JP3872023B2 - Optical fiber communication system using distributed Raman amplification. - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical fiber communication system that performs distributed Raman amplification in an installed optical fiber that is a transmission line.
[0002]
[Prior art]
FIG. 8 shows a configuration of a conventional optical fiber communication system. A transmission fiber 1 that is a transmission line and a linear repeater 2 are connected. The linear repeater 2 combines an erbium-doped fiber amplifier (EDFA) 3 that is a lumped optical amplifier, a pumping light source 4 for distributed Raman amplification, and pumping light from the pumping light source 4 with signal light. For controlling the optical component for detecting the Raman gain (G) of the signal light by the distributed Raman amplification, that is, the optical spectrum analyzer (optical spectrum analyzer) 6, the tapping force plastic 7 and the excitation light source 4. The control circuit 8 is provided. The optical spectrum analyzer 6 generally has a wavelength tunable optical filter 11 and a highly sensitive light receiver 12. The high-sensitivity light receiver 12 is an electronic circuit using an avalanche photodiode (APD) or an expensive photodiode that is not affected by dark current noise. The gain medium of the distributed Raman amplification is the transmission fiber 1 itself, and pumping light is introduced into the transmission fiber 1 to optically pump the transmission fiber 1.
[0003]
In FIG. 8, a lossy body (optical connector or patch cord) LE-1 in the linear repeater 2 and a lossy body (fiber fusion point or optical connector) LE-2 in the transmission fiber 1 are depicted. Loss body LE-2 changes before and after repair in the process of repairing transmission fiber breakage due to accidents during road construction. For example, the typical amount of change is about 0.5 to 1.0 dB. Further, the loss body LE-1 changes when the connection of the transmission fiber 1 is changed due to the trouble transfer. For example, the typical amount of change is about 0.5 to 2.0 dB. When the loss values of the loss bodies LE-1 and LE-2 change, the pump light power of the path average that propagates through the transmission fiber 1 changes, and the Raman gain changes. Therefore, conventionally, the following control is performed.
[0004]
The EDFA 13 drawn at the left end of FIG. 8 represents the EDFA in the upstream linear repeater. In order to detect the Raman gain, after being transmitted from the EDFA 13 and propagating through the transmission fiber 1, wavelength multiplexed (WDM) signal light (having wavelengths of λ1, λ2,. ) Is branched by the tap coupler 7 and enters the optical spectrum analyzer 6. The spectrum of the signal light incident on the optical spectrum analyzer 6 is analyzed, and the Raman gain (Raman gain spectrum) at each wavelength is calculated by, for example, comparing with the light reception signal light level when there is no Raman gain in advance. Further, the excitation light source 4 is controlled by the control circuit 8 so that the Raman gain spectrum becomes an expected value. Specifically, if the measured Raman gain is smaller than the expected value, the pumping light power is increased. Conversely, if the measured Raman gain is larger than the expected value, the pumping light power is decreased. In general, the excitation light source is composed of a multi-wavelength laser diode. The transmission fiber 1 and the linear repeater 2 are connected by a pair of optical connectors. When this optical connector is mistakenly removed for maintenance work of the linear repeater 2 or the like, high-power excitation light is emitted from the optical connector on the linear repeater 2 side.
[0005]
[Non-Patent Document 1]
Yano et al., "Examination of pumping light power automatic adjustment method for gain flattening of multi-wavelength pumping Raman amplifier (2)", IEICE General Conference, B-10-46, p.483, 2002
[Non-Patent Document 2]
Isobe et al., “Examination of pumping light power automatic adjustment method for gain flattening of multi-wavelength pumping Raman amplifier (1)”, IEICE General Conference, B-10-45, p.482, 2002
[0006]
[Problems to be solved by the invention]
As described above, the prior art requires an expensive optical spectrum analyzer 6. Further, since it is necessary to measure in advance the signal light spectrum incident on the linear repeater 2 from the EDFA 13 in the case where there is no Raman gain, a multi-wavelength signal light source is installed in the upstream linear repeater to obtain high accuracy. It is necessary to operate. However, the multi-wavelength signal light source is expensive, and there is a problem that it takes a lot of trouble to operate it with high accuracy. Further, when high-power excitation light is emitted from the optical connector, there is a problem that a danger such as injury occurs in the eyes of a work maintenance worker.
[0007]
The present invention has been made in view of the above circumstances, and an object thereof is an optical fiber communication system using distributed Raman amplification that can be configured at low cost and can be installed without any special effort. Ru near be provided.
[0008]
[Means for Solving the Problems]
The present invention has been made to solve the above-described problems, and the invention according to claim 1 is a transmission path for signal light, wherein a transmission fiber having a first loss body is connected to the transmission fiber. An optical fiber communication system comprising a linear repeater, wherein the linear repeater combines a pumping light source that outputs pumping light for Raman pumping the transmission fiber, and the pumping light and the signal light. , A second lossy body present between the multiplexer and the transmission fiber, and a reflection pump that is installed between or within the excitation light source and reflected from the transmission fiber. Outgoing excitation light emitted from the excitation light source, a demultiplexer for demultiplexing depending on the difference in propagation direction, a first receiver for receiving reflected excitation light emitted from the demultiplexer, and the first Of the light received by the receiver Based on a change amount of the excitation light level, increases the amount of the first of the excitation light power, the so that half of the reduction of the reflected excitation light level based on the variation of the loss of the second loss material An optical fiber communication system using distributed Raman amplification, comprising a control circuit for controlling the pumping light source.
[0009]
The invention according to claim 2 is a transmission path for signal light, and is an optical fiber communication system comprising a transmission fiber having a first loss body and a linear repeater to which the transmission fiber is connected, A linear repeater exists between a pumping light source that outputs pumping light for Raman pumping the transmission fiber, a multiplexer that combines the pumping light and the signal light, and between the multiplexer and the transmission fiber. A second lossy body, outgoing excitation light that is installed between or within the excitation light source and within the excitation light source, and that is reflected excitation light reflected from the transmission fiber and emitted from the excitation light source, and its propagation direction A demultiplexer for demultiplexing according to the difference, a first light receiver for receiving reflected excitation light emitted from the demultiplexer, a change amount of the reflected excitation light level received by the first light receiver, and the The first from the linear repeater Based on the distance information to loss material, an optical fiber communication system using distributed Raman amplification, characterized in that it comprises a control circuit for controlling the excitation light source as the Raman gain is constant.
The invention according to claim 3 is a transmission path for signal light, and is an optical fiber communication system comprising a transmission fiber having a first loss body and a linear repeater to which the transmission fiber is connected, A linear repeater exists between a pumping light source that outputs pumping light for Raman pumping the transmission fiber, a multiplexer that combines the pumping light and the signal light, and between the multiplexer and the transmission fiber. A second lossy body, outgoing excitation light that is installed between or within the excitation light source and within the excitation light source, and that is reflected excitation light reflected from the transmission fiber and emitted from the excitation light source, and its propagation direction A demultiplexer for demultiplexing due to the difference, a first light receiver for receiving reflected excitation light emitted from the demultiplexer, a tap coupler installed in a signal light path, and a propagating light branched by the tap coupler From other than signal light A fixed wavelength optical filter for removing sound light, a second light receiving device for detecting the total signal light power emitted from the fixed wavelength light filter, and a change amount of the reflected excitation light level received by the first light receiving device. And a control circuit for controlling the excitation light source so that the input signal light power to the linear repeater becomes constant based on the total signal light power received by the second light receiver. 1 is an optical fiber communication system using distributed Raman amplification.
[0011]
According to a fourth aspect of the present invention, there is provided an optical fiber communication system using distributed Raman amplification according to the third aspect, further comprising monitoring channel light receiving means for detecting the number of channels of signal light, wherein the control circuit comprises: Calculated from the amount of change in the reflected excitation light level received by the first light receiver, the total signal light power received by the second light receiver, and the number of signal light channels obtained by the monitoring channel light receiving means The pump light source is controlled based on the signal light power per channel so that the input signal light power to the linear repeater is constant.
[0013]
According to a fifth aspect of the present invention, in the optical fiber communication system using distributed Raman amplification according to any one of the first to fourth aspects, the duplexer is a circulator.
[0014]
A sixth aspect of the present invention is the optical fiber communication system using distributed Raman amplification according to any one of the first to fifth aspects, wherein the output pumping light level is detected in the pumping light source. And a light receiver for receiving the excitation light emitted from the tap coupler.
The invention according to claim 7, in the optical fiber communication system using distributed Raman amplification according to any one of claims 1 to claim 5, adjacent to the laser diode rear end surface in the excitation light source, It is characterized by comprising a light receiver for detecting the outgoing excitation light level.
According to an eighth aspect of the present invention, in the optical fiber communication system using distributed Raman amplification according to any one of the first to fifth aspects, the drive level and emission of the excitation light source are included in the control circuit. An excitation light level table is provided.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
[First embodiment]
FIG. 1 is a block diagram showing a configuration of an optical fiber communication system according to a first embodiment of the present invention. The embodiment shown in this figure is different from the prior art shown in FIG. 8 in the following points. In the present embodiment, the Raman gain is monitored by detecting the Rayleigh backscattered light RBS of the excitation light. On the other hand, in the prior art, the signal light is tapped and the Raman gain is calculated from the monitor value of the signal light power. Rayleigh backscattered light RBS generated in the transmission fiber 1 travels back and forth through the loss bodies LE-1 and LE-2 to reach the signal light / pumping light combiner 22 and return to the direction of the pumping light source 23. To do. The Rayleigh backscattered light RBS emitted from the multiplexer 22 is separated from the excitation light emitted from the excitation light source 23 by the demultiplexer 24 installed between the multiplexer 22 and the excitation light source 23, and is separated. Is incident on a photodiode (PD) 25 connected to. This embodiment is a case of so-called backward pumping in which the directions of the signal light and the pumping light are opposite to each other. Obviously the same holds true from the subjectivity.
[0016]
Now, let the power of Rayleigh backscattered light RBS received by the PD 25 be Prefl, and the excitation light power emitted from the excitation light source 23 be Pin. Note that Prefl and Pin are values in dB. In addition, the Prefl and Pin values in the initial state are the Prefl and Pin values when at least one of Prefl1 and Pin1, and the loss values (L1 and L2) of the loss bodies LE-1 and LE-2 change, respectively. Are Prefl2 and Pin2, respectively. Decrease the amount of Prefl by ΔPrefl = Pref1-Prefl2
Also, the amount of increase in Pin is expressed as ΔPin = Pin2-Pin1
And In this embodiment,
ΔPin = ΔPrefl / 2
That is, control is performed so that ΔPin is half of ΔPrefl.
[0017]
FIG. 2 shows a Raman gain spectrum in the present embodiment. The excitation light wavelength of the excitation light source 23 was 2 wavelengths (1460 nm and 1500 nm). The gain wavelength region is the so-called L band (about 1570-1600 nm), and the spectrum average gain in the initial state is about 8 dB. When the loss L1 of the loss body LE-1 increases by 1.6 dB, that is, when ΔPrefl = 1.6 dB, the Raman gain decreases by about 3 dB when there is no control. On the other hand, when control is performed, the Raman gain changes. Was within about 0.1 dB.
[0018]
FIG. 3 shows the loss part distance dependency of the amount of change in Raman gain. The loss portion distance is a distance in the fiber axial direction from the excitation light source 23 to the loss body LE-1 or LE-2. Usually, the distance from the excitation light source 23 to the loss body LE-1 is several hundreds at most. The transmission fiber length was about 100 km. The loss value increase amount (ΔL) of the loss body LE-1 or LE-2 is shown for 1.6 dB and 0.6 dB. When the control was not performed, the change amount (reduction amount) ΔG of Raman gain ΔG was 1.6 dB and 0.6 dB, and the maximum value of ΔG was 2.9 dB and 1.4 dB.
[0019]
On the other hand, in the case of control, ΔG had maximum values of 0.8 dB and 0.4 dB when ΔL was 1.6 dB and 0.6 dB. Therefore, according to the present embodiment, it can be seen that constant control of the Raman gain is realized with an accuracy within 0.8 dB. In particular, control accuracy is good when the loss distance is within about 1 km, and control within about 0.1 dB is realized. This is because, when the loss part distance is within about 1 km, △ Prefl / 2 is almost equal to △ L, so the loss of pumping light by the lossy body LE-1 or LE-2 is increased by the increase of Pin △ Pin = △ This is because it is almost completely compensated by Prefl / 2. Therefore, this embodiment is particularly effective when the loss part distance is within about 1 km.
[0020]
The detected light level in this embodiment, that is, the power level Prefl of the Rayleigh backscattered light RBS is about −7 dBm. On the other hand, the detection light level of each signal light channel in the prior art, that is, the light reception level at the optical spectrum analyzer 6 was about -35 dBm. Therefore, the APD 12 that is a highly sensitive photodiode is required in the prior art, but this embodiment has an advantage that an inexpensive normal sensitivity photodiode can be used.
Furthermore, signal light, which is detection light of the prior art, has a narrow line width and high coherence, and thus is susceptible to interference noise degradation. On the other hand, the excitation light, which is the detection light of the present embodiment, has an advantage that it has a wide line width and low coherence, so that it is less susceptible to interference noise degradation.
[0021]
[Second Embodiment]
FIG. 4 is a block diagram showing a configuration of an optical fiber communication system according to the second embodiment of the present invention. The embodiment shown in this figure is different from the first embodiment of the present invention shown in FIG. 1 in the following points. In the first embodiment, the reflection level Prefl of the excitation light from the PD 25 is used as input information used for control. On the other hand, in this embodiment, in addition to Prefl, distance information from the linear repeater 31 of the loss body LE-2 is input to the control circuit 32. Let that distance be D2. When the loss value of the loss body LE-2 is the same, the decrease amount Prefl of Prefl decreases as the distance D2 increases. On the other hand, the decrease amount ΔG of the Raman gain G also decreases as the distance D2 increases, but the decrease amount of ΔPrefl is larger than the decrease amount of ΔG. This is because the Raman gain G is proportional to the average power (Pave) of the pumping light power over the transmission fiber length, whereas Prefl is an amount having a good correlation with the square of Pave.
[0022]
When the distance D2 is known, the loss Ld2 of the pumping light from the linear repeater 31 to the lossy body LE-2 can be found, and the loss value L2 of the lossy body LE-2 can be calculated from △ Prefl, from Ld2 and L2 The correspondence relationship of the gain G to the input pumping light power Pin can be seen. Therefore, the value of Pin (Pin2) that makes the gain G constant can be calculated regardless of the change in L2, and the excitation light source can be driven by the control circuit 32 to perform constant gain G control.
[0023]
In this embodiment, when the loss values (L1 and L2) of the loss bodies LE-1 and LE-2 change, first, the constant spectrum control of the Raman gain G is performed based on the Prefl reduction amount ΔPrefl information. At this time, due to changes in the loss values L1 and L2, the signal light level reaching the linear repeater 31 slightly changes even if the gain G is constant. That is, the signal light level decreases by the increase in the loss values L1 and L2. Therefore, the following control (constant control of the input signal light power of the linear repeater 31) can be added to compensate for the signal light level reduction. From the initial value of the gain G and the Raman gain coefficient of the transmission fiber 1 examined in advance, the amount of change in Pin (Pin3-Pin2) that gives an increase in G equal to the increase in the loss values L1 and L2 can be calculated. However, Pin3 is the final Pin setting value. The excitation light source 23 is driven by the control circuit 32 so that Pin3 is obtained.
[0024]
[Third embodiment]
FIG. 5 shows an optical fiber communication system according to a third embodiment of the present invention. Although similar to the first embodiment of the present invention shown in FIG. 1, the following points are mainly different. In the first embodiment, the excitation light reflection level Prefl from the PD 25 is used as input information used for control. On the other hand, in this embodiment, in addition to Prefl, the signal light total power Pstot input to the linear repeater 41, or the total power Pstot and the number of signal light channels (Nch) received by the monitoring channel light (SVC) light receiver 42 Use information. The total power Pstot is detected by using the tap coupler 43, the fixed wavelength optical filter 44 for removing noise light other than the signal light, and the second PD 45. However, the PD 25 that detects Prefl is the first PD. Further, the number of signal light channels Nch is detected by using the SVC light receiver 42 and a tap coupler and a wavelength fixed optical filter for SVC branching, which are not shown for simplicity.
[0025]
In this embodiment, when the loss values L1 and L2 of the loss bodies LE-1 and LE-2 change, first, the spectrum constant control of the Raman gain G is performed based on the Prefl reduction amount ΔPrefl information. At this time, the signal light level reaching the linear repeater 41 slightly changes due to changes in the loss values L1 and L2, even if the gain G is constant. That is, the signal light level decreases by the increase in the loss values L1 and L2. Therefore, the following control (constant control of the linear repeater input signal light power) can be added to compensate for the decrease in the signal light level.
[0026]
First, when the number of signal light channels is constant, the change amount of the total power Pstot in the gain G spectrum constant control can be measured. From the initial value of the gain G and the Raman gain coefficient of the transmission fiber 1 checked in advance, the amount of change in Pin that gives an increase in gain G equal to the increase in the loss values L1 and L2 can be calculated. Next, when the number of signal light channels Nch changes, the amount of change in the total power Pstot in the gain G spectrum constant control can be measured, and the signal light power per channel can be measured from the Nch and the total power Pstot. From the initial value of the gain G and the Raman gain coefficient of the transmission fiber 1 examined in advance, the amount of change in Pin that gives an increase in G equal to the decrease in signal light power per channel can be calculated. The excitation light source 23 is driven by the control circuit 46 based on the amount of change in Pin.
[0027]
[Fourth embodiment]
FIG. 6 shows an optical fiber communication system according to a fourth embodiment of the present invention. Although the operation is the same as that of the first embodiment of the present invention shown in FIG. 1, the specific configuration differs from that of the first embodiment as follows. In this embodiment, a circulator 53 is used as a demultiplexer for excitation light installed adjacent to the excitation light source 52. The excitation light source 52 includes two-wavelength (1500 nm and 1460 nm) laser diode modules (LDM) 54 and 55, a two-wavelength excitation light multiplexer 56, and a tap coupler that branches output power from the LDMs 54 and 55. 57 and 58 and photodiodes 59 and 60 for receiving the tapped excitation light.
[0028]
A tap coupler is generally used as a duplexer because it is inexpensive. The typical value of the branching ratio is 95: 5. On the other hand, when the circulator 53 that is generally more expensive than the tab coupler is used, the reflection component of the excitation light is demultiplexed 100% by the circulator 53 and guided to the PD 25. Therefore, when the circulator 53 is used, the light receiving level at the PD 25 is about 20 times (13 dB) higher. A typical light receiving power when the circulator 53 is used is about -7 dBm. On the other hand, a typical light receiving power when a tap coupler is used is about −20 dBm. Therefore, using the circulator 53 has a higher light receiving power level and is less susceptible to dark current noise of a PD (photodiode), so that an inexpensive PD 25 and its associated electronic circuit should be used as the reflected light detector. There is an advantage that you can.
[0029]
In the present embodiment, tap couplers 57 and 58 are used on the pumping light output sides of the LDMs 54 and 55 to monitor the output power of the pumping light of each wavelength. As another method for monitoring the output power of pumping light, there is a method in which pumping light emitted from the rear end face of each laser diode is received by the nearest PD (usually mounted in a 14-pin module). When the tap couplers 57 and 58 are used, the pumping light output power is reduced due to the insertion loss of the tap couplers 57 and 58, but the pumping light output power can be accurately monitored. On the other hand, the hot water bath using the PD at the rear end has the advantage that there is no insertion loss, but has the disadvantage that the pumping light output power cannot be accurately monitored in many cases. Further, when the control circuit 61 has an A / D conversion circuit and a CPU (central processing unit) and can perform digital information processing, each LDM 54, using a table of drive current versus output power characteristics of each laser diode, The output pumping light power from 55 can be monitored and controlled. In this case, there is an advantage that the PD for monitoring the output pumping light power can be omitted.
[0030]
One or a plurality of demultiplexers of the excitation light reflection component may be installed between the LDMs 54 and 55 and the multiplexer 56. However, the loss bodies LE-1 and LE-2 generally have a wavelength-dependent loss value that cannot be ignored when the wavelength interval between two wavelengths is large. Therefore, by installing a demultiplexer for each LDM 54 and 55 and taking control of each pumping light wavelength in consideration of the loss value wavelength dependency, highly accurate control can be performed. However, when a demultiplexer (circulator 53) is installed on the output side of the excitation light source 52 as shown in FIG. 6, the average loss value for the excitation light of two wavelengths can be monitored, and high-precision control can be performed by a simple method. There is an advantage that can be performed.
[0031]
[Fifth Embodiment]
FIG. 7 shows an optical fiber communication system according to the fifth embodiment of the present invention. The following points are mainly different from the first embodiment shown in FIG. In the present embodiment, the reflection component of the excitation light at the connector pairs 72 and 73 is received to detect connector disconnection and connector residual reflection abnormality. When this excitation light reflection level is R, when the connector is disconnected, interface Fresnel reflection between the optical fiber glass and air occurs, so R is about -14 dB. Further, when physical contact (PC) connection is incomplete and R is large, R is about -30 dB to -20 dB. Incidentally, typical R for a good PC connection is about -40 dB or less.
[0032]
When the PC connection is good, the light received by the PD 25 is mainly Rayleigh backscattered light RBS from the transmission fiber 1. At that time, the total reflection level Rtot of the pumping light as viewed from the end face of the linear repeater 71 is the level of the Rayleigh backscattered light RBS from the transmission fiber 1 and is about −30 dB. When the connector is attached or detached during system operation, the PC connection becomes poor, and R in the PC connection deteriorates to, for example, -30 dB, Rtot becomes about -27 dB. Therefore, since the light reception level at the PD 25 is increased by about 3 dB, Prefl is increased by about 3 dB, and the connector residual reflection abnormality can be detected. Also, when R deteriorates to about -20dB, Rtot becomes about -20dB, Prefl rises by about 10dB, and connector residual reflection abnormality can be detected. Furthermore, when the connector is disconnected, Rtot is about -14 dB, and Prefl is increased by about 16 dB. From the above, for example, the increase amount of Prefl may be 14 dB or more as the detection level of connector disconnection. Further, as the detection level of the connector residual reflection abnormality, the increase amount of Prefl may be 2 dB or more and less than 14 dB.
[0033]
As described above, when the disconnection of the connector is detected, the excitation light source is shut down for the safety of the system maintainer, and the excitation light level emitted from the connector is set to a predetermined level or less. In addition, when a connector residual reflection abnormality is detected, if there is a concern about deterioration of system characteristics, an operation such as cleaning the connector is added.
As described above, according to the present embodiment, it is possible to detect connector disconnection and connector residual reflection abnormality which are not considered in the prior art.
[0034]
【The invention's effect】
As described above, according to the present invention, an effective spectrum analyzer and a multi-wavelength signal light source are not required, and thereby, it can be configured at low cost and can be installed without any special effort. effect Ru obtained.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an optical fiber communication system according to a first embodiment of the present invention.
FIG. 2 is a diagram for explaining the effect of the first embodiment;
FIG. 3 is a diagram for explaining the effect of the first embodiment;
FIG. 4 is a block diagram showing a configuration of an optical fiber communication system according to a second embodiment of the present invention.
FIG. 5 is a block diagram showing a configuration of an optical fiber communication system according to a third embodiment of the present invention.
FIG. 6 is a block diagram showing a configuration of an optical fiber communication system according to a fourth embodiment of the present invention.
FIG. 7 is a block diagram showing a configuration of an optical fiber communication system according to a fifth embodiment of the present invention.
FIG. 8 is a block diagram showing a configuration of a conventional optical fiber communication system.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Transmission fiber 21, 31, 41, 51, 71 ... Linear repeater 22, 56 ... Multiplexer 23 ... Excitation light source 24 ... Demultiplexer 25, 45, 59, 60 ... Photodiode 26, 32, 46, 61 , 74 ... Control circuit 42 ... SVC light receivers 43, 57, 58 ... Tap coupler 44 ... Fixed wavelength optical filter 53 ... Circulators 54, 55 ... Laser diode modules 72, 73 ... Connectors
LE-1, LE-2 ... Lost body

Claims (8)

An optical fiber communication system comprising a transmission fiber having a first loss body and a linear repeater to which the transmission fiber is connected, which is a transmission path for signal light,
The linear repeater is
An excitation light source that outputs excitation light for Raman excitation of the transmission fiber;
A multiplexer that combines the excitation light and the signal light;
A second loss body existing between the multiplexer and the transmission fiber;
Installed between the multiplexer and the pumping light source or in the pumping light source, the reflected pumping light reflected from the transmission fiber is separated from the outgoing pumping light emitted from the pumping light source and the difference in propagation direction. Waver,
A first light receiver for receiving reflected excitation light emitted from the duplexer;
Based on the amount of change in the reflected excitation light level received by the first light receiver, the amount of increase in the excitation light power is based on the variation in the amount of loss in the first and second loss bodies. A control circuit for controlling the excitation light source to be ½ of the decrease amount of
An optical fiber communication system using distributed Raman amplification. An optical fiber communication system comprising a transmission fiber having a first loss body and a linear repeater to which the transmission fiber is connected, which is a transmission path for signal light,
The linear repeater is
An excitation light source that outputs excitation light for Raman excitation of the transmission fiber;
A multiplexer that combines the excitation light and the signal light;
A second loss body existing between the multiplexer and the transmission fiber;
Installed between the multiplexer and the pumping light source or in the pumping light source, the reflected pumping light reflected from the transmission fiber is separated from the outgoing pumping light emitted from the pumping light source and the difference in propagation direction. Waver,
A first light receiver for receiving reflected excitation light emitted from the duplexer;
Based on the amount of change in the reflected pump light level received by the first light receiver and distance information from the linear repeater to the first lossy body, the pump light source is controlled so that the Raman gain is constant. A control circuit to
Optical fiber communication system using distributed Raman amplification, characterized in that it comprises a. An optical fiber communication system comprising a transmission fiber having a first loss body and a linear repeater to which the transmission fiber is connected, which is a transmission path for signal light,
  The linear repeater is
  An excitation light source that outputs excitation light for Raman excitation of the transmission fiber;
  A multiplexer that combines the excitation light and the signal light;
  A second loss body existing between the multiplexer and the transmission fiber;
  Installed between the multiplexer and the excitation light source or in the excitation light source, the reflected excitation light reflected from the transmission fiber is demultiplexed according to the difference in propagation direction from the exit excitation light emitted from the excitation light source. Waver,
  A first light receiver for receiving reflected excitation light emitted from the duplexer;
  A tap coupler installed in the signal light path;
  A fixed wavelength optical filter that removes noise light other than signal light from the propagating light branched by the tap coupler;
  A second light receiver for detecting the total signal light power emitted from the fixed wavelength optical filter;
  The input signal light power to the linear repeater is made constant based on the amount of change in the reflected excitation light level received by the first light receiver and the total signal light power received by the second light receiver. A control circuit for controlling the excitation light source;
  An optical fiber communication system using distributed Raman amplification. A monitoring channel light receiving means for detecting the number of signal light channels;
The control circuit includes a change amount of the reflected excitation light level received by the first light receiver, the total signal light power received by the second light receiver, and a signal light obtained by the monitoring channel light receiving means. 4. The distributed Raman amplification according to claim 3 , wherein the pumping light source is controlled so that the input signal light power to the linear repeater is constant based on the signal light power per channel calculated from the number of channels. The optical fiber communication system used. The optical fiber communication system using distributed Raman amplification according to any one of claims 1 to 4 , wherein the duplexer is a circulator. 6. The pump light source according to claim 1 , further comprising: a tap coupler for detecting the outgoing pumping light level; and a light receiver for receiving the pumping light emitted from the tap coupler. An optical fiber communication system using distributed Raman amplification according to any one of the items. The distributed Raman according to any one of claims 1 to 5 , further comprising a light receiver for detecting an outgoing excitation light level adjacent to a rear end face of the laser diode in the excitation light source. An optical fiber communication system using amplification. The optical fiber using distributed Raman amplification according to any one of claims 1 to 5 , wherein the control circuit includes a table of drive levels and emission pumping light levels of the pumping light source. Communications system.

Images