Title of Invention

"LIGHT WAVE COMMUNICATION SYSTEM FOR TRANSMISSION OF VOICE SIGNAL"

Abstract

A light wave communication system for transmission of voice signal over the single mode optical fiber comprising a transmitter, a single mode fiber enabling the light rays to travel in parallel with fiber, optical amplifier and a receiver characterized in that the said optical amplifier comprises an optical isolator, wavelength division multiplexer (WDM) coupler connected in series with the said isolator, a pump laser such as herein described feeding the predetermined desired signal to the wavelength division multiplexer coupler (WDM), predetermined length of Erbium doped fiber connected to the said wavelength division multiplexer (WDM) in series synchronizing the input signal in conjunction with the signal from said pump laser to enable the strengthening of input signal to the desired level while weakening the pump laser signal correspondingly, a second isolator connected in series with the said Erbium doped fiber to avoid the signal to flow backwards enabling the signal to reach at a greater distance with higher decibels (db).

Full Text

The present invention relates to a light wave communication system for transmission of voice signals over the single mode optical fiber over long distance with minimum noise to signal ratio. The main embodiment of the present invention lies in the optical amplifier amplifying the signal from 1480±15 nanometers to 1550±20 nanometers. The light wave communication has been advancing very rapidly, the scientists and engineers are relentless in developing new designs for fiber systems that can operate at a faster rate, for a longer distance and with a better efficiency. The conventional lightwave communication system generally uses Laser or LED as source, Optical fiber made of silica glass as transmission medium and photodiodes as detectors. These light emitting diodes used as transmitters generally operated at a wavelength of approximately 870 nanometers. In these systems, light from the transmitters generally operated at a wavelength of approximately 870 nanometers. In these systems, light from the transmitter travelling in the Silica glass fiber can attenuate as well as disperse or even broaden. Excessive loss and dispersion causes the receiver to make detection errors that translate into a High Bit Error Ration (for Digital Systems) and degradation in SNR (for analog communication). The attenuation in light is due to microbends, light absorptions and scattering within the fiber. The microbends are defined as small deviations of fiber from it's ideal axis that causes the light rays to reflect partially rather than totally when they strike the corecladding interface. Scattering occurs due to minute impurities or defects that arise from non-ideal manufacturing processes of the fiber that can absorb or scatter light when the rays strike them. Dispersion from the light pulse occurs because light rays travelling in parallel with fiber arrive at the destination sooner than, those making many reflections (intermodal dispersion) and different wavelengths travel at different velocities in the fiber (intramodal). Optical fibers that transport signals for the telecommunications industry can carry an enormous amount of information between widely separated terminals. Although optical fibers are used precisely because of their low transmission losses, regeneration is still necessary to compensate for transmission and splitting losses. During the late 1970's advanced fiber technology techniques led to reduced impurities in fiber, so attenuation in fiber can be drastically reduced. In addition a new type of fiber was developed - single mode fiber, which forces the light rays to travel in parallel with the fiber so intermodal dispersion is eliminated. Injection laser diodes with wavelenghts of 1310 nanometers and 1550 nanometers proved to be the ideal transmitters. Even with the above mentioned progresses, the distance between transmitter and receiver is still limited to about 40-60 Km; Optical repeaters or regenerators must be used in longer routes. In conventional systems requirement for repeaters or regenerators arises in long haul because with standard terminal equipment the required length of distance can not be bridged. Basic function of a repeater is to receive the incoming optical signal, convert it into an electrical signal (0/E conversion) and then to reconvert the electrical signal into an optical signal (E/0 conversion) with a higher optical power output . These 0/E & E/0 conversion processes using opto-electronic components are not very efficient. From an economic point of view repeaters are unattractive as special facilities such as buildings, roadside cabinets, underwater housings, power supplies, battery backups and complex supervisory equipment are required. This poses a problem especially in remote or inaccessible locations. A recent breakthrough in optical communication introduced optical amplifiers which could make opto-electronic regenerators obsolete. In optical amplifiers, intensity of light is amplified without requiring the optoelectronic conversion of the optical signal. Therefore unlike many new technologies, optical amplifiers are rather simple with very few electronic components. Due to their simple structure, optical amplifiers should be more reliable and cost effective than regenerators as the elimination of repeaters not only saves repeaters stations, but also reduces installation and maintenance costs.Thus it becomes cheap and bit rate independent. Another major advantage of the present system is that the future systems operating at lOGbit/s or higher can operate over the optical network already in place thereby reusing both fiber and optical repeaters. Thus the optical amplifiers are also future proof which would be an essential feature for developing countries where enough resources are not available to frequently replace old technology with new better and improved technology within a span of few years. Therefore, one of the prime objectives of the introduction of optical amplifiers is to increase the number of links which can be bridged by repeaterless terminal-to-terminal transmission. An optical amplifier amplifies the intensity of light pulses travelling in fiber. It provides energy to these pulses without the complex and expensive 0/E and E/0 conversions. The present invention relates to a light wave communication system targeted at increasing the range of distance covered by a signal from a transmitter and a receiver . The light wave technology has been upgraded with the advent of the optical amplifiers. The optical amplifiers that replaced the conventionally used repeaters and regenerators basically belong to two categories. One of them is Fiber-amplifier and the other is Semiconductor Laser Amplifiers. Compared to Semiconductor Laser Amplifiers, the Fiber-amplifiers with innovative features are being used to give better performance at longer distances. A Fiber amplifier though a simple device, it's main components are a predetermined length of fiber doped uniformly upto a desired thickness with a certain chemical element such as Erbium, Praseodymium and Neodymium; a pumping laser source; optical couplers; optical isolators. A feed back loop may also be used to stabilize the laser source for a particular output power. The fiber is doped in the desired phemical element by a process that injects a controlled amount of a specific chemical element into the glass without altering the transmission characteristics of the fiber. Optical energy generated by the pumping laser source is converted by the doped fiber to optical energy at the same wavelength and phase as the incoming optical signal. The laser source continuously pumps energy to the optical coupler, which in turn transfers the energy to the doped fiber. The energy absorbed by the ions in the said doped fiber stimulates the said ions to a highly unstable state. When a weakened signal enters the doped fiber, these "excited" dopants transfer their energy to "rejuvenate" the signal through a process known as stimulated emission . Optical isolators prevent noise reflections induced from lasing or backscattering of the higher power and rejuvenated signal and the feedback loop monitors the output power and increases or decreases the pumping source to obtain a desired output. The net effect of this is a signal output of higher powers which maintains the phase of the input signal. The dopants used are Erbium, Praseodymium and Neodymium. Most of the fiber systems operate at the wavelenghts of about 1550nm and 1310nm and generally give an output of low decibels (db) , thus limiting the distance between the transmitter and receiver. Therefore the focus has been to amplify the signals around these wavelengths . Accordingly the 1550 nanometer optical amplifier, commonly known as Erbium doped fiber amplifier (EDFA) boosts the signal around 1550±20 nm. The dopant in this case is the rare earth element Er3+ . Erbium has the atomic number 68 and belongs to Group III B of the transition metals in the periodic table . Erbium has a pair of energy levels with displacement near the 1500nm. Although several pumping laser sources can stimulate Erbium , sources at 1480nm (InGaAsP diode laser) and 980nm (Ti-sapphire laser) proved to have a best efficiency in energizing Erbium atoms and therefore, provide the best gain. However Erbium doped fiber amplifiers (EDFA) are most suitable for use due to it's high gain, high output power, reliability and less polarization dependence. Moreover the fabrication of the constituent components of EDFA are easier compared to others. These Erbium doped fiber amplifiers promise to revolutionize lightwave technology, lowering systems costs while enhancing network performance and reliability. The high gain (G40 decibels), high output power (P100 milliwatts), and near ideal noise performance achieved by EDFAs, which operate in the 1550 nm telecommunications window, have been unparalleled by any competing simplifier technology. EDFAs are inherently fiber compatible, insensitive to polarization effects, and immune to crosstalk among wavelength multiplexed channels. The present system uses EDFAs as a power amplifiers to boost transmitter power, optical repeaters to amplify weak signals, and as optical preamplifiers to increase receiver sensitivity. The success of EDFA system experiments and the decision to use EDFAs as repeaters in the next generation of transoceanic submarine lightwave systems demonstrate the practical benefits of EDFAs and their potential in lightwave systems. In current systems, regeneration requires use of a complicated optoelectronic regenerators in which a photodetector converts the attenuated optical signal into an electrical signal. High speed electronic circuitry then reshapes and amplifies the electrical signals. Finally a laser transmits the regenerated optical signal. The erbium doped fiber amplifiers (EDFAs) on the other hand, directly amplifies optical signals and promises to revolutionize optical signals and consequently optical communications. Gain, output power and amplifier noise are the most important characteristics of the EDFAs for use in the communication systems. Gain is defined as the ratio of optical signal power to the input signal power . The modest pump power needed to achieve high gain is the key to practicality of the EDFA; such power is within the capabilities of a compact semiconductor diode 'laser powered by several hundred milliamperes of drive current . Saturation occurs when large signal output power from the amplifier . This saturation results when the signal power grows large and causes stimulated emission in such a high rate that the inversion is decreased, i.e. the number of excited Erbium ions decreases substantially . The output signal power is limited only by the available pump power . The EDFAs may replace optoelectronic repeaters in many existing applications such as : a) Power amplifiers , which boost transmitter power and increase span length in transmission systems, or which compensate losses in networking systems. b) Preamplifiers, which enhance receiver sensitivity c) Preamplifiers which boost the signal periodically in long distance systems . The present invention relates to light wave communication system with the emphasis on the line amplifiers which boost the signal periodically in long distance systems . Light wave communication system has advanced rapidly since the 1970's with the optical fiber amplifier replacing the conventional optical communication methods . The Erbium Doped Fiber Amplifiers popularly known as EDFAs have revolutionized the communication technology . The remarkable attributes of EDFAs like it being inherently fiber compatible, insensitive to polarization effects and immunity to crosstalk among wavelength multiplexed channels alongwith the ease with which they can be realized have propelled EDFAs from their discovery in the research laboratories to commercial availability in a short span of less than three years . The present invention relates to a light wave communication system wherein the main embodiment lies in the preamplifiers which boost the signal periodically in long distance system. According to the present invention a light wave communication system for transmission of voice signal over the single mode fiber enabling the light rays to travel in parallel with fiber, optical amplifier and a receiver characterized in that the said optical amplifier comprises of an isolator, wavelength division multiplexer (WDM) coupler connected in series with the said isolator, a pump laser feeding the predetermined desired signal to the wavelength division multiplexer coupler (WDM), predetermined length of Erbium doped fiber connected to the said wavelength division multiplexer (WDM) in series synchronizing the input signal in conjunction with the signal from said pump laser to enable strengthening of the input signal to the desired level while weakening the pump laser signal correspondingly, a second isolator connected in series with the said Erbium doped fiber to avoid the signal to flow backwards enabling the signal to reach at a greater distance with higher decibels (db). The wavelength of the input signal in the present invention is 1550±20 nanometer, preferably the wavelength is 1550 nanometers whereas the wavelength of the pump laser signal is 1480±15 nanometer, preferably is of 1480 nanometers. According to the present invention there is provided a light wave communication system for transmission of voice signal over the single mode optical fiber comprising a transmitter, a single mode fiber enabling the light rays to travel in parallel with fiber, optical amplifier and a receiver characterized in that the said optical amplifier comprises an optical isolator, wavelength division multiplexer (WDM) coupler connected in series with the said isolator, a pump laser such as herein described feeding the predetermined signal such as herein described to the wavelength division multiplexer coupler (WDM), predetermined length of Erbium doped fiber connected to the said wavelength division multiplexer (WDM) in series synchronizing the input signal in conjunction with the signal from said pump laser to enable the strengthening of input signal to the desired level while weakening the pump laser signal correspondingly, a second isolator connected in series with the said Erbium doped fiber to avoid the signal to flow backwards enabling the signal to reach at a greater distance with higher decibels (db). BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS The invention will be described more explicitly with reference to the accompanying drawings wherein Figure 1 shows the schematic diagram representation of the Erbium doped fiber amplifier and Figure 2 shows the schematic diagram showing the optical amplifiers in point to point transmission system. The Figure 1 represents the schematic diagram of the Erbium doped fiber amplifier (EDFA). Here the FC/APC connector-1 provides input in the amplifier and is angled at 45° to stop any back reflection of the optical wave, thereby decreasing the noise factor. This connector I is connected further to an Isolator-1 which allows passage of light in one direction only and prevents back reflection of light in similar way as Connector-1. The Isolator 1 thereby passes on the input signal to the WDM coupler which is also connected in parallel to the pump laser at one side and to the Erbium doped fiber at the other end. The Erbium doped fiber is linked to an Isolator-2. The Isolator-2 is further. connected to FC/APC Connector-2 . The Isolator-2 performs the same function as the Isolator-1 and does not allow any back reflection of the signal thereby ensuring the passage of the signal only in one direction i.e. forward direction. The optical energy from the pump laser is inserted into the signal path by a WDM coupler. Inside the Erbium doped fiber the photons of pump energy are absorbed by the Erbium (ER3+) ions, causing them to rise to a higher levels of energy. From this level, the ions decay rapidly to a metastable state, here they remain for a relatively long time thereby creating a population inversion with respect to the ground state. The arrival of a signal proton of wavelength corresponding to the energy difference between these two states stimulates an ion in the metastable state to drop to the ground state, releasing its energy in the form of a photon equal in wavelength and phase to the signal photon. This effect is repeated many times throughout the length of the Erbium doped fiber resulting in amplification. In the present invention the Erbium ions are pumped up to an upper energy level by the absorption of light from the pump source at 1480±15 nanometers.The arrival of a signal photon of wavelength 1550±20 nanometers corresponding to the energy difference between these two states stimulates an ion in the metastable state to drop to the ground state. The transition to the ground state emits a photon and as there are photons present which possess the transition energy, stimulated emission occurs. The long lifetime of the excited state ensures that the instead of emitting noise by spontaneous emission most erbium ions will Vait to amplify signals by stimulated emission. The transition to the ground state is accompanied by the release in energy in the form of a photon equal in wavelength and phase to the incoming wavelength i.e. amplification of the incoming signal at a wavelength of 1550±20 nanometers occurs whereas the signal from the pump laser at a wavelength of 1480±15 nanometers weakens correspondingly. The Figure 2 depicts the application of the optical amplifiers in point to point transmission systems.The EDFA has the capability of replacing the optoelectronic repeaters in many existing applications as is evident from the present representation. The transmitter (1) sends a signal of 1-2 db which is amplified by the power amplifier (2), which simultaneously increases the noise signal and is further amplified by conventional line amplifier. The amplified signal is further amplified in the novel designed preamplifier (3) where the signal is amplified 12-14 times, while the laser signal is weakened, such that the noise signal is diminished to a great extent. WE CLAIM: 1. A light wave communication system for transmission of voice signal over the single mode optical fiber comprising a transmitter, a single mode fiber enabling the light rays to travel in parallel with fiber, optical amplifier and a receiver characterized in that the said optical amplifier comprises an optical isolator, wavelength division multiplexer (WDM) coupler connected in series with the said isolator, a pump laser such as herein described feeding the predetermined signal such as herein described to the wavelength division multiplexer coupler (WDM), predetermined length of Erbium doped fiber connected to the said wavelength division multiplexer (WDM) in series synchronizing the input signal in conjunction with the signal from said pump laser to enable the strengthening of input signal to the desired level while weakening the pump laser signal correspondingly, a second isolator connected in series with the said Erbium doped fiber to avoid the signal to flow backwards enabling the signal to reach at a greater distance with higher decibels (db). 2. A light wave communication system for transmission of voice signal as claimed in claim 1, wherein the said Erbium doped fiber is configured to boost the level of the weak input signal to a output signal of desirable power. 3. A light wave communication system for transmission of voice signal as claimed in claim 1, wherein the said pump laser is configured to generate sufficient power enough to boost the weak input signal into an output signal of power level such as herein described. 4. A light wave communication system for transmission of voice signal as claimed in claim 1, wherein the said Erbium doped fiber is having a doping of 220 parts per million. 5. A light wave communication system for transmission of voice signal as claimed in claim 1, wherein the wavelength of the input signal is 1550±20 nanometers preferably at 1550 nanometers. 6. A light wave communication system for transmission of voice signal as claimed in claim 1, wherein the wavelength of the pump laser signal 1480±15 nanometers preferably 1480 nanometers. 7. A light wave communication system for transmission of voice signal as claimed in claim 1, wherein the said isolators are placed between the WDM coupler and Erbium doped fiber respectively to obtain 15-20 times the output as compared to input. 8. A light wave communication system for transmission of voice signal as claimed in claim 1, wherein the thickness of doping enables the output to a voice level of 12-13 decibel (db). 9. A light wave communication system for transmission of voice signal as claimed in claim 1, wherein the length of the said erbium doped fiber is 18-24 meters. 10. A light wave telecommunication system for transmission of voice signal substantially as hereinbefore described in accordance with the accompanying drawings.

Documents:

933-del-1996-abstract.pdf

933-del-1996-claims.pdf

933-del-1996-correspondence-others.pdf

933-del-1996-correspondence-po.pdf

933-del-1996-description (complete).pdf

933-del-1996-drawings.pdf

933-del-1996-form-1.pdf

933-del-1996-form-19.pdf

933-del-1996-form-2.pdf

933-del-1996-form-4.pdf

933-del-1996-gpa.pdf