CN110086611B - Wavelength division multiplexing polarization compensation method and device - Google Patents

Wavelength division multiplexing polarization compensation method and device Download PDF

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CN110086611B
CN110086611B CN201910341141.2A CN201910341141A CN110086611B CN 110086611 B CN110086611 B CN 110086611B CN 201910341141 A CN201910341141 A CN 201910341141A CN 110086611 B CN110086611 B CN 110086611B
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polarization
reference light
conjugate
module
output
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CN110086611A (en
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王金东
赵家钰
杜聪
源毅萍
陈艳辉
马瑞丽
何昱霏
唐璨
何广强
魏正军
於亚飞
张智明
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South China Normal University
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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/27—Optical coupling means with polarisation selective and adjusting means
    • G02B6/2746—Optical coupling means with polarisation selective and adjusting means comprising non-reciprocal devices, e.g. isolators, FRM, circulators, quasi-isolators
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/27—Optical coupling means with polarisation selective and adjusting means
    • G02B6/2753—Optical coupling means with polarisation selective and adjusting means characterised by their function or use, i.e. of the complete device
    • G02B6/2773—Polarisation splitting or combining
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/60—Receivers
    • H04B10/61—Coherent receivers
    • H04B10/616—Details of the electronic signal processing in coherent optical receivers
    • H04B10/6162—Compensation of polarization related effects, e.g., PMD, PDL
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
    • H04L9/08—Key distribution or management, e.g. generation, sharing or updating, of cryptographic keys or passwords
    • H04L9/0816—Key establishment, i.e. cryptographic processes or cryptographic protocols whereby a shared secret becomes available to two or more parties, for subsequent use
    • H04L9/0852—Quantum cryptography
    • H04L9/0858—Details about key distillation or coding, e.g. reconciliation, error correction, privacy amplification, polarisation coding or phase coding

Abstract

The invention provides a wavelength division multiplexing polarization compensation device, comprising: the device comprises a conjugate reference optical module, a dense wavelength division multiplexer, an electric control polarization controller, an optical circulator, a dense multiplexer, a polarization detection module and a control module; the conjugate reference light output module includes: the device comprises a 2 x 2 polarization-maintaining polarization beam splitter and a Faraday rotator, wherein the beam splitter is provided with two input ports and two output ports, the 2 x 2 polarization-maintaining polarization beam splitter is used for receiving reference light, one output port is connected with the Faraday rotator, and the reference light output from the Faraday rotator and the reference light output from the other output port form conjugate reference light. The compensation system provided by the invention shortens the control time of the control module on the electric control polarization controller through the control of the control module, thereby ensuring the stability of the quantum key distribution system and effectively reducing the error rate of the system.

Description

Wavelength division multiplexing polarization compensation method and device
Technical Field
The present invention relates to the field of communications technologies, and in particular, to a wavelength division multiplexing polarization compensation method and apparatus.
Background
The development of human communication systems has been left without the word "security", and both morse code and ennergma cipher in the last century and the RSA public key encryption algorithm proposed until 1977 have come to the end of information security. Since quantum computer systems are proposed, RSA-acknowledged security is greatly threatened, and the traditional encryption mode is not enough to ensure the security of information in the communication and processing processes. Therefore, a quantum key distribution system (QKD) of "one-time pad" is also proposed. To date, long-distance, high-rate QKD systems have been continuously designed. Quantum keys are continuously concerned by military, banks and other large security industries due to the 'absolute security' property of quantum keys based on the 'uncertainty principle' and 'quantum unclonable principle' of quantum characteristics. In recent years, many quantum communication systems have been successively completed, and it is needless to say that the security of communication is guaranteed, and the research of quantum communication systems is also getting more and more intense, and QKD systems of polarization encoding and phase encoding are becoming the main research direction. The polarization encoded QKD system works as follows: the single photon source is controlled to emit pulse laser in different polarization states by generating random numbers, and then the pulse laser is modulated in intensity to form a decoy state. Then, single photon pulses carrying quantum information are transmitted to a receiving end through a long-distance optical fiber, the receiving end detects and demodulates through a random polarization base, a certain random number sequence is restored, and a transmitting end is informed of the random polarization base used for detection through a classical channel. After receiving the probe sequence information, the sender informs the receiver of which codes on the bits are valid and reliable through a classical channel, and then the sender and the receiver screen out the same codebook. And finally, both parties publish partial cipher books to check the error rate so as to detect whether monitoring and attack exist, and simultaneously correct the keys to form codes.
The existing polarization-encoded quantum key distribution system comprises an information transmitting end, an information receiving end and a transmission medium, and because the existing transmitting end mostly adopts 4 linear polarization states required by single photon random preparation encoding, the four linear polarizations are respectively a horizontal polarization state, a vertical polarization state, a 45-degree polarization state and a 135-degree polarization state. However, because the transmission medium used at present is an optical fiber, and because of the characteristics of the optical fiber, the four prepared polarization states change randomly after being transmitted through an optical fiber channel, and therefore the four prepared polarization states cannot be decoded when reaching an information receiving party, thereby causing the defect of high error rate.
When the polarization compensation is performed in the wavelength division multiplexing mode, it is necessary to ensure that the reference light output by the information transmitting end is conjugate reference light on the premise that the reference light reaches conjugate output and is subjected to channel compensation, so that any polarization state of the signal light can be compensated, and the compensation accuracy can be improved. However, when the wavelength division multiplexing polarization compensation device is used, the conjugate reference light output from the information transmitting end passes through the dense wavelength division multiplexer and the electric control polarization controller in sequence, then is demultiplexed by the dense wavelength division multiplexer at the receiving end, and then is sent to the FPGA through the a/D conversion module, and the electric control polarization controller is controlled by the FPGA to realize error code compensation. When the electric control polarization controller uses a piezoelectric ceramic polarization controller, although four squeezers of the piezoelectric ceramic have determined half-wave voltage, the four squeezers are influenced by some factors such as environment and the like, so that the rotation angle under each determined voltage is different, and the electric control polarization controller cannot be controlled by using a table look-up mode and the like, so that the electric control polarization controller needs to be controlled by using an algorithm; therefore, a control algorithm is designed to control the polarization controller, and the current control method affects the actual key transmission due to the long control time, thereby reducing the error rate of the compensation system.
Disclosure of Invention
The present invention is directed to solve the above-mentioned drawbacks of the prior art, and provides a fast and effective control method and apparatus, which can effectively shorten the control time and ensure that the error rate of the system is effectively reduced.
A wavelength division multiplexing polarization compensation apparatus comprising:
a conjugate reference light module for outputting conjugate reference light;
the dense wavelength division multiplexer is used for combining the two beams of conjugate reference light to an optical fiber channel;
the electric control polarization controller is used for changing the polarization state of the conjugate reference light on the optical fiber channel to form conjugate polarized light and outputting the conjugate polarized light;
the optical circulator is used for enabling the conjugate polarized light output from the electric control polarization controller to be output to the receiving end dense wavelength division multiplexer according to a specified port;
a dense multiplexer for separating the conjugate polarized light output from the optical circulator;
the polarization detection module is used for respectively detecting the polarization states of the two beams of conjugate polarized light output by the dense multiplexer;
the control module is used for compensating the polarization state of the electric control polarization controller according to the detected polarization state, so that the polarization state of the conjugate reference light output by the electric control polarization controller is in a preset compensation range;
the conjugate reference light output module includes: a 2 x 2 polarization-maintaining polarization beam splitter, faraday rotator;
the 2 x 2 polarization-maintaining polarization beam splitter has two input ports and two output ports, the 2 x 2 polarization-maintaining polarization beam splitter is used for receiving reference light, one output port is connected with the Faraday rotator, and the reference light output from the Faraday rotator and the reference light output from the other output port of the 2 x 2 polarization-maintaining polarization beam splitter form conjugate reference light.
Further, the wavelength division multiplexing polarization compensation apparatus as described above, the polarization detection module includes:
the system comprises two polarization detectors respectively connected with the output ends of the dense multiplexer, two multiplexing subtraction circuits respectively connected with the two polarization detectors, and two A/D conversion modules respectively connected with the two multiplexing subtraction circuits, wherein the output ends of the two A/D conversion modules are connected with a control module.
In one step, the compensation method of the control module in the wavelength division multiplexing polarization compensation apparatus includes the following steps:
step 1, after receiving the signals converted by the two A/D conversion modules, the control module converts the signals into signals according to a formula V1 a AD1+ b; acquiring voltage values corresponding to different a/D signals by using V2 ═ a × AD2+ b, wherein the voltage values corresponding to the a/D conversion module 1 are V10, V11, V12 and V13; the voltage values corresponding to the A/D conversion module 2 are V20, V21, V22 and V23;
step 2, calculating Stokes parameter values S10, S11, S20 and S22 corresponding to the current voltage value according to the voltage value corresponding to the A/D signal and the M matrix corresponding to different wavelengths given by the polarization detection module; the calculation formula is as follows: m is V;
and 3, carrying out normalization processing on the Stokes parameter values in the following processing mode:
SS1＝S11/S10、SS2＝S22/S20；
step 4, calculating the difference value E11 between the current normalized Stokes parameter and the target Stokes parameters sst1 and sst2 to be sst1-SS1 and E22 to be sst2-SS 2; and applying the sum of the two differences E-E11 + E22, comparing the difference sum with the set range Ethr, and compensating if the difference sum exceeds the range;
step 5, during compensation, firstly storing the calculated E value in E1, and then adding a dithering voltage D, namely V to the electric control polarization controller by the control modulei＝Vi+ D, controlling the electrically controlled polarization controller to generate slight jitter, calculating the deviation E value through the steps, storing the value in E2, calculating the gradient value grad equal to E2-E1, and calculating the formula Vi＝r(Vi-D) + τ x (E2-E1) to obtain updated voltage values, and control the electronically controlled polarization controller until the polarization state is compensated to a suitable range;
and 6, repeating the steps from the step 1 to the step 5 to ensure that the polarization state is within the set range.
The wavelength division multiplexing polarization compensation method comprises the following steps:
step S1, two beams of reference light with different wavelengths sent by a reference light emitting module pass through a conjugate reference light module to output two beams of conjugate reference light, the two beams of conjugate reference light are demultiplexed by a dense wavelength division multiplexer, an electric control polarization controller, an optical circulator and a dense multiplexer in sequence, and then polarization states of the two beams of conjugate polarized light are respectively detected by a polarization detection module;
step S2, the polarization detection module outputs the detected polarization information into four paths of analog voltage signals, the four paths of voltage signals pass through a multiplexing subtraction circuit and then respectively pass through an A/D conversion module 1 and an A/D conversion module 2, then digital information is sent to a control module FPGA, and the control module FPGA synchronously reads data signals of the A/D conversion module 1 and the A/D conversion module 2;
step S3, after the control module FPGA receives the A/D signal, according to the formula V1 a AD1+ b; acquiring voltage values corresponding to different a/D signals by using V2 ═ a × AD2+ b, wherein the voltage values corresponding to the a/D conversion module 1 are V10, V11, V12 and V13; the voltage values corresponding to the A/D conversion module 2 are V20, V21, V22 and V23;
step S4, calculating Stokes parameter values S10, S11, S20 and S22 corresponding to the current voltage value according to the voltage value corresponding to the A/D signal and the M matrix corresponding to different wavelengths given by the polarization detection module; the calculation formula is as follows: m is V;
step S5, the Stokes parameter value is normalized in the following way:
SS1＝S11/S10、SS2＝S22/S20；
step S6, calculating the difference value E11-sst 1-SS1 and E22-sst 2-SS2 between the current normalized Stokes parameter and the target Stokes parameters sst1 and sst 2; and applying the sum of the two differences E-E11 + E22, comparing the difference sum with the set range Ethr, and compensating if the difference sum exceeds the range;
step S7, when compensation is carried out, the calculated E value is stored in E1, and then the control module FPGA adds a dithering voltage D, namely V, to the electric control polarization controlleri＝Vi+ D, controlling the electric control polarization controller to generate slight shake, and thenCalculating the deviation E value through the steps, storing the value in E2, calculating the gradient value grad to E2-E1, and calculating the formula Vi＝r(Vi-D) + τ x (E2-E1) to obtain updated voltage values, and control the electronically controlled polarization controller until the polarization state is compensated to a suitable range;
and step S8, repeating the steps S1 to S7 to ensure that the polarization state is within the set range.
Has the advantages that:
the wavelength division multiplexing polarization compensation device provided by the invention realizes the output of conjugate reference light by adopting a brand new mode, even 2 × 2PBS (polarization maintaining polarization beam splitter) is used for ensuring the alignment of axes, two beams of reference light signals are connected with the input end of the 2 × 2PBS, one output end of the 2 × 2PBS is connected with FR (Faraday rotator) so as to output the conjugate reference light. In addition, if the polarization state on the optical fiber channel is in the condition of rapid disturbance, the polarization compensation device is caused to be continuously in the compensation process, so that the quantum key distribution system is unstable, and the error rate is also increased.
The reason why the device provided by the invention can reduce the error rate is that the invention changes the polarization state back to the polarization state when transmitting, and the device can not form codes without the compensation. The compensation device can be stabilized for a period of time to ensure that the receiving and transmitting polarization states are always similar, so that the reduction of the error rate in the period of time can be ensured to be stable.
For the control time, the control time of the compensation method provided by the invention is less than the time of polarization change, and if the control time is more than the time of polarization change, the system is always in a polarization compensation stage, and the whole system cannot form codes.
Drawings
FIG. 1 is a schematic view of a wavelength division multiplexing polarization compensation device according to the present invention;
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention are described clearly and completely below, and it is obvious that the described embodiments are some, not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Fig. 1 is a schematic structural diagram of a wavelength division multiplexing polarization compensation device of the present invention, and as shown in fig. 1, the wavelength division multiplexing polarization compensation device provided by the present invention includes:
a conjugate reference light module for outputting conjugate reference light; the yoke reference light module includes: a 2 x 2 polarization-maintaining polarization beam splitter, faraday rotator;
the 2 x 2 polarization-maintaining polarization beam splitter has two input ports and two output ports, the 2 x 2 polarization-maintaining polarization beam splitter is used for receiving reference light, one output port is connected with the Faraday rotator, and the reference light output from the Faraday rotator and the reference light output from the other output port of the 2 x 2 polarization-maintaining polarization beam splitter form conjugate reference light.
A dense wavelength division multiplexer DWDM1 for combining the two beams of conjugate reference light onto the fiber channel;
the electronic control polarization controller EPC is used for changing the polarization state of the conjugate reference light on the optical fiber channel to form conjugate polarized light and outputting the conjugate polarized light;
the CIR circulator is used for enabling the conjugate polarized light output from the electric control polarization controller to be output to the receiving end dense wavelength division multiplexer according to a specified port;
a dense multiplexer DWDM2 for separating the conjugate polarization light output from the optical circulator;
the polarization detection module is used for respectively detecting the polarization states of the two beams of conjugate polarized light output by the dense multiplexer;
the control module FPGA is used for compensating the polarization state of the electric control polarization controller according to the detected polarization state, so that the polarization state of the conjugate reference light output by the electric control polarization controller is in a preset compensation range;
specifically, the polarization detection module includes:
the polarization detection device comprises two polarization detectors POD respectively connected with the output ends of a dense multiplexer DWDM1, two multiplexing subtraction circuits respectively connected with the two polarization detectors POD, and two A/D conversion modules respectively connected with the two multiplexing subtraction circuits, wherein the output ends of the two A/D conversion modules are connected with a control module FPGA.
The working principle of the whole system is as follows:
the invention adopts a polarization compensation system in a wavelength division multiplexing mode, so three beams of light are selected according to the specification of a dense wavelength division multiplexer DWDM, wherein two beams of light are reference light, one beam of light is signal light, the wavelength of the reference light selected by the invention is 1550.92nm1549.32nm, the wavelength of the signal light is 1550.12nm, and the wavelength of the signal light must be between the two beams of reference light. After the conjugate reference light is output by the conjugate reference light output module, the two reference lights are combined into an optical fiber channel by a dense wavelength division multiplexer DWDM1, then are unfolded by an electrically controlled polarization controller EPC and a port 3 of a circulator CIR by DWDM2, and then reach a POD polarization detector to detect polarization change. And then, the polarization state is changed by controlling the EPC through the FPGA until the polarization state detected by the POD is the polarization state set in the program of the invention, and the compensation is finished (the two polarization states are also conjugate, and the reference light of the invention is set to 0 degree, namely 0 degree after the compensation). After compensation is completed, the signal light is input from the 1 port of the circulator CIR, passes through the polarization controller and the optical fiber, reaches the dense wavelength division multiplexer DWDM1, is decoded by the PBS, and is detected.
The structure for preparing the conjugate reference light module is that a manual polarization controller is used for controlling the polarization state of the output conjugate, so that the following problems occur: (1) manual pc uses a single-mode fiber, and the polarization state changes after a while, so that the output is not conjugated, inaccurate compensation is caused, and the error rate is increased. (2) When manual pc adjustment is used, it cannot be completely guaranteed that the output polarization states are under the same base (the device of the present invention guarantees that the output polarization states are completely under one base through the PBS), which also causes inaccurate later compensation, causes an increase in bit error rate, does not have a particularly significant influence on stability, and is mainly related to the control algorithm used. However, if a manual PC is used for conjugate output, it may cause polarization change at the polarization state of the reference light output to disturb the whole system, resulting in instability of the whole system. Therefore, the system is compensated by the compensation method of the invention.
The whole polarization compensation and quantum key distribution are carried out simultaneously, and the signal light sent at the ALICE end is the processing carried out by the coding in the quantum key distribution and is decoded after reaching the BOB end. The change of the polarization state in the optical fiber is compensated through the control of the EPC on the reference light, and when the signal light is reversely transmitted, the polarization is changed through the EPC, and then the reverse transformation is performed through the optical fiber, so that the polarization compensation is realized.
The compensation system provided by the invention has the following compensation method:
the system uses 2 × 2PBS (polarization maintaining polarization beam splitter) to ensure the alignment of axes, two reference light signals are connected with the input end of the 2 × 2PBS, one output end of the 2 × 2PBS is connected with FR (faraday rotator), so that the output is conjugate reference light.
The reference light emitting module sends two beams of reference light with different wavelengths, one path of the reference light is connected with the Faraday rotator after passing through 2 × 2PBS, the other path of the reference light is not connected, so that the two reference light outputs are in non-orthogonal polarization states under the same axis, then the reference light outputs pass through a DWDM (dense wavelength division multiplexer), an EPC (electronic control polarization controller), then the reference light outputs are demultiplexed by a receiver dense wavelength division multiplexer, and then the reference light outputs pass through two PODs (polarization detectors) to respectively detect the information of the current polarization state.
The two PODs (polarization detectors) output the detected polarization information as four paths of analog voltage signals, and the four paths of voltage signals pass through a multiplexing subtraction circuit, then pass through the a/D conversion modules AD1 and AD2, and then send digital information to the FPGA. The FPGA synchronously reads the data signals of the AD1 and the AD 2.
After receiving the a/D signal, according to formula V1 ═ a × AD1+ b; v2 is a × AD2+ b, and the voltage values corresponding to different AD signals are calculated (the values of a, b are modified according to the set circuit parameters, a is 0.05, and b is 0.02).
According to the calculated voltage values V10, V11, V12 and V13; v20, V21, V22 and V23 correspond to matrixes M corresponding to different wavelengths given by POD (polarization detector), values S10, S11, S20 and S22 corresponding to current voltage values are calculated according to a formula M V, and then normalization processing SS1 is carried out on the measured Stokes parameters to S11/S10, and SS2 is carried out to S22/S20.
Wherein the matrix is as follows:
Figure GDA0003241746800000111
calculating the difference value E11-sst 1-SS1 and E22-sst 2-SS2 between the current normalized Stokes parameter and the target Stokes parameters sst1 and sst 2; and the sum of the two differences E is E11+ E22, the difference sum is compared with a set range Ethr, and compensation is carried out when the difference sum exceeds the range (Ethr is set according to the system requirement and is generally set to be 0.1).
When compensation is carried out, the calculated E value is firstly stored in E1, and then the FPGA adds a jitter voltage D, namely V to the electric control polarization controlleri＝Vi+ D, controlling the electrically controlled polarization controller to generate slight jitter, calculating the deviation E value through the steps, storing the value in E2, calculating the gradient value grad equal to E2-E1, and calculating the formula Vi＝r(ViD) + τ x (E2-E1) to get the updated voltage value, convert it into a 12-bit control signal, and control the electronically controlled polarization controller until the polarization state is compensated to the proper range (where the momentum value r is 0.9 and the t value is 430).
The steps of S1 through S5 are repeated continuously to ensure that the polarization state is within the set range.
In the process of distributing the quantum key for polarization coding, four polarization states are used, and correspond to two bases, namely a horizontal vertical base (corresponding to the polarization states of 0 degree and 90 degrees) and a diagonal base (corresponding to the polarization states of 45 degrees and 135 degrees), and the two bases are conjugated with each other. Therefore, in the compensation, two bases are compensated respectively, so the invention outputs a horizontal polarization state and a polarization state of 45 degrees, and then compensates respectively, thereby realizing the compensation of all polarization states under the whole base.
When the voltage signal is calculated in the FPGA, the detected voltage signal needs to be converted into a stokes parameter for calculation, so the matrix M must be used for conversion, the matrix can be called a mueller matrix, the specific matrix content is provided by a polarization detector manufacturer, and different wavelengths correspond to each other.
The error value is the difference between the stokes parameters when converted into the stokes parameters by the matrix M. The Stokes parameters are used for expressing the situation of one polarization state, so that errors can be generated between the set polarization state and the detected polarization state, the relation between the detected polarization state and the set polarization state can be ensured by setting the difference value between the Stokes parameters, and if the difference value is 0, the situation is exactly the same as the set polarization state.
Example (b):
firstly, the laser LD1 used by reference light has different LD2 wavelengths, the LD1 can be 1549.32nm, the LD2 can be 1550.92nm, the two lasers are respectively connected with one input end of 2 x 2PBS (polarization maintaining beam splitter) after passing through an ISO isolator, and then one output end is connected with FR (Faraday rotator), so that the output polarization state is ensured to be a non-orthogonal polarization state.
Then the signals reach DWDM2 through a dense wavelength division multiplexer DWDM1 and an electronic control polarization controller EPC, after demultiplexing, the signals are detected through two polarization detectors POD1 and POD2, the information of the current polarization state is output, four paths of voltage signals are output respectively, after the signals pass through a multiplexing circuit, the voltage signals are input into an FPGA for calculation through an AD converter, the FPGA calculates the current polarization state and then compares the current polarization state with a target polarization state to obtain a new error value E1, if the current polarization state exceeds a reasonable range, compensation is started, firstly, the FPGA adds a jitter voltage D to the FPGA, a new error value E2 is calculated through feedback, then the gradient Grad is calculated as E2-E1 according to the error value, and then the gradient Grad is calculated as E2-E1 according to the error valueVi＝r(ViD) + τ x (E2-E1) apply a new voltage to the polarization controller until the error value reaches a reasonable range.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.

Claims (4)

1. A wavelength division multiplexing polarization compensation apparatus comprising:
a conjugate reference light module for outputting conjugate reference light;
the dense wavelength division multiplexer is used for combining the two beams of conjugate reference light to an optical fiber channel;
the electric control polarization controller is used for changing the polarization state of the conjugate reference light on the optical fiber channel to form conjugate polarized light and outputting the conjugate polarized light;
the optical circulator is used for enabling the conjugate polarized light output from the electric control polarization controller to be output to the receiving end dense multiplexer according to a specified port;
a dense multiplexer for separating the conjugate polarized light output from the optical circulator;
the polarization detection module is used for respectively detecting the polarization states of the two beams of conjugate polarized light output by the dense multiplexer;
the control module is used for compensating the polarization state of the electric control polarization controller according to the detected polarization state, so that the polarization state of the conjugate reference light output by the electric control polarization controller is in a preset compensation range;
wherein the conjugate reference light output module comprises: a 2 x 2 polarization-maintaining polarization beam splitter, faraday rotator;
the 2 x 2 polarization-maintaining polarization beam splitter has two input ports and two output ports, the 2 x 2 polarization-maintaining polarization beam splitter is used for receiving reference light, one output port is connected with the Faraday rotator, and the reference light output from the Faraday rotator and the reference light output from the other output port of the 2 x 2 polarization-maintaining polarization beam splitter form conjugate reference light.
2. The WDM polarization compensation apparatus of claim 1, wherein the polarization detection module comprises:
the system comprises two polarization detectors respectively connected with the output ends of the dense multiplexer, two multiplexing subtraction circuits respectively connected with the two polarization detectors, and two A/D conversion modules respectively connected with the two multiplexing subtraction circuits, wherein the output ends of the two A/D conversion modules are connected with a control module.
3. The WDM polarization compensation apparatus of claim 2, wherein the compensation method of the control module comprises the steps of:
step 1, after receiving the signals converted by the two A/D conversion modules, the control module converts the signals into signals according to a formula V1 a AD1+ b; acquiring voltage values corresponding to different a/D signals by using V2 ═ a × AD2+ b, wherein the voltage values corresponding to the a/D conversion module 1 are V10, V11, V12 and V13; the voltage values corresponding to the A/D conversion module 2 are V20, V21, V22 and V23;
step 2, calculating Stokes parameter values S10, S11, S20 and S22 corresponding to the current voltage value according to the voltage value corresponding to the A/D signal and the M matrix corresponding to different wavelengths given by the polarization detection module; the calculation formula is as follows: m is V;
and 3, carrying out normalization processing on the Stokes parameter values in the following processing mode:
SS1＝S11/S10、SS2＝S22/S20；
step 4, calculating the difference value E11 between the current normalized Stokes parameter and the target Stokes parameters sst1 and sst2 to be sst1-SS1 and E22 to be sst2-SS 2; and applying the sum of the two differences E-E11 + E22, comparing the difference sum with the set range Ethr, and compensating if the difference sum exceeds the range;
step 5, when compensation is carried out, firstly, the meter is measuredThe calculated value of E is stored in E1, and the control module applies a dithering voltage D, i.e. V, to the electrically controlled polarization controlleri＝Vi+ D, controlling the electric polarization controller to generate slight shake, calculating the deviation E value through the steps, storing the value in E2, calculating the gradient value grad which is E2-E1, and calculating the formula Vi＝r(Vi-D) + τ x (E2-E1) to obtain updated voltage values, controlling the electric polarization controller until the polarization state is compensated to a suitable range;
and 6, repeating the steps 1 to 5 to ensure that the polarization state is within the set range.
4. A method of wavelength division multiplexing polarization compensation, comprising the steps of:
step S1, two beams of reference light with different wavelengths sent by a reference light emitting module pass through a conjugate reference light module to output two beams of conjugate reference light, the two beams of conjugate reference light are demultiplexed by a dense wavelength division multiplexer, an electric control polarization controller, an optical circulator and a dense multiplexer in sequence, and then polarization states of the two beams of conjugate polarized light are respectively detected by a polarization detection module;
step S2, the polarization detection module outputs the detected polarization information into four paths of analog voltage signals, the four paths of voltage signals pass through a multiplexing subtraction circuit and then respectively pass through an A/D conversion module 1 and an A/D conversion module 2, then digital information is sent to a control module FPGA, and the control module FPGA synchronously reads data signals of the A/D conversion module 1 and the A/D conversion module 2;
step S3, after the control module FPGA receives the A/D signal, according to the formula V1 a AD1+ b; acquiring voltage values corresponding to different a/D signals by using V2 ═ a × AD2+ b, wherein the voltage values corresponding to the a/D conversion module 1 are V10, V11, V12 and V13; the voltage values corresponding to the A/D conversion module 2 are V20, V21, V22 and V23;
step S4, calculating Stokes parameter values S10, S11, S20 and S22 corresponding to the current voltage value according to the voltage value corresponding to the A/D signal and the M matrix corresponding to different wavelengths given by the polarization detection module; the calculation formula is as follows: m is V;
step S5, the Stokes parameter value is normalized in the following way:
SS1＝S11/S10、SS2＝S22/S20；
step S6, calculating the difference value E11-sst 1-SS1 and E22-sst 2-SS2 between the current normalized Stokes parameter and the target Stokes parameters sst1 and sst 2; and applying the sum of the two differences E-E11 + E22, comparing the difference sum with the set range Ethr, and compensating if the difference sum exceeds the range;
step S7, when compensation is carried out, the calculated E value is stored in E1, and then the control module FPGA adds a dithering voltage D, namely V, to the electric control polarization controlleri＝Vi+ D, controlling the electric polarization controller to generate slight shake, calculating the deviation E value through the steps, storing the value in E2, calculating the gradient value grad which is E2-E1, and calculating the formula Vi＝r(Vi-D) + τ x (E2-E1) to obtain updated voltage values, controlling the electric polarization controller until the polarization state is compensated to a suitable range;
and step S8, repeating the steps S1 to S7 to ensure that the polarization state is within the set range.
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