JP2007088326A - Light amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light amplifier that rarely distorts an output light signal waveform. <P>SOLUTION: A natural light generated by optical signal input to an optical fiber amplifier 101 is input to an optical filter 103 together with an input optical signal. The optical filter 103 passes an optical signal using a wavelength different from that of the input optical signal as a center wavelength. The optical signal passed through the optical filter 103 is input to an optical coupler 105 as a control light via an optical switch 104, and then combined with the input optical signal. Because the intensities of natural light generated via the optical fiber amplifier 101 and input optical signal are complementary, the intensity variation of output optical signal form the optical coupler 105 lowers. Namely, the gain variation of the optical fiber amplifier 101 lowers depending on the intensity variation of an input optical signal, and consequently, waveform distortion is suppressed in the output optical signal. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical amplifying device, and more particularly to an optical amplifying device that reduces disturbance in the waveform of an optical signal to be amplified.

  2. Description of the Related Art Optical amplifiers are widely used as devices that make up transmission distance by compensating for propagation loss of optical signals in optical fibers. In particular, so-called optical fiber amplifiers that optically excite a rare earth such as erbium ion added to an optical fiber are widely used because they cover a part of the low-loss wavelength band of quartz fiber.

  In such an optical fiber amplifier, it is possible to perform optical amplification with the optical fiber. And the fusion technique with the external fiber has matured, and further, the output of the semiconductor laser for optical excitation has been increased. Therefore, by using such optical fiber amplification, it is possible to configure a high-power optical amplification device with little optical S / N degradation. In addition, since a plurality of wavelength-multiplexed optical signals can be amplified at a time, it has been put to practical use as a basic device that brings transmission distance and capacity.

  The optical amplification in the optical amplifying apparatus is established by exciting a laser medium such as a rare earth doped fiber with external light and absorbing light between specific energy levels and emitting light. The average lifetime of light emission determines the low-frequency cutoff of the optical amplifier. Therefore, the optical gain of the optical amplifying device is substantially constant for an optical signal whose optical intensity is modulated at a speed sufficiently faster than the low-frequency cutoff frequency.

  On the other hand, when the intensity modulation frequency of the optical signal is close to the low cut-off frequency, the waveform of the optical signal output from the optical amplifying device can be greatly disturbed by the influence of the average life time of light emission. In order to amplify an optical signal including an intensity modulation component in the vicinity of such a low cut-off frequency, a wavelength-multiplexed dummy light source different from the optical signal to be amplified is wavelength-multiplexed, and the intensity-modulated frequency of the wavelength-multiplexed optical signal Must be far away from the low cutoff frequency of the optical amplifier. The dummy light source may be an optical signal whose light intensity is not modulated or an intensity-modulated optical signal whose modulation frequency is sufficiently higher than the low-frequency cutoff frequency.

  As a technique for realizing such optical amplification, an optical amplifying device is disclosed in which an optical fiber amplifier including a rare-earth doped fiber, an optical coupler, and a pumping laser is provided with an optical feedback path including an optical filter, an optical attenuator, and an optical circulator. (For example, refer nonpatent literature 1).

  In this example, the spontaneous emission noise light output from the optical fiber amplifier is separated from the input optical signal by the optical circulator, wavelength-selected by the optical filter, and then fed back to the optical fiber amplifier through the optical attenuator and optical circulator. ing. The intensity of spontaneous emission noise light output from the optical filter is weak, but the light intensity is gradually increased by passing through the feedback path and the optical fiber amplifier a plurality of times. When the optical loss of the feedback path is canceled by the gain of the optical amplifier, laser oscillation light at the transmission center wavelength of the optical filter is obtained from the optical fiber amplifier.

  When the light intensity modulation signal to be amplified is input to the light amplification device, the intensity of the spontaneous emission light that is the source of the laser oscillation light is weakened at the time when the intensity of the light intensity modulation signal is large. When the intensity is weak, the intensity of spontaneous emission light is increased. For this reason, the intensity of the laser oscillation light from the feedback path and the optical fiber amplifier can reverse the strength relationship with the light intensity modulation signal to be amplified. As a result, the average light intensity of the wavelength multiplexed optical signal combining the laser oscillation light and the light intensity modulation signal is made substantially uniform, and the gain of the optical fiber amplifier can be made uniform.

In order to perform optical amplification with excellent noise characteristics for the light intensity modulation signal, the output level of the laser oscillation light from the optical feedback path and the optical fiber amplifier is the same as that of the light intensity modulation signal input to the light amplification device. Since it is desirable to control according to the extinction ratio and the average intensity, in the optical amplifying device disclosed in Non-Patent Document 1, the light intensity in the optical feedback path is detected by a photodetector, and the optical intensity in the optical feedback path is detected. The method of controlling the output level of the pump laser in the fiber amplifier based on the above information is taken.
M.M. Hashimoto et. al, “The charactoristic of WDM systems with Hybrid AGC EDFA in the photonics network,” Optical Fiber Communications (OFC) 2002, ThR, 2002 (Figure).

  In the above-described prior art, the gain of the optical fiber amplifier is adjusted by controlling the output light intensity of the pump laser in the optical fiber amplifier based on the light intensity information of the optical feedback path. When the rare earth doped fiber is included, there is a problem that the waveform of the optical signal output from the optical fiber amplifier is disturbed by the influence of the response time of light emission in the rare earth doped fiber.

  Here, when the light intensity modulation signal to be amplified is a burst signal, the low frequency cutoff frequency of the optical fiber amplifier is included in the band. When the instantaneous modulation frequency of the light intensity modulation signal having a high extinction ratio is in the frequency range of about 1 octave (about 0.1 to 10 times) with respect to the low-frequency cutoff of the optical fiber amplifier, the light of the rare earth doped fiber Due to the influence of the emission, the waveform of the optical signal amplified by the optical fiber amplifier is likely to be disturbed. In particular, when wavelength multiplexed signals are amplified together by an optical fiber amplifier, the waveform of the optical signal of the other channel is output at the output of the optical fiber amplifier by inputting a channel signal having a high extinction ratio and a burst intensity modulated optical signal. The problem of disturbing also arises.

  As described above, in the conventional optical amplifying device, since the laser medium such as the rare earth fiber is included in the gain control system of the optical amplifier, depending on the extinction ratio and the modulation band of the input light intensity modulation signal, There is a problem that the waveform of the optical signal output from the optical amplifying device is disturbed due to the influence of the response time of the medium.

  The present invention has been made to solve the above-described problems of the prior art, and provides an optical amplifying device that can reduce the disturbance of the waveform of an optical signal output from an optical fiber amplifier. Objective.

  In order to achieve the above object, an optical amplifying device of the present invention is an optical amplifying device for amplifying an input optical signal, and is disposed at a stage subsequent to an optical fiber amplifier and the optical fiber amplifier. An optical signal having a central wavelength that is different from the central wavelength of the input optical signal by inputting one of the first optical coupler that branches the output optical signal and the optical signal branched by the first optical coupler. An optical filter that passes through the optical fiber amplifier, a second optical coupler that is arranged in front of the optical fiber amplifier and combines the input optical signal and the output optical signal from the optical filter, the optical filter, and the second optical filter. And an optical switch that is disposed between the optical filter and controls input of an optical signal from the optical filter to the second optical coupler.

  According to the present invention, among the spontaneous emission light generated from the optical fiber amplifier, an optical noise component having a wavelength different from that of the input optical signal is fed back to the optical fiber amplifier and amplified, and this is used as control light. It is possible to reduce the disturbance of the waveform of the output optical signal from the optical fiber amplifier.

  Hereinafter, embodiments of the present invention will be described.

(First embodiment)
FIG. 1 shows a configuration diagram of an optical amplifying apparatus 100 according to the first embodiment of the present invention. In the following, the center wavelength of an optical signal (hereinafter referred to as an input optical signal) input to the optical amplifying apparatus 100 according to the first embodiment of the present invention is represented by λ1 as shown in FIG. It will be explained as a thing.

  An optical amplifying apparatus 100 according to the first embodiment includes an optical fiber amplifier 101, a first optical coupler 102 (hereinafter referred to as a first optical coupler) that branches an output optical signal from the optical fiber amplifier 101, and An optical filter 103 that inputs one of the optical signals branched by the first optical coupler 102 and transmits an optical signal having a central wavelength λ2 different from the central wavelength λ1 of the input optical signal, and the input optical signal and the optical signal A second optical coupler 105 (hereinafter referred to as a second optical coupler) that combines the output optical signal from the filter 103 to generate a wavelength multiplexed optical signal, and the optical filter 103 to the second optical coupler 105 And an optical switch 104 that controls input of an optical signal.

  Next, the operation of the optical amplifying apparatus 100 according to the first embodiment of the present invention will be described with reference to FIG.

  First, an input optical signal having a center wavelength λ 1 is input to the second optical coupler 105. The second optical coupler 105 multiplexes the input optical signal and the optical signal input from the optical switch 104. Details of the operations of the second optical coupler 105 and the optical switch 104 will be described later. The second optical coupler 105 inputs the combined optical signal to the optical fiber amplifier 101.

  The optical fiber amplifier 101 receiving the input from the second optical coupler 105 amplifies the input optical signal and sends the amplified output optical signal to the first optical coupler 102. At this time, the optical fiber amplifier 101 generates optical noise due to spontaneous emission light. This optical noise is output together with the optical signal amplified by the optical fiber amplifier 101 and input to the first optical coupler 102.

  The first optical coupler 102 branches the optical signal output from the optical fiber amplifier 101 and sends one of the branched optical signals to the optical filter 103. The other branched optical signal is output as an output of the optical amplifying device 100 to an external circuit connected to the optical amplifying device 100.

  The optical filter 103 transmits an optical signal having a specific wavelength among the input optical signals. Here, the center wavelength of the optical signal transmitted through the optical filter 103 is represented by λ2. The center wavelength λ2 of the optical signal transmitted through the optical filter 103 is set to be different from the center wavelength λ1 of the input optical signal. As described above, the optical filter 103 transmits the optical signal having the central wavelength λ2 different from the central wavelength λ1 of the input optical signal, so that the light generated in the optical fiber amplifier 101 in the optical filter 103 is transmitted. Among noises, it becomes possible to extract an optical noise component having a wavelength of λ2 as a center wavelength. In the following, the optical noise component having the center wavelength of the wavelength of λ2 obtained by transmitting through the optical filter 103 in this way is referred to as control light.

  The control light output from the optical filter 103 is then input to the optical switch 104.

  The optical switch 104 receives a driving signal from the outside, and controls the input of control light from the optical filter 103 to the second optical coupler 105 in accordance with the driving signal.

  The control light that has passed through the optical switch 104 is then input to one input port of the second optical coupler 105. An input optical signal to be amplified is input to the other input port of the second optical coupler 105.

  In the second optical coupler 105, the two input optical signals (input optical signal and control light) are combined to generate a wavelength-multiplexed optical signal. Then, the wavelength-multiplexed optical signal is input again to the optical fiber amplifier 101, and both optical signals are amplified together.

  Thus, out of the optical noise generated from the optical fiber amplifier 101, an optical noise component having a specific wavelength λ2 as the center wavelength is extracted via the optical filter 103, and this is fed back to the optical fiber amplifier 101 as control light. As a result, the intensity of the optical noise component having the wavelength of λ2 as the center wavelength is increased.

  In this case, the optical signal output from the optical fiber amplifier 101 and branched by the first optical coupler 102 is an optical signal having a center wavelength of λ1 and an optical signal having a center wavelength of λ2. It is an optical signal. Therefore, in order to obtain an optical signal having a center frequency of λ1, the signal branched from the first optical coupler 102 and output from the optical amplifying device 100 is demultiplexed for each wavelength, and the center frequency is λ1. It is sufficient to extract only the optical signal.

  Here, the intensity of the spontaneous emission light that is the source of the control light depends on the intensity of the input optical signal having the wavelength λ1. That is, the intensity of the input optical signal having the wavelength λ1 is complementary to the intensity of the control light having the wavelength λ2, and the intensity of the spontaneous emission light is weakened if the intensity of the input optical signal is high. If it is weak, the intensity of spontaneous emission is increased. Therefore, if a wavelength multiplexed signal light generated by combining the control light of wavelength λ2 with the input optical signal of wavelength λ1 is input to the optical fiber amplifier 101, only the input optical signal of wavelength λ1 is input to the optical fiber amplifier 101. Compared with the case where it does, it becomes possible to suppress the intensity | strength change of the optical signal input into the optical fiber amplifier 101. FIG. Therefore, if such wavelength multiplexed signal light is input to the optical fiber amplifier 101, fluctuations in optical gain caused by intensity changes of the optical signal (wavelength λ1) input to the optical fiber amplifier 101 can be reduced. It is possible to suppress the disturbance of the waveform of the optical signal output from the optical amplifying apparatus 100.

  As described above, according to the first embodiment of the present invention, among the optical noise components generated in the optical fiber amplifier 101, the optical noise having a specific wavelength different from the wavelength of the input optical signal in the optical filter 103 as the center wavelength. Since the components are transmitted and combined as control light by the second optical coupler and input to the optical fiber amplifier 101, a change in the intensity of the optical signal input to the optical fiber amplifier 101 can be reduced. it can. Therefore, it is possible to reduce fluctuations in the gain of the optical fiber amplifier 101 due to changes in the intensity of the input optical signal, and as a result, it is possible to suppress disturbance in the waveform of the output optical signal from the optical amplifying apparatus 100. Become.

  By the way, it is desirable to adjust the intensity of the control light having the wavelength λ2 in accordance with the average intensity of the input optical signal, the extinction ratio, or the modulation band. For this purpose, it is necessary to make the optical loss amount of the optical feedback path in the first coupler 102, the second coupler 105, the optical filter 103, and the optical switch 104 variable.

  For this purpose, for example, the average optical intensity of the input optical signal having the wavelength λ1 and the control light having the wavelength λ2 is detected, and the open / close state of the optical switch 104 is controlled based on the information on the average optical intensity. What should I do? By doing so, it becomes possible to perform gain / output control of optical amplification without providing control means inside the optical fiber amplifier 101, so there is no need to modify an existing optical fiber amplifier in the transmission line. Economical.

  In the above-described embodiment, the optical signal is branched using the optical coupler. For example, as disclosed in Non-Patent Document 1, the control light and the input signal light are combined using the optical circulator. It is also possible to separate them. When the input optical signal is always a burst intensity modulation signal, the optical switch 104 may always be in the ON state regardless of the intensity of the input optical signal or the control light.

(Second Embodiment)
In the second embodiment of the present invention, an embodiment will be described in which an optical switch in a feedback path of an optical amplification device is driven by an electric pulse signal from a pulse signal source to control the open / close state of the switch.

  FIG. 2 is a configuration diagram of an optical amplifying apparatus 200 according to the second embodiment of the present invention. That is, the optical amplifying apparatus 200 according to the second embodiment of the present invention includes a pulse signal source 206 for driving the optical switch 204 and an input optical signal in addition to the configuration of the optical amplifying apparatus 100 according to the first embodiment. The intensity of the input optical signal is detected using the optical coupler 207 that branches the optical signal, the photodetector 208 that is a conversion element that photoelectrically converts one of the optical signals branched by the optical coupler 207, and the signal that is photoelectrically converted by the photodetector 208. Light intensity monitor 209.

  Hereinafter, the operation of the optical amplifying apparatus 200 according to the second embodiment of the present invention will be described with reference to FIG. Note that description of the parts (the optical fiber amplifier 201, the optical coupler 202, the optical filter 203, and the optical coupler 205) that perform the same operations as those of the optical amplifying apparatus 100 according to the first embodiment will be omitted.

  First, the input optical signal is branched by the optical coupler 207. One of the optical signals branched by the optical coupler 207 is photoelectrically converted by the photodetector 208 and input to the light intensity monitor 209. The light intensity monitor 209 uses the signal from the photodetector 208 to detect the intensity of the input optical signal. The pulse signal source 206 generates a pulse signal in which the period and the pulse width of the pulse signal are controlled based on the intensity of the input optical signal detected by the light intensity monitor 209, and drives the optical switch 204 by this pulse signal. . Thus, by controlling the open / close state of the optical switch 204, the intensity of the control light input from the optical filter 203 to the optical coupler 205 can be adjusted.

  The feature of the second embodiment of the present invention is that the optical switch 204 is controlled by the pulse signal generated by the pulse signal source 206 to control the light intensity of the control light passing through the feedback path instantaneously. Therefore, the gain of the optical fiber amplifier 201 can be controlled regardless of the response time of a laser medium such as a rare earth-doped optical fiber. As a result, even if the intensity of the input optical signal having the wavelength λ1 changes greatly, the optical gain of the optical fiber amplifier 201 can be adjusted immediately.

  As the control light having the wavelength λ2, the spontaneous emission light emitted from the optical fiber amplifier 201 passes through the first optical coupler 202, the optical filter 203, the optical switch 204, and the second optical coupler 205 again, and is again an optical fiber amplifier. It is generated by circling a feedback path input to 201. At this time, if the period of the electric pulse signal that drives the optical switch 204 is made to correspond to almost an integral multiple of the time required for the control light to circulate in the feedback path, the generation efficiency of the control light can be improved. It becomes. FIG. 3 shows an example of the light intensity of the control light when the period of the electric pulse signal generated by the pulse signal source 206 is an integral multiple of the time for circulating around the feedback path. As described above, when the period of the pulse signal generated by the pulse signal source 206 is an integral multiple of the time for circulating around the feedback path, the light intensity of the control light is modulated in a pulse shape as shown in FIG.

  Here, when the period of the pulse signal generated by the pulse signal source 206 is narrowed, the pulse width of the control light is narrowed, the stimulated emission in the rare earth fiber of the optical fiber amplifier 201 is strengthened, and the peak intensity of the control light is increased. It will be. This is shown in FIG. FIG. 4A shows the state of the control light waveform when the period of the pulse signal is made approximately the same as the time for which the control light circulates in the feedback path. On the other hand, when the period of the pulse signal becomes longer, the control light is subjected to pulse modulation with a further increased pulse width. This is shown in FIG.

  When the period of the pulse signal is increased, the extinction time of the control light input to the optical fiber amplifier 201 is extended, so that the stimulated emission by the control light in the rare earth fiber of the optical fiber amplifier 201 is weakened. In this state, when an optical signal having a high extinction ratio or high average light intensity is input to the optical fiber amplifier 201, the input optical signal dominates the stimulated emission of the rare earth fiber. The waveform may deteriorate.

  In order to deal with such a problem, the frequency of the pulse signal generated by the pulse signal source 206 is about two orders of magnitude higher than the low-frequency cutoff frequency of the optical fiber amplifier 201 (the reciprocal of the response time of the rare earth-doped fiber). In this way, the period of the pulse signal may be set. The reason is that if the repetition frequency of the pulsed control light is sufficiently high, the gain of the optical fiber amplifier 201 with respect to the input signal light having the wavelength λ1 becomes uniform.

In the case of an erbium-doped optical fiber amplifier that is usually used well, the length of the erbium-doped fiber that is a laser medium is about 5 m to 20 m. In the configuration of the second embodiment of the present invention, if the length of the fiber from the first optical coupler 202 to the second optical coupler 205 is about 5 m, the time τ required for the control light to circulate in the optical amplification device _{The loop} is approximately 50 ns to 125 ns. Therefore, a pulse signal having a period corresponding to a time that is an integral multiple of the circulation time τ _loop may be used as the drive signal for the optical switch 204. The specific period of the pulse signal may be appropriately set in consideration of the optical loss amount of the optical switch 204, the first optical coupler 202, the second optical coupler 205, and the like. The upper limit value should be 1/100 or less of the response time determined by the low-frequency cutoff of the optical fiber amplifier (about 1 ms when an erbium-doped fiber is used as the laser medium).

  In order to realize an optical amplifying device with little waveform degradation of the amplified output regardless of the input light intensity and extinction ratio of the input optical signal of wavelength λ1, the first optical coupler 202, the second optical coupler 205, the optical filter 203, and The average optical loss in the feedback path composed of the optical switch 204 needs to be varied and controlled. Therefore, the average light intensity of the input optical signal is detected by the light intensity monitor 209, and the pulse width of the pulse signal is determined according to the magnitude, or the period of the pulse signal is changed minutely.

  Furthermore, it is also possible to detect the intensity of the output optical signal from the optical filter 203 and adjust the pulse width of the pulse signal of the pulse signal source 206 or the period of the pulse signal according to the magnitude. In this case, as shown in FIG. 5, an optical coupler 210 is provided between the optical filter 203 and the optical switch 204 to branch the output optical signal from the optical filter 203, and the branched optical signal is photoelectrically converted by the photodetector 211. Then, the intensity of the output optical signal from the optical filter 203 may be detected by the light intensity monitor 212 using the converted signal, and the detected intensity may be input to the pulse signal source 206.

  Hereinafter, a method for controlling the pulse signal generated by the pulse signal source 206 in accordance with the outputs from the light intensity monitor 209 and the light intensity monitor 212 will be described.

When the average optical intensity of the input optical signal is large at the input port of the optical amplifier and the average intensity of the output optical signal after optical amplification exceeds half of the maximum output intensity of the optical fiber amplifier 201, the input optical signal causes a rare earth The pumping state of the fiber is modulated, and as a result, the gain of the optical fiber amplifier 201 changes, and the waveform of the optical signal after amplification can deteriorate. Therefore, in order to deal with this, the period of the pulse signal generated by the pulse signal source 206 is set to the same number of digits as the circulation time τ _loop . By doing so, the peak light intensity of the pulsed control light can be increased, and the influence of the gain change of the rare earth doped fiber due to the input optical signal can be reduced. At this time, the average intensity of the amplified optical signal having the wavelength λ1 can be made uniform by adjusting the pulse width of the pulse signal. By controlling the pulse signal as described above, it is possible to reduce the deterioration of the waveform of the output optical signal from the optical fiber amplifier 201.

On the other hand, when the extinction ratio of the input optical signal is large but the average light intensity is not large, the period of the electric pulse signal does not necessarily have the same number of digits as the circulation time τ _loop, and is set to about 1 μs, for example. do it. The average intensity of the amplified optical signal having the wavelength λ1 can be made uniform by adjusting the period of the pulse signal.

  As described above, according to the optical amplifying apparatus 200 according to the second embodiment of the present invention, the optical switch 204 is driven by the pulse signal generated by the pulse signal source 206, and the input optical signal detected by the light intensity monitor 209 is detected. By making it possible to control the period and pulse width of the pulse signal based on the intensity, it is possible to reduce the disturbance of the waveform of the optical signal output from the optical fiber amplifier 201.

  The optical switch 204 used in the present embodiment can be an acousto-optic optical switch, an optical switch using the gain modulation phenomenon of a semiconductor optical amplifier, or an optical modulator using a lithium niobate waveguide. Among these optical switches and optical modulators, the optical switch operation has polarization dependency, but in order to eliminate such polarization dependency, a linear polarizer is introduced to the input part of the optical switch 204, and It is only necessary to match the polarization direction of the control light with the axial direction of the optical switch and the optical modulator.

  The applicable area of the optical amplifying apparatus 200 according to the second embodiment of the present invention is a general optical fiber communication system that uses many optical switches, and is characterized by being independent of the modulation method and modulation band of an optical signal. is there. For example, in an add / drop system in which a wavelength multiplexed signal is wavelength-separated in a transmission system, only a desired wavelength channel signal is extracted, another signal is newly generated and wavelength-multiplexed again with another channel signal. When wavelength multiplexed signals are collectively amplified by a single optical amplifier in a state where the average optical intensity level difference between the extracted signal and the newly added signal is large, the gain state of the optical amplifier changes due to the new signal. However, it may affect the transmission characteristics of other channel signals. In such a situation, if the optical amplifying apparatus according to the present embodiment is used, it is possible to suppress the influence of gain fluctuations caused by the optical fiber amplifier and to prevent the deterioration of the transmission characteristics of all channel signals.

(Third embodiment)
In the third embodiment of the present invention, another control method of the pulse signal source for driving the optical switch will be described.

  FIG. 6 is a configuration diagram of an optical amplifying apparatus 300 according to the third embodiment of the present invention. That is, the optical amplifying apparatus 300 according to the third embodiment of the present invention has a specific band in the signal photoelectrically converted by the photodetector 308 in addition to the configuration of the optical amplifying apparatus 200 according to the second embodiment. A band-pass circuit 310 that transmits a signal having a frequency to which the signal belongs is provided. The pulse signal source 306 controls the pulse signal generated from the pulse signal source 306 based on the output signal from the band pass circuit 310 and the intensity of the input optical signal output from the light intensity monitor 309.

  The bandpass circuit 310 is used to determine whether or not the intensity change of the input optical signal is bursty. Specifically, the transmission band is the low-frequency cutoff frequency of the optical fiber amplifier 301. Is set to transmit a signal having a frequency of about 0.1 to 10 times.

  Hereinafter, a pulse signal control method in the pulse signal source 306 will be described.

  First, when the average optical intensity level is low even when the extinction ratio of the input optical signal having the wavelength λ1 is high, or when the average output level of the bandpass circuit is low even when the average optical intensity level is high, the optical fiber amplifier 301 is used. A pulse signal for turning off the optical switch 304 is output from the pulse signal source 306 so as to remove the gain control.

  On the other hand, when the average intensity level of the input optical signal having the wavelength λ1 is high and the average output level of the bandpass circuit 310 is high, the optical switch 304 is driven as described in the second embodiment. A pulse signal is output from the pulse signal source 306 (that is, the optical switch 304 is turned on), and the gain control of the optical fiber amplifier 301 is operated.

  As described above, according to the third embodiment of the present invention, the optical fiber amplification is performed only when the input optical signal includes an intensity modulation component in the range of about one octave with respect to the low cutoff frequency of the optical fiber amplifier 301. Gain control of the device 301 can be performed. As a result, the gain and output intensity of the optical fiber amplifier 301 can be increased as in the non-control period during a period in which no burst signal exists. Further, the transmission signal itself is not a burst signal, and the lower limit of the transmission band is sufficiently higher than the low cut-off frequency of the optical fiber amplifier 301, and wavelength multiplexing is performed only by extracting and inserting a specific channel signal such as an add / drop system. The present embodiment is also effective when the average light intensity level of the signal fluctuates in a burst manner. At this time, the pulse signal source 306 can be controlled using only the output signal from the bandpass circuit 310 without using the light intensity monitor 309, and the configuration of the optical amplification device can be simplified.

  Also, in order to enable gain control of the optical fiber amplifier only when the input optical signal has an intensity modulation component in the range of about one octave with respect to the low-frequency cutoff of the optical fiber amplifier. 7, the output amplitude value of the bandpass circuit 410 is adjusted by the variable gain amplifier 411 based on the information on the average optical intensity of the input optical signal (center wavelength λ1), and is variable in the multiplier 412. The signal output from the gain amplifier 411 and the output signal from the pulse signal source 406 may be multiplied, and the output of the multiplier 412 may be used as a drive signal for the optical switch.

  According to such an embodiment, even if the input optical signal is not a single wavelength signal but a multi-channel wavelength multiplexed optical signal, the burst component and the wavelength multiplexed signal included in the wavelength multiplexed signal according to the same embodiment. , The optical switch 404 is turned on / off based on the pulse signal from the pulse signal source 406, and the execution / stop of the gain control of the optical fiber amplifier 401 is automated. it can.

(Fourth embodiment)
In the fourth embodiment of the present invention, for example, when there is an accident such as disconnection of an optical fiber and the intensity of the input optical signal is weakened, the wavelength of the input light is reduced without using the laser for the dummy optical signal. An optical amplifying apparatus capable of outputting the same dummy optical signal as the signal will be described.

  FIG. 8 is a configuration diagram of an optical amplification apparatus 500 according to the fourth embodiment of the present invention. That is, the optical amplifying apparatus 500 according to the fourth embodiment of the present invention includes an optical switch 510 that switches the wavelength of the optical signal transmitted through the optical filter 503 in addition to the configuration of the optical amplifying apparatus 200 according to the second embodiment. It has.

  Hereinafter, the operation of the optical amplifying apparatus 500 according to the fourth embodiment of the present invention will be described.

  The light intensity monitor 509 detects the intensity of the input optical signal having the wavelength λ1. The detected intensity of the input optical signal is sent to the optical switch 510 together with the pulse signal source 506.

  The optical switch 510 can switch the transmission wavelength of the optical filter 503 to the center wavelength λ1 of the input optical signal and use the control light as it is as the light source when the intensity of the input optical signal is significantly reduced or zero. To. The control light transmitted through the optical filter 503 is combined with the input optical signal by the optical coupler 505, and is output as a dummy optical signal having the same wavelength as the input optical signal.

  As the optical filter 503 capable of switching the transmission wavelength, a wavelength variable filter, two reflection type optical filters having reflection wavelengths λ1 and λ2 (for example, an optical fiber grating, etc.), and the like can be used. . FIG. 9 shows a configuration example of the optical switch 510 and the optical filter 503 when two reflective optical filters are used. The 1 × 2 reflective optical switch 511 is connected to the feedback path via the optical circulator 512, and switches the connection state of the optical switch 511 according to the intensity of the input optical signal detected by the optical intensity monitor 509. Alternatively, the control light of λ2 can be selectively transmitted.

  As described above, according to the fourth embodiment of the present invention, even when the intensity of the input optical signal is weakened, the dummy optical signal having the same wavelength as the input optical signal is used without using the laser for the dummy optical signal. Can be output.

  Note that the fourth embodiment of the present invention can be applied to an optical node for performing optical add / drop for wavelength-separated wavelength-multiplexed signals, extracting specific channel signals, and inserting new signals. In particular, this embodiment is effective when the average light intensity of the extracted signal is not equal to the average light intensity of the inserted optical signal, or when either extraction or insertion is performed at the optical node.

  Specifically, when the wavelength multiplexed signal at the optical node output is collectively amplified by the optical fiber amplifier, the gain of the optical fiber amplifier changes if the average optical intensity of the wavelength multiplexed optical signal fluctuates greatly due to the passage of the optical node. It may affect the transmission characteristics of the channel signal. Further, when the switching operation of the optical switch is close to the low cut-off frequency of the optical fiber amplifier, there is a possibility that the influence of the optical gain variation due to the channel switching may affect all channel signals.

  However, if this embodiment is used, the optical amplifier is used as a dummy optical signal source even if the number of channel signals wavelength-multiplexed due to extraction of a specific channel signal varies greatly. The average intensity of the input optical signal to the installed optical fiber amplifier can be made uniform, and the deterioration of transmission characteristics due to channel switching can be prevented. Even if the switching operation of the optical switch is close to the low-frequency cutoff of the optical fiber amplifier, it is possible to suppress the gain fluctuation.

  FIG. 10 shows an example in which the optical amplifying apparatus according to this embodiment is applied to an optical node for performing optical add / drop. As shown in FIG. 10, the insertion position of the optical amplifying apparatus 600 according to the present embodiment is between the wavelength demultiplexing / multiplexing unit (FIG. 10A) by the optical demultiplexer 601 and the optical multiplexer 602 (FIG. 10 (a)). The output side of the device 602 (FIG. 10B) may be used.

  In the former case, the optical amplifying device 600 is individually provided in each wavelength channel port of the optical demultiplexer 601. When the average light intensity of the input optical signal to the optical amplifying device 600 is significantly reduced, or when only extracting the optical signal and not inserting a new signal at the node, the optical filter in the optical amplifying device 600 The central transmission wavelength is switched to the channel wavelength corresponding to the port, used as a light source, and led to the optical multiplexer 602. As a result, the average light intensity of each channel is kept above a certain level, and the signal waveform quality of all channels can be maintained even if the wavelength multiplexed signal output from the optical multiplexer 602 is amplified by a conventional optical fiber amplifier. It becomes.

  On the other hand, in the latter case, the center transmission wavelength of the optical filter in the optical amplification device 600 is matched with the center wavelength of the extraction channel in the optical node, and the output of the optical multiplexer 602 is collectively amplified by the optical amplification device 600. The wavelength multiplexing of the control light generated in the optical amplifying apparatus 600 and the output of the optical multiplexer 602 can be performed substantially.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the components without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

1 is a configuration diagram of an optical amplifying device according to a first embodiment of the present invention. The block diagram of the optical amplifier concerning the 2nd Embodiment of this invention. The figure showing the mode of the waveform of the control light of the 2nd Embodiment of this invention. The figure showing the mode of the waveform of the pulse signal of the 2nd Embodiment of this invention, and control light. The block diagram of the optical amplifier concerning the modification of the 2nd Embodiment of this invention. The block diagram of the optical amplifier concerning the 3rd Embodiment of this invention. The block diagram of the optical amplifier concerning the modification of the 3rd Embodiment of this invention. The block diagram of the optical amplifier concerning the 4th Embodiment of this invention. The figure which shows the structural example of the optical switch and optical filter of the 4th Embodiment of this invention. The figure which shows the application example of the optical amplifier concerning the 4th Embodiment of this invention.

Explanation of symbols

100, 200, 300, 400, 500, 600 ... optical amplifiers 101, 201, 301, 401, 501 ... optical fiber amplifiers 102, 105, 202, 205, 207, 210, 302, 305, 402, 405, 407, 502, 505, 507 ... Optical couplers 103, 203, 303, 403, 503 ... Optical filters 104, 204, 304, 404, 504, 510, 511 ... Optical switches 206, 306, 406, 506 ... Pulse signal sources 208, 211, 308, 408, 508 ... Photodetectors 209, 212, 309, 409, 509 ... Light intensity monitors 310, 410 ... Band pass circuit 411 ... Variable gain amplifier 412... Multiplier 512... Optical circulator 601. · Multiplexer

Claims (9)

An optical amplification device for amplifying an input optical signal,
An optical fiber amplifier;
A first optical coupler disposed downstream of the optical fiber amplifier and branching an optical signal output from the optical fiber amplifier;
An optical filter that inputs one of the optical signals branched by the first optical coupler and transmits an optical signal having a central wavelength different from the central wavelength of the input optical signal;
A second optical coupler that is arranged in front of the optical fiber amplifier and multiplexes the input optical signal and the output optical signal from the optical filter;
An optical amplifying apparatus comprising: an optical switch that is disposed between the optical filter and the second optical coupler and controls input of an optical signal from the optical filter to the second optical coupler. A pulse signal source for generating a pulse signal for driving the optical switch;
A conversion element for photoelectrically converting the input optical signal;
A monitor that detects the intensity of the input optical signal using a signal photoelectrically converted by the conversion element;
The optical amplifying apparatus according to claim 1, wherein the pulse signal source controls a pulse width and a period of a pulse signal based on an intensity of the input optical signal detected by the monitor. A pulse signal source for generating a pulse signal for driving the optical switch;
A first conversion element for photoelectrically converting the input optical signal;
A first monitor that detects the intensity of the input optical signal using a signal photoelectrically converted by the first conversion element;
A second conversion element that photoelectrically converts an output optical signal from the optical filter;
A second monitor for detecting the intensity of the output optical signal from the optical filter using the signal photoelectrically converted by the second conversion element;
The pulse signal source includes a pulse width of a pulse signal based on the intensity of the input optical signal detected by the first monitor and the intensity of the output optical signal from the optical switch detected by the second monitor. The optical amplifying apparatus according to claim 1, wherein the period is controlled.   The pulse signal source controls the pulse signal so that the period of the generated pulse signal is an integral multiple of the time until the optical signal output from the optical switch returns to the optical switch. The optical amplifying device according to claim 2.   3. The pulse signal source according to claim 2, wherein the pulse signal source controls the pulse signal so that a period of the generated pulse signal is 1/100 or less of a reciprocal of a low cut-off frequency of the optical fiber amplifier. Item 4. The optical amplifying device according to Item 3. A pulse signal source for generating a pulse signal for driving the optical switch;
A conversion element for photoelectrically converting the input optical signal;
A monitor that detects the intensity of the input optical signal using a signal photoelectrically converted by the conversion element;
A band-pass circuit that transmits a signal having a frequency of 0.1 to 10 times the low-frequency cutoff of the optical fiber amplifier among the signals photoelectrically converted by the conversion element;
2. The pulse signal source generates a pulse signal for driving the optical switch based on an intensity of the input optical signal detected by the monitor and an output signal from the bandpass circuit. The optical amplifying device described. A pulse signal source for generating a pulse signal for driving the optical switch;
A conversion element for photoelectrically converting the input optical signal;
A monitor that detects the intensity of the input optical signal using a signal photoelectrically converted by the conversion element;
A band-pass circuit that transmits a signal having a frequency of 0.1 to 10 times the low-frequency cutoff of the optical fiber amplifier among the signals photoelectrically converted by the conversion element;
A variable gain amplifier that amplifies an output signal from the bandpass circuit based on the intensity of the input optical signal detected by the monitor;
The circuit further comprises a multiplying circuit disposed between the optical switch and the pulse signal source and multiplying a pulse signal output from the pulse signal source by an output signal from the variable gain amplifier. 2. The optical amplifying device according to 1. An optical amplification device for amplifying an input optical signal,
An optical fiber amplifier;
A first optical coupler disposed downstream of the optical fiber amplifier and branching an optical signal output from the optical fiber amplifier;
One of the optical signals branched by the first optical coupler is input, and an optical signal having the same wavelength as the central wavelength of the input optical signal or a light having a central wavelength different from the central wavelength of the input optical signal An optical filter that transmits any of the signals;
A first optical switch that switches a center wavelength of an optical signal transmitted by the optical filter;
A second optical coupler that is arranged in front of the optical fiber amplifier and multiplexes the input optical signal and the output optical signal from the optical filter;
A second optical switch disposed between the optical filter and the second optical coupler and controlling input of an optical signal from the optical filter to the second optical coupler. Amplification equipment. A conversion element for photoelectrically converting the input optical signal;
A monitor that detects the intensity of the input optical signal using a signal photoelectrically converted by the conversion element;
The first optical switch transmits an optical signal having the same wavelength as the center wavelength of the input optical signal through the optical filter and detected by the monitor when the intensity detected by the monitor is below a certain threshold value. When the intensity is greater than the threshold, the center wavelength of the optical signal transmitted through the optical filter is switched so that an optical signal having a wavelength different from the central wavelength of the input optical signal is transmitted through the optical filter. The optical amplifying device according to claim 8.

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