JP2006253782A - Optical fiber communication system using distribution amplification - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To avoid faults in a conventional technique such as higher costs and complicated control by establishing a system without increasing types of EDFAs. <P>SOLUTION: The optical fiber communication system has a constitution in which an optical fiber of a transmission path is excited from the same direction as the propagation direction of signal light. The system is provided with a gain equalizer having a loss spectrum decided from a Raman gain spectrum of the signal light. The gain equalizer is composed, for example, so that the loss spectrum expressed in units of dB has a shape of subtracting a wavelength-independent constant value from the Raman gain spectrum expressed in units of dB. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a distributed Raman amplification system that optically amplifies an optical signal in an optical fiber laid in a city as a transmission path.

  FIG. 17 shows a configuration example of a conventional distributed Raman amplification system (DRA system) used in a wavelength division multiplexing (WDM) optical fiber communication system. FIG. 17A shows the case of backward excitation DRA, and FIG. 17B shows the case of bidirectional excitation DRA. In the drawings, only portions related to the description are denoted by reference numerals.

  In the case of the backward pumping DRA of FIG. 17A, an optical fiber laid in the city as the transmission line optical fiber 2 is emitted from the pumping light source 220 of the downstream linear repeater 22 in the signal light propagation direction. The WDM signal light is distributed and amplified in a distributed manner by Raman amplification. The linear repeater 21 includes an optical amplification unit 210 that intensively amplifies the signal light, a pumping light source 211 that emits the pumping light, and a multiplexer 212 that combines the pumping light with the signal light.

  The optical amplifying unit 210 includes EDFAs 213 and 214 as erbium-doped fiber amplifiers (EDFAs) at the front stage and the rear stage, and a gain equalizer 215 installed between the EDFAs 213 and 214. The loss spectrum shape of the gain equalizer 215 is determined by the Raman gain of the Raman amplification and the gain spectra of the EDFAs 213 and 214, and equalizes the gain spectrum.

  The downstream linear repeater 22 has the same configuration as the linear repeater 21. The linear repeater 21 may be an optical transmitter, and the linear repeater 22 may be an optical receiver.

  On the other hand, in the case of the bidirectional pumping DRA in FIG. 17B, in addition to the backward pumping DRA, the linear repeater 23 emits pumping light for pumping the transmission line optical fiber 2 from the front. 230 and a multiplexer 231 for multiplexing the excitation light and the signal light.

  The optical amplifying unit 232 of the linear repeater 23 has a net gain spectrum corresponding to the Raman spectrum of the backward pumping and the Raman gain of the backward pumping.

  The gain spectrum is determined by the gains of the front and rear EDFAs 233 and 234 installed in the optical amplifying unit 232 and the loss of the gain equalizer 235 installed between the EDFAs 233 and 234. Further, the downstream linear repeater 24 has the same configuration as the linear repeater 23.

  In a general long-distance relay system, whether to use the backward pumping DRA or the dual pumping DRA is determined according to the transmission path loss in each section.

  According to the prior art shown in FIG. 17, the EDFAs 213 and 214 and the gain equalizer 215 are required in the section using the backward pumping DRA, and the EDFAs 233 and 234 and the gain are used in the section using the bi-directional pumping DRA. An equalizer 235 is required. At this time, the EDFAs 213 and 214 and the EDFAs 233 and 234 are different types of EDFAs.

  However, in general, since EDFA is expensive and complicated in control, it is not preferable that there are many types. That is, the prior art optical fiber communication system has the disadvantage that it is expensive and complicated to control depending on the EDFA used.

  The present invention has been made under such a background, and it is possible to construct a system without increasing the number of types of EDFA, and to avoid the disadvantages of the prior art that it is expensive and complicated to control. An object is to provide a fiber communication system.

  The present invention Raman-amplifies signal light propagating from the upstream linear repeater to the downstream linear repeater, upstream linear repeater with respect to the signal light propagation direction, downstream linear repeater with respect to the signal light propagation direction, and Light comprising: a transmission path optical fiber; and a pumping light source that emits pumping light that pumps the transmission path optical fiber installed in the upstream linear repeater or the downstream linear repeater from the same direction as the signal light propagation direction. It is a fiber system.

  Here, a feature of the present invention is that a first gain equalizer having a loss spectrum determined from the Raman gain spectrum of the signal light is provided.

  According to this, since the EDFA used in the backward pumping DRA configuration section of the prior art can be used as it is in the bidirectional pumping DRA configuration, a system can be constructed without increasing the type of EDFA, and it is expensive and complicated to control. The disadvantage of the prior art optical fiber communication system can be avoided.

  The present invention will be described in more detail. For example, the first gain equalizer has a shape in which a loss spectrum expressed in dB is obtained by subtracting a wavelength-independent constant value from the Raman gain spectrum expressed in dB. It is.

  Alternatively, the upstream linear repeater includes a second gain equalizer having a loss spectrum shape determined by a fiber input signal light power spectrum determined by nonlinearity of signal light in the transmission line optical fiber, The downstream linear repeater can include the first gain equalizer.

  Alternatively, the upstream linear repeater includes the second gain equalizer, and the downstream linear repeater has a dB unit from the loss spectrum of the first gain equalizer expressed in dB unit. A third gain equalizer having a loss spectrum shape obtained by subtracting the loss spectrum of the second gain equalizer expressed by the following formula and further subtracting a constant value independent of the wavelength can be provided.

  Alternatively, the linear repeater includes the first gain equalizer, and downstream of the first gain equalizer is a signal light splitter and a unit of dB connected to the splitter. A first optical filter having a spectral shape obtained by vertically inverting the loss spectrum of the first gain equalizer shown above, and a light receiver connected to the first optical filter can be provided.

  Alternatively, the linear repeater includes the second gain equalizer, and downstream of the second gain equalizer is a signal light splitter and a unit of dB connected to the splitter. A second optical filter having a spectral shape obtained by vertically inverting the loss spectrum of the second gain equalizer shown above, and a light receiver connected to the second optical filter can be provided.

  Alternatively, the linear repeater includes the third gain equalizer, and downstream of the third gain equalizer is a signal light splitter and a unit of dB connected to the splitter. A third optical filter having a spectral shape obtained by inverting the loss spectrum of the third gain equalizer shown above and a light receiver connected to the third optical filter can be provided.

  Alternatively, the linear repeater includes a demultiplexer for demultiplexing the monitoring light from the signal light, a monitoring light receiver connected to the demultiplexer, and a channel power reference table in which a predetermined channel power is recorded. And a control circuit for controlling the channel power of the upstream or downstream linear repeater based on the channel information of the signal light obtained by the monitoring light receiver and the channel power reference table.

  Further, an optical transmitter may be provided instead of the upstream linear repeater, and an optical receiver may be provided instead of the downstream linear repeater.

  According to the present invention, since the EDFA used in the backward pumping DRA configuration section of the prior art can be used as it is in the bidirectional pumping DRA configuration section, the system can be constructed without increasing the type of EDFA, and it is expensive and controllable. The disadvantages of the prior art fiber optic communication systems that are complex can be avoided.

  Embodiments of the present invention will be described below with reference to the drawings. In the drawings, only portions related to the description are denoted by reference numerals. Further, in order to distinguish between the gain equalizer of the prior art and the gain equalizer of the present invention, the description of the (conventional) gain equalizer of the prior art is added to the drawing.

(First Example)
An optical fiber communication system according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram of the optical fiber communication system of the first embodiment. As shown in FIG. 1, the first embodiment has a linear repeater 1 upstream in the signal light propagation direction, a linear repeater 3 downstream in the signal light propagation direction, and a linear repeater downstream from the upstream linear repeater 1. The transmission line optical fiber 2 for Raman amplification of the signal light propagating to the optical device 3 and the transmission line optical fiber 2 installed in the upstream linear repeater 1 or the downstream linear repeater 3 are excited from the same direction as the signal light propagation direction. An optical fiber communication system including a pumping light source 25 that emits pumping light, and includes a first gain equalizer 26 having a loss spectrum determined from a Raman gain spectrum of signal light.

  The first gain equalizer 26 has a shape in which a loss spectrum expressed in dB unit is obtained by subtracting a wavelength-independent constant value from the Raman gain spectrum expressed in dB unit.

  The configuration of the optical fiber communication system of the first embodiment using the bidirectional pumping DRA shown in FIG. 1 has a configuration similar to the configuration using the bidirectional pumping DRA of the prior art of FIG. Differ mainly in the following points. That is, the optical amplification unit 27 of the linear repeater 1 of this embodiment uses the same type of EDFA as the EDFAs 213 and 214 used in the configuration using the forward pumping DRA of the prior art in FIG. Further, the optical amplifying unit 27 includes a new first gain equalizer 26 in addition to the gain equalizer 215 of the prior art.

  FIG. 2 (a) shows a typical forward Raman gain spectrum expressed in dB in this embodiment. The transmission line optical fiber is a dispersion shifted fiber (DSF), the signal light band is L band (approximately 1570 to 1610 nm), and the pumping light wavelength is approximately 1440 nm. FIG. 2B shows a typical input signal light spectrum in this embodiment. The signal light power in the short wavelength region is set lower than the signal light power in the long wavelength region. This is because the shorter wavelength region is closer to the zero dispersion wavelength region (near 1550 nm) of the DSF, the nonlinearity is stronger, and the signal quality is significantly deteriorated.

  FIG. 3 shows an optical component loss spectrum expressed in dB unit in this embodiment. The optical components are a multiplexer 28 and a first gain equalizer 26. FIG. 3 shows the sum of loss spectra of the multiplexer 28 and the first gain equalizer 26. The loss spectrum of the first gain equalizer 26 is set so that the sum of the loss spectra is equal to the Raman gain spectrum shown in FIG. That is, the loss spectrum of the first gain equalizer 26 is obtained by subtracting the loss spectrum of the multiplexer 28 from the Raman gain spectrum. In general, the loss spectrum of the multiplexer 28 is independent of wavelength as shown in FIG.

  If the optical component loss spectrum shown in FIG. 3 is used, the EDFAs 213 and 214 and the gain equalizer 215 used in the configuration of the backward pumping DRA shown in FIG. 17A and the first gain newly installed in this embodiment are used. The equalizer 26 can be used to equalize the gain spectrum in the bidirectional excitation DRA configuration. That is, when FIG. 17A is compared with FIG. 1, the sum of the Raman gain spectrum of the forward excitation DRA and the loss spectrum of the multiplexer 28 and the first gain equalizer 26 are balanced. However, the dispersion of the loss value of the transmission line optical fiber 2 can generally be compensated by adjusting the loss value of a variable attenuator separately installed in the linear repeater 1.

  As described above, according to the present embodiment, since the EDFA used in the backward pumping DRA configuration section of the prior art can be used as it is in the bidirectional pumping DRA configuration, the system can be constructed without increasing the types of EDFAs. The disadvantage of the prior art optical fiber communication system, which is expensive and complicated to control, can be avoided.

(Second embodiment)
The optical fiber communication system of the second embodiment will be described with reference to FIG. FIG. 4 is a diagram showing the configuration of the optical fiber communication system of the second embodiment. 1 has a configuration similar to that of the first embodiment shown in FIG. 1, except for the following points. That is, in the present embodiment, the first gain equalizer 51 is installed after the rear EDFA 50 instead of before.

  Therefore, the configuration of the optical amplifying unit 52 of the present embodiment is the same as the configuration of the optical amplifying unit 210 in the backward pumping DRA of the prior art shown in FIG. There is an advantage that can be used. However, since an optical component having a loss is installed after the optical amplifying unit, the output of the linear repeater 5 is lower than that in the first embodiment. This is because the output of the optical amplifier 52 is mainly determined by the output of the EDFA 50, and the output of the EDFA 50 is not significantly different between the first and second embodiments.

  Similar to the first embodiment, according to this embodiment, since the EDFA used in the backward pumping DRA configuration section of the prior art can be used as it is in the bidirectional pumping DRA configuration, the system can be used without increasing the type of EDFA. Therefore, it is possible to avoid the disadvantages of the prior art optical fiber communication system that is expensive and complicated to control.

(Third embodiment)
An optical fiber communication system according to a third embodiment of the present invention will be described with reference to FIGS. FIG. 5 is a block diagram of the optical fiber communication system of the third embodiment. In the third embodiment, as shown in FIG. 5, the upstream linear repeater 8 has a loss spectrum shape determined by the fiber input signal light power spectrum determined by the nonlinearity of the signal light in the transmission line optical fiber 2. The second gain equalizer 80 is provided, and the downstream linear repeater 9 is provided with a first gain equalizer 90.

  The configuration of the optical fiber communication system of the third embodiment shown in FIG. 5 has a configuration similar to the configuration of the first embodiment of FIG. 1, except for the following points. That is, in this embodiment, the section of the transmission line optical fiber 2 uses backward pumping DRA, and the section of the transmission path optical fiber 4 uses bidirectional pumping DRA. Therefore, the input signal light power spectrum to the transmission line optical fiber 2 is flat, and the input signal light power spectrum to the transmission line optical fiber 4 is the spectrum shown in FIG.

  Therefore, in this embodiment, a new second gain equalizer 80 is installed in the optical amplifying unit 81 of the linear repeater 8. FIG. 6 shows the loss spectrum of the second gain equalizer 80. The loss spectrum has a high loss value in the short wavelength region and a low loss value in the long wavelength region, and has a shape obtained by vertically inverting the input signal light power spectrum of FIG. Therefore, an input signal light power spectrum to the flat transmission line optical fiber 4 is obtained. FIG. 7 shows the input signal light power spectrum.

  Therefore, according to the present embodiment, since the EDFA used in the backward pumping DRA configuration section of the prior art can be used as it is in the bidirectional pumping DRA configuration section, a system can be constructed without increasing the type of EDFA, and it is expensive. In addition, the disadvantages of the prior art optical fiber communication system that the control is complicated can be avoided.

(Fourth embodiment)
An optical fiber communication system according to a fourth embodiment of the present invention will be described with reference to FIGS. FIG. 8 is a diagram showing the configuration of the optical fiber communication system of the fourth embodiment.

  The configuration of the optical fiber communication system according to the fourth embodiment shown in FIG. 8 has a configuration similar to that of the third embodiment shown in FIG. 5, except for the following points. That is, in the third embodiment, an accurate signal light power spectrum is obtained at the input of the transmission line optical fiber 4 by using the second gain equalizer 80 in the linear repeater 8. On the other hand, in the fourth embodiment, an approximate signal light power spectrum is obtained at the input of the transmission line optical fiber 4 by using the first gain equalizer 120 in the linear repeater 12.

  As shown in FIG. 3, the first gain equalizer 120 has the same spectral shape as the Raman gain spectrum, which is different from the spectral shape of the second gain equalizer 80 shown in FIG. .

  However, the loss spectra of the first gain equalizer 120 and the second gain equalizer 80 have similar characteristics. That is, as shown in FIGS. 3 and 6, both spectra have a larger loss in the short wavelength region than in the long wavelength region.

  FIG. 7 shows an input signal light power spectrum in this embodiment. Compared with the input signal light power spectrum of the third embodiment shown in the figure, both show a good correlation. Therefore, generally good signal quality can be obtained over the entire signal light wavelength range.

  The advantage of this embodiment is that in the third embodiment, the types of gain equalizers required by using the forward excitation DRA are the second gain equalizer 80 and the first gain equalizer 90. In the present embodiment, the number of gain equalizers required is only one of the first gain equalizers (120, 130). Therefore, an inexpensive and simple optical fiber communication system can be constructed.

  Therefore, according to the present embodiment, since the EDFA used in the backward pumping DRA configuration section of the prior art can be used as it is in the bidirectional pumping DRA configuration section, a system can be constructed without increasing the type of EDFA, and it is expensive. In addition, the disadvantages of the prior art optical fiber communication system that the control is complicated can be avoided.

(Fifth embodiment)
An optical fiber communication system according to a fifth embodiment of the present invention will be described with reference to FIGS. FIG. 9 is a diagram showing the configuration of the optical fiber communication system of the fifth embodiment.

  In the fifth embodiment, as shown in FIG. 9, the upstream linear repeater 15 includes a second gain equalizer 150, and the downstream linear repeater 16 includes a first unit expressed in dB. A third gain equalizer 160 having a loss spectrum shape obtained by subtracting the loss spectrum of the second gain equalizer expressed in dB from the loss spectrum of the gain equalizer and further subtracting a constant value independent of wavelength is provided. .

  The configuration of the optical fiber communication system of the fifth embodiment shown in FIG. 9 has a configuration similar to the configuration of the third embodiment of FIG. 5, except for the following points. That is, in the third embodiment, the transmission line optical fiber 10 is a section using forward pumping DRA, but in this embodiment, the transmission path optical fiber 10 is a section not using forward pumping DRA. That is, in this embodiment, the pumping light source and the multiplexer for forward pumping DRA are not installed in the linear repeater 16.

  Therefore, in this embodiment, a new third gain equalizer 160 is used in the linear repeater 16. FIG. 10A shows loss spectrum synthesis characteristics in this example. FIG. 10A shows the loss spectrum (1) of the first gain equalizer, the loss spectrum of the second gain equalizer inverted (2), and (1) and (2 ) ((1) + (2)) is shown. Here, it should be noted that (2) is obtained by removing the wavelength-independent component of the Raman gain spectrum of the forward excitation DRA. FIG. 10B shows the loss spectrum of the third gain equalizer 160. From the sum of (1) and (2) shown in FIG. It is the deduction.

  From another viewpoint, the loss spectrum of the third gain equalizer 160 is obtained by subtracting the loss spectrum of the second gain equalizer from the loss spectrum of the first gain equalizer, and further subtracting the wavelength-independent component. It is the deduction.

  The input signal light spectrum to the linear repeater 15 is flat, and the third gain equalizer 160 is caused by the loss spectrum of the second gain equalizer 150 and the forward pumping DRA in the transmission line optical fiber 4. Since it has a loss spectrum shape that cancels the Raman gain spectrum, the input signal light spectrum in the transmission line optical fiber 10 becomes flat. That is, transmission of signal light in the transmission line optical fiber 10 is performed under optimum conditions.

  Therefore, according to the present embodiment, since the EDFA used in the backward pumping DRA configuration section of the prior art can be used as it is in the bidirectional pumping DRA configuration section, a system can be constructed without increasing the type of EDFA, and it is expensive. In addition, the disadvantages of the prior art optical fiber communication system that the control is complicated can be avoided.

(Sixth embodiment)
An optical fiber communication system according to the sixth embodiment of the present invention will be described with reference to FIGS. FIG. 11 is a diagram showing the configuration of the optical fiber communication system of the sixth embodiment.

  In the sixth embodiment, as shown in FIG. 11, the linear repeater 18 is provided with a first gain equalizer 180, and downstream of the first gain equalizer 180 is a signal light splitter. 181, a first optical filter 182 having a spectrum shape obtained by vertically inverting the loss spectrum of the first gain equalizer 180 expressed in dB connected to the branching unit 181, and the first optical filter 182 And a light receiver 183 connected to.

  Alternatively, a second gain equalizer (not shown) is provided instead of the first gain equalizer 180, and a second gain equalizer expressed in dB unit is used instead of the first optical filter 182. A second optical filter (not shown) having a spectral shape obtained by vertically inverting the loss spectrum can also be provided.

  Alternatively, a third gain equalizer (not shown) is provided instead of the first gain equalizer 180, and a third gain equalizer expressed in dB unit is used instead of the first optical filter 182. A third optical filter (not shown) having a spectral shape obtained by inverting the loss spectrum up and down can also be provided.

  The configuration of the optical fiber communication system of the sixth embodiment shown in FIG. 11 has a configuration similar to the configuration of the fourth embodiment of FIG. 8, except for the following points. That is, compared with the fourth embodiment, in this embodiment, the following parts are added in the linear repeater 18. These are a branching unit 181 installed at the subsequent stage of the optical amplification unit 184, an optical filter 182 connected to the branching unit 181, and a light receiver 183 connected to the optical filter 182. However, the light receiver 183 may be replaced with an optical spectrum analyzer (optical spectrum analyzer).

  Also in the prior art, the branching unit 181 and the light receiver 183 are used for controlling the linear repeater 18. That is, the linear repeater 18 is controlled so that the signal light is branched by the branching unit 181 and the level of the signal light received by the light receiving unit 183 becomes a predetermined value. However, the power spectrum of WDM signal light can be regarded as flat (constant regardless of wavelength) in the prior art. Therefore, if the number of wavelengths of the WDM signal light is N and the signal light power is Pstop, the signal light power per wavelength (or one channel) is Pstop / N.

  However, in this embodiment, as shown in the above-described embodiment, the input signal light power spectrum to the transmission line using the bi-directional pumping DRA is not flat.

  The signal light spectrum at each point (A to D) described in FIG. 11 is shown in FIG. However, only the spectral shape is shown, and the signal light power on the vertical axis has an arbitrary value. As shown in FIG. 12, the spectra at points A, C, and E are flat. The spectra at points B and D have a shape obtained by vertically inverting the Raman gain spectrum of the forward excitation DRA. FIG. 13 shows the loss spectrum of the optical filter 182. This loss spectrum also has a shape obtained by vertically inverting the Raman gain spectrum.

  In this embodiment, the signal light spectrum at the point D is non-flat as shown in FIG. 12, but the signal light passing through the point D and passing through the optical filter 182 has a flat spectrum at the point E. Have. This is because the signal light at the point D is attenuated by the optical filter 182 so as to receive a greater loss as the signal light in the longer wavelength region according to the Raman gain.

  As described above, in this embodiment, the WDM signal light incident on the light receiver 183 has a flat power spectrum, so that the linear repeater 18 can be controlled in the same manner as in the prior art. That is, if the number of wavelengths of the WDM signal light received by the light receiver 183 is N and the signal light power is Pstop, the signal light power per wavelength (or one channel) is Pstop / N. Therefore, the linear repeater 18 is controlled so that the light reception signal light power becomes a predetermined value. When an optical spectrum analyzer is used instead of the light receiver 183, the linear repeater 18 is controlled so that the signal light spectrum measured by the optical spectrum analyzer becomes flat.

  In summary, when the type of the gain equalizer in the linear repeater 18 is the same as that of the fourth embodiment of FIG. 8, the spectrum of the signal light input to the light receiver 183 is flattened using the optical filter 182. ing. On the other hand, when the type of the gain equalizer in the linear repeater 18 is the same as that of the third embodiment of FIG. 5, the second optical filter having the loss spectrum shown in FIG. , The spectrum of the signal light input to the light receiver 183 can be flattened.

  If the type of the gain equalizer in the linear repeater 18 is the same as that of the fifth embodiment of FIG. 9, the third optical filter having the loss spectrum shown in FIG. , The spectrum of the signal light input to the light receiver 183 can be flattened.

  As described above, according to the present embodiment, since the EDFA used in the backward pumping DRA configuration section of the prior art can be used as it is in the bidirectional pumping DRA configuration section, a system can be constructed without increasing the type of EDFA. And avoids the disadvantages of the prior art optical fiber communication systems that are expensive and complex to control.

(Seventh embodiment)
An optical fiber communication system according to the seventh embodiment of the present invention will be described with reference to FIG. FIG. 16 is a diagram showing the configuration of the optical fiber communication system of the seventh embodiment.

  In the seventh embodiment, as shown in FIG. 16, a linear repeater 20 is connected to a demultiplexer 200 that demultiplexes monitoring light (hereinafter referred to as OSC light) from signal light, and to this demultiplexer 200. Based on the OSC optical receiver 201, the channel power reference table 202 in which a predetermined channel power is recorded, the channel information of the signal light obtained by the OSC optical receiver 201 and the channel power reference table 202, the linear repeater And a control circuit 203 for controlling 20 channel powers.

  The configuration of the optical fiber communication system of the seventh embodiment shown in FIG. 16 has a configuration similar to the configuration of the first embodiment of FIG. 1, except for the following points. That is, compared with the first embodiment, in this embodiment, the following parts are added in the linear repeater 20. They are the OSC optical duplexer 200 installed in the preceding stage of the optical amplification unit 204, the OSC optical receiver 201 connected to the duplexer 200, the channel power reference table 202, and the control circuit 203 of the linear repeater 20. is there. However, the OSC light transmits channel information regarding the WDM signal light, that is, the number of channels (number of wavelengths), channel arrangement, and signal light power for each channel from the upstream linear repeater to the downstream linear repeater.

  The channel information obtained by the OSC optical receiver 201 is sent to the control circuit 203, and is compared with the channel power reference table 202 in the control circuit 203. Thereafter, the control circuit 203 controls the linear repeater 20, that is, the optical amplifying unit 204 and the pumping light sources 205 and 206 so that the channel power set in the channel power reference table 202 is obtained. However, the OSC light is used for controlling the linear repeater also in the prior art. In the prior art, as described above, since the power spectrum of the WDM signal light is set flat, the control based on the channel power reference table 202 performed in this embodiment is not necessary.

  Specifically, the control of the present embodiment is performed as follows. For example, when the WDM signal light has two channels near 1570 nm and the output of the two-channel linear repeater 20 is set to −5 dBm per channel in the channel power reference table 202, the total output of the linear repeater 20 Is controlled to be −2 dBm.

  On the other hand, when the WDM signal light has two channels near 1610 nm and the output of the two-channel linear repeater 20 is set to −3 dBm per channel in the channel power reference table 202, the total output of the linear repeater 20 Is controlled to be 0 dBm. Thus, in this embodiment, the power of the WDM signal light is different for each channel.

  As described above, according to the present embodiment, since the EDFA used in the backward pumping DRA configuration section of the prior art can be used as it is in the bidirectional pumping DRA configuration section, a system can be constructed without increasing the type of EDFA. And avoids the disadvantages of the prior art optical fiber communication systems that are expensive and complex to control.

  The description of the above embodiment can be similarly applied even if the upstream linear repeater in the above embodiment is replaced with an optical transmitter and the downstream linear repeater is replaced with an optical receiver.

  According to the present invention, it is possible to construct an optical fiber communication system that is inexpensive and easy to control.

The block diagram of the optical fiber communication system of a 1st Example. The figure which shows the forward excitation Raman gain spectrum and transmission line input signal light spectrum in a 1st Example. The figure which shows the optical component loss spectrum in a 1st Example. The block diagram of the optical fiber communication system of a 2nd Example. The block diagram of the optical fiber communication system of a 3rd Example. The figure which shows the optical component loss spectrum in a 3rd Example. The figure which shows the transmission-path input signal light spectrum in a 3rd and 4th Example. The block diagram of the optical fiber communication system of 4th Example. The block diagram of the optical fiber communication system of 5th Example. The figure which shows the gain equalizer loss spectrum characteristic in 5th Example. The block diagram of the optical fiber communication system of 6th Example. The figure which shows the signal light spectrum in a 6th Example. The figure which shows the loss spectrum of a 1st optical filter. The figure which shows the loss spectrum of a 2nd optical filter. The figure which shows the loss spectrum of a 3rd optical filter. The block diagram of the optical fiber communication system of 7th Example. The block diagram of the conventional optical fiber communication system.

Explanation of symbols

1, 3, 5-9, 11-20, 21-24 Linear repeater 2, 4, 10 Transmission path optical fiber 25, 205, 211, 220, 230 Excitation light source 26, 51, 90, 120, 130, 180 One gain equalizer 27, 52, 81, 184, 204 210, 232 Optical amplifiers 28, 212, 231 Multiplexer 50, 213, 214, 233, 234 EDFA
80, 150 Second gain equalizer 160 Third gain equalizer 181 Branch unit 182 Optical filter 183 Optical receiver 200 Demultiplexer 201 OSC optical receiver 202 Channel power reference table 203 Control circuit 215, 235 (conventional) ) Gain equalizer

Claims (9)

An upstream linear repeater in the signal light propagation direction;
A linear repeater downstream in the signal light propagation direction;
A transmission line optical fiber for Raman amplification of signal light propagating from the upstream linear repeater to the downstream linear repeater;
In an optical fiber communication system comprising: an excitation light source that emits excitation light for exciting the transmission line optical fiber installed in the upstream linear repeater or the downstream linear repeater from the same direction as the signal light propagation direction;
An optical fiber communication system comprising a first gain equalizer having a loss spectrum determined from a Raman gain spectrum of signal light.   The optical fiber communication system according to claim 1, wherein the first gain equalizer has a shape in which a loss spectrum expressed in dB is obtained by subtracting a wavelength-independent constant value from the Raman gain spectrum expressed in dB. . The upstream linear repeater includes a second gain equalizer having a loss spectrum shape determined by a fiber input signal light power spectrum determined by nonlinearity of signal light in the transmission line optical fiber,
The optical fiber communication system according to claim 1, wherein the downstream linear repeater includes the first gain equalizer. The upstream linear repeater includes the second gain equalizer,
The downstream linear repeater is subtracted from the loss spectrum of the first gain equalizer expressed in dB from the loss spectrum of the first gain equalizer expressed in dB, and is wavelength independent. The optical fiber communication system according to claim 1, further comprising a third gain equalizer having a loss spectrum shape obtained by subtracting a constant value. The linear repeater includes the first gain equalizer,
Downstream of this first gain equalizer
A signal light splitter;
A first optical filter having a spectral shape obtained by vertically inverting the loss spectrum of the first gain equalizer expressed in dB connected to the splitter;
The optical fiber communication system according to claim 1, further comprising: a light receiver connected to the first optical filter. The linear repeater includes the second gain equalizer,
Downstream of this second gain equalizer
A signal light splitter;
A second optical filter having a spectral shape obtained by vertically inverting the loss spectrum of the second gain equalizer expressed in dB connected to the splitter;
The optical fiber communication system according to claim 1, further comprising: a light receiver connected to the second optical filter. The linear repeater includes the third gain equalizer,
Downstream of this third gain equalizer
A signal light splitter;
A third optical filter having a spectral shape obtained by vertically inverting the loss spectrum of the third gain equalizer expressed in dB connected to the splitter;
The optical fiber communication system according to claim 1, further comprising: a light receiver connected to the third optical filter. The linear repeater includes
A demultiplexer for demultiplexing the monitoring light from the signal light;
A monitoring light receiver connected to the duplexer;
A channel power reference table in which a predetermined channel power is recorded, and
The optical fiber communication according to claim 1, further comprising: a control circuit that controls channel power of the upstream or downstream linear repeater based on channel information of the signal light obtained by the monitoring light receiver and the channel power reference table. system. An optical transmitter instead of the upstream linear repeater,
The optical fiber communication system according to claim 1, further comprising an optical receiver instead of the downstream linear repeater.

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