant supply tank 60 through the nozzles 66 towards the outside of the quartz tube 50, thereby forming the porous layer 76 over the core layer 74 formed on the inside of the quartz tube 50. However, this also suffers from a drawback in that it is difficult to mount the nozzles radially on the inner perimeter of the nozzle support annular tube 64, so that the number of assembly steps is increased, reducing productivity. In addition, it is impossible to attach or detach a quartz tube to or from a lathe during processing because the nozzle support annular tube 64 is made of a single continuous ring. Summary of the Invention It is an objective of the present invention to address the above disadvantages and accordingly, the present invention provides apparatus for cooling a quartz tube during fabrication of an optical fibre preform by modified chemical vapour deposition (MCVD), the apparatus comprising a nozzle adapted to surround the quartz tube and including a plurality of vents for ejecting a coolant inwards towards the quartz tube, the nozzle being formed from at least two separable nozzle sections, so as to allow the quartz tube to be removed from the nozzle without requiring either end of the quartz tube to pass through the nozzle. Preferably, the nozzle consists of first and second nozzle sections. The vents may be formed in at least two lines along the inside of the nozzle sections and are so arranged 4 as to provide substantially uniform cooling to the quartz tube. Preferably, the vents are radially symmetrically formed along the inside of the nozzle sections at substantially constant intervals. The apparatus may be adapted for use with, for example, water or nitrogen gas as the coolant. The apparatus preferably further comprises a bracket for supporting the nozzle and a coolant collector for, collecting coolant ejected from the vents. For example, where the nozzle consists of first and second nozzle sections, the apparatus may further comprise a first connecting arm for pivotally connecting the first nozzle section to the bracket and a second connecting arm for pivotally connecting the second nozzle section to the bracket such that the first and second nozzle sections may be pivotally closed to enclose the quartz tube and pivotally opened from each other so as to enable said quartz tube to be removed. Preferably, the first connecting arm is connected at its end opposite to the first neazle section by a first hinge and the second connecting arm is connected at its end opposite to the second nozzle section by a second hinge. The first and second connecting arms may be fastened together by a screw so as to prevent them from being moved when closed together. In the case where the bracket is connected between the nozzle and the coolant collector, the apparatus preferably comprises a coolant supply line for supplying coolant to the nozzle sections, a coolant regulator for regulating the coolant supplied to the coolant supply line and a coolant reservoir for storing the coolant from the coolant collector. The present invention also provides a method of cooling a quartz tube during fabrication of an optical fibre preform 5 by modified chemical vapour deposition (MCVD), the method comprising surrounding the quartz tube with a nozzle formed from at least two separable nozzle sections and including a plurality of vents, ejecting a coolant inwards towards the quartz tube via the vents and separating the nozzle sections and removing the quartz tube from the nozzle without either end of the quartz tube passing through the nozzle. Preferably, a porous layer is formed within the optical fibre preform. The method may be performed during fabrication of an optical fibre preform for a light amplifier, such as an erbium doped optical fibre preform. Brief Description of the accmpanying Drawings The present invention will now be described by way of example with reference to the accompanying drawings in which: Fig. 1 illustrates the conventional fabrication of an optical fibre preform using MCVD; Fig. 2 illustrates the step of forming a porous layer during fabrication of an optical fibre preform for a light amplifier using a conventional cooling apparatus; Fig. 3 illustrates the step of forming a porous layer during fabrication of an optical fibre preform for a light amplifier using another conventional cooling apparatus; Fig. 4 is a perspective view of a cooling apparatus for forming such a porous layer according to the present invention; and Fig. 5 illustrates the step of forming, a porous layer during fabrication of an optical fibre preform for a light amplifier using the cooling apparatus of FIG. 4. Detailed Description of the Preferred Embodiment Referring to Fig. 4, a cooling apparatus 10 includes a nozzle 78 consisting of a first nozzle section 12 and a second nozzle section 14, supplied with a coolant 48 such as water or nitrogen gas through a coolant supply line 38. The first and second nozzle sections 12 and 14 are designed 6 to be separated to allow a quartz tube 5 0 to be detached from a lathe upon which it is mounted. A plurality of vents 16 are formed with a constant circumferential interval and radially symmetrically along the inside of the nozzle sections 12 and 14 for ejecting the coolant. The vents 16 are arranged in at least one line along the inner perimeter of the nozzle consisting of the first and second nozzle sections, to provide uniform cooling to the quartz tube 50, so as to achieve a uniform porous layer 76 for an optical fibre preform for a light amplifier. The first nozzle section 12 has at one side a first connection hole 18 connected with a first coolant supply tube 38a for guiding the coolant to the first nozzle section 12. Likewise, the second nozzle section 14 has at one side a second connection hole 2 0 connected with a second coolant supply tube 3 8b for guiding the coolant to the second nozzle section 14. The first and second coolant tubes 38a and 38b branch from the coolant supply line 38. Of course, the first and second coolant supply tubes may be separately arranged. A coolant collector 40 is arranged below the nozzle 78 to collect the coolant ejected out of the vents 16. The coolant collector 40 is connected with a coolant reservoir 46 through a discharge tube 44. A bracket 32 is provided to support the nozzle 78 and connect it with the coolant collector 40. The bracket 32 is arranged to move the nozzle 78 along the quartz tube 50 to be cooled. If the coolant 48 is a gas, the coolant collector 40, coolant reservoir 46 and discharge tube 44 are separate from the cooling apparatus 10. A first connecting arm 22 is provided to pivotally connect the first nozzle section 12 to the bracket 32 by means of a first hinge 34. Likewise, a second connecting arm 24 is provided to pivotally connect the second nozzle section 14 7 to the bracket 32 by means of a second hinge 36. The first and second connecting arms 22 and 24 are fastened together by means of a screw 30 to prevent the first and second nozzle sections 12 and 14 from being moved when they have been closed together. The screw 3 0 is inserted through a first and a second screw hole 26 and 28 respectively formed in the first and second connecting arms. A coolant regulator 42 is connected with the coolant supply line 38 to regulate the supplying of the coolant 48. The cooling apparatus may be used in all processes requiring a quartz tube, from which optical fibre preforms are fabricated using MCVD, to be cooled, and in particular to form the porous layer in the quartz tube for fabrication into an optical fibre preform for a light amplifier or an erbium doped optical fibre preform. In a quartz tube for fabrication into an optical fibre preform for a light amplifier, there are sequentially formed a clad layer 72 for preventing penetration of foreign matter and a core layer 74 for transmitting light on the inside of a quartz tube 50 fixedly attached to a lathe. Then, the quartz tube 50 is placed between the first and second nozzle sections 12 and 14 by pivoting the first and second connecting arms 22 and 24 respectively on the first and second hinges 34 and 36 towards each other. The first and second nozzle sections 12 and 14 are firmly fastened by means of the screw 3 0 to complete the nozzle 78. Of course, the quartz tube 50 may easily be detached as desired by unscrewing the screw 3 0 to separate the first and second nozzle sections 12 and 14. Thereafter, the coolant 48 is regulated by the coolant regulator 42 and supplied to the coolant supply line 38. The first and second nozzle sections 12 and 14 are respectively supplied with the coolant 48 through the first and second coolant supply tubes 38a and 38b. The coolant is finally ejected through the vents 16 towards the outside of the quartz tube 50 so as to uniformly cool it, so that a 8 porous layer is formed over the core layer 74. The ejected coolant 48 is collected by the coolant collector 40, and flows through the discharge tube 44 into the coolant reservoir 46. As described above, the present invention provides means for uniformly forming a porous layer in a quartz tube. Instead of using a plurality of specially prepared nozzles, the cooling apparatus consists of a plurality of vents directly formed in the annular nozzle, so that the process of assembly is greatly simplified, resulting in considerable reduction in costs. In addition, the nozzle is divided into the first and second nozzle sections so as to allow easy attachment and detachment of a quartz tube to and from a lathe. Moreover, the first and second nozzle sections are separately structured making it possible to supply the coolant only to a part of the quartz tube if desired. Furthermore, the bracket may move the nozzle along the quartz tube so as to adjust the position of the cooling apparatus. WE CLAIM; 1. Apparatus (10) for cooling a quartz tube (50) during fabrication of an optical fibre preform by modified chemical vapour deposition (MCVD), the apparatus (10) comprising a nozzle (78) adapted to surround the quartz tube (50), a plurality of vents (16) for ejecting a coolant (48) inwards towards the quartz tube (50), the nozzle (78) being formed from at least two separable nozzle sections (12., 14), so as to allow the quartz tube (50) to be removed from said nozzle (78) without requiring either end of the quartz tube (50) to pass through said nozzle (78). 2. Apparatus as claimed in claim 1, wherein said nozzle (78) comprises first (12) and second nozzle (14) sections. 3. Apparatus as claimed in claim 1 or claim 2, wherein said vents (16) are formed in at least two lines along the inside of said nozzle sections (12, 14) to provide substantially uniform cooling to said quartz tube (50). 4. Apparatus as claimed in claim 3, wherein said vents(16) are radially symmetrically formed along the inside of said nozzle sections (12, 14) at substantially constant intervals. 5. Apparatus as claimed in any of the preceding claims is adaptable for use with water or with nitrogen gas as the coolant. 9 6. Apparatus as claimed in any of the preceding claims wherein said nozzle provided with a bracket (32) for supporting said nozzle (78) for connecting it to a coolant collector (40) collecting coolant (48) ejected from said vents (16). 7. Apparatus as claimed in claim 6, wherein said first and second nozzle sections (12, 14) comprises a first connecting arm (22) for pivotally connecting said first nozzle section (12) to said bracket (32) and a second connecting arm (24) for pivotally connecting said second nozzle section (14) to said bracket (32) such that said first and second nozzle sections (12, 14) can be pivotally closed to enclose said quartz tube (50) and pivotally opened from each other so as to enable said quartz tube (50) to be removed. 8. Apparatus as claimed in claim 7, wherein said first connecting arm (22) is connected at its end opposite to said first nozzle section (12) by a first hinge (34) and said second connecting arm (24) connected at its end opposite to said second nozzle section (14) by a second hinge (36). 9. Apparatus as claimed in claim 7 or claim 8, wherein said first and second connecting arms (22, 24) are fastened together by a screw (30) so as to prevent them from being moved when closed together. 10. Apparatus as claimed in any one of claims 6-9 wherein said bracket (32) is connected between said nozzle (78) and said coolant collector (40). 10 11 11. Apparatus as claimed in claim 6, comprising a coolant supply line (33) for supplying coolant (48) to said nozzle sections (12,14), a coolant regulator (42) for regulating said coolant (48) supplied in said coolant supply line (38); and a coolant reservoir (46) for storing the coolant (48) from said coolant collector (40). Disclosed is an apparatus for cooling a quartz tube used in fabrication of an optical fiber preform by MCVD, which comprises a nozzle part supplied with a coolant consisting of at least two vent sections so as to be separated for detaching the quartz tube from a lathe mounting it during processing, and a plurality of vents formed along the inside of the vent sections for ejecting the coolant.

Documents:

01681-cal-1997-abstract.pdf

01681-cal-1997-claims.pdf

01681-cal-1997-correspondence-1.1.pdf

01681-cal-1997-correspondence-1.2.pdf

01681-cal-1997-description(complete).pdf

01681-cal-1997-drawings.pdf

01681-cal-1997-form-1.pdf

01681-cal-1997-form-2.pdf

01681-cal-1997-form-3.pdf

01681-cal-1997-form-5.pdf

01681-cal-1997-p.a.pdf

01681-cal-1997-priority document.pdf

1681-cal-1997-granted-abstract.pdf

1681-cal-1997-granted-claims.pdf

1681-cal-1997-granted-correspondence.pdf

1681-cal-1997-granted-description (complete).pdf

1681-cal-1997-granted-drawings.pdf

1681-cal-1997-granted-examination report.pdf

1681-cal-1997-granted-form 1.pdf

1681-cal-1997-granted-form 2.pdf

1681-cal-1997-granted-form 3.pdf

1681-cal-1997-granted-form 5.pdf

1681-cal-1997-granted-letter patent.pdf

1681-cal-1997-granted-pa.pdf

1681-cal-1997-granted-priority document.pdf

1681-cal-1997-granted-reply to examination report.pdf

1681-cal-1997-granted-specification.pdf

1681-cal-1997-granted-translated copy of priority document.pdf