CN114710204A - A single-polarization coherent detection system and method for avoiding polarization fading - Google Patents

Abstract

The invention provides a single-polarization coherent detection system and method for avoiding polarization fading, which relates to the technical field of optical communication and signal processing, and is based on the framework of a traditional single-polarization coherent detection system to tolerate and resist the polarization fading in the single-polarization coherent detection system. , and then improve the transmission performance of the system as the goal, introduce a low-cost polarization scrambler, forward error correction coding, and timing interleaving scheme, and use the low-cost polarization scrambler to accelerate the polarization change of the single-polarized optical signal to obtain a highly random polarization state, thereby Avoid the polarization fading time for too long, in order to reduce the number of consecutive bit errors caused by polarization fading, thereby reducing the requirement for the length of the timing interleaving, and finally correct the randomized bit errors caused by the polarization fading through the forward error correction coding technology. The scheme has low cost and simple structure, which not only effectively reduces the scrambling speed requirement of the low-cost polarizer, but also effectively reduces the time sequence interleaving length requirement, thereby ensuring the feasibility of practical application.

Description

A single-polarization coherent detection system and method for avoiding polarization fading

technical field

The present invention relates to the technical field of optical communication and signal processing, and more particularly, to a single-polarization coherent detection system and method for avoiding polarization fading.

Background technique

In optical fiber communication systems, coherent modulation-coherent detection is widely used for its advantages of high transmission rate, high transmission capacity, and high spectrum utilization, compared with the cost-sensitive and simple-structured intensity modulation-direct detection system. Coherent detection is a signal demodulation mechanism. It uses the continuous light emitted by the local oscillator and the received signal light to mix, and then demodulates the modulated signal through the receiver. The detection method can improve the spectral efficiency and the reception. Sensitivity, but requires frequency/wavelength synchronization, phase synchronization, and polarization alignment of the local laser and the detected signal. The above preconditions are all realized by digital signal processing algorithms at the receiver.

In a conventional single-polarization coherent detection system, if there is no special device to handle the polarization, when the polarization state of the received signal light is inconsistent with the local oscillator light, the signal amplitude detected coherently will fading, that is, the phenomenon of polarization fading, especially when the two When the polarization states of the beams are orthogonal, the detected signal amplitude will decay to zero. In general, the polarization state of the signal light needs to be matched with the polarization state of the local oscillator light to ensure that the coherent detection system can better demodulate the signal. Instantaneous polarization state mismatch will also lead to damage or even loss of the signal, resulting in a short system. crashed. Moreover, as we all know, compared with the traditional direct detection, the coherent detection system is complex and the cost is higher, and some application fields are sensitive to the price of communication system equipment. Therefore, how to avoid polarization fading and reduce the complexity of polarization-related hardware has become an urgent need to alleviate and overcome problems.

SUMMARY OF THE INVENTION

In order to reduce and avoid system performance degradation caused by polarization fading, and to reduce the complexity of the solution, the present invention proposes a single-polarization coherent detection system and method for avoiding polarization fading, which avoids excessively long polarization fading through a low-cost polarizer Duration and timing interleaving randomize the continuous burst error caused by polarization fading to improve the error correction performance of the previous term, and forward error correction technology corrects and recovers the error code at the receiving end, and realizes the polarization fading phenomenon in the single polarization coherent system. resistance and tolerance, its structure is simple and compatible with traditional schemes, and it is cost-effective.

In order to achieve above-mentioned technical effect, technical scheme of the present invention is as follows:

A single-polarization coherent detection system that avoids polarization fading, including an optical transmitter, an optical fiber link, and an optical receiver including a low-cost polarizer, the optical transmitter includes a transmitter DSP, an electrical amplifier, a single-polarization vector modulator, and a laser , wherein the transmitter DSP includes forward error correction coding and timing interleaving, the optical receiver includes an optical filter, a low-cost scrambler, a local oscillator, a coherent receiver and a receiver DSP, wherein the receiver DSP includes a timing solution Interleaving and forward error correction decoding; in the transmitter DSP at the optical transmitter end, the signal source passes through serial/parallel conversion, channel coding operations including the previous error correction coding and timing interleaving, and then the baseband power is obtained through digital/analog conversion. The signal is output to the single-polarization vector modulator after the electric amplifier, loaded on the continuous optical carrier generated by the laser, and after the single-polarization optical signal is generated, it is sent to the optical fiber link for transmission;

Complete the optical fiber link transmission, filter out the out-of-band noise single-polarized optical signal through the optical filter, accelerate the random change of polarization through the low-cost scrambler, and then enter the coherent receiver together with the local oscillator light emitted by the local oscillator. Mixing detection is performed in the coherent receiver to generate coherent detection light;

Set the polarization fading amplitude threshold of the coherent detection light as A _th , when the amplitude of the coherent detection light is lower than A _th , the continuous burst error at the corresponding moment is caused by the polarization fading, and the time lower than A _th is the polarization fading time ΔT _th , the introduction and application of the low-cost polarizer, accelerate the polarization change of the single-polarized optical signal, and reduce the polarization fading time ΔT _th ; the single-polarized optical signal produces continuous bit errors within ΔT _th , and the timing interleaving in the transmitter DSP will be caused by polarization fading The continuous burst errors are converted into random errors to improve the error correction capability of the previous item, and the forward error correction coding is used to correct the errors at the receiving end;

The coherent detection optical signal is sent to the receiver DSP of the optical receiver, and the sink is obtained through analog/digital conversion, channel decoding including timing deinterleaving and forward error correction decoding, and parallel/serial conversion operations;

In this technical solution, based on the processing of the optical transmission signal by the transmitter and the receiver in the traditional single-polarization coherent detection system, with the goal of tolerating the polarization fading in the single-polarization coherent detection system, a low-cost polarization scrambler and a front-end polarization scrambler are introduced. Combining error correction coding and timing interleaving, low-cost polarizers are used to accelerate the polarization change of single-polarized optical signals to obtain a highly random polarization state, so as to prevent the polarization fading time from continuing too long, reduce the number of consecutive bit errors, and reduce the need for timing interleaving. Time length requirements, and finally correct the error code through forward error correction, which ensures the feasibility of practical application.

Preferably, the optical fiber link includes an optical fiber and an optical amplifier for transmitting single-polarized optical signals. Preferably, the low-cost polarizer is an extruded optical fiber.

Preferably, the low-cost polarizer is a deflection fiber coil with a simple structure.

Here, it is considered that the optical devices used for polarization tracking or maintaining polarization are relatively expensive. Compared with this, a polarization scrambler that realizes random polarization changes based on a simple form such as extruded fiber is low in cost.

Preferably, suppose that the time sequence interleaving time is T _in , the number of time sequence interleaving bits is n, and the duration of each bit during transmission is T _b , then:

T _in =n*T _b ;

The relationship between the timing interleaving time T _in and the polarization fading time ΔT _th should satisfy:

时，以时序交织时间为代价，将突发连续误码错误随机化，配合前向纠错编码技术，提高纠正误码能力以实现对偏振衰落的容忍与抵抗。That is, the timing interleaving time T _in covers the polarization fading time ΔT _th is the minimum requirement to convert the continuous bit errors caused by polarization fading into random bit errors through timing interleaving in the time dimension;

At the expense of time sequence interleaving time, the burst continuous bit error is randomized, and the forward error correction coding technology is used to improve the error correction ability to achieve tolerance and resistance to polarization fading.

时，因前向纠错技术纠正连续误码的能力有限，此时无论时序交织与否均不能有效纠正误码，反之，时序交织在更大的时间维度内将偏振衰落导致的连续误码随机分布，有利于前向纠错技术性能的提高，实现误码纠正。优选地，设低成本扰偏器的扰偏时间间隔为T_scram，低成本扰偏器的扰偏时间间隔T_scram与偏振衰落时间ΔT_th的关系应满足：Here, the setting of the timing interleaving time T _in is closely related to the polarization fading time ΔT _th . When the timing interleaving is not sufficient to cover the polarization fading time ΔT _th in the time dimension, that is,

At this time, due to the limited ability of forward error correction technology to correct continuous bit errors, no matter whether timing interleaving or not, it cannot effectively correct bit errors. The distribution is beneficial to the improvement of the performance of the forward error correction technology and the realization of error correction. Preferably, the scrambling time interval of the low-cost polarizer is set to be T _scram , and the relationship between the scrambling time interval T _scram of the low-cost polarizer and the polarization fading time ΔT _th should satisfy:

That is, the introduction of the low-cost polarizer is intended to take the polarization fading time ΔT _th based on the scrambling time interval T _scram , and make a finer division in the time dimension, and within each scrambling time interval T _scram , the The random polarization state created by the polarization can make the coherent detection light amplitude not less than the polarization fading amplitude threshold A _th , and reduce the polarization fading time ΔT _th , thereby reducing or even avoiding the bit errors caused by it.

时，时序交织时间T_in更能被有效优化，节省更多寄存器资源。Preferably, the smaller the scrambling time interval T _scram of the low-cost polarizer is, the smaller the polarization fading time ΔT _th is, so that the timing interleaving time T _in is also reduced. when

, the timing interleaving time T _in can be more effectively optimized, saving more register resources.

Here, the application of low-cost scrambler can effectively improve the requirement for the timing interleaving length. Therefore, the scrambling time interval T _scram of the low-cost scrambler is to meet the premise of being reasonably smaller than the polarization fading time ΔT _th . Reasonable optimization of interleaving length (timing interleaving time T _in ).

Preferably, when the time-series interleaving converts continuous code errors into random code errors, the codewords after the forward error correction encoding are randomly arranged in the time dimension, thereby improving the forward error correction performance.

Preferably, the channel coding in the transmitter DSP includes forward error correction coding and timing interleaving, and the channel decoding in the receiver DSP includes timing deinterleaving and forward error correction decoding, for coordinating timing interleaving and forward error correction Operation, the two are inherently logically related to the low-cost polarizer, and should be considered comprehensively and applied in combination.

The present invention also provides a single-polarization coherent detection method for avoiding polarization fading, the method comprising:

S1. In the transmitter DSP of the optical transmitter, after the signal source is operated by serial/parallel conversion, channel coding, etc., the baseband electrical signal is obtained by digital/analog conversion, and then output to the single-polarization vector modulator after the electrical amplifier; wherein, The channel coding process includes forward error correction coding and timing interleaving;

S2. The amplified baseband electrical signal is loaded on the continuous optical carrier generated by the laser through the single-polarization vector modulator, and after the single-polarization optical signal is generated, it is sent to the optical fiber link for transmission; wherein, the optical fiber link includes the optical fiber and the optical amplifier ;

S3. At the optical receiver end, complete the optical fiber link transmission and filter out the out-of-band noise single-polarized optical signal through the optical filter, accelerate the random change of polarization through the low-cost scrambler, and then combine with the local oscillator emitted by the local oscillator. The light is input to the coherent receiver together, and the frequency mixing detection is performed in the coherent receiver to generate coherent detection light;

S4. Set the polarization fading amplitude threshold A _th of the coherent detection light. When the amplitude of the coherent detection light is lower than the threshold A _th , continuous burst errors will be caused at the corresponding moment due to polarization fading, and the time below the threshold is the polarization fading time ΔT _th ; the introduction and application of low-cost polarizers can accelerate the polarization change of single-polarized optical signals and reduce the polarization fading time ΔT _th ;

S5. Within the polarization fading time ΔT _th , the single-polarized optical signal generates continuous bit errors, and the channel coding includes forward error correction coding and timing interleaving, wherein the timing interleaving converts the continuous burst errors caused by polarization fading into random errors. , in order to improve the error correction capability of the preceding item, and the forward error correction coding is used to correct the error code at the receiving end;

S6. The coherent detection optical signal is sent to the receiver DSP, and the sink is obtained through operations such as analog/digital conversion, channel decoding, and parallel/serial conversion; wherein, the channel decoding includes timing deinterleaving and forward error correction decoding.

Compared with the prior art, the beneficial effects of the technical solution of the present invention are:

The present invention proposes a single-polarization coherent detection system and method for avoiding polarization fading. Based on the processing of the optical transmission signal by the transmitter and the receiver in the traditional single-polarization coherent detection system, it can tolerate and resist the single-polarization coherent detection system. With the goal of polarization fading, a low-cost polarization scrambler is introduced to cooperate with forward error correction coding and timing interleaving, and the low-cost polarization scrambler is used to accelerate the polarization change of a single-polarized optical signal to obtain a highly random polarization state, thereby avoiding excessively long polarization. The fading duration effectively reduces the requirement on the length of time sequence interleaving and ensures the feasibility of practical application; the sequence interleaving randomizes the continuous burst errors caused by polarization fading to improve the error correction performance of the preceding item; the final forward error correction technology Correct and recover bit errors at the receiving end to achieve resistance and tolerance to polarization fading in single-polarization coherent systems. The scheme has a simple structure, is compatible with traditional schemes, and is cost-effective. Low-cost scramblers are more conducive to the current mainstream Integration of the system structure.

Description of drawings

1 shows a schematic structural diagram of a single-polarization coherent detection system for avoiding polarization fading proposed in Embodiment 1 of the present invention;

2 shows a schematic diagram of an optical signal transmission code stream without applying a low-cost scrambler proposed in Embodiment 2 of the present invention;

3 shows a schematic diagram of an optical signal transmission code stream using a low-cost scrambler proposed in Embodiment 2 of the present invention;

4 shows a schematic diagram of a binary code stream when there is no timing interleaving proposed in Embodiment 2 of the present invention and a phenomenon of polarization fading is generated;

5 shows a schematic diagram of a binary code stream when a polarization fading phenomenon is generated during the time sequence interleaving proposed in Embodiment 2 of the present invention;

FIG. 6 is a schematic flowchart of a single-polarization coherent detection method for avoiding polarization fading proposed in Embodiment 3 of the present invention.

Detailed ways

The accompanying drawings are for illustrative purposes only, and should not be construed as limitations on this patent;

In order to better illustrate this embodiment, some parts of the drawings are omitted, enlarged or reduced, which do not represent the actual size;

For those skilled in the art, it is understandable that descriptions of certain well-known contents in the accompanying drawings may be omitted.

The technical solutions of the present invention will be further described below with reference to the accompanying drawings and embodiments.

The positional relationship described in the drawings is only for exemplary illustration, and should not be construed as a limitation on this patent;

Example 1

In this embodiment, as shown in FIG. 1, a single-polarization coherent detection system is proposed to avoid polarization fading. The system includes an optical transmitter, an optical fiber link, an optical receiver including a low-cost polarizer, and an optical transmitter. Including transmitter DSP, electric amplifier, single polarization vector modulator, laser, wherein, transmitter DSP includes forward error correction coding and timing interleaving, optical receiver includes optical filter, low-cost polarization scrambler, local oscillator, coherent Receiver and receiver DSP, in which the receiver DSP includes timing deinterleaving and forward error correction decoding; in the transmitter DSP at the optical transmitter end, the signal source is converted through serial/parallel conversion, including the preceding error correction coding and timing After the interleaved channel coding operation, the baseband electrical signal is obtained by digital/analog conversion, and then output to the single-polarization vector modulator after the electrical amplifier, loaded onto the continuous optical carrier generated by the laser, and then sent into the optical fiber after generating the single-polarized optical signal. link for transmission;

Complete the optical fiber link transmission, filter out the out-of-band noise single-polarized optical signal through the optical filter, accelerate the random change of polarization through the low-cost scrambler, and then enter the coherent receiver together with the local oscillator light emitted by the local oscillator. Mixing detection is performed in the coherent receiver to generate coherent detection light;

Set the polarization fading amplitude threshold of the coherent detection light as A _th , when the amplitude of the coherent detection light is lower than A _th , the continuous burst error at the corresponding moment is caused by the polarization fading, and the time lower than A _th is the polarization fading time ΔT _th , the introduction and application of the low-cost polarizer, accelerate the polarization change of the single-polarized optical signal, and reduce the polarization fading time ΔT _th ; the single-polarized optical signal produces continuous bit errors within ΔT _th , and the timing interleaving in the transmitter DSP will be caused by polarization fading The continuous burst errors are converted into random errors to improve the error correction capability of the previous item, and the forward error correction coding is used to correct the errors at the receiving end;

The coherent detection optical signal is sent to the receiver DSP of the optical receiver, and the sink is obtained through analog/digital conversion, channel decoding including timing deinterleaving and forward error correction decoding, and parallel/serial conversion operations;

In this embodiment, the entire system is based on the processing of the optical transmission signal by the transmitter and the receiver in the traditional single-polarization coherent detection system, aiming to tolerate polarization fading in the single-polarization coherent detection system, and introduces low-cost interference. The polarizer cooperates with forward error correction coding and timing interleaving, and uses a low-cost polarizer to accelerate the polarization change of a single-polarized optical signal, so as to obtain a highly random polarization state, so as to prevent the polarization fading time from continuing too long, and reduce continuous bit errors. It reduces the requirement on the time length of time sequence interleaving and ensures the feasibility of practical application.

In this embodiment, referring to FIG. 1 , the optical fiber link includes an optical fiber and an optical amplifier for transmitting a single-polarized optical signal. In this embodiment, the low-cost polarizer used can be a simple extruded fiber or a deflected fiber coil, which is low in cost. Other polarizers may also be used to generate random but not deterministic polarization changes, but relatively Due to complex and expensive polarization controllers and other devices, polarization fading resistance in single-polarization coherent detection systems can be realized with low complexity and low cost.

Referring to FIG. 1, the channel coding in the transmitter DSP includes forward error correction coding and timing interleaving, and the channel decoding in the receiver DSP includes timing deinterleaving and forward error correction decoding, which are used to cooperate with timing interleaving and forward correction. Incorrect operation, the two are inherently logically related to low-cost polarizers and should be used in combination.

Example 2

This embodiment specifically describes the realization of polarization fading resistance in a single-polarization coherent detection system. Compared with a high-speed optical modulation code stream (>10Gb/s), the polarization state change of light can be regarded as a slow-changing process (usually on the order of milliseconds). , microsecond-level changes occasionally occur in special environments), set the polarization fading amplitude threshold of coherent detection light as A _th , see Figure 2, the abscissa represents time, and the ordinate represents polarization fading. When the coherent detection light amplitude is lower than When the polarization fading amplitude threshold is set, the optical transmission signal at the corresponding moment (the duration varies randomly, for the sake of simplicity, its average value ΔT _th can be used to discuss) will generate continuous bit errors due to polarization fading, as shown in the "slope" in Figure 2 The code stream is divided into blocks. At this time, Figure 2 shows the schematic diagram of the code stream when the low-cost scrambler is not applied. After the low-cost scrambler is introduced, the schematic diagram of the code stream is shown in Figure 3. It can be seen from the comparison between Figure 3 and Figure 2 , the application of low-cost scrambler effectively reduces the duration that the polarization of the scrambled signal is lower than the polarization fading threshold A _th , thereby effectively reducing the number of consecutive bit errors caused by polarization fading. However, in order to ensure practical feasibility, low When the cost scrambler is combined with the timing interleaving technology, the low-cost scrambler should ensure a reasonable scrambling rate, and finally correct the error code through the forward error correction technology.

Usually, in order to convert continuous errors into random errors, timing interleaving is introduced to rearrange the bit positions in the binary code stream sequence to improve the forward error correction performance. Discretely distributed in a wider time dimension, take Figure 4 as an example, set the forward error correction code to be (7,4) Hamming code, it is known that one (7,4) Hamming codeword can correct the maximum number of errors in the codeword. 1 bit error, if the encoded binary code stream causes 2 consecutive bit errors due to polarization fading at a certain moment, as indicated by the arrow in Figure 4. In the case of no timing interleaving, 2 consecutive errors correspond to the same Hamming codeword N, and the forward error correction coding fails due to the inability to correct the erroneous bits. The bits in the word are reordered. When sequential interleaving assists forward error correction coding to convert continuous errors into random errors, the bits of the codeword after forward error correction are randomly arranged in the time dimension. The original position before interleaving is shown in Figure 5, then the time sequence interleaving operation converts 2 consecutive error bits in one Hamming codeword in Figure 4 into two Hamming codewords indicated by the arrows in Figure 5, each of which transmits 1 error. Therefore, the (7,4) Hamming code can correct the respective erroneous bits in the two groups, avoiding the error caused by polarization fading. Under the premise of fixed forward error correction coding, combined with low-cost polarization scrambler To optimize the timing interleaving time, set the timing interleaving time to be T _in , the number of timing interleaving bits to be n, and the duration of each bit during transmission to be T _b , then:

T _in =n*T _b ;

Generally, the relationship between the timing interleaving time T _in and the polarization fading time ΔT _th should basically satisfy:

That is, the interleaving time T _in covers the polarization fading time ΔT _th , which is the minimum requirement to convert the continuous bit errors caused by the polarization fading into random bit errors through the time sequence interleaving in the time dimension.

时，因前向纠错技术纠正连续误码的能力有限，此时无论时序交织与否均不能有效纠正误码，反之，如图5所示，时序交织有利于前向纠错编码纠正因偏振衰落引起的连续误码。当

时，前向纠错编码的纠错能力趋于理想。然而，过长的比特序列进行时序交织将极大占用存储与算力资源，令前向纠错编码配合时序交织技术在克服慢速的偏振衰落时面临严峻挑战，缺乏实用价值。Here, the setting of the timing interleaving time T _in is closely related to the polarization fading time ΔT _th . When the timing interleaving is not sufficient to cover the polarization fading time ΔT _th in the time dimension, that is,

At this time, due to the limited ability of forward error correction technology to correct continuous errors, no matter whether timing interleaving or not, it cannot effectively correct errors. On the contrary, as shown in Fig. Consecutive bit errors due to fading. when

, the error correction capability of forward error correction coding tends to be ideal. However, timing interleaving of too long bit sequences will greatly occupy storage and computing resources, which makes forward error correction coding and timing interleaving technology face severe challenges in overcoming slow polarization fading and lacks practical value.

Therefore, the introduction of low-cost polarization scrambler accelerates the change speed of the polarization state of the signal light with a certain rule, and obtains a highly random polarization state, thereby avoiding the polarization fading duration is too long, that is, effectively reducing the coherent detection light amplitude below the threshold value At the time ΔT _th of A _th , the application of a low-cost polarizer can effectively improve the requirement on the timing interleaving length and reduce T _in .

Therefore, in actual implementation, the scrambling time interval of the low-cost polarizer is set as T _scram , and the relationship between the scrambling time interval T _scram of the low-cost polarizer and the polarization fading time ΔT _th should satisfy:

That is, the introduction of the low-cost polarizer is intended to take the polarization fading time ΔT _th based on the scrambling time interval T _scram , and make a finer division in the time dimension, and within each scrambling time interval T _scram , the The random polarization state created by the polarization can make the coherent detection light amplitude not less than the polarization fading amplitude threshold A _th , and reduce the polarization fading time ΔT _th , thereby reducing or even avoiding the bit errors caused by it.

时，时序交织时间T_in更能被有效优化，节省更多寄存器资源。低成本扰偏器而低成本扰偏器的扰偏时间间隔T_scram越小，即低成本扰偏器的速率要求

越高。实际实施时，低成本扰偏器的扰偏时间间隔T_scram应在满足合理小于偏振衰落时间ΔT_th的前提下，实现对时序交织长度(时序交织时间T_in)的合理优化。The smaller the scrambling time interval T _scram of the low-cost polarizer is, the smaller the polarization fading time ΔT _th is, and the time sequence interleaving time T _in is also reduced. when

, the timing interleaving time T _in can be more effectively optimized, saving more register resources. Low-cost scrambler and the smaller the scrambling time interval T _scram of the low-cost scrambler, that is, the rate requirement of the low-cost scrambler

higher. In actual implementation, the scrambling time interval T _scram of the low-cost polarizer should be reasonably less than the polarization fading time ΔT _th to achieve reasonable optimization of the timing interleaving length (timing interleaving time T _in ).

The low-cost polarization scrambler is different from the existing solution for processing the polarization mode dispersion of the polarization multiplexed signal in the coherent detection system.

Example 3

Referring to FIG. 6 , the present invention also proposes a single-polarization coherent detection method for avoiding polarization fading. The flow chart of the method is shown in FIG. 6 and includes the following steps:

S1. In the transmitter DSP of the optical transmitter, after the signal source is operated by serial/parallel conversion, channel coding, etc., the baseband electrical signal is obtained by digital/analog conversion, and then output to the single-polarization vector modulator after the electrical amplifier; wherein, The channel coding process includes forward error correction coding and timing interleaving;

S2. The amplified baseband electrical signal is loaded on the continuous optical carrier generated by the laser through the single-polarization vector modulator, and after the single-polarization optical signal is generated, it is sent to the optical fiber link for transmission; wherein, the optical fiber link includes the optical fiber and the optical amplifier ;

S3. At the optical receiver end, complete the optical fiber link transmission and filter out the out-of-band noise single-polarized optical signal through the optical filter, accelerate the random change of polarization through the low-cost scrambler, and then combine with the local oscillator emitted by the local oscillator. The light is input to the coherent receiver together, and the frequency mixing detection is performed in the coherent receiver to generate coherent detection light;

S4. Set the polarization fading amplitude threshold A _th of the coherent detection light. When the amplitude of the coherent detection light is lower than the threshold A _th , continuous burst errors will be caused at the corresponding moment due to polarization fading, and the time below the threshold is the polarization fading time ΔT _th ; the introduction and application of low-cost polarizers can accelerate the polarization change of single-polarized optical signals and reduce the polarization fading time ΔT _th ;

S5. Within the polarization fading time ΔT _th , the single-polarized optical signal generates continuous bit errors, and the channel coding includes forward error correction coding and timing interleaving, wherein the timing interleaving converts the continuous burst errors caused by polarization fading into random errors. , in order to improve the error correction capability of the preceding item, and the forward error correction coding is used to correct the error code at the receiving end;

S6. The coherent detection optical signal is sent to the receiver DSP, and the sink is obtained through operations such as analog/digital conversion, channel decoding, and parallel/serial conversion; wherein, the channel decoding includes timing deinterleaving and forward error correction decoding.

Obviously, the above-mentioned embodiments of the present invention are only examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those of ordinary skill in the art, changes or modifications in other different forms can also be made on the basis of the above description. There is no need and cannot be exhaustive of all implementations here. Any modifications, equivalent replacements and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the claims of the present invention.

Claims (10)

1. a single-polarization coherent detection system that avoids polarization fading, is characterized in that, comprises optical transmitter, optical fiber link, comprises the optical receiver of low-cost scrambler, optical transmitter comprises transmitter DSP, electric amplifier, single Polarization vector modulator and laser, wherein the transmitter DSP includes forward error correction coding and timing interleaving, and the optical receiver includes an optical filter, a low-cost polarizer, a local oscillator, a coherent receiver and a receiver DSP, wherein, The receiver DSP includes timing deinterleaving and forward error correction decoding; in the transmitter DSP at the optical transmitter side, after the signal source passes through serial/parallel conversion, channel coding operations including the preceding error correction coding and timing interleaving, The baseband electrical signal is obtained by /mode conversion, which is output to the single-polarization vector modulator after the electrical amplifier, loaded on the continuous optical carrier generated by the laser, and then sent to the optical fiber link for transmission after the single-polarized optical signal is generated; Complete the optical fiber link transmission, filter out the out-of-band noise single-polarized optical signal through the optical filter, accelerate the random change of polarization through the low-cost scrambler, and then enter the coherent receiver together with the local oscillator light emitted by the local oscillator. Mixing detection is performed in the coherent receiver to generate coherent detection light; Set the polarization fading amplitude threshold of the coherent detection light as A _th , when the amplitude of the coherent detection light is lower than A _th , the continuous burst error at the corresponding moment is caused by the polarization fading, and the time lower than A _th is the polarization fading time ΔT _th , the introduction and application of the low-cost polarizer, accelerate the polarization change of the single-polarized optical signal, and reduce the polarization fading time ΔT _th ; the single-polarized optical signal produces continuous bit errors within ΔT _th , and the timing interleaving in the transmitter DSP will be caused by polarization fading The continuous burst errors are converted into random errors to improve the error correction capability of the previous item, and the forward error correction coding is used to correct the errors at the receiving end; The coherent detection optical signal is sent to the receiver DSP of the optical receiver, and the sink is obtained through analog/digital conversion, channel decoding including timing deinterleaving and forward error correction decoding, and parallel/serial conversion operations. 2 . The single-polarization coherent detection system for avoiding polarization fading according to claim 1 , wherein the optical fiber link comprises an optical fiber and an optical amplifier for transmitting a single-polarization optical signal. 3 . 3 . The single-polarization coherent detection system for avoiding polarization fading according to claim 2 , wherein the low-cost polarization scrambler is an extruded optical fiber. 4 . 4 . The single-polarization coherent detection system for avoiding polarization fading according to claim 2 , wherein the low-cost polarization scrambler is a deflection fiber coil. 5 . 5. the single-polarization coherent detection system that avoids polarization fading according to claim 1, is characterized in that, setting the time sequence interleaving time to be T _in , the time sequence interleaving bit number is n, and the duration of each bit during transmission is T _b , then satisfy: T _in =n*T _b ; The relationship between the timing interleaving time T _in and the polarization fading time ΔT _th should satisfy:

That is, the timing interleaving time T _in covers the polarization fading time ΔT _th is the minimum requirement to convert the continuous bit errors caused by polarization fading into random bit errors through timing interleaving in the time dimension;

At the expense of time sequence interleaving time, the burst continuous bit error is randomized, and the forward error correction coding technology is used to improve the error correction ability to achieve tolerance and resistance to polarization fading. 6. the single-polarization coherent detection system that avoids polarization fading according to claim 5, it is characterized in that, let the scrambling time interval of low-cost polarizer be T _scram , the scrambling time interval T _scram of low-cost polarizer The relationship with the polarization fading time ΔT _th should satisfy:

That is, the introduction of the low-cost polarizer is intended to take the polarization fading time ΔT _th as the benchmark, and make a detailed division in the time dimension based on the scrambling time interval T _scram , and within each scrambling time interval T _scram , the The random polarization state is achieved to make the coherent detection light amplitude not less than the polarization fading amplitude threshold A _th , reducing the polarization fading time ΔT _th , thereby reducing or even avoiding the bit errors caused by it. 7. The single-polarization coherent detection system for avoiding polarization fading according to claim 6, characterized in that, the smaller the scrambling time interval T _scram of the low-cost polarization scrambler is, the less the polarization fading time ΔT _th is immediately, thereby making the time sequence The interleaving time T _in also decreases; when

, the timing interleaving time T _in can be effectively optimized, saving register resources; the smaller the scrambling time interval T _scram of the low-cost scrambler, the faster the

The larger the value is, the higher the requirements for low-cost scramblers are; the scrambling time interval T _scram of the low-cost scrambler is to achieve a reasonable timing interleaving time T _in on the premise of being reasonably smaller than the polarization fading time ΔT _th optimization. 8. the single-polarization coherent detection system that avoids polarization fading according to claim 7, is characterized in that, when time sequence interleaving changes continuous code error into random code error, it is shown as random arrangement of forward error correction coding in time dimension After the codeword, thereby improving the forward error correction performance. 9. The single-polarization coherent detection system that avoids polarization fading according to claim 8, wherein the channel coding in the transmitter DSP comprises forward error correction coding and timing interleaving, and the channel decoding in the receiver DSP comprises timing Deinterleaving and forward error correction decoding are used to cooperate with timing interleaving and forward error correction operations. The two are inherently logically related to low-cost scramblers, and should be comprehensively considered and applied in combination. 10. A single-polarization coherent detection method for avoiding polarization fading, wherein the method comprises: S1. In the transmitter DSP of the optical transmitter, after the signal source is operated by serial/parallel conversion, channel coding, etc., the baseband electrical signal is obtained by digital/analog conversion, and then output to the single-polarization vector modulator after the electrical amplifier; wherein, The channel coding process includes forward error correction coding and timing interleaving; S2. The amplified baseband electrical signal is loaded on the continuous optical carrier generated by the laser through the single-polarization vector modulator, and after the single-polarization optical signal is generated, it is sent to the optical fiber link for transmission; wherein, the optical fiber link includes the optical fiber and the optical amplifier ; S3. At the optical receiver end, complete the optical fiber link transmission and filter out the out-of-band noise single-polarized optical signal through the optical filter, accelerate the random change of polarization through the low-cost scrambler, and then combine with the local oscillator emitted by the local oscillator. The light is input to the coherent receiver together, and the frequency mixing detection is performed in the coherent receiver to generate coherent detection light; S4. Set the polarization fading amplitude threshold A _th of the coherent detection light. When the amplitude of the coherent detection light is lower than the threshold A _th , continuous burst errors will be caused at the corresponding moment due to polarization fading, and the time below the threshold is the polarization fading time ΔT _th ; the introduction and application of low-cost polarizers can accelerate the polarization change of single-polarized optical signals and reduce the polarization fading time ΔT _th ; S5. Within the polarization fading time ΔT _th , the single-polarized optical signal generates continuous bit errors, and the channel coding includes forward error correction coding and timing interleaving, wherein the timing interleaving converts the continuous burst errors caused by polarization fading into random errors. , in order to improve the error correction capability of the preceding item, and the forward error correction coding is used to correct the error code at the receiving end; S6. The coherent detection optical signal is sent to the receiver DSP, and the sink is obtained through operations such as analog/digital conversion, channel decoding, and parallel/serial conversion; wherein, the channel decoding includes timing deinterleaving and forward error correction decoding.

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