JP5632805B2 - Optical transmission / reception system and optical transmission / reception method - Google Patents

Description

  The present invention relates to an optical transmission / reception technique for reducing signal degradation due to optical fiber propagation using wavelength multiplexing.

  In the backbone network of an optical transmission system, as a next-generation optical transmission technology of 100 Gbps per channel, a technology that combines dual-polarization quadrature phase shift keying (DP-QPSK) and digital coherent detection Preparations for introduction are underway. This is the first time that polarization multiplexing technology has been fully introduced in commercial optical transmission systems. Furthermore, since the demand for transmission capacity exceeding 100 Gbps per channel will increase in the future, it is expected that the transmission rate will continue to increase, that is, the multilevel per symbol and the symbol rate will continue to increase. However, in future optical transmission systems, such high-speed modulated and polarization-multiplexed optical signals are susceptible to signal degradation due to various factors. It is expected that the requirements will be stricter in the future.

  The factors of signal degradation can be broadly divided into those that work deterministically and those that work stochastically. Examples of the latter include polarization dependent loss (PDL) and polarization mode dispersion (PMD). It is known that the magnitude of these changes depending on the wavelength and time (for example, see Non-Patent Document 1), and the frequency follows a specific probability density distribution (for example, see Non-Patent Document 2). Here, signal degradation due to these factors will be collectively referred to as polarization-induced degradation.

  Polarization-induced degradation is generally accompanied by great difficulty when compensating for signal degradation due to its stochastic behavior. However, in a digital signal processing (DSP) circuit that is a component of the above-described digital coherent detection, compensation for time-varying signal deterioration due to PMD is performed using an adaptive blind equalization processing algorithm. (For example, refer nonpatent literature 3).

Misha Borodsky, Misha Brodsky, Nicholas J. et al. Frigo, Peter Magill, and L.M. Raddatz, “In-Service Measurements of Polarization-Mode Dispersion and Correlation to Bit-Error Rate”, IEEE PHOTOTONICS TECHNOLOGY LETTERS, VOL. 15, NO. 4, pp. 572-574, APRIL 2003 ITU-T Recommendation G. 680, “Physical transfer functions of optical network elements”, 2007 Olga Vassilieva, Inwoong Kim, Takao Naito, “Systematic Investigation of Interplay Between Nonlinear and Polarized Dependent Loss Effects.” M.M. Shtaiif et al. , IEEE Photonics Technol. Lett. , Vol. 12, no. 1, pp. 53-55, 2000. John Cameron, Xiaooy Bao, John Stears, “Time evolution of polarization-mode dispersion for aerial and buried cables”, OFC '98, WM51 Kisaka et al., "Effect of FEC on transmission characteristics degradation by PMD", B-10-91, 2000 IEICE Communication Society Conference

  However, compensation by the DSP circuit is effective for compensation of inter-symbol interference by PMD, but is not effective for compensation for degradation of the optical signal-to-noise ratio caused by PDL (see, for example, Non-Patent Document 3). Furthermore, in future optical transmission systems aiming to improve the transport capability of optical signals at higher speeds and more economically, the introduction of polarization multiplexing, the increase in the symbol rate of optical signals, the increase in the number of node passes, the transmission distance A situation such as stretching is expected, and polarization-induced degradation due to PDL or the like becomes a more serious concern than the present in terms of system design. Therefore, there is a problem that a measure for improving the proof stress that can alleviate the polarization-induced deterioration is required.

  The present invention has been made in view of such a problem, and provides an optical transmission / reception system and an optical transmission / reception method capable of improving proof strength mainly against deterioration that behaves stochastically, for example, polarization-induced deterioration. It aims to be realized.

  In order to achieve such an object, the present invention is a wavelength division multiplexing transmission system for interleaving recombination and recombination between signal sequences. Specifically, an interleave coder that interleaves m (m: integer greater than or equal to 2) signal sequences into n (n: integer greater than or equal to 2) signal sequences, and an n interleaved recombination from the interleave coder. N optical modulation circuits for optically modulating carrier lights having different wavelengths in each signal sequence and outputting n optical modulation signals; and n optical modulation signals from the n optical modulation circuits. An optical transmission device comprising: a multiplexing circuit that multiplexes and transmits the optical signal to an optical fiber; and receives the wavelength-multiplexed n optical modulation signals from the optical fiber and demultiplexes the wavelength for each of the n wavelengths. A demultiplexing circuit that performs optical detection on each of the n optical modulation signals wavelength-demultiplexed from the demultiplexing circuit and outputs n signal strings, and the n optical signals. The n signal sequences detected by the light from the detection circuit are converted into m signals. And interleave decoder for returning set interleaved sequence, an optical transmission and reception system having a light receiving device comprising a.

  According to the present invention, it is possible to improve the proof stress with respect to, for example, polarization-induced degradation, which has a different degradation amount depending on the wavelength.

  Here, interleave recombination means that m (m: integer greater than or equal to 2) signal sequences are interchanged in information units to generate new n (n: integer greater than or equal to 2) signal sequences. Say. Inversely, interleaving recombination refers to reproducing m signal sequences from n signal sequences that have been interleaved.

  In the present invention, the optical transmission device includes a forward error correction coder that performs forward error correction coding of the m signal sequences before the interleave coder, and the optical reception device includes the forward error correction coder after the interleave decoder. A forward error correction decoder that performs forward error correction decoding on m signal sequences may be provided.

  According to the present invention, it is possible to increase the forward error correction capability against burst errors.

  In the present invention, the wavelength interval of the carrier light having the different wavelengths may be equal to or greater than the wavelength interval at which the stochastic transmission characteristic deterioration behavior can be regarded as independent.

In the present invention, the wavelength interval Δλ of the carrier light having different wavelengths is expressed by the following equations (1) and (2): Δf = 0.64 / <τ> (1)
Δλ = Δf · λ ² / v (2)
The above is desirable.
Where Δf is the frequency interval of the carrier light of different wavelengths, <τ> is the average value of the group delay time difference between the polarization modes of the transmission line, λ is the wavelength of the carrier light, and v is the optical modulation signal in the optical fiber. Is the group velocity.

  In order to achieve such an object, the present invention is a wavelength division multiplexing transmission method for interleaving recombination and recombination between signal sequences. Specifically, m (m: integer greater than or equal to 2) signal sequences are interleaved and rearranged into n (n: integer greater than or equal to 2) signal sequences, and each of the interleaved rearranged n signal sequences is different. The carrier light of the wavelength is optically modulated to output n optical modulation signals, the n optical modulation signals are wavelength-multiplexed and transmitted to an optical fiber, and the wavelength-multiplexed n optical signals from the optical fiber are transmitted. The optical modulation signal is received and wavelength-demultiplexed for each of the n wavelengths. The n optical modulation signals that have been wavelength-demultiplexed are optically detected to output n signal sequences, and the optical detection is performed. This is an optical transmission / reception method in which n signal sequences are interleaved back into m signal sequences.

  According to the present invention, it is possible to improve the proof stress with respect to, for example, polarization-induced degradation, which has a different degradation amount depending on the wavelength.

  Here, interleave recombination means that m (m: integer greater than or equal to 2) signal sequences are interchanged in information units to generate new n (n: integer greater than or equal to 2) signal sequences. Say. Inversely, interleaving recombination refers to reproducing m signal sequences from n signal sequences that have been interleaved.

  In the present invention, the m signal sequences may be subjected to forward error correction coding before interleave recombination, and the m signal sequences may be subjected to forward error correction decoding after interleaving recombination.

  According to the present invention, it is possible to increase the forward error correction capability against burst errors.

  In the present invention, the wavelength interval of the carrier light having the different wavelengths may be equal to or greater than the wavelength interval at which the stochastic transmission characteristic deterioration behavior can be regarded as independent.

In the present invention, the wavelength interval Δλ of the carrier light having different wavelengths is expressed by the following equations (1) and (2): Δf = 0.64 / <τ> (1)
Δλ = Δf · λ ² / v (2)
The above is desirable.
Where Δf is the frequency interval of the carrier light of different wavelengths, <τ> is the average value of the group delay time difference between the polarization modes of the transmission line, λ is the wavelength of the carrier light, and v is the optical modulation signal in the optical fiber. Is the group velocity.

  As described above, according to the present invention, it is possible to realize an optical transmission / reception system and an optical transmission / reception method capable of improving the proof strength against deterioration mainly probabilistically, for example, polarization-induced deterioration. it can.

It is a figure showing the example of a structure of the optical transmission / reception system to which this invention is applied. It is a figure explaining interleave rearrangement and interleave recombination. It is a figure explaining interleave rearrangement and interleave recombination. It is a figure explaining interleave rearrangement and interleave recombination. Furthermore, it is a figure showing the structural example of the optical transmission / reception system to which a forward error correction technique is applied.

  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.

(Embodiment 1)
In the present embodiment, m (m: integer greater than or equal to 2) signal sequences are interleaved and rearranged into n (n: integer greater than or equal to 2) signal sequences on the transmission side. The optical signals of the carrier light having different wavelengths in the column are optically modulated to output n optical modulation signals, and the optically modulated n optical modulation signals are wavelength-multiplexed and transmitted to the optical fiber. On the receiving side, wavelength-multiplexed n optical modulation signals from the optical fiber are received, wavelength-demultiplexed for each of the n wavelengths, and the wavelength-demultiplexed n optical modulation signals are optically detected. n signal trains are output, and the n signal trains subjected to optical detection are interleaved back into m signal trains.

  An example of an apparatus configuration in this embodiment is shown in FIG. FIG. 1 is an example of an optical transmission / reception system that interleaves between different signal sequences. 100 is an optical transmitter, 101 is an interleave coder, 102 is an optical modulator, 103 is a multiplexer, 200 is an optical receiver, 201 is an interleave decoder, 202 is an optical detector, 203 is a demultiplexer, and 300 is an optical fiber. It is.

  The optical transmission device 100 includes an interleave coder 101, n optical modulation circuits 102, and a multiplexing circuit 103. The optical receiving apparatus 200 includes a demultiplexing circuit 203, n optical detection circuits 202, and an interleave decoder 201. The optical transmitter 100 and the optical receiver 200 are connected by an optical fiber 300.

  The interleave coder 101 interleaves and rearranges m signal sequences into n signal sequences. Interleaving recombination means that m signal sequences are interchanged in units of information to generate new n signal sequences. The n light modulation circuits 102 light-modulate carrier lights having different wavelengths (λ1 to λn) by n signal sequences interleaved and rearranged by the interleave coder 101, and output n light modulation signals. The modulation format does not matter. The multiplexing circuit 103 wavelength-multiplexes the n optical modulation signals from the n optical modulation circuits 102 and transmits the multiplexed signals to the optical fiber 300.

  The n signal trains are transmitted at different wavelengths and suffer from different signal degradation at the respective wavelengths.

  The demultiplexing circuit 203 demultiplexes the wavelength-multiplexed n optical modulation signals from the optical fiber 300 for every n wavelengths. The n optical detection circuits 202 optically detect the n optical modulation signals wavelength-demultiplexed by the demultiplexing circuit 203 and output n signal sequences. Any detection method is acceptable. It suffices if the optical modulation signal optically modulated by the optical modulation circuit 102 can be reproduced in the original signal sequence. The interleave decoder 201 interleaves and reassembles the n signal sequences detected by the optical detection circuit 202 into m signal sequences. Interleaving recombination refers to reproducing m signal sequences from n signal sequences that have been interleaved.

  The reassembled m signal trains are transmitted at different wavelengths for each information unit, and are subjected to different signal degradation depending on the respective wavelengths. Therefore, it is possible to improve the proof strength against the polarization-induced deterioration in which the deterioration amount differs for each wavelength.

  More specifically, the polarization-induced degradation takes different values depending on the wavelength when viewed at a certain time. The transmission characteristic for the optical modulation signal in the optical receiver applied to the present optical transmission / reception system can be treated as an average of the transmission characteristics for the optical modulation signals of different wavelengths. Therefore, effective transmission characteristics are transmission characteristics obtained by averaging the transmission characteristics at the respective wavelengths. This is because this transmission characteristic is represented by a random variable. According to the central limit theorem, as the number of wavelengths increases, the probability density distribution converges to a normal distribution shape that reduces the variance value of the original distribution and makes the average value equal to the original distribution. It is expected that. Since the shape of the probability density distribution changes, it is possible to expect a reduction in system unavailability and relaxation of conditions required for system design. For the reasons described above, increasing the number n of signal sequences for interleaved recombination of m signal sequences increases the number n of wavelengths to be wavelength multiplexed, and generally increases the effect obtained by this method. Presumed to work.

In the optical transmission / reception system of this embodiment, it is desirable that the wavelength interval of the carrier light having different wavelengths is equal to or greater than the wavelength interval at which the behavior of the transmission characteristic deterioration can be regarded as independent. The wavelength interval at which the behavior of transmission characteristic deterioration can be regarded as independent can be estimated, for example, from the wavelength interval at which the main polarization mode of the transmission path cannot be regarded as constant. Based on Non-Patent Document 4, the wavelength interval Δλ can be estimated from Equations (1) and (2). Δf = 0.64 / <τ> (1)
Δλ = Δf · λ ² / v (2)
The above is desirable.
Where Δf is the frequency interval [Hz] of the carrier light of different wavelengths, <τ> is the average value of the group delay time difference between the polarization modes of the transmission path [s], and λ is the wavelength of the carrier light [m], v Is the group velocity [m / s] of the optical modulation signal in the optical fiber.

  In general, Δλ depends on the average value of the group delay time difference between the polarization modes of the optical transmission path and the wavelength of the carrier light. According to the equations (1) and (2), for example, <τ> = 4 [ps]. When λ = 1550 [nm], Δλ = 1.3 [nm] or more is desirable. If adjacent wavelength channels are separated by this amount on the wavelength axis, it can be expected that the deterioration of transmission characteristics can be regarded as independent.

  The signal processing flows of the interleave coder 101 in the optical transmitter 100 and the interleave decoder 201 in the optical receiver 200 are shown in FIGS.

  FIG. 2 is a schematic diagram in which m = 3 signal sequences are interleaved to n = 3 signal sequences and interleaved. In FIG. 2, when m = 3 signal sequences (signal sequence # 1, signal sequence # 2, signal sequence # 3) are input to the interleave coder 101, they are rearranged in order for each bit, and a new n = 3 signal sequences (signal sequence # 1, signal sequence # 2, signal sequence # 3) are generated. In the interleave decoder 201, on the contrary, n = 3 signal sequences (signal sequence # 1, signal sequence # 2, signal sequence # 3) are reassembled into the original signal sequence for each bit, and m = 3 The signal train (signal train # 1, signal train # 2, signal train # 3) is reproduced. The information unit for interleaving recombination and interleaving recombination is not limited for each bit. It may be every several bits, or may be in byte units, word units, frame units, symbol units, or the like. The same applies to the following embodiments.

  FIG. 3 is a schematic diagram in which m = 3 signal sequences are interleaved to n = 4 signal sequences and interleaved. In FIG. 3, when m = 3 signal sequences (signal sequence # 1, signal sequence # 2, signal sequence # 3) are input to the interleave coder 101, they are rearranged in order for each bit, and a new n = 4 signal sequences (signal sequence # 1, signal sequence # 2, signal sequence # 3, signal sequence # 4) are generated. On the other hand, in the interleave decoder 201, n = 4 signal sequences (signal sequence # 1, signal sequence # 2, signal sequence # 3, signal sequence # 4) are recombined into the original signal sequence for each bit, m = 3 signal sequences (signal sequence # 1, signal sequence # 2, signal sequence # 3) are reproduced.

  FIG. 4 is a schematic diagram in which m = 4 signal sequences are interleaved to n = 3 signal sequences and interleaved. In FIG. 4, when m = 4 signal sequences (signal sequence # 1, signal sequence # 2, signal sequence # 3, signal sequence # 4) are input to the interleave coder 101, they are rearranged in order for each bit. Thus, n = 3 signal sequences (signal sequence # 1, signal sequence # 2, signal sequence # 3) are newly generated. In the interleave decoder 201, on the contrary, n = 3 signal sequences (signal sequence # 1, signal sequence # 2, signal sequence # 3) are reassembled into the original signal sequence for each bit, and m = 4 The signal train (signal train # 1, signal train # 2, signal train # 3, signal train # 4) is reproduced.

  As described above, in the optical transmission / reception system and optical transmission / reception method of the present embodiment, degradation that mainly behaves stochastically by interleaving recombination and interleaving recombination between signal sequences, for example, polarization-induced degradation, etc. The proof stress can be improved.

(Embodiment 2)
In the present embodiment, m (m: integer greater than or equal to 2) signal sequences are interleaved with n (n: integer greater than or equal to 2) signal sequences on the transmission side with respect to the transmission / reception system of the first embodiment. Before recombination, m signal sequences are subjected to forward error correction coding. On the receiving side, n signal sequences are interleaved back into m signal sequences, and then m signal sequences are subjected to forward error correction decoding.

  An example of the apparatus configuration in this embodiment is shown in FIG. FIG. 5 is an example of an optical transmission / reception system that interleaves signal sequences between different wavelengths. 100 is an optical transmission device, 101 is an interleave coder, 102 is an optical modulation circuit, 103 is a multiplexing circuit, 104 is a forward error correction coder (hereinafter sometimes abbreviated as FEC coder), 200 is an optical reception device, 201 Is an interleave decoder, 202 is an optical detection circuit, 203 is a demultiplexing circuit, 204 is a forward error correction decoder (hereinafter abbreviated as FEC decoder), and 300 is an optical fiber.

  The optical transmission device 100 includes an interleave coder 101, n optical modulation circuits 102, a multiplexing circuit 103, and an FEC coder 104. The optical receiving apparatus 200 includes a demultiplexing circuit 203, n optical detection circuits 202, an interleave decoder 201, and an FEC decoder 204. The optical transmitter 100 and the optical receiver 200 are connected by an optical fiber 300.

  As in the present embodiment, the FEC coder 104 is arranged for each of the m signal sequences in the preceding stage of the interleave coder 101 in the optical transmission apparatus 100, and the m stage in the subsequent stage of the interleave decoder 201 in the optical receiving apparatus 200. If the FEC decoder 204 is arranged for each signal sequence, it is possible to further improve the resistance to polarization-induced degradation, which has a different degradation amount for each wavelength.

  In other words, even if there is a burst error, the error is dispersed by interleaving and interleaving the signals between wavelengths, so that the error correction capability by the forward error correction code is further exerted.

  In general, a signal error due to polarization-induced degradation is a signal whose fluctuation order is much longer than the bit period (see Non-Patent Document 5, for example), the error is bursty, and has undergone polarization-induced degradation. On the other hand, even if a forward error correction code is applied, the theoretical correction capability cannot be obtained (for example, see Non-Patent Document 6). However, if a technique for interleaving and interleaving the signals between signal sequences is used, errors that occur in bursts are converted into errors that follow a Poisson distribution. On the other hand, the correction capability of the forward error correction code becomes as theoretical when a signal error occurs randomly such that it follows a Poisson distribution. Therefore, when the technique of interleaving and interleaving the signals between the signal sequences and the forward error correction code are applied together, the burst property of the signal error can be weakened, thereby correcting the correction ability of the forward error correction code to the theoretical value. It becomes possible to approach.

  Examples of the forward error correction code include, but are not limited to, turbo code, Reed-Solomon code, Golay code, BCH code, and Hamming code.

  As described above, in the optical transmission / reception system and optical transmission / reception method of the present embodiment, the probability is mainly determined by applying the technique for interleaving and interleaving the signals between the signal sequences and the forward error correction code together. It is possible to further improve the proof stress against the deterioration that behaves theoretically, for example, the polarization-induced deterioration.

  The present invention can be used in the communication industry to which an optical transmission system is applied.

100: optical transmitter 101: interleave coder 102: optical modulation circuit 103: multiplexing circuit 104: forward error correction coder (may be abbreviated as FEC coder)
200: optical receiver 201: interleave decoder 202: optical detection circuit 203: demultiplexing circuit 204: forward error correction decoder (may be abbreviated as FEC decoder)
300: Optical fiber

Claims (8)

an interleave coder that interleaves m (m: integer greater than or equal to 2) signal sequences into n (n: integer greater than or equal to 2) signal sequences;
N light modulation circuits for optically modulating carrier lights of different wavelengths with n signal sequences interleaved from the interleave coder and outputting n light modulation signals;
A multiplexing circuit that wavelength-multiplexes the n optical modulation signals from the n optical modulation circuits and sends them to an optical fiber;
An optical transmission device comprising:
A demultiplexing circuit that receives the wavelength-multiplexed n optical modulation signals from the optical fiber and demultiplexes the signals for each of the n wavelengths;
N optical detection circuits that respectively detect the n optical modulation signals that have undergone wavelength demultiplexing from the demultiplexing circuit and output n signal sequences;
An interleave decoder that interleaves and reassembles the n signal sequences detected from the n optical detection circuits into m signal sequences;
Equipped with a,
It said different wavelength intervals of the optical carrier wavelength, an optical transmitting and receiving system including the optical receiver Ru der than the wavelength spacing behavior of the deterioration of the stochastic transmission characteristics can be regarded as independent.   an interleave coder that interleaves m (m: integer greater than or equal to 2) signal sequences into n (n: integer greater than or equal to 2) signal sequences;
  N light modulation circuits for optically modulating carrier lights of different wavelengths with n signal sequences interleaved from the interleave coder and outputting n light modulation signals;
  A multiplexing circuit that wavelength-multiplexes the n optical modulation signals from the n optical modulation circuits and sends them to an optical fiber;
An optical transmission device comprising:
  A demultiplexing circuit that receives the wavelength-multiplexed n optical modulation signals from the optical fiber and demultiplexes the signals for each of the n wavelengths;
  N optical detection circuits that respectively detect the n optical modulation signals that have undergone wavelength demultiplexing from the demultiplexing circuit and output n signal sequences;
  An interleave decoder that interleaves and reassembles the n signal sequences detected from the n optical detection circuits into m signal sequences;
With
  The wavelength interval Δλ of the carrier light having different wavelengths is expressed by the following equations (1) and (2).
    Δf = 0.64 / <τ> (1)
    Δλ = Δf · λ ² / V (2)
An optical transmission / reception system characterized by the above.
  Where Δf is the frequency interval of the carrier light of different wavelengths, <τ> is the average value of the group delay time difference between the polarization modes of the transmission line, λ is the wavelength of the carrier light, and v is the optical modulation signal in the optical fiber. Is the group velocity.   The wavelength interval Δλ of the carrier light having different wavelengths is expressed by the following equations (1) and (2).
    Δf = 0.64 / <τ> (1)
    Δλ = Δf · λ ² / V (2)
The optical transmission / reception system according to claim 1, which is as described above.
  Where Δf is the frequency interval of the carrier light of different wavelengths, <τ> is the average value of the group delay time difference between the polarization modes of the transmission line, λ is the wavelength of the carrier light, and v is the optical modulation signal in the optical fiber. Is the group velocity. The optical transmitter includes a forward error correction coder that performs forward error correction coding on the m signal sequences before the interleave coder,
The optical receiving apparatus, after the interleave decoder, the optical transmission and reception system according to any of claims 1 3, characterized in that it comprises a forward error correction decoder for forward error correction decoding the m pieces of signal sequence . m (m: integer greater than or equal to 2) signal sequences are interleaved and rearranged into n (n: integer greater than or equal to 2) signal sequences,
The interleaved n signal trains optically modulate carrier lights of different wavelengths and output n optical modulation signals,
Wavelength-multiplexing the n light modulation signals and sending them to an optical fiber;
Receiving the wavelength-multiplexed n optical modulation signals from the optical fiber and demultiplexing the signals for every n wavelengths;
Each of the n optical modulation signals subjected to wavelength demultiplexing is optically detected to output n signal sequences,
N optically detected n signal sequences are interleaved back into m signal sequences ,
The wavelength interval of the carrier light having the different wavelength is not less than the wavelength interval at which the stochastic transmission characteristic deterioration behavior can be regarded as independent.
An optical transmission / reception method characterized by the above.   m (m: integer greater than or equal to 2) signal sequences are interleaved and rearranged into n (n: integer greater than or equal to 2) signal sequences,
  The interleaved n signal trains optically modulate carrier lights of different wavelengths and output n optical modulation signals,
  Wavelength-multiplexing the n light modulation signals and sending them to an optical fiber;
  Receiving the wavelength-multiplexed n optical modulation signals from the optical fiber and demultiplexing the signals for every n wavelengths;
  Each of the n optical modulation signals subjected to wavelength demultiplexing is optically detected to output n signal sequences,
  N optically detected n signal sequences are interleaved back into m signal sequences,
  The wavelength interval Δλ of the carrier light having different wavelengths is expressed by the following equations (1) and (2).
    Δf = 0.64 / <τ> (1)
    Δλ = Δf · λ ² / V (2)
An optical transmission / reception method characterized by the above.
  Where Δf is the frequency interval of the carrier light of different wavelengths, <τ> is the average value of the group delay time difference between the polarization modes of the transmission line, λ is the wavelength of the carrier light, and v is the optical modulation signal in the optical fiber. Is the group velocity.   The wavelength interval Δλ of the carrier light having different wavelengths is expressed by the following equations (1) and (2).
    Δf = 0.64 / <τ> (1)
    Δλ = Δf · λ ² / V (2)
The optical transmission / reception method according to claim 5, which is as described above.
  Where Δf is the frequency interval of the carrier light of different wavelengths, <τ> is the average value of the group delay time difference between the polarization modes of the transmission line, λ is the wavelength of the carrier light, and v is the optical modulation signal in the optical fiber. Is the group velocity. Before interleaving, the m signal sequences are forward error correction encoded,
8. The optical transmission / reception method according to claim 5 , wherein the m signal sequences are subjected to forward error correction decoding after interleaving.

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