JP2004240278A - Optical fiber communication system using distribution raman amplification - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical fiber communication system using distribution Raman amplification which is constructed at low cost and installed without especially spending time and effort. <P>SOLUTION: A transmission fiber 1 is a transmission route of signal light and has a loss material LE-2. A linear relay device 21 is connected to the transmission fiber 1. The linear relay device 21 is equipped with a excitation light source 23, a multiplexer 22 to multiplex excitation light and the signal light, the loss material LE-1 existing between the multiplexer 22 and the transmission fiber 1, a demultiplexer 24 to separate reflected excitation light reflected by the transmission fiber 1 and emitted excitation light emitted from the excitation light source 23, a receiver 25 to receive the reflected excitation light emitted from the demultiplexer 24 and a control circuit 26 to control the excitation light source so as to keep Raman gain constant based on variation of a level of the reflected excitation light received with the receiver 25. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical fiber communication system for performing distributed Raman amplification of an optical signal in an optical fiber laid as a transmission line.
[0002]
[Prior art]
FIG. 8 shows a configuration of a conventional optical fiber communication system. A transmission fiber 1 as a transmission path and a linear repeater 2 are connected. The linear repeater 2 includes an erbium-doped fiber amplifier (EDFA) 3 which is a lumped-constant optical amplifier, an excitation light source 4 for distributed Raman amplification, and multiplexes the excitation light from the excitation light source 4 with the signal light. Components for detecting the Raman gain (G) of the signal light by the distributed Raman amplification, that is, for controlling the optical spectrum analyzer (optical spectrum analyzer) 6, the tapping force plug 7, and the pumping light source 4. Control circuit 8. The optical spectrumr 6 generally has a 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 which is not affected by dark current noise. The gain medium of the distributed Raman amplification is the transmission fiber 1 itself, and pump light is introduced into the transmission fiber 1 to optically pump the transmission fiber 1.
[0003]
FIG. 8 illustrates a loss body (optical connector or patch cord) LE-1 in the linear repeater 2 and a loss body (fiber fusion point or optical connector) LE-2 in the transmission fiber 1. The loss body LE-2 changes before and after the repair in the process of repairing the transmission fiber break due to an accident during road construction. For example, the typical variation is about 0.5-1.0 dB. The loss body LE-1 changes when the connection of the transmission fiber 1 is changed due to trouble transfer. For example, the typical variation is about 0.5-2.0 dB. When the loss values of the loss bodies LE-1 and LE-2 change, the average power of the pump light propagating through the transmission fiber 1 changes, and the Raman gain changes. Therefore, the following control is conventionally 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, wavelength multiplexed (WDM) signal light (the wavelengths are λ1, λ2,..., Λn) emitted from the EDFA 13, propagated through the transmission fiber 1, and then incident on the linear repeater 2. ) Are branched by the tap coupler 7 and enter the optical spectrumr 6. The spectrum of the signal light incident on the optical spectrumr 6 is analyzed, and the Raman gain (Raman gain spectrum) at each wavelength is calculated by, for example, comparing with the received light signal light level when there is no Raman gain. Further, the pumping light source 4 is controlled by the control circuit 8 so that the Raman gain spectrum becomes a desired value. Specifically, if the measured Raman gain is smaller than the desired value, the pumping light power is increased, and if the measured Raman gain is larger than the desired value, the pumping light power is decreased. In general, the excitation light source comprises a multi-wavelength laser diode. The transmission fiber 1 and the linear repeater 2 are connected by a pair of optical connectors. If this optical connector is accidentally removed for maintenance work of the linear repeater 2, a high-output excitation light is emitted from the optical connector on the linear repeater 2 side.
[0005]
[Non-patent document 1]
Yano et al., "Study of Automatic Adjustment Method of Pumping Light Power for Multi-Wavelength Pumping Raman Amplifier Gain Flattening (2)", IEICE General Conference, B-10-46, p. 483, 2002
[Non-patent document 2]
Sobe et al., “Study of Automatic Adjustment Method of Pumping Light Power for Multi-Wavelength Pumped Raman Amplifier Gain Flattening (1)”, IEICE General Conference, B-10-45, p. 482, 2002
[0006]
[Problems to be solved by the invention]
As described above, the conventional technique requires an expensive optical spectrumr 6. In addition, since it is necessary to measure the signal light spectrum incident on the linear repeater 2 from the EDFA 13 in advance when there is no Raman gain, a multi-wavelength signal light source is installed in the upstream linear repeater to achieve high precision. It is necessary to operate. However, there is a problem that a multi-wavelength signal light source is expensive, and it takes much time and effort to operate it with high accuracy. In addition, when high-output excitation light is emitted from the optical connector, there is a problem that a danger such as injury to the eyes of the operator may occur.
[0007]
SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide an optical fiber communication system using distributed Raman amplification that can be configured at low cost and that can be installed without special effort. Is to provide.
Another object of the present invention is to use distributed Raman amplification that can immediately detect an abnormality in an optical connector and thereby prevent a risk of causing a failure to eyes of an operator or a maintenance person. An object of the present invention is to provide an optical fiber communication system.
[0008]
[Means for Solving the Problems]
SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and the invention according to claim 1 is a transmission path for signal light, in which a transmission fiber having a first loss body and the transmission fiber are connected. An optical fiber communication system comprising: a linear repeater, the linear repeater comprising: a pump light source that outputs pump light for Raman pumping the transmission fiber; and a multiplexing device that multiplexes the pump light and the signal light. A second loss body existing between the multiplexer and the transmission fiber; and a reflection pump disposed between the multiplexer and the excitation light source or in the excitation light source and reflected from the transmission fiber. A demultiplexer for demultiplexing light according to a difference in the direction of propagation of the emitted excitation light from the excitation light source, a first light receiver for receiving the reflected excitation light emitted from the demultiplexer, The reflection received by the receiver of 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 based on the amount of change Okoshiko level.
[0009]
According to a second aspect of the present invention, in the optical fiber communication system using the distributed Raman amplification according to the first aspect, the control circuit is configured such that the amount of increase in the pumping light power is equal to the first and second loss bodies. The excitation light source is controlled so as to be １ ／ of the amount of decrease in the level of the reflected excitation light based on the variation of the loss amount of the excitation light.
According to a third aspect of the present invention, in the optical fiber communication system using the distributed Raman amplification according to the first aspect, the control circuit is configured to perform the control based on a distance from the linear repeater to the first loss body. The excitation light source is drive-controlled.
[0010]
According to a fourth aspect of the present invention, in the optical fiber communication system using the distributed Raman amplification according to the first aspect, a tap coupler installed in a signal light path and a propagation light branched by the tap coupler other than a signal light. Further comprising: a wavelength-fixed optical filter for removing noise light; and a second light receiver for detecting a total signal light power emitted from the wavelength-fixed optical filter, wherein the control circuit includes a first light receiver. Controlling the pump light source such that the input signal light power to the linear repeater becomes constant based on the amount of change in the level of the reflected pump light received and the total signal light power received by the second light receiver. It is characterized by.
[0011]
According to a fifth aspect of the present invention, in the optical fiber communication system using the distributed Raman amplification according to the fourth aspect, a monitoring channel light receiving unit for detecting the number of signal light channels is further provided, and the control circuit comprises: It was calculated from the amount of change in the level of the reflected excitation light 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 monitor channel light receiving means. The pump 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.
[0012]
The invention according to claim 6 is an optical fiber communication system including a transmission fiber that is a transmission path of signal light and a linear repeater to which the transmission fiber is connected, wherein the linear repeater includes the transmission fiber. A pumping light source that outputs pumping light for Raman pumping, a multiplexer that combines the pumping light and the signal light, and a transmission device that is installed between the multiplexer and the pumping light source or in the pumping light source, A splitter for splitting the reflected excitation light reflected from the fiber out of the pumping light emitted from the pumping light source according to a difference in the propagation direction thereof, and a first light receiving device for receiving the reflected excitation light emitted from the splitter. A pair of connectors for connecting the transmission fiber to a linear repeater, and a disconnection of the connector pair or a residual reflection difference of the connector based on the amount of change in the level of the reflected excitation light received by the first light receiver. An optical fiber communication system using distributed Raman amplification, characterized in that it comprises a control circuit for detecting a.
[0013]
According to a seventh aspect of the present invention, in the optical fiber communication system according to the sixth aspect, when the control circuit detects that the connector pair has come off, the control circuit shuts off the excitation light source by the control circuit. It is characterized in that the excitation light level is controlled to be lower than the safety level of the system maintenance person.
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 seventh aspects, the duplexer is a circulator.
[0014]
According to a ninth aspect of the present invention, in the optical fiber communication system using the distributed Raman amplification according to any one of the first to eighth aspects, the output pump light level is detected in the pump light source. And a light receiver for receiving the excitation light emitted from the tap coupler.
According to a tenth aspect of the present invention, in the optical fiber communication system using the distributed Raman amplification according to any one of the first to eighth aspects, adjacent to a rear end face of a laser diode in the pump light source, A light receiver for detecting the output excitation light level is provided.
According to an eleventh aspect of the present invention, in the optical fiber communication system using distributed Raman amplification according to any one of the first to eighth aspects, the drive level and the emission level of the pump light source are provided in the control circuit. An excitation light level table is provided.
[0015]
BEST MODE FOR CARRYING OUT 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 differs 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 related art, the signal light is tapped, and the Raman gain is calculated from the monitor value of the signal light power. The Rayleigh backscattered light RBS generated in the transmission fiber 1 makes a round trip through the loss bodies LE-1 and LE-2, reaches the multiplexer 22 for the signal light and the pump light, and propagates back to the pump light source 23. I 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 a duplexer 24 installed between the optical multiplexer 22 and the excitation light source 23, and Incident on the photodiode (PD) 25 connected to the. The present embodiment is a case of so-called backward pumping in which the directions of the signal light and the pumping light are opposite, but the configuration of the so-called forward pumping in which the directions of the signal light and the pumping light are the same direction is also used. Obviously the same holds true for symmetry.
[0016]
Now, let the power of the Rayleigh backscattered light RBS received by the PD 25 be Prefl, and let the excitation light power emitted from the excitation light source 23 be Pin. However, it is assumed that Prefl and Pin are values in dB units. Further, the values of Prefl and Pin in the initial state are Prefl1 and Pin1, respectively, and the values of Prefl and Pin when at least one of the loss values (L1 and L2) of the loss bodies LE-1 and LE-2 is changed. Are Prefl2 and Pin2, respectively. Prefl decrease amount
ΔPrefl = Pref1-Prefl2
Also, increase the amount of Pin
ΔPin = Pin2-Pin1
And In this embodiment,
ΔPin = ΔPrefl / 2
That is, control is performed so that ΔPin becomes 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 two wavelengths (1460 nm and 1500 nm). The gain wavelength range is the so-called L band (about 1570-1600 nm), and the average spectral 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, when no control is performed, the Raman gain decreases by about 3 dB. On the other hand, when control is performed, Raman gain decreases. The gain change was within about 0.1 dB.
[0018]
FIG. 3 shows the loss part distance dependency of the Raman gain change amount. The loss part distance is a distance in the fiber axial direction from the pump 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 at most several hundred meters. The transmission fiber length was about 100 km. The case where the loss value increase (ΔL) of the loss body LE-1 or LE-2 is 1.6 dB and 0.6 dB is shown. As for the Raman gain change amount (decrease amount) ΔG without control, when ΔL was 1.6 dB and 0.6 dB, the maximum values of ΔG were 2.9 dB and 1.4 dB.
[0019]
On the other hand, when ΔL was 1.6 dB and 0.6 dB with control, the maximum values of ΔG were 0.8 dB and 0.4 dB. Therefore, according to the present embodiment, it can be seen that the constant control of the Raman gain is realized with an accuracy within 0.8 dB. In particular, the control accuracy is good when the loss part distance is within about 1 km, and control within about 0.1 dB is realized. This is because when the loss portion distance is about 1 km or less, △ Prefl / 2 becomes substantially equal to △ L, so that the loss of the pump light due to the loss body LE-1 or LE-2 is increased and the increase of Pin is △ Pin = △ This is because the compensation is made almost completely by Prefl / 2. Therefore, this embodiment is particularly effective when the distance between the loss portions is within about 1 km.
[0020]
The detection light level in the present embodiment, that is, the power level Prefl of the Rayleigh backscattered light RBS was 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 in the optical spectrumr 6, was about -35 dBm. Therefore, in the related art, the APD 12 which is a high-sensitivity photodiode is required. However, the present embodiment has an advantage that an inexpensive normal-sensitivity photodiode can be used.
Further, the signal light, which is the detection light of the related art, has a narrow line width and high coherence, and thus is susceptible to interference noise deterioration. On the other hand, the excitation light, which is the detection light of the present embodiment, has the advantage that the line width is wide and the coherence is low, so that the excitation light is hardly affected by interference noise deterioration.
[0021]
[Second embodiment]
FIG. 4 is a block diagram showing the configuration of the optical fiber communication system according to the second embodiment of the present invention. The embodiment shown in this figure differs 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 the present embodiment, in addition to Prefl, distance information of the loss body LE-2 from the linear repeater 31 is input to the control circuit 32. The distance is defined as D2. When the loss value of the loss body LE-2 is the same, the reduction amount ΔPrefl of Prefl becomes smaller as the distance D2 becomes longer. On the other hand, the decrease ΔG of the Raman gain G also decreases as the distance D2 increases, but the decrease of ΔPrefl is larger than the decrease of ΔG. This is because the Raman gain G is proportional to the average power (Pave) of the pump light power over the transmission fiber length, while 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 pump light from the linear repeater 31 to the loss body LE-2 is known, the loss value L2 of the loss body LE-2 can be calculated from △ Prefl, and the loss value L2 can be calculated from Ld2 and L2. The correspondence between the gain G and the input pump light power Pin can be understood. Therefore, the value of Pin (Pin2) that keeps the gain G constant regardless of the change in L2 can be calculated, and the control circuit 32 drives the excitation light source to perform gain G constant control.
[0023]
In the present 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 decrease amount △ Prefl 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 when the gain G is constant. That is, the signal light level decreases by an 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) for compensating the decrease in the signal light level can be added. From the initial value of the gain G and the Raman gain coefficient of the transmission fiber 1 that has been checked in advance, the amount of change in Pin (Pin3-Pin2) that gives the G increase equal to the increase in the loss values L1 and L2 can be calculated. However, Pin3 is the final set value of Pin. The control circuit 32 drives the excitation light source 23 so as to obtain the Pin3.
[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 the present embodiment, in addition to Prefl, the signal light total power Psot input to the linear repeater 41 or the total power Psot and the number of signal light channels (Nch) received by the monitor channel light (SVC) light receiver 42. Use information. The total power Pspot is detected using a tap coupler 43, a fixed wavelength optical filter 44 for removing noise light other than signal light, and a second PD 45. However, the PD 25 that detects Prefl is the first PD. The number Nch of signal light channels is detected using the SVC light receiver 42 and a tap coupler for SVC branch and a fixed wavelength optical filter, which are not shown for simplicity.
[0025]
In the present 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 information of the amount of decrease ΔPrefl of Prefl. At this time, due to changes in the loss values L1 and L2, the signal light level reaching the linear repeater 41 slightly changes even if the gain G is constant. That is, the signal light level decreases by an increase in the loss values L1 and L2. Therefore, the following control (constant control of the linear repeater input signal light power) for compensating the signal light level decrease can be added.
[0026]
First, when the number of signal light channels is constant, the amount of change in the total power Pstop 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 that has been checked in advance, the amount of change in Pin that gives an increase in the 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 Pspot 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 Pspot. From the initial value of the gain G and the Raman gain coefficient of the transmission fiber 1 that has been checked 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 Pin change amount.
[0027]
[Fourth embodiment]
FIG. 6 shows an optical fiber communication system according to a fourth embodiment of the present invention. It operates according to the same operating principle as the first embodiment of the present invention shown in FIG. 1, but differs from the first embodiment in the specific configuration as described below. In the present embodiment, a circulator 53 is used as a splitter for the excitation light installed adjacent to the excitation light source 52. The pumping light source 52 includes laser diode modules (LDMs) 54 and 55 having two wavelengths (1500 nm and 1460 nm), a multiplexer 56 for pumping light having two wavelengths, and a tap coupler for branching output power from each of the LDMs 54 and 55. 57 and 58 and photodiodes 59 and 60 for receiving the tapped excitation light.
[0028]
In general, tap couplers are used because they are inexpensive. A typical value of the branching ratio is 95: 5. On the other hand, when a circulator 53 that is generally more expensive than a tab coupler is used, the reflection component of the excitation light is 100% demultiplexed 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. Typical light receiving power when the circulator 53 is used is about -7 dBm. On the other hand, a typical received light power when a tap coupler is used is about -20 dBm. Therefore, the use of the circulator 53 has a higher received light power level and is less susceptible to the influence of dark current noise of the PD (photodiode), so that the inexpensive PD 25 and its associated electronic circuit can 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 pump light output sides of the LDMs 54 and 55 to monitor the output power of the pump light of each wavelength. As another method of monitoring the output power of the pumping light, there is a method of receiving the pumping light emitted from the rear end face of each laser diode by the nearest PD (usually mounted in a 14-pin module). When the tap couplers 57 and 58 are used, there is a disadvantage that the pumping light output power is reduced by the insertion loss of the tap couplers 57 and 58, but there is an advantage that the pumping light output power can be accurately monitored. On the other hand, when using the PD at the rear end face, there is an advantage that there is no insertion loss, but there is a disadvantage that the pumping light output power cannot be accurately monitored in many cases. If 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, It is possible to monitor and control the power of the output pump light from 55. In this case, there is an advantage that the PD for monitoring the output pump light power can be omitted.
[0030]
In addition, one or a plurality of splitters for the excitation light reflection component may be provided 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 the two wavelengths is large. Therefore, by installing a demultiplexer for each of the LDMs 54 and 55 and performing control for each pumping light wavelength in consideration of the loss value wavelength dependency, highly accurate control can be performed. However, when the branching filter (circulator 53) is installed on the output side of the pumping light source 52 as shown in FIG. 6, the average loss value with respect to the pumping light of two wavelengths can be monitored, and highly accurate control can be performed by a simple method. Has the advantage that it can be performed.
[0031]
[Fifth Embodiment]
FIG. 7 shows an optical fiber communication system according to a 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 components of the excitation light at the connector pairs 72 and 73 are received to detect disconnection of the connector and abnormal reflection of the connector residual reflection. Assuming that the reflection level of the excitation light is R, when the connector is disconnected, R is about -14 dB because Fresnel reflection occurs at the interface between the optical fiber glass and air. Further, when the physical contact (PC) connection is incomplete and R is large, R is about -30 dB to -20 dB. By the way, a 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 the Rayleigh backscattered light RBS from the transmission fiber 1. At this time, the total reflection level Rtot of the pump 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 a connector is attached and detached during system operation and the PC connection becomes defective, and R in the PC connection deteriorates to, for example, -30 dB, Rtot becomes about -27 dB. Accordingly, the light receiving level at the PD 25 rises by about 3 dB, so that Prefl rises by about 3 dB, and it is possible to detect a residual reflection abnormality of the connector. Further, when R deteriorates to about -20 dB, Rtot becomes about -20 dB, Prefl increases by about 10 dB, and it is possible to detect an abnormal residual reflection of the connector. Further, when the connector is disconnected, Rtot becomes approximately −14 dB, and Prefl increases by approximately 16 dB. From the above, for example, the increase level of Prefl may be 14 dB or more as the detection level of the connector disconnection. In addition, the detection level of the connector residual reflection abnormality may be that the amount of increase of Prefl is 2 dB or more and less than 14 dB.
[0033]
As described above, when disconnection of the connector is detected, the excitation light source is shut down for safety of a system maintenance person, and the level of the excitation light emitted from the connector is set to a predetermined level or less. In addition, when the connector residual reflection abnormality is detected, if there is a concern about deterioration of the system characteristics, operations such as cleaning the connector are added.
As described above, according to the present embodiment, it is possible to detect a connector detachment or a connector residual reflection abnormality that is not considered in the related art.
[0034]
【The invention's effect】
As described above, according to the present invention, there is no need for an effective spectrumr and a multi-wavelength signal light source, so that it can be configured at low cost and can be installed without special effort. The effect is obtained. Further, according to the present invention, an abnormality of the optical connector can be immediately detected, and thereby, there is an effect that a danger of causing a trouble to eyes of an operator and a maintenance person can be prevented.
[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 an effect of the first embodiment.
FIG. 3 is a diagram for explaining an 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 illustrating a configuration of an optical fiber communication system according to a fourth embodiment of the present invention.
FIG. 7 is a block diagram illustrating 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]
1 ... Transmission fiber
21, 31, 41, 51, 71 ... linear repeater
22, 56 ... multiplexer
23 ... Excitation light source
24 ... Diplexer
25, 45, 59, 60 ... photodiode
26, 32, 46, 61, 74 ... control circuit
42 ... SVC receiver
43, 57, 58 ... tap coupler
44 ... wavelength fixed optical filter
53 ... Circulator
54, 55 ... Laser diode module
72, 73 ... connector
LE-1, LE-2 ... Loss body

Claims (11)

An optical fiber communication system, which is a transmission path for signal light, including a transmission fiber having a first loss body and a linear repeater to which the transmission fiber is connected,
The linear repeater is
An excitation light source that outputs excitation light that Raman excites the transmission fiber,
A multiplexer for multiplexing the pump light and the signal light,
A second loss body existing between the multiplexer and the transmission fiber;
A component that is disposed between the multiplexer and the pump light source or in the pump light source, and that separates the reflected pump light reflected from the transmission fiber from the output pump light emitted from the pump light source and the difference in the propagation direction thereof. With a wave device,
A first light receiver for receiving the reflected excitation light emitted from the duplexer;
A control circuit that controls the pump light source so that Raman gain is constant based on the amount of change in the level of the reflected pump light received by the first light receiver;
An optical fiber communication system using distributed Raman amplification, characterized by comprising: The control circuit controls the pumping light source such that the amount of increase in the pumping light power is の of the amount of decrease in the reflected pumping light level based on the variation in the loss amount of the first and second loss bodies. The optical fiber communication system using distributed Raman amplification according to claim 1, wherein the optical fiber communication system performs control. The optical fiber communication system using distributed Raman amplification according to claim 1, wherein the control circuit drives and controls the pumping light source based on a distance from the linear repeater to the first loss body. . A tap coupler installed in the signal light path,
A fixed wavelength optical filter that removes noise light other than signal light from the propagation light branched by the tap coupler,
A second optical receiver for detecting a total signal light power emitted from the wavelength-fixed optical filter,
The control circuit controls the input signal light power to the linear repeater based on the amount of change in the level of the reflected excitation light received by the first light receiver and the total signal light power received by the second light receiver. The optical fiber communication system using distributed Raman amplification according to claim 1, wherein the pump light source is controlled so as to be constant. Further comprising a monitoring channel light receiving means for detecting the number of channels of the signal light,
The control circuit is configured to control the amount of change in the level of the reflected excitation light received by the first light receiver, the total signal light power received by the second light receiver, and the signal light obtained by the monitor channel light receiving means. The distributed Raman amplification according to claim 4, wherein the pumping light source is controlled so that the input signal light power to the linear repeater becomes constant based on the signal light power per channel calculated from the number of channels. Optical fiber communication system used. A transmission fiber which is a transmission path of signal light, and an optical fiber communication system including a linear repeater to which the transmission fiber is connected,
The linear repeater is
An excitation light source that outputs excitation light that Raman excites the transmission fiber,
A multiplexer for multiplexing the pump light and the signal light,
A component that is disposed between the multiplexer and the pump light source or in the pump light source, and that separates the reflected pump light reflected from the transmission fiber from the output pump light emitted from the pump light source and the difference in the propagation direction thereof. With a wave device,
A first light receiver for receiving the reflected excitation light emitted from the duplexer;
A connector pair for connecting the transmission fiber to a linear repeater,
A control circuit that detects disconnection of the connector pair, or a connector residual reflection abnormality, based on a change amount of the reflected excitation light level received by the first light receiver;
An optical fiber communication system using distributed Raman amplification, characterized by comprising: The control circuit, when detecting disconnection of the connector pair, shuts off the excitation light source by the control circuit, and controls the output excitation light level to be equal to or lower than a safety level of a system maintenance person. 7. The optical fiber communication system according to 6. The optical fiber communication system using distributed Raman amplification according to any one of claims 1 to 7, wherein the branching filter is a circulator. 9. The pump light source according to claim 1, further comprising: a tap coupler for detecting the level of the emitted excitation light; and a light receiver for receiving the excitation light emitted from the tap coupler. An optical fiber communication system using the distributed Raman amplification according to any one of the above items. The distributed Raman according to any one of claims 1 to 8, further comprising a photodetector adjacent to a rear end face of the laser diode in the excitation light source for detecting an output excitation light level. Optical fiber communication system using amplification. The optical fiber using distributed Raman amplification according to any one of claims 1 to 8, wherein a table of a drive level of the pump light source and an output pump light level is provided in the control circuit. Communications system.

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