JP2012220893A - Nonlinear optical effect suppressor and optical relay device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress nonlinear optical effects generated by interaction between wavelength channels and extend a transmittable distance in a wavelength-division-multiplexed optical transmission system.SOLUTION: A nonlinear optical effect suppressor according to the present invention includes: a demultiplexing part 12 for demultiplexing wavelength multiplexed signal light formed by multiplexing optical signals of a plurality of wavelength channels into the optical signals of the respective wavelength channels; an individual delay applying part 11 for applying delays with delay amounts that are different according to the respective wavelength channels, to the optical signals of the respective wavelength channels from the demultiplexing part 12; and a multiplexing part 13 for multiplexing the optical signals of the respective wavelength channels from the individual delay applying part 11.

Description

  The present invention relates to a nonlinear optical effect suppressor and an optical repeater for extending a transmittable distance in a wavelength division multiplexing optical transmission system.

  In a wavelength division multiplexing optical transmission system using wavelength division multiplexing, a signal to be transmitted is expressed by modulating the amplitude and phase of a light wave, and transmission is performed by assigning different signal channels to a plurality of wavelengths. Optical signals of a plurality of wavelength channels generated at the transmission node are multiplexed by a multiplexer, and transmitted to a reception node through a relay optical node composed of an optical fiber transmission line and an optical amplifier. At the receiving node, the optical signal of each wavelength channel is converted from an optical signal to an electric signal by an optical receiver, and the transmitted signal is determined by sign determination.

  Further, in a wavelength division multiplexing optical transmission system of 100 Gb / s or more, it is possible to compensate for linear signal degradation such as chromatic dispersion by using digital signal processing at the time of code determination.

D. Sperti, P.M. Serena and A.M. Bononi, “A comparison of differential options to improve PDM-QPSK resilience against cross-channel nonlinearities,” 36th European Conference on Op. 9. A. 1, 2010.

  In the wavelength division multiplexing optical transmission system, signal degradation due to the nonlinear optical effect generated in the optical fiber transmission line and the optical amplifier is a problem (Non-Patent Document 1). Since these nonlinear optical effects increase in accordance with the intensity of the transmitted optical signal, they are factors that limit the transmittable distance in the wavelength division multiplexing optical transmission system.

  Among nonlinear optical effects, those due to the interaction of multiple wavelength channels such as cross-phase modulation (XPM) and four-wave mixing (FWM) are difficult to compensate using digital signal processing at the receiving end. In particular, in the transmission method in which coherent detection is performed at the receiving end, the phase of the optical signal is greatly deviated from the correct signal state due to cross-phase modulation, which causes a significant transmission penalty.

  An object of the present invention is to suppress the nonlinear optical effect caused by the interaction between wavelength channels and to extend the transmission distance in the wavelength division multiplexing optical transmission system.

  In order to achieve the above object, according to the present invention, in wavelength division multiplexing transmission, adjacent wavelength channels are demultiplexed, different delays are given to the respective wavelength channels, and the respective wavelength channels are multiplexed. This suppresses the nonlinear optical effect due to the interaction of a plurality of wavelength channels and enables long-distance transmission in wavelength division multiplex transmission.

  Specifically, the nonlinear optical effect suppressor of the present invention includes a demultiplexing unit for branching wavelength multiplexed signal light, in which optical signals of a plurality of wavelength channels are multiplexed, into optical signals of each wavelength channel, and the demultiplexing unit To each optical signal of each wavelength channel from, an individual delay applying unit that applies a delay of a different delay amount in each wavelength channel, and a multiplexing unit that combines the optical signals of each wavelength channel from the individual delay applying unit, Is provided.

  Since the nonlinear optical effect suppressor of the present invention includes a demultiplexing unit and an individual delay providing unit, it is possible to apply a delay having a different delay amount in each wavelength channel. For this reason, it is possible to suppress the nonlinear optical effect caused by the interaction between the wavelength channels and to extend the transmission distance in the wavelength division multiplexing optical transmission system.

In the nonlinear optical effect suppressor of the present invention, the individual delay applying unit is configured so that a delay difference having a time width of half or more of the symbol interval of the optical signal is generated between adjacent wavelength channels. It is preferable to add a delay to the optical signal.
According to the present invention, it is possible to suppress the influence of the nonlinear optical effect received from the same symbol of adjacent wavelength channels, and it is possible to improve the signal quality.

In the nonlinear optical effect suppressor of the present invention, a common chromatic dispersion compensator having a group delay characteristic opposite to the group delay characteristic of the optical fiber transmission line that propagates the wavelength-multiplexed signal light is further provided before the demultiplexing part. Prepare.
According to the present invention, it is possible to compensate for signal distortion caused by chromatic dispersion that occurs in an optical fiber transmission line, and thus it is possible to further suppress the nonlinear optical effect.

  Specifically, the nonlinear optical effect suppressor of the present invention includes a demultiplexing unit for branching wavelength multiplexed signal light, in which optical signals of a plurality of wavelength channels are multiplexed, into optical signals of each wavelength channel, and the demultiplexing unit An individual chromatic dispersion compensator that passes the optical signal of each wavelength channel from a medium having a group delay characteristic opposite to the group delay characteristic of each wavelength channel in the optical fiber transmission line that propagates the wavelength multiplexed signal light; A multiplexing unit that combines the optical signals of the respective wavelength channels from the individual chromatic dispersion compensation unit.

  Since the nonlinear optical effect suppressor of the present invention includes a demultiplexing unit and an individual chromatic dispersion compensation unit, delays having different delay amounts can be given to the respective wavelength channels. For this reason, it is possible to suppress the nonlinear optical effect caused by the interaction between the wavelength channels and to extend the transmission distance in the wavelength division multiplexing optical transmission system.

  Specifically, in the optical repeater of the present invention, wavelength multiplexed signal light in which optical signals of a plurality of wavelength channels are multiplexed is input from an optical fiber transmission line, and the input wavelength multiplexed signal light is amplified. A non-linear optical effect suppressor according to the present invention, which receives a wavelength-division multiplexed signal light from the first optical amplifier and suppresses a non-linear optical effect generated in the optical fiber transmission line; and the non-linear optical effect A second optical amplifier that amplifies the wavelength multiplexed signal light from the suppressor.

  Since the optical repeater according to the present invention includes an optical amplifier, signal loss in the optical fiber transmission line can be compensated by the optical amplifier. In addition, since the optical repeater according to the present invention includes the nonlinear optical effect suppressor, the nonlinear optical effect caused by the interaction between the wavelength channels can be suppressed. Therefore, the optical repeater of the present invention can extend the transmission distance in the wavelength division multiplexing optical transmission system.

  Specifically, the nonlinear optical effect suppression method of the present invention demultiplexes wavelength multiplexed signal light, in which optical signals of a plurality of wavelength channels are multiplexed, into optical signals of each wavelength channel, and has different delay amounts for each wavelength channel. And an individual delay adding procedure for multiplexing the optical signals of the respective wavelength channels after the delay is added.

  Since the nonlinear optical effect suppressing method of the present invention has an individual delay providing procedure, it is possible to apply a delay having a different delay amount in each wavelength channel. For this reason, it is possible to suppress the nonlinear optical effect caused by the interaction between the wavelength channels and to extend the transmission distance in the wavelength division multiplexing optical transmission system.

In the nonlinear optical effect suppressing method of the present invention, each wavelength channel is set such that, in the individual delay providing procedure, a delay difference having a time width of half or more of a symbol interval of the optical signal is generated between adjacent wavelength channels. It is preferable to add a delay to the optical signal.
According to the present invention, it is possible to suppress the influence of the nonlinear optical effect received from the same symbol of adjacent wavelength channels, and it is possible to improve the signal quality.

In the nonlinear optical effect suppressing method of the present invention, the common wavelength dispersion compensation for allowing the wavelength multiplexed signal light to pass through a medium having a group delay characteristic opposite to the group delay characteristic of the optical fiber transmission line that propagates the wavelength multiplexed signal light. A procedure may further be included before the individual delay provision procedure.
According to the present invention, it is possible to compensate for signal distortion caused by chromatic dispersion that occurs in an optical fiber transmission line, and thus it is possible to further suppress the nonlinear optical effect.

  Specifically, the nonlinear optical effect suppression method of the present invention demultiplexes wavelength-multiplexed signal light obtained by multiplexing optical signals of a plurality of wavelength channels into optical signals of each wavelength channel, and converts the optical signals of each wavelength channel. And passing the optical signal of each wavelength channel after passing through the medium through the medium having the group delay characteristic opposite to the group delay characteristic of each wavelength channel in the optical fiber transmission line that propagates the wavelength multiplexed signal light. And an individual chromatic dispersion compensation procedure.

  Since the nonlinear optical effect suppressing method of the present invention has an individual chromatic dispersion compensation procedure, it is possible to give delays having different delay amounts in each wavelength channel. For this reason, it is possible to suppress the nonlinear optical effect caused by the interaction between the wavelength channels and to extend the transmission distance in the wavelength division multiplexing optical transmission system.

  Specifically, in the optical repeater of the present invention, a wavelength multiplexed signal light in which optical signals of a plurality of wavelength channels are multiplexed is input from an optical fiber transmission line, and the input wavelength multiplexed signal light is amplified. One optical amplification procedure and wavelength multiplexed signal light amplified in the first optical amplification procedure are input, and the nonlinear optical effect generated in the optical fiber transmission line is suppressed using the nonlinear optical effect suppression method according to the present invention. And a second optical amplification procedure for amplifying the wavelength multiplexed signal light whose nonlinear optical effect is suppressed by the nonlinear optical effect suppression procedure.

  Since the optical repeater of the present invention has an optical amplification procedure, it can compensate for signal loss in the optical fiber transmission line. In addition, since the optical relay method of the present invention has a nonlinear optical effect suppression procedure, it is possible to suppress the nonlinear optical effect caused by the interaction between wavelength channels. Therefore, the optical relay method of the present invention can extend the transmission distance in the wavelength division multiplexing optical transmission system.

  The above inventions can be combined as much as possible.

  ADVANTAGE OF THE INVENTION According to this invention, the nonlinear optical effect produced by the interaction between wavelength channels can be suppressed, and the transmission possible distance can be extended in a wavelength division multiplexing optical transmission system.

The structural example of the nonlinear optical effect suppressor which concerns on 1st embodiment is shown. An example of the group delay characteristic of each wavelength channel after applying the individual delay providing unit 11 is shown. The evaluation result of the relationship between delay difference Δτ and transmission quality is shown. The evaluation result of the relationship between the direction of delay amount and transmission quality is shown. An example of the relationship between the compensation ratio of chromatic dispersion and transmission quality is shown. The structural example of the nonlinear optical effect suppressor which concerns on 4th embodiment is shown. An example of the group delay characteristic of the nonlinear optical effect suppressor which concerns on 4th embodiment is shown. An example of the group delay characteristic of each wavelength channel after applying the nonlinear optical effect suppressor 102 which concerns on 4th embodiment is shown. The device structural example of the nonlinear optical effect suppressor 102 shown in 4th embodiment is shown. The structural example of the wavelength selective switch using the nonlinear optical effect suppression function shown in 4th embodiment is shown. An example of the group delay characteristic of each wavelength channel in a configuration in which a fixed amount of delay is applied by the individual delay applying unit 11 is shown. An example of group delay characteristics of each wavelength channel in a configuration in which a variable amount of delay is imparted by the individual delay imparting unit 11 is shown. The structural example of the nonlinear optical effect suppressor which concerns on 9th embodiment is shown. An example of the group delay characteristic of the nonlinear optical effect suppressor 201 which concerns on 9th embodiment is shown. An example of the group delay characteristic of each wavelength channel after applying the nonlinear optical effect suppressor 201 which concerns on 9th embodiment is shown. The structural example of the device which implement | achieves the nonlinear optical effect suppressor 201 shown in 9th embodiment is shown. An example of the phase modulation amount of the reflective liquid crystal element shown in the tenth embodiment will be shown. An example of the group delay characteristic of each wavelength channel after applying the nonlinear optical effect suppressor 201 according to the tenth embodiment is shown. 2 shows a configuration example of a wavelength selective switch according to the first embodiment. The structural example of the wavelength division multiplexing optical transmission system which concerns on 12th embodiment is shown. The structural example of the wavelength division multiplexing optical transmission system which concerns on 14th embodiment is shown. The structural example of the wavelength division multiplexing optical transmission system which concerns on 16th embodiment is shown.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. In the present specification and drawings, the same reference numerals denote the same components.

(First embodiment)
The nonlinear optical effect suppression method according to the present embodiment has an individual delay provision procedure. The configuration of the nonlinear optical effect suppressor according to this embodiment is shown in FIG. The nonlinear optical effect suppressor 101 according to this embodiment includes a demultiplexing unit 12, an individual delay applying unit 11, and a multiplexing unit 13.

In the individual delay providing procedure, the nonlinear optical effect suppressor 101 operates as follows.
Wavelength multiplexed signal light in which optical signals of a plurality of wavelength channels are multiplexed is input to the demultiplexing unit 12. The demultiplexing unit 12 branches the input wavelength multiplexed signal light into optical signals of each wavelength channel. The number of branches of the optical signal is made equal to the number N of wavelength channels multiplexed by wavelength division multiplexing. The individual delay applying units 11 _{1 to} 11 _N add delays having different delay amounts in the respective wavelength channels to the optical signals of the respective wavelength channels from the demultiplexing unit 12. For example, the delay amounts of the individual delay applying units 11 _{1 to} 11 _N are different from each other. The multiplexing unit 13 multiplexes the optical signals of the respective wavelength channels from the individual delay providing unit 11. As a result, the wavelength channels to which the delay is added are multiplexed, and the original wavelength division multiplexed signal is output again.

  FIG. 2 shows an example of the group delay characteristic of each wavelength channel after the delay is added by the individual delay adding unit 11. There is a delay difference of Δτ between the group delay of the wavelength channel CH1 and the group delay of the wavelength channel CH2. In this way, the individual delay adding unit 11 gives a delay so that a delay difference of Δτ is created between adjacent wavelength channels.

  As described above, the nonlinear optical effect suppressor 101 gives a delay having a different delay amount in each wavelength channel. Thereby, the nonlinear optical effect can be suppressed.

(Second embodiment)
In the individual delay adding procedure shown in the first embodiment, the individual delay adding unit 11 adds a delay to the optical signal branched for each wavelength channel so that a delay difference of Δτ is created between adjacent wavelength channels. To do. The delay difference Δτ is set to Δτ ≧ Ts / 2 (Ts is a symbol interval of the optical signal) so that a delay difference having a time width of half or more of the symbol interval Ts of the optical signal is generated.

  When a 112 Gb / s polarization multiplexed quaternary phase modulation (DP-QPSK) signal is transmitted in the L band with a dispersion shifted fiber, the relationship between the delay difference Δτ imparted between adjacent wavelength channels and the transmission quality is tested. FIG. 3 shows the result evaluated by the above. From the result of FIG. 3, it can be seen that the signal quality can be improved by setting the delay difference Δτ added between the wavelength channels to 17.9 ps or more, which is a half of the symbol interval Ts of optical signal 35.7 ps. Therefore, the delay difference Δτ added between adjacent wavelength channels is Δτ ≧ Ts / 2 (Ts is the symbol interval of the optical signal). When Δτ ≧ Ts / 2, the influence of the nonlinear optical effect received from the same symbol of the adjacent wavelength channel can be suppressed, and the signal quality can be improved.

  When the nonlinear optical effect suppressor 101 shown in the first embodiment is configured using an optical device, the delay difference Δτ between adjacent wavelength channels is Δτ ≧ Ts / 2 (Ts is the symbol interval of the optical signal). In scope, it depends on the design of the device to be realized.

(Third embodiment)
The direction of the delay difference Δτ imparted between the wavelength channels in the individual delay imparting unit 11 of the nonlinear optical effect suppressor 101 shown in the first embodiment is the same as or opposite to the group delay generated in the optical fiber transmission line 100. I do not care. FIG. 4 shows the result of evaluating the relationship between the direction of the delay amount given between the wavelength channels and the transmission quality in a 128 Gb / s polarization multiplexed quaternary phase modulation signal by computer simulation.

  Regarding each plot in FIG. 4, black circles are evaluation results when a delay difference is given in the same direction as the group delay, and white circles are evaluation results when a delay difference is given in the direction opposite to the group delay. From the result of FIG. 4, at 15.6 ps, which is half the symbol interval Ts = 31.3 ps of the optical signal, there is no difference in transmission quality depending on the direction in which the delay difference is given. Therefore, when the delay difference Δτ between wavelength channels given between wavelength channels is Δτ ≧ Ts / 2 (Ts is the symbol interval of the optical signal), there is no difference in transmission quality depending on the direction in which the delay difference is given. When the delay difference Δτ between the wavelength channels is given in the direction opposite to the group delay generated in the optical fiber transmission line 100, the transmission delay of the entire wavelength division multiplexing optical transmission system can be suppressed.

(Fourth embodiment)
It is desirable to compensate the chromatic dispersion of each wavelength channel generated in the optical fiber transmission line by the nonlinear optical effect suppressor shown in the second embodiment. In this case, the common chromatic dispersion compensation procedure is further provided before the individual delay provision procedure shown in the second embodiment. In the common chromatic dispersion compensation procedure, a medium having a group delay characteristic opposite to the group delay characteristic of the optical fiber transmission line 100 is passed through the wavelength multiplexed signal light.

  FIG. 5 shows the relationship between the chromatic dispersion compensation ratio and the transmission quality when compensating for the chromatic dispersion generated in the optical fiber transmission line in the relay system. As shown in FIG. 5, the chromatic dispersion accumulation generated in the optical fiber transmission line is completely compensated, and the signal distortion due to the chromatic dispersion is compensated, thereby suppressing the peak power of the optical signal and further suppressing the nonlinear optical effect. Is possible.

  FIG. 6 shows an outline of a nonlinear optical effect suppressor having a configuration having a chromatic dispersion compensation function. The nonlinear optical effect suppressor 102 shown in FIG. 6 includes a common chromatic dispersion compensation unit 14, a demultiplexing unit 12, an individual delay applying unit 11, and a multiplexing unit 13. The common chromatic dispersion compensation unit 14 has a group delay characteristic opposite to the group delay characteristic of the optical fiber transmission line 100. As a result, the chromatic dispersion accumulation in the optical fiber transmission line 100 is completely compensated in the common chromatic dispersion compensator 14.

  The functions and operations of the demultiplexing unit 12, the individual delay adding unit 11, and the multiplexing unit 13 are as described in the first embodiment and the second embodiment. That is, the demultiplexing unit 12 branches the wavelength multiplexed signal light into optical signals of the respective wavelength channels. The number of branches of the optical signal is made equal to the number N of wavelength channels multiplexed by wavelength division multiplexing. The individual delay providing unit 11 provides a delay difference between the branched wavelength channels, and the multiplexing unit 13 multiplexes the wavelength channels to which the delay is provided, and outputs the original wavelength multiplexed signal light again.

  FIG. 7 shows an example of the group delay characteristic of the nonlinear optical effect suppressor 102 according to this embodiment. Since the common chromatic dispersion compensation unit 14 is provided, the group delay characteristic of the nonlinear optical effect suppressor 102 has a group delay characteristic opposite to the group delay generated in the optical fiber transmission line 100. FIG. 8 shows an example of the group delay characteristic of each wavelength channel after applying the nonlinear optical effect suppressor 102 according to this embodiment. Since the common chromatic dispersion compensation unit 14 is provided, the chromatic dispersion in each channel can be completely compensated. Thereby, it is possible to further suppress the nonlinear optical effect.

(Fifth embodiment)
FIG. 9 shows a device configuration example of the nonlinear optical effect suppressor 102 shown in the fourth embodiment. In FIG. 9, a waveguide type dispersion compensator is used as the common chromatic dispersion compensation unit 14, and a diffraction grating is used as the demultiplexing unit 12 and the multiplexing unit 13. After the chromatic dispersion received by the optical signal on the optical fiber transmission line is compensated by the waveguide type dispersion compensator 14, it is branched for each of the N wavelength channels by the diffraction grating as the demultiplexing unit 12. With respect to the branched wavelength channel, a delay difference of Δτ is given between the wavelength channels according to the optical path length of the waveguide through which each branch. Δτ is Δτ ≧ Ts / 2 (Ts is a symbol interval of the optical signal). The wavelength channel to which the delay difference Δτ is given is multiplexed again by the diffraction grating as the multiplexing unit 13, and the wavelength multiplexed signal light is output to the output port.

  By configuring the common chromatic dispersion compensation unit 14 and the individual delay adding unit 11 with a planar lightwave circuit, the functional unit of the nonlinear optical effect suppressor 102 can be integrated on a single lightwave circuit substrate. The common chromatic dispersion compensator 14 may have a configuration of a dispersion compensator by adjusting the refractive index characteristics of the waveguide in addition to the configuration of the waveguide type dispersion compensator shown in FIG.

(Sixth embodiment)
A configuration of a wavelength selective switch using the nonlinear optical effect suppressor 102 shown in the fourth embodiment is shown in FIG. The wavelength selective switch includes a common chromatic dispersion compensation unit 14, a demultiplexing unit 12, a 1 × N switch 15, an individual delay providing unit 11, and a multiplexing unit 13. Here, N is the number of wavelength channels of wavelength multiplexed signal light. M, L, and K are the number of wavelength channels multiplexed in each output port.

  The chromatic dispersion received from the optical fiber transmission line 100 by the optical signal input to the wavelength selective switch is compensated by the common chromatic dispersion compensator 14, and the demultiplexing unit 12 converts the wavelength multiplexed signal light into an optical signal of each wavelength channel. Branch. After selecting the output port of each wavelength channel by the 1 × N switch 15 for each branched wavelength channel, the delay difference between the plurality of wavelength channels output to the same port by the individual delay adding unit 11 Is granted. The multiplexing unit 13 multiplexes the optical signals given the delay difference with the optical signals of a plurality of wavelength channels output to the same port, and outputs the wavelength multiplexed signal light to each output port.

(Seventh embodiment)
In the sixth embodiment, when the delay difference to be given to each wavelength channel in the individual delay giving unit 11 is a fixed value, the delay difference Δτ to be given to each wavelength channel is between the adjacent channels of the wavelength division multiplexing grid. The delay difference Δτ is given, and Δτ ≧ Ts / 2 (Ts is the symbol interval of the optical signal). FIG. 11 shows the group delay characteristics of each wavelength channel in a configuration in which a fixed amount of delay is applied by the individual delay applying unit 11.

(Eighth embodiment)
In the sixth embodiment, when the delay difference imparted to each wavelength channel can be variably controlled in the individual delay imparting unit 11, the delay difference Δτ is imparted between the wavelength channels output to the same output port. It is assumed that Δτ ≧ Ts / 2 (Ts is the symbol interval of the optical signal). The delay amount given to each wavelength channel is reset every time the output port of the 1 × N switch 15 is switched. When adjacent channels on the wavelength division multiplexing grid are not output to the same output port, a delay difference Δτ is given to the next closest wavelength channel.

  FIG. 12 shows the group delay characteristics of each wavelength channel when the number of output ports is 2 in the configuration in which a variable amount of delay is applied by the individual delay adding unit 11. 12A shows the group delay characteristic at the output port 1, and FIG. 12B shows the group delay characteristic at the output port 2. The output port 1 outputs optical signals of the wavelength channels CH1 and CH3, and the output port 2 outputs optical signals of the wavelength channels CH2 and CH4. In this case, the wavelength channels CH1 and CH3 have a delay difference Δτ, and the wavelength channels CH2 and CH4 have a delay difference Δτ. By adopting the configuration of FIG. 12, it is possible to keep the absolute value of the delay amount given to each wavelength channel low compared to the configuration shown in the seventh embodiment.

(Ninth embodiment)
The nonlinear optical effect suppression method according to the present embodiment has an individual chromatic dispersion compensation procedure. FIG. 13 shows the configuration of the nonlinear optical effect suppressor according to this embodiment. The nonlinear optical effect suppressor 201 according to this embodiment includes a demultiplexing unit 22, an individual chromatic dispersion compensation unit 21, and a multiplexing unit 23.

  In the individual chromatic dispersion compensation procedure, the nonlinear optical effect suppressor 201 operates as follows. The nonlinear optical effect suppressor 201 according to this embodiment performs chromatic dispersion compensation for each wavelength channel. The nonlinear optical effect suppressor 201 according to this embodiment includes a demultiplexing unit 22, an individual chromatic dispersion compensation unit 21, and a multiplexing unit 23.

The demultiplexing unit 22 branches the wavelength multiplexed signal light into optical signals of each wavelength channel. The individual chromatic dispersion compensation unit 21 includes individual chromatic dispersion compensation units 21 _{1 to} 21 _N provided for each of the demultiplexed wavelength channels. The individual chromatic dispersion compensators 21 _{1 to} 21 _N pass the optical signals of the respective wavelength channels from the demultiplexing unit 22 through a medium having chromatic dispersion characteristics that are opposite to the group delay characteristics of the respective wavelength channels. Let Thereby, the individual chromatic dispersion compensation unit 21 compensates the chromatic dispersion of the optical signal received in the optical fiber transmission line 100 by the individual chromatic dispersion compensation unit 21 for each branched wavelength channel. The multiplexing unit 23 multiplexes the wavelength channels compensated for chromatic dispersion, and outputs the original wavelength multiplexed signal light again.

FIG. 14 shows an example of the group delay characteristic of the nonlinear optical effect suppressor 201 according to this embodiment.
FIG. 15 shows an example of the group delay characteristic of each wavelength channel after applying the nonlinear optical effect suppressor 201 according to this embodiment. In the configuration of the present embodiment, the group delay difference generated in each wavelength channel in the optical fiber transmission line 100 is preserved even after compensating for chromatic dispersion. For this reason, if the group delay difference generated in the optical fiber transmission line 100 is sufficiently large, the same group delay characteristic can be obtained without the individual delay applying unit 11.

(Tenth embodiment)
FIG. 16 shows a configuration example of a device that realizes the nonlinear optical effect suppressor 201 shown in the ninth embodiment. The nonlinear optical effect suppressor 201 according to this embodiment includes a circulator 31, a diffraction grating 32, a collimator 33, and a reflective liquid crystal element 34. The diffraction grating 32 functions as the multiplexing unit 22 and the demultiplexing unit 23, and the reflective liquid crystal element 34 functions as the individual chromatic dispersion compensation unit 21.

  The circulator 31 causes the wavelength multiplexed signal light input from the input port to enter the diffraction grating 32. The diffraction grating 32 branches the wavelength multiplexed signal light into optical signals of each wavelength channel. The collimator 33 converts the optical signal of the wavelength channel branched in the space into parallel light and makes it incident on the reflective liquid crystal element 34. The reflective liquid crystal element 34 compensates for chromatic dispersion added in the optical fiber transmission line by applying phase modulation to each wavelength channel. The diffraction grating 32 combines the optical signals of the wavelength channels reflected by the reflective liquid crystal element 34 again, and outputs them as wavelength multiplexed signal light.

  FIG. 17 shows an example of the phase modulation amount of the reflective liquid crystal element 34. In FIG. 17, the change in the phase modulation amount in the wavelength direction becomes steeper as the wavelength channel CH1, wavelength channel CH2, and wavelength channel CH3 change. Since the amount of change in the wavelength direction of the phase modulation amount provided by the reflective liquid crystal element 34 is expressed by a quadratic function, the amount of dispersion to be compensated can be changed by changing the proportionality constant.

  FIG. 18 shows an example of the group delay characteristic of each wavelength channel after the nonlinear optical effect suppressor 201 is applied. In chromatic dispersion compensation by phase modulation, chromatic dispersion compensation can be performed independently for each wavelength channel, so that the group delay difference between wavelength channels can be preserved. For this reason, a delay of a different delay amount can be given to each wavelength channel, and the nonlinear optical effect can be suppressed.

(First embodiment)
FIG. 19 shows a configuration example of the wavelength selective switch according to the present embodiment. The wavelength selective switch 202 according to this embodiment uses the nonlinear optical effect suppressor 201 shown in the ninth embodiment. The wavelength selective switch 202 includes a demultiplexing unit 22, an individual chromatic dispersion compensation unit 21, a 1 × N switch 25, and a multiplexing unit 23. Here, N is the number of wavelength channels of wavelength multiplexed signal light. The demultiplexing unit 22 branches the wavelength multiplexed signal light into optical signals of each wavelength channel. The individual chromatic dispersion compensator 21 compensates the chromatic dispersion received by the optical signal in the optical fiber transmission line 100 for each branched wavelength channel. The 1 × N switch 25 selects an output port of each wavelength channel. The multiplexing unit 23 multiplexes the wavelength channels output to the same port, and outputs the wavelength multiplexed signal light to each output port.

(First Embodiment)
The configuration of the wavelength division multiplexing optical transmission system according to this embodiment is shown in FIG. The wavelength division multiplexing optical transmission system according to the present embodiment suppresses nonlinear optical effects between wavelength channels at the relay node 130 as an optical repeater when transmitting wavelength multiplexed signal light from the transmission node 110 to the reception node 120. Do. The relay node 130 is a node that is inserted into a medium to long distance transmission line such as between stations.

  The relay node 130 relays the wavelength multiplexed signal light using the optical relay method according to the present embodiment. For example, the relay node 130 includes a first optical amplifier 132, a nonlinear optical effect suppressor 131 according to the present invention, and a second optical amplifier 133. The optical relay method shown in FIG. 20 has a first optical amplification procedure, a nonlinear optical effect suppression procedure, and a second optical amplification procedure in this order. In the nonlinear optical effect suppression procedure, the nonlinear optical effect is suppressed by using the nonlinear optical effect suppressor shown in the fourth to ninth embodiments.

  In the first optical amplification procedure, the first optical amplifier 132 receives a wavelength multiplexed signal light obtained by multiplexing optical signals of a plurality of wavelength channels from the optical fiber transmission line 100 and amplifies the input wavelength multiplexed signal light. . Thereby, the first optical amplifier 132 compensates for the signal loss accumulated in the optical fiber transmission line 100 by the first optical amplifier 132.

  In the nonlinear optical effect suppression procedure, the nonlinear optical effect suppressor 131 suppresses the nonlinear optical effect generated by the interaction between the wavelength channels by the nonlinear optical effect suppressor. The nonlinear optical effect suppressor 131 has the configuration of the fourth to ninth embodiments and compensates for the chromatic dispersion accumulated in the optical fiber transmission line 100. Thereafter, in the configuration using the fourth embodiment, a delay difference Δτ is given between the wavelength channels. The extension difference Δτ is Δτ ≧ Ts / 2 (Ts is the symbol interval of the optical signal).

In the second optical amplification procedure, the second optical amplifier 133 amplifies the wavelength multiplexed signal light from the nonlinear optical effect suppressor 131.
In the present embodiment, the first optical amplification procedure, the nonlinear optical effect suppression procedure, and the second optical amplification procedure are performed in order, but the present invention is not limited to this. For example, the first optical amplification procedure and the nonlinear optical effect suppression procedure may be sequentially performed, or the nonlinear optical effect suppression procedure and the second optical amplification procedure may be sequentially performed.

(First Embodiment)
In the first embodiment, when optical signals having different symbol rates are multiplexed in adjacent wavelength channels, the nonlinear optical effect suppressor 131 uses a signal format having the widest symbol interval in the nonlinear optical effect suppression procedure. Add half-symbol delay. For example, in a wavelength division multiplexing optical transmission system in which signal bit rates of 10 Gb / s, 40 Gb / s, and 100 Gb / s are mixed, the delay difference Δτ added between wavelength channels is half the symbol interval in a 10 Gb / s optical signal. That is 50 ps.

(Fourth embodiment)
FIG. 21 shows a configuration example of the wavelength division multiplexing optical transmission system according to the present embodiment. The wavelength division multiplexing optical transmission system according to this embodiment uses the wavelength selective switch 103 or 202 shown in the sixth embodiment to the first embodiment, and suppresses nonlinear optical effects between wavelength channels in an optical add / drop multiplexer. Do. In the optical node 140, the signal loss accumulated in the optical fiber transmission line 100 is compensated by the optical amplifier 141, and the wavelength selection switch 143 for inserting / passing / branching the wavelength path in the optical add / drop multiplexer is used in the sixth embodiment to the sixth embodiment. The wavelength selective switch 103 or 202 of the first embodiment is used to compensate for the chromatic dispersion added to the wavelength path during transmission on the optical fiber transmission line 100 in each optical node 140. Thereafter, in the configuration using the sixth embodiment, a delay difference Δτ is given between the wavelength channels with respect to the wavelength path passing through the optical node 140. The delay difference Δτ is Δτ ≧ Ts / 2 (Ts is the symbol interval of the optical signal).

(Fifteenth embodiment)
In the first embodiment, when optical signals having different symbol rates are multiplexed in adjacent wavelength channels, a delay corresponding to a half symbol of a signal format having the widest symbol interval is given. For example, in a wavelength division multiplexing optical transmission system in which signal bit rates of 10 Gb / s, 40 Gb / s, and 100 Gb / s are mixed, the delay difference Δτ added between wavelength channels is half the symbol interval in a 10 Gb / s optical signal. That is 50 ps.

(Sixteenth embodiment)
FIG. 22 shows a configuration example of a wavelength division multiplexing optical transmission system according to this embodiment. The wavelength division multiplexing optical transmission system according to this embodiment uses the wavelength selective switch 103 or 202 shown in the sixth embodiment to the first embodiment, and performs nonlinear optical effect suppression between wavelength channels in the optical cross-connect. . In the optical node 150, the signal loss accumulated in the optical fiber transmission line 100 is compensated by the optical amplifiers 155 to 158, and the wavelength selection switches 151 to 154 for switching the path of the wavelength path in the optical cross-connect are used in the sixth embodiment to the sixth embodiment. Using the wavelength selective switch 103 or 202 of the first embodiment, each optical node 150 compensates for chromatic dispersion added to the wavelength path during transmission through the optical fiber transmission line 100. Thereafter, in the configuration using the sixth embodiment, a delay difference Δτ is given between the wavelength channels with respect to the wavelength path passing through the optical node 150. The delay difference Δτ is Δτ ≧ Ts / 2 (Ts is the symbol interval of the optical signal).

(Seventh embodiment)
In the sixteenth embodiment, when optical signals having different symbol rates are multiplexed in adjacent wavelength channels, a delay corresponding to a half symbol of a signal format having the widest symbol interval is given. For example, in a wavelength division multiplexing optical transmission system in which signal bit rates of 10 Gb / s, 40 Gb / s, and 100 Gb / s are mixed, the delay difference Δτ added between wavelength channels is half the symbol interval in a 10 Gb / s optical signal. That is 50 ps.

  The present invention can be applied to the information communication industry.

11, 11 ₁ , 11 ₂ , 11 ₃ , 11 _N−1 , 11 _N : Individual delay applying units 12, 22: Demultiplexing units 13, 13 ₁ , 13 ₂ , 13 _N , 23: Multiplexing unit 14: Common wavelength Dispersion compensation units 15, 15 ₁ , 15 ₂ , 15 _N , 25, 25 ₁ , 25 ₂ , 25 _N : 1 × N switches 21, 21 ₁ , 21 ₂ , 21 ₃ , 21 _N−1 , 21 _N : individual wavelengths Dispersion compensation unit 31: circulator 32: diffraction grating 33: collimator 34: reflective liquid crystal element 100: optical fiber transmission path 101, 102, 121, 131, 201: nonlinear optical effect suppressor 103, 143, 151, 152, 153, 154, 202: Wavelength selective switch 110: Transmission node 111: Transmitter 112: Multiplexer 113, 122, 141, 144, 155, 156, 157, 158: Optical amplifier 120: Reception node 123: Demultiplexer 124: Receiver 130: Relay node 132: First optical amplifier 133: Second optical amplifier 140, 150: Optical node

Claims (10)

A demultiplexing unit for branching the wavelength multiplexed signal light, in which the optical signals of a plurality of wavelength channels are multiplexed, into optical signals of each wavelength channel;
An individual delay applying unit that applies a delay of a different delay amount in each wavelength channel to the optical signal of each wavelength channel from the demultiplexing unit;
A multiplexing unit for multiplexing the optical signals of the respective wavelength channels from the individual delay adding unit;
A nonlinear optical effect suppressor.   The individual delay adding unit adds a delay to the optical signal of each wavelength channel so that a delay difference having a time width of half or more of the symbol interval of the optical signal is generated between adjacent wavelength channels. The nonlinear optical effect suppressor according to claim 1, wherein:   3. The non-linearity according to claim 1, further comprising a common chromatic dispersion compensation unit having a group delay characteristic opposite to a group delay characteristic of an optical fiber transmission line that propagates the wavelength-multiplexed signal light, at a preceding stage of the demultiplexing unit. Optical effect suppressor. A demultiplexing unit for branching the wavelength multiplexed signal light, in which the optical signals of a plurality of wavelength channels are multiplexed, into optical signals of each wavelength channel;
Individual wavelength dispersion for passing the optical signal of each wavelength channel from the demultiplexing unit through a medium having a group delay characteristic opposite to the group delay characteristic of each wavelength channel in the optical fiber transmission line that propagates the wavelength multiplexed signal light A compensation section;
A multiplexing unit for multiplexing the optical signals of the respective wavelength channels from the individual chromatic dispersion compensation unit;
A nonlinear optical effect suppressor. A first optical amplifier for amplifying the wavelength-division-multiplexed signal light that is input from a fiber-optic transmission line, and the wavelength-multiplexed signal light in which optical signals of a plurality of wavelength channels are multiplexed;
The nonlinear optical effect suppressor according to any one of claims 1 to 4, wherein wavelength-division multiplexed signal light from the first optical amplifier is input, and the nonlinear optical effect generated in the optical fiber transmission line is suppressed.
A second optical amplifier for amplifying the wavelength multiplexed signal light from the nonlinear optical effect suppressor;
An optical repeater.   The wavelength-multiplexed signal light in which the optical signals of the plurality of wavelength channels are multiplexed is demultiplexed into the optical signals of the respective wavelength channels, delays having different delay amounts are given to the respective wavelength channels, and the respective wavelength channels after the delays are given. A nonlinear optical effect suppression method including an individual delay providing procedure for multiplexing optical signals.   In the individual delay providing procedure, the optical signal of each wavelength channel is given a delay so that a delay difference having a time width of half or more of the symbol interval of the optical signal is generated between adjacent wavelength channels. The nonlinear optical effect suppression method according to claim 6, wherein:   A common chromatic dispersion compensation procedure for allowing the wavelength multiplexed signal light to pass through a medium having a group delay characteristic opposite to the group delay characteristic of the optical fiber transmission line through which the wavelength multiplexed signal light has propagated, before the individual delay providing procedure. The nonlinear optical effect suppression method according to claim 6 or 7, further comprising:   Wavelength multiplexed signal light, in which optical signals of a plurality of wavelength channels are multiplexed, is demultiplexed into optical signals of each wavelength channel, and the optical signals of each wavelength channel are transmitted to the optical fiber transmission lines that propagate the wavelength multiplexed signal light. A nonlinear optical effect suppression method including an individual chromatic dispersion compensation procedure for passing through a medium having a group delay characteristic opposite to a group delay characteristic of a wavelength channel and multiplexing the optical signals of the respective wavelength channels after passing through the medium. A first optical amplification procedure for amplifying the wavelength-division multiplexed signal light that is input from the optical fiber transmission line, and the wavelength-division multiplexed signal light obtained by multiplexing the optical signals of a plurality of wavelength channels;
Wavelength multiplexed signal light amplified in the first optical amplification procedure is input, and the nonlinear optical effect generated in the optical fiber transmission line is reduced using the nonlinear optical effect suppression method according to claim 6. Non-linear optical effect suppression procedure to suppress,
A second optical amplification procedure for amplifying the wavelength multiplexed signal light in which the nonlinear optical effect is suppressed by the nonlinear optical effect suppression procedure;
An optical relay method.

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