JP2006012979A - Light amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light amplifier using EDFA which amplifies two or more waves simultaneously at low costs and with high stability. <P>SOLUTION: A light amplifier 1 is provided with a wavelength band filter 4a for branching light signals La and Lb carried out by wavelength division multiplexing, an excitation light source 10 for emitting light in excitation light Le, a distribution coupler 11 for distributing the excitation light Le from the excitation light source 10, two or more WDM 5a and 5b for superimposing on each light signal La and Lb the demultiplexed excitation lights Lea and Leb distributed from the distribution coupler 11 with the wavelength band filter 4a, amplification media 6a and 6b for amplifying the light signal outputted from these WDM 5a and 5b respectively by the excitation lights Lea and Leb, and a multiplexer 4c for multiplexing the light signal amplified by these amplification media 6a and 6b. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical amplifier that amplifies a wavelength division multiplexed optical signal with pumping light.

  In conventional optical communication, there is a method of transmitting an optical signal by wavelength division multiplexing (WDM) in order to increase the transmission capacity of the transmission path.

  In transmission of this optical signal, it is a common practice to extend the transmission distance by performing optical amplification.

  A prior art optical amplifier is shown in FIG.

  The optical signal outputs of the optical transmitters 2a and 2b that transmit optical signals having different wavelengths are wavelength division multiplexed by the WDM 3a and transmitted. The transmitted multiplexed optical signal is amplified by the optical amplifier 31 in an optical repeater or the like. That is, the multiplexed optical signal input to the optical amplifier 31 is superimposed with the pumping light emitted from the pumping light source 10 by the WDM 5c, and the optical signal of each wavelength input using the superimposed pumping light as the energy source is amplified. Simultaneously amplified by the medium 6c. The optical signals of the respective wavelengths amplified by the same amplification medium 6c are output via the coupler 7c.

  A part of the optical signal branched from the coupler 7c is monitored by detecting the level of the optical signal by the photodiode 8c. The optical signal amplified by the optical amplifier 31 is transmitted, and the transmitted optical signal is demultiplexed by the WDM 3c and received by the optical receivers 9a and 9b.

  As prior art document information related to the invention of this application, the following is disclosed.

Japanese Patent Laid-Open No. 7-140422 JP-A-11-112434

  However, the rare earth-doped fiber type amplification medium 6c such as EDFA (Erbium Dropped Fiber Amplifier) used in the prior art has wavelength dependency in its gain characteristics, so that the optical transmitter 2a When the optical signal and the optical signal from the optical transmitter 2b are multiplexed and amplified simultaneously, the amplified power is not good at both wavelengths even though the optical signals of both wavelengths 1530nm and 1550nm have the same input power. There was a problem that it became equal (see FIG. 4).

  Also, when an optical signal of a certain wavelength is added depending on the communication status or any signal is removed due to some kind of failure, the output fluctuations due to the mutual influence of each amplified wavelength signal There was also a problem that was remarkable.

  In order to avoid this output non-uniformity, it can be considered that amplification is performed by a separate amplifier 31 for each single wavelength. Since the pumping light powers for obtaining the same output at both wavelengths are substantially equal, if they are amplified by separate amplifying media 6c, an equal light output can be obtained, but the number of optical amplifiers 31 is doubled and the cost is also doubled. There is a problem of becoming.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an optical amplifier using an EDFA that is low-cost and highly stable and amplifies two or more wavelengths simultaneously.

  The present invention was devised to achieve the above object, and the first invention is a wavelength band filter for demultiplexing an optical signal that has been wavelength-division multiplexed, an excitation light source that emits excitation light, and the excitation A distribution coupler that distributes the excitation light from the light source, a plurality of WDMs for superimposing the excitation light distributed from the distribution coupler on each optical signal demultiplexed by the wavelength band filter, and outputs from these WDMs The optical amplifier includes an amplification medium for amplifying each of the optical signals to be amplified by the pumping light, and a multiplexer for multiplexing the optical signals amplified by these amplification media.

  In the second invention, the optical signal is composed of an optical signal having a wavelength of 1550 nm and an optical signal having a wavelength of 1530 nm.

  In a third aspect of the invention, the excitation light source emits excitation light having a wavelength of 980 nm or excitation light having a wavelength of 1480 nm.

  A fourth invention includes a photodiode for monitoring the output of each of the amplification media.

  According to the present invention, it is possible to obtain an optical amplifier using an EDFA that is low in cost, highly stable, and simultaneously amplifies two or more wavelengths.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the accompanying drawings.

  FIG. 1 shows a configuration of an optical amplifier and connected peripheral devices according to a preferred embodiment of the present invention.

  As illustrated, the optical amplifier 1 includes a wavelength band filter 4a that demultiplexes the wavelength-division multiplexed optical signals La and Lb, a pumping light source 10 that emits pumping light Le, and pumping light Le from the pumping light source 10. A distribution coupler 11 for distribution, and two or more WDMs 5a and 5b for superimposing the excitation lights Lea and Leb distributed from the distribution coupler 11 on the respective optical signals La and Lb demultiplexed by the wavelength band filter 4a; Amplifying media 6a and 6b for amplifying optical signals output from the WDMs 5a and 5b by the distributed pumping light Lea and Leb, and optical signals amplified by the amplifying media 6a and 6b are combined. Couplers 7a and 7b that branch the amplified optical signals between the output sides of the amplification media 6a and 6b and the input side of the multiplexer 4c as necessary. Photodiodes 8a for monitoring, and the 8b are provided.

  The wavelength band filter 4a filters two-wavelength optical signals La and Lb multiplexed by a connected WDM 3a, which will be described later, and demultiplexes them into optical signals La and Lb for each wavelength similar to those before multiplexing. It is a bandpass filter.

  The WDM 5a is an optical component that superimposes the input optical signal La and the distributed excitation light Lea, and the WDM 5b is an optical component that superimposes the input optical signal Lb and the distributed excitation light Leb. is there.

  The amplification media (EDFA) 6a and 6b are optical amplifying elements for each wavelength for amplifying the input optical signals La and Lb of each wavelength. The amplification media 6a and 6b are optical fiber amplifiers to which rare earth (erbium) that uses the stimulated emission action of the excitation light Le emitted from the excitation light source 10 is added. For example, the optical signals La and Lb of 1530 nm and 1550 nm are respectively transmitted. Amplify.

  The couplers 7a and 7b are optical distributors for branching the monitoring optical signal to the photodiodes 8a and 8b, respectively, in order to monitor the level of the optical signal amplified and output by the amplification media 6a and 6b.

  The photodiodes 8a and 8b are photodetectors for monitoring the level of the optical signal amplified by the amplification media 6a and 6b by the optical signal for monitoring branched by the couplers 7a and 7b. The photodiodes 8a and 8b are provided separately for each output of the amplification media 6a and 6b. This is because, when optical output control (not shown) performed in the optical amplifier 1 is performed by optical output constant control (ALC), This is because each optical signal output level is individually monitored so as to maintain the amplification stability of each wavelength with respect to addition / removal of wavelengths.

  In the optical amplifier 1, in order not to increase the number of active element components, a tap is provided on the output side of the multiplexer 4c on which two wavelengths are superimposed, and another wavelength band filter is provided between one photodiode. Further, it may be inserted and redistributed, and the wavelength of each redistributed optical signal may be monitored with a photodiode.

  Such a configuration is effective in suppressing the increase in the number of parts as much as possible in order to maintain the stability of the optical amplifier 1, and is the most desirable form for performing constant gain control (AGC) in the optical amplifier 1.

  The excitation light source 10 is an optical component that emits excitation light Le for optical amplification of the optical signals La and Lb by the amplification media 6a and 6b. For example, excitation light having a wavelength of 980 nm and 1480 nm using a laser diode or the like is used. An element that emits light of a single wavelength is typical and is generally used as an energy source for amplification of the amplification media 6a and 6b.

  The multiplexer 4c is a band-pass filter for filtering optical signals of two wavelengths from the connected couplers 7a and 7b, multiplexing the signals in the same transmission path, and outputting the multiplexed signals.

  The distribution coupler 11 is an optical distributor for distributing the excitation light Le emitted from the excitation light source 10 and inputting it to the WDMs 5a and 5b.

  The distribution coupler 11 for distributing the pumping light Le has a variable power distribution ratio. As the distribution coupler 11, a thermo-optic optical waveguide 1 × 2 coupler or the like may be used.

  The distribution coupler 11 can adjust the ratio of the intensity (power) of the distributed excitation lights Lea and Leb input to the amplification media 6a and 6b via the WDMs 5a and 5b, respectively, by applying power. . When both the optical signals La and Lb of both wavelengths demultiplexed by the wavelength band filter 4a are amplified together, the WDMs 5a and 6b have the power distribution ratio set in advance in both the amplification media 6a and 6b. When the distribution coupler 11 is adjusted so as to be input via 5b and only the optical signals La and Lb of either wavelength are amplified, the amplification medium 6a that requires the pumping light Lea and Leb for amplification is required. , 6b, the distribution coupler 11 may be adjusted so as to be input only.

  The excitation light from the excitation light source 10 is supplied to individual amplification media 6a and 6b for amplifying wavelengths 1530 nm and 1550 nm via the WDMs 5a and 5b, respectively, with a distribution ratio set in advance by the distribution coupler 11. By adjusting the distribution ratio of the distribution coupler 11, the intensity of the excitation light injected into the amplification media 6a and 6b can be freely varied.

  Naturally, when it is known that an optical signal is not input to either of the amplification media 6a and 6b, excitation light to the amplification media 6a and 6b to which no optical signal is input by adjusting the distribution ratio of the distribution coupler 11 The supply of Lea and Leb can be stopped, and when it is known that neither of the amplification media 6a and 6b receives an optical signal, the supply of the excitation light Le emitted from the excitation light source 10 can be stopped. is there.

  Before and after the optical amplifier 1, optical transmitters 2a and 2b for transmitting optical signals La and Lb, WDMs 3a and 3c for wavelength division multiplexing, and optical receivers 9a and 9b for receiving optical signals, Is connected.

  The optical transmitters 2a and 2b are transmitters for performing communication using optical signals, and transmit optical signals La and Lb of 1530 nm and 1550 nm, for example.

  The optical receivers 9a and 9b are receivers for optical communication that receive and demodulate the optical signals transmitted from the optical transmitters 2a and 2b, respectively.

  The WDM 3a is an optical component for multiplexing the optical signals La and Lb sent from the optical transmitters 2a and 2b and outputting the multiplexed signals to the optical amplifier 1. The WDM 3b filters the optical signals amplified and multiplexed by the optical amplifier. Thus, the optical components are divided into optical signals having respective wavelengths before multiplexing, and the divided optical signals are output to the optical receivers 9a and 9b.

  Next, connection of the optical amplifier 1 and peripheral devices will be described with reference to the drawings.

  The output terminals of the optical transmitter 2a and the optical transmitter 2b are each connected to the input side of the WDM 3a. The output side of the WDM 3a is connected to the input side of the wavelength band filter 4a. The demultiplexed outputs of the wavelength band filter 4a are connected to the WDMs 5a and 5b, respectively.

  The output side of the WDM 5a is connected to the amplification medium 6a. The output side of the amplification medium 6a is connected to the coupler 7a. The output side of the coupler 7a is connected to the multiplexer 4c, and the branched output side of the coupler 7a is connected to the photodiode 8a.

  The output side of the WDM 5b is connected to the amplification medium 6b. The output side of the amplification medium 6b is connected to the coupler 7b. The output side of the coupler 7b is connected to the multiplexer 4c, and the branched output side of the coupler 7b is connected to the photodiode 8b.

  The output side of the multiplexer 4c is connected to the WDM 3c. The branched output side of the WDM 3c is connected to the optical receivers 9a and 9b, respectively.

  The excitation light source 10 is connected to the distribution coupler 11. The distributed outputs of the distribution coupler 11 are connected to the WDMs 5a and 5b, respectively.

  Each of the photodiodes 8a and 8b is provided with a monitor terminal.

  Next, the function and effect of the optical amplifier 1 will be described.

  The optical signals La and Lb respectively transmitted from the optical transmitters 2a and 2b are wavelength division multiplexed by the WDM 3a and output. The multiplexed optical signal output from the WDM 3 a is transmitted through the optical fiber and input to the optical amplifier 1.

  The optical signals La and Lb input to the wavelength band filter 4a of the optical amplifier 1 are demultiplexed by the wavelength band filter 4a into optical signals La and Lb before being multiplexed by the WDM 3a. The demultiplexed optical signals La and Lb are input to the WDMs 5a and 5b, respectively.

  On the other hand, the excitation light Le emitted from the excitation light source 10 is input to the distribution coupler 11. The pumping light Le input to the distribution coupler 11 is distributed at a preset power distribution ratio, and the distributed pumping light Lea and Leb are input to the WDMs 5a and 5b, respectively.

  The optical signal La input to the WDM 5a and the excitation light Lea distributed by the distribution coupler 11 are superimposed by the WDM 5a and output to the amplification medium 6a. The optical signal La input to the amplifying medium 6a is amplified by stimulated emission using the excitation light Lea input at the same time as an energy source. The amplified optical signal is output to the coupler 7a. The optical signal input to the coupler 7a is branched to monitor the amplification level of the optical signal partially amplified. The branched optical signal is input to the photodiode 8a, and the optical signal level is detected. Most of the power input to the coupler 7a passes through the coupler 7a as it is and is input to the multiplexer 4c.

  The optical signal Lb input to the WDM 5b and the excitation light Leb distributed by the distribution coupler 11 are superimposed by the WDM 5b and output to the amplification medium 6b. The optical signal Lb input to the amplifying medium 6b is amplified by stimulated emission action using the excitation light Leb input at the same time as an energy source. The amplified optical signal is output to the coupler 7b. The optical signal input to the coupler 7b is branched to monitor the amplification level of the optical signal partially amplified. The branched optical signal is input to the photodiode 8b, and the optical signal level is detected. Most of the power input to the coupler 7b passes through the coupler 7b as it is and is input to the multiplexer 4c.

  In the embodiment of FIG. 1, since the optical signals La and Lb are separately amplified by the amplification media 6a and 6b, the two optical signals shown in FIG. 3 are amplified by the same amplification media 6c. Such output non-uniformity does not occur, and a uniform amplified output can be obtained regardless of the wavelength.

  Further, since the base noise of the signals when the optical signals La and Lb are amplified is also amplified separately by the amplification media 6a and 6b in the embodiment of FIG. 1, the two optical signals shown in FIG. 3 are the same. Amplified output having a substantially uniform S / N ratio regardless of the wavelength without causing a non-uniformity of the S / N ratio (Signal to Noise: signal / noise ratio) as in the conventional amplification amplified with the amplification medium. Is obtained.

  FIG. 4 shows the output of the prior art optical amplifier 31. In the figure, the horizontal axis represents the wavelength (unit: nm) of the optical signal, and the vertical axis represents the signal intensity (unit: dBm).

  As can be seen, the output P at 1530 nm has a signal intensity of about −16 dBm, whereas the output Q at 1550 nm has a signal intensity of −5.55 dBm (in the figure, the TMkr (Peak) marker is indicated by an arrow). The wavelength is displayed at the upper left in the figure as 1552.5 nm.), And the level of each wavelength is uneven. Further, the level of the base noise is also unequal as indicated by R and S in the figure.

  On the other hand, FIG. 2 shows the output of the optical amplifier 1 of the present embodiment. In the figure, the horizontal axis represents the wavelength (unit: nm) of the optical signal, and the vertical axis represents the signal intensity (unit: dBm).

  As can be seen from the figure, the output X at 1530 nm has a signal intensity of about −6 dBm, whereas the output Y at 1550 nm has a signal intensity of −5.84 dBm (in the figure, a TMkr (Peak) marker is indicated by an arrow). The wavelength is displayed at the upper left in the figure as 1552.5 nm.) The level of each wavelength is almost uniform. Further, the level of the base noise is substantially uniform as indicated by Z in the figure, and the problems of the conventional technique are solved.

  The amplification degree and the S / N ratio of these amplification media 6a and 6b are the concentration of erbium added to the amplification media 6a and 6b used, the length of the optical fiber used, and the distributed excitation light Lea and Leb. Depends on light intensity etc. Therefore, by sufficiently adjusting the erbium concentration added to the optical fiber, the length of the optical fiber to be used, and the light intensity of the pumping light Lea and Leb, it is possible to realize the amplifying media 6a and 6b with equal amplification degree, Optical signals La and Lb of each wavelength can be amplified evenly.

  Further, since the optical signals La and Lb of both wavelengths pass through separate amplification media 6a and 6b, even if the optical signals La and Lb of either wavelength are added or removed, the other optical signals La and Lb are amplified. The outputs of the amplifying media 6a and 6b can independently obtain a stable output level. That is, the stability of the optical transient response characteristic can be obtained in the configuration shown in FIG.

  When the optical signals La and Lb of one wavelength are suddenly removed for some reason, the excitation lights Lea and Leb are still input to the amplification media 6a and 6b on the side where the optical signals La and Lb are removed. As a result, ASE (Amplified Spountaneous Emission, amplified spontaneous emission light) increases and noise increases due to this ASE, but each wavelength of the combined wavelength band filter 4a and multiplexer 4c is increased. If the isolation is sufficient, the increase in noise due to the influence of ASE and the mutual interference are sufficiently reduced.

  When the addition or removal of the optical signals La and Lb is known in advance, it is natural to adjust the distribution ratio to the above-described distribution coupler 11 so as not to depend on the isolation of the wavelength band filter 4a and the multiplexer 4c. By changing the intensity of the excitation light Lea and Leb, noise increase and interference due to the influence of ASE can be effectively removed.

  The two amplified optical signals input to the multiplexer 4c are combined and output by the multiplexer 4c. The optical signal combined by the multiplexer 4c is transmitted through an optical cable or the like and input to the WDM 3c. The two amplified optical signals input to the WDM 3c are demultiplexed, and the demultiplexed optical signals are input to the optical receivers 9a and 9b, respectively. The optical receivers 9a and 9b that have received the demultiplexed optical signals amplify and demodulate the received optical signals.

  The multiplexed optical signal amplified and transmitted as described above is obtained by optically amplifying the two-wavelength optical signals La and Lb by the individual amplification media 6a and 6b for the respective optical signals. An excellent effect is achieved in that the signal can be evenly amplified.

  In this way, the optical signals amplified by the amplification media 6a and 6b for each wavelength exhibit an excellent effect that their S / N ratios are output almost equally.

  Further, since the optical signals La and Lb of both wavelengths pass through separate amplification media 6a and 6b, even if the optical signals La and Lb of either wavelength are added or removed, the other optical signals La and Lb are amplified. The outputs of the amplifying media 6a and 6b can independently obtain a stable output level.

  Further, although the amplification media 6a and 6b are required as many as the number of wavelengths to be multiplexed, an excitation light source 10 using a laser having a high unit cost and a driver (not shown) for the excitation light source 10 are added. Therefore, since only one excitation light source 10 and driver are required as in the prior art, an increase in cost can be suppressed as much as possible.

  Further, by providing the photodiodes 8a and 8b individually, there is an effect that the amplification outputs of the amplification media 6a and 6b can be individually monitored with high accuracy.

  As described above, the optical amplifier 1 according to the embodiment described so far is an optical module for amplification using an EDFA that can amplify optical signals of two or more wavelengths uniformly, and is excellent in obtaining a highly stable output. Demonstrate the effect.

It is a block diagram which shows the optical amplifier which is embodiment which concerns on this invention, and its peripheral device. It is a characteristic figure which shows the state of amplification of the optical amplifier of this Embodiment. It is a block diagram which shows the optical amplifier of a prior art, and its peripheral device. It is a characteristic view which shows the state of amplification of the optical amplifier of a prior art.

Explanation of symbols

1 Optical amplifier 2a, 2b Optical transmitter 3a, 3c WDM
4a Wavelength band filter 4b Multiplexer 5a, 5b WDM
6a, 6b Amplification medium 7a, 7b Coupler 8a, 8b Photodiode (PD)
9a, 9b Optical receiver 10 Excitation light source 11 Distribution coupler La, Lb Optical signal Le Excitation light Lea, Leb Excitation light (distributed excitation light)

Claims (4)

  The wavelength band filter for demultiplexing the wavelength division multiplexed optical signal, the excitation light source for emitting the excitation light, the distribution coupler for distributing the excitation light from the excitation light source, and the excitation light distributed from the distribution coupler described above A plurality of WDMs for superimposing on the respective optical signals demultiplexed by the wavelength band filter, an amplification medium for amplifying the optical signals output from these WDMs by the excitation light, and An optical amplifier comprising: a multiplexer that multiplexes the amplified optical signals.   2. The optical amplifier according to claim 1, wherein the optical signal comprises an optical signal having a wavelength of 1550 nm and an optical signal having a wavelength of 1530 nm.   The optical amplifier according to claim 1, wherein the excitation light source emits excitation light having a wavelength of 980 nm or excitation light having a wavelength of 1480 nm. The optical amplifier according to claim 1, further comprising a photodiode for monitoring an output of each of the amplification media.

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