CN113572562B - Transmitting device and receiving device of wavelength division multiplexing polarization compensation system - Google Patents

Abstract

The embodiment of the invention discloses a transmitting device and a receiving device of a wavelength division multiplexing polarization compensation system, wherein the transmitting device comprises: a reference light transmitting module, a signal light transmitting module and a wavelength division multiplexing module; the reference light transmitting module is used for preparing a group of weak light narrow pulse conjugated polarized light as a reference light signal; the signal light transmitting module is used for transmitting a signal light signal; the wavelength division multiplexing module is used for obtaining a wavelength division multiplexing optical signal after the reference optical signal and the signal optical signal are subjected to wavelength division multiplexing. The embodiment of the invention avoids the problem that reference light with different wavelengths is affected differently by polarization state change in the optical fiber channel by adopting two non-orthogonal polarization state reference lights with the same wavelength, reduces the influence of noise of the reference light on signal light detection by setting the reference light as single photon magnitude, and can keep high compensation rate operation of a system, reduce the error rate of the system and realize stable operation by providing a novel real-time detection compensation algorithm in a receiving device.

Description

Sending device and receiving device of wavelength division multiplexing polarization compensation system

technical field

The invention relates to the field of quantum communication, in particular to a sending device and a receiving device of a wavelength division multiplexing polarization compensation system.

Background technique

Compared with traditional communication technology, quantum communication has the advantages of large information transmission capacity, absolute security of information transmission and high transmission rate. It is the fastest-growing and most practical quantum secret communication based on quantum key distribution in quantum communication. Technology, in recent years by the military, national defense, aerospace, banking and other industries focus. Quantum key distribution is based on Heisenberg's uncertainty principle in quantum mechanics and the basic principle of quantum state unclonability. A shared key is established between the sending end and the receiving end, and the "one-time secret" encryption method is used to realize the true meaning. unconditional safety property.

At present, the coding methods mainly used in the quantum key distribution system include polarization coding and phase coding. The quantum key distribution system using photon polarization coding has the advantage of high key generation efficiency. The polarization coding method usually uses two sets of light To encode, that is, use the horizontal polarization state |H>, vertical polarization state |V>, 45° polarization state |+> and 135° polarization state |-> to implement encoding. In an ideal single-mode fiber, the optical signal exists in the form of mutually perpendicular linear polarization modes, and the two mutually perpendicular polarization modes have the same transmission constant, and the coupled polarization state will not be affected during transmission. However, ordinary optical fibers are prone to birefringence effects caused by various factors such as stress, temperature, polarization effects, or defects in the fiber itself, which will lead to random changes in the polarization state of communication photons transmitted in the channel, such as signal sources sending horizontally polarized State |H>, the polarization state is easy to change after being transmitted through the ordinary optical path, and the light received by the receiving end may no longer be in the horizontal polarization state, so the polarization information is lost.

Contents of the invention

In view of this, the purpose of this application is to overcome the deficiencies in the prior art and provide a sending device and receiving device of a wavelength division multiplexing polarization compensation system, which uses a group of weak light narrow pulse conjugate polarized light with the same wavelength as Reference light, to avoid the problem that different wavelengths of reference light are affected by different polarization state changes of channels, reduce the influence of reference light scattering noise on signal light detection, reduce system bit error rate and realize real-time polarization compensation.

In a first aspect, the present invention provides a sending device of a wavelength division multiplexing polarization compensation system, including a reference light sending module, a signal light sending module, and a wavelength division multiplexing module;

The reference light sending module includes a laser, an intensity modulator, a polarization encoder, and an attenuator connected in sequence; the laser is used to generate continuous polarized light, and the intensity modulator is used to amplitude modulate the continuous polarized light, obtaining narrow pulse polarized light; the polarization encoder is used to process the narrow pulse polarized light and output a set of narrow pulse conjugate polarized light with the same wavelength; the attenuator is used to attenuate the narrow pulse conjugate polarized light To the single photon level, a group of weak light narrow pulse conjugate polarized light is obtained as a reference light signal;

The signal light sending module is used to send signal light signals;

The wavelength division multiplexing module is used for performing wavelength division multiplexing on the reference optical signal and the signal optical signal to obtain a wavelength division multiplexed optical signal.

In an optional embodiment, the polarization encoder includes a beam splitter at the sending end, an optical delay device, a manual polarization controller at the sending end, a Faraday rotator at the sending end, and a coupler;

The first end of the beam splitter at the sending end is connected to the output end of the intensity modulator, the second end of the beam splitter at the sending end is connected to the input end of the manual polarization controller at the sending end, and the sending end The third end of the end beam splitter is connected to the input end of the optical delay device;

The output end of the manual polarization controller at the sending end is connected to the first end of the coupler through the Faraday rotator at the sending end, and the second end of the coupler is connected to the output end of the optical delayer, The third end of the coupler is connected to the attenuator;

The narrow-pulse polarized light is divided into the first reference light and the second reference light at the sending end through the beam splitter at the sending end, and the first reference light is adjusted by the manual polarization controller at the sending end to pass through the The Faraday rotator at the sending end rotates the polarization state of the first reference light by 45°, and then enters the coupler;

The second reference light enters the coupler after passing through the optical delay device; the first reference light and the second reference light output a group of conjugated narrow pulses with the same wavelength through the coupler polarized light.

In an optional embodiment, it also includes:

The pulse signal generator is used to control the intensity modulator to perform amplitude modulation on the continuous polarized light signal output by the laser, so as to obtain a narrow pulse polarized light signal.

In a second aspect, the present invention provides a receiving device for a wavelength division multiplexing polarization compensation system, including a wavelength division multiplexing module, a reference light receiving module, a signal light receiving module, and a control module;

The demultiplexing module is used to demultiplex the wavelength division multiplexed optical signal from the transmitting device of the wavelength division multiplexed polarization compensation system to obtain a reference optical signal and a signal optical signal;

The reference light receiving module includes a receiving end beam splitter, a first receiving module, and a second receiving module; the receiving end beam splitter is used to divide the reference light into first reference light and second reference light at the receiving end; The first receiving module and the second receiving module are respectively used to detect and count the first reference light and the second reference light, and output the detection results to the control module;

The signal light receiving module is used to receive signal light signals;

The control module is configured to perform a polarization compensation operation on the reference optical signal according to the detection result.

In an optional embodiment, the first receiving module includes a first manual polarization controller at the receiving end, a Faraday rotator at the receiving end, a first polarization beam splitter, and a first single photon detector; the second receiving module Including a second manual polarization controller at the receiving end, a second polarization beam splitter and a second single photon detector; both the first polarization beam splitter and the second polarization beam splitter include a first port, a second port, third port and fourth port;

The first end of the beam splitter at the receiving end is used to receive the reference optical signal output by the demultiplexing module, and the second end of the beam splitter at the receiving end is connected to the first manual polarization controller at the receiving end The input end of the beam splitter at the receiving end is connected to the input end of the second manual polarization controller at the receiving end; the output end of the first manual polarization controller at the receiving end passes through the receiving end The end Faraday rotator is connected to the second port of the first polarization beam splitter, and the fourth port of the first polarization beam splitter is connected to the first single photon detector;

The output end of the second manual polarization controller at the receiving end is connected to the first port of the second polarization beam splitter, and the third port of the second polarization beam splitter at the receiving end is connected to the second single photon detector connection;

The first reference light passes through the first manual polarization controller at the receiving end and the Faraday rotator at the receiving end, rotates the polarization state of the first reference light by 45°, and then enters the first polarization beam splitter The second port of the first single photon detector is used to select and detect and count the optical signal output by the fourth port of the first polarization beam splitter to obtain the first detection result;

The second reference light enters the first port of the second polarization beam splitter after passing through the second manual polarization controller at the receiving end, and the second single photon detector is used to split the second polarization The optical signal output by the third port of the beamer is selected and detected and counted to obtain the second detection result;

The control module is configured to perform a polarization compensation operation on the reference optical signal according to the first detection result and the second detection result.

In an optional implementation manner, the first polarizing beam splitter and the second polarizing beam splitter are 2*2 polarizing beam splitters of the same type, and the second port of the first polarizing beam splitter uses For inputting the polarized light aligned with the fast axis, the fourth port of the first polarization beam splitter is used to output the polarized light aligned with the fast axis. The first port of the second polarization beam splitter is used for inputting the polarized light aligned with the slow axis, and the third port of the second polarization beam splitter is used for outputting the polarized light aligned with the slow axis.

In an optional embodiment, a motorized polarization controller is also included, and the control module includes a programmable gate array module:

The optical input end of the motorized polarization controller is used to receive the wavelength division multiplexing optical signal, and the electrical signal input end of the motorized polarization controller is connected to the programmable gate array module; the programmable gate array module respectively connected to the data output terminals of the first single photon detector and the second single photon detector;

The programmable gate array module controls the motorized polarization controller to perform a polarization compensation operation on the wavelength division multiplexed optical signal according to the detection results output by the first single-photon detector and the second single-photon detector .

In an optional implementation manner, the polarization compensation operation includes the following steps:

Step S1: The first single-photon detector and the second single-photon detector respectively select target photon number signals and send them to the programmable gate array module, and the programmable gate array module selects all The target photon number signal is obtained to obtain the current photon number signal for calculation;

Step S2: The operation includes, when selecting the current photon number signal of a set of reference light for operation, the programmable gate array module compares the current photon number signal with the polarization state of the selected reference light when it is correctly received The intermediate value of the photon number obtained by the test is made to obtain a difference value, and the binary number intermediate value corresponding to the data control bit of the programmable gate array module is summed or differenced with the difference value to obtain the current photon number signal corresponding to binary value; making a difference between the binary value corresponding to the current photon number signal and the binary value corresponding to the intermediate value to obtain a distance value;

Step S3: Perform the operation on the current photon number signals of the two groups of reference lights to obtain the first distance value and the second distance value; use the sum of the first distance value and the second distance value as the total distance value, compare the total distance value with the bit error rate threshold, if the total distance value is less than the bit error rate threshold, no compensation operation is required, and if the total distance value is greater than the bit error rate threshold, control the motorized polarization controller Perform polarization compensation;

Step S4: The motorized polarization controller has controllable voltages V1, V2, V3, and V4, wherein V1, V3, V2, and V4 respectively control a certain polarized light to rotate around one of two mutually perpendicular axes on the Poincare sphere to To obtain the required polarization state optical signal, when compensating the selected group of reference lights, the programmable gate array module controls by selecting two voltages corresponding to one axis, and according to the calculation of the selected set of reference lights corresponding to Set the jitter value for the distance value, and try jitter on different axes;

Step S5: Determine whether the total distance value after compensation reaches the threshold range of the bit error rate, if not, calculate the distance value after compensation corresponding to the selected set of reference lights, and compare the compensation The size of the distance after compensation and the distance value before compensation, if the distance value after the compensation is greater, then replace the axis described in step S4 and re-compensate until the total distance value after compensation reaches the bit error rate threshold range.

Step S6: Repeat steps S1-S5 until the polarization states of the signal light and the reference light in the wavelength division multiplexed optical signal reach the range of the bit error rate threshold.

In a third aspect, the present invention provides a wavelength division multiplexing polarization compensation system, including the sending device according to any one of the foregoing implementations and the receiving device according to any one of the foregoing implementations.

In a fourth aspect, the present invention provides a quantum key distribution system, including the wavelength division multiplexing polarization compensation system according to the foregoing implementation manner.

The beneficial effects of the sending device and the receiving device of the wavelength division multiplexing polarization compensation system provided by the present invention are:

The transmitting device and the receiving device of the wavelength division multiplexing polarization compensation system of the present invention avoid the problem that reference lights of different wavelengths are affected differently by polarization state changes in the optical fiber channel by using a group of conjugated state reference lights with the same wavelength. A brand-new output method is to prepare the conjugated state with a Faraday rotator and an optical delay device, and use a weak light narrow pulse modulation method to reduce the energy value of the reference light and reduce the influence of the reference light scattering noise on the signal light detection. Through the receiving device The detection and compensation method in this paper can maintain a high compensation rate and realize real-time monitoring and compensation of the polarization state, thereby reducing the bit error rate of the system and achieving stable operation.

Description of drawings

In order to illustrate the technical solution of the present invention more clearly, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded It is regarded as limiting the protection scope of the present invention. In the respective drawings, similar components are given similar reference numerals.

FIG. 1 shows a schematic diagram of a sending device of a wavelength division multiplexing polarization compensation system according to an embodiment of the present application;

FIG. 2 shows a schematic diagram of a receiving device of a wavelength division multiplexing polarization compensation system according to an embodiment of the present application;

Fig. 3 shows a schematic diagram of a wavelength division multiplexing polarization compensation system according to an embodiment of the present application.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention.

The components of the embodiments of the invention generally described and illustrated in the figures herein may be arranged and designed in a variety of different configurations. Accordingly, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative efforts belong to the protection scope of the present invention.

Hereinafter, the terms "comprising", "having" and their cognates that may be used in various embodiments of the present invention are only intended to represent specific features, numbers, steps, operations, elements, components or combinations of the foregoing, And it should not be understood as first excluding the existence of one or more other features, numbers, steps, operations, elements, components or combinations of the foregoing or adding one or more features, numbers, steps, operations, elements, components or a combination of the foregoing possibilities.

In addition, the terms "first", "second", "third", etc. are only used for distinguishing descriptions, and should not be construed as indicating or implying relative importance.

Unless otherwise defined, all terms (including technical terms and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which various embodiments of the present invention belong. Terms (such as those defined in commonly used dictionaries) will be construed as having the same meanings as their contextual meanings in the relevant technical field and will not be construed as having idealized or overly formal meanings, unless in Various embodiments of the invention are clearly defined.

Example 1

Referring to FIG. 1 , this embodiment provides a sending device 10 of a wavelength division multiplexing polarization compensation system, including a reference light sending module 110 , a signal light sending module 120 and a wavelength division multiplexing module 130 .

In one embodiment, as shown in FIG. 2 , the reference light sending module 110 includes a laser LD, an intensity modulator IM, a polarization encoder 101, and an attenuator ATT connected in sequence; the laser LD is used to generate continuous polarized light, and the intensity modulation The IM is used to amplitude modulate the continuous polarized light to obtain narrow pulse polarized light; the polarization encoder 101 is used to process the narrow pulse horizontally polarized light and then output a set of narrow pulse conjugate polarized light with the same wavelength; the attenuator ATT It is used to attenuate the narrow-pulse conjugate polarized light to the single-photon level, and obtain a group of weak-light narrow-pulse conjugate polarized light as a reference optical signal. The signal optical sending module 120 is used for sending the signal optical signal; the wavelength division multiplexing module 130 is used for performing wavelength division multiplexing on the reference optical signal and the signal optical signal to obtain a wavelength division multiplexed optical signal. The above-mentioned wavelength division multiplexing optical signal can be output to the receiving device of the wavelength division multiplexing polarization compensation system through the optical fiber channel. Generally, the optical fiber channel can be a disk fiber of km level.

Due to the influence of the experimental environment, a slight offset may occur when preparing the conjugated reference light, which affects the polarization compensation operation of the receiving device. In order to more accurately adjust the conjugated state of the reference light, exemplary, the above-mentioned polarization encoder 101 It includes beam splitter BS1 at the sending end, optical delayer ODL, manual polarization controller PC11 at the sending end, Faraday rotator FR1 at the sending end and coupler BS2. Exemplarily, the optical signal passes through the manual polarization controller PC11 at the transmitting end before entering the Faraday rotator FR1 at the transmitting end, so that the conjugate state of the reference light can be adjusted more precisely, and the value received by the detector in the receiving device is more stable. Optionally, the manual polarization controller PC11 at the sending end and the Faraday rotator FR1 at the sending end may be connected through a fixed attenuation head.

Wherein, the first end of the beam splitter BS1 at the sending end is connected to the output end of the intensity modulator IM, the second end of the beam splitter BS1 at the sending end is connected to the input end of the manual polarization controller PC11 at the sending end, and the beam splitter at the sending end The third terminal of BS1 is connected with the input terminal of the optical delay device ODL. The output end of the manual polarization controller PC11 at the sending end is connected to the first end of the coupler BS2 through the Faraday rotator FR1 at the sending end, the second end of the coupler BS2 is connected to the output end of the optical delay device ODL, and the second end of the coupler BS2 The three terminals are connected with the attenuator ATT.

The above-mentioned narrow pulse polarized light is divided into the first reference light and the second reference light at the sending end through the beam splitter BS1 at the sending end: after the first reference light is adjusted to the polarization state by the manual polarization controller PC11 at the sending end, it passes through the Faraday rotator FR1 at the sending end Rotate the polarization state of the first reference light by 45°, and then enter the coupler BS2; the second reference light enters the coupler BS2 after passing through the optical delay device ODL; the first reference light and the second reference light output a group through the coupler BS2 Narrow pulses of conjugate polarized light of the same wavelength. Optionally, the polarization state of the first reference light is 45°, and the optical delay device ODL delays the second reference light, that is, the 0° polarized light, and the first reference light and the second reference light are distinguished in the time domain The conjugated state (45°, 0°), where the 45° polarized light is in the front and the 0° polarized light is behind. Optionally, the second reference light may also be time-delayed through a fixed polarization fiber.

In one embodiment, the sending device 10 of the wavelength division multiplexing polarization compensation system includes a pulse signal generator SS connected to the above-mentioned intensity modulator IM, for controlling the continuous polarized light output by the above-mentioned intensity modulator IM to the laser LD The signal is amplitude modulated to obtain a narrow pulse polarized light signal.

This embodiment adopts a group of conjugate state reference lights with the same wavelength, which avoids the problem that reference lights of different wavelengths are affected by polarization state changes in the optical fiber channel. The conjugated state is prepared by using a device and an optical delay device ODL, and the weak light narrow pulse modulation method is used to reduce the energy value of the reference light, which reduces the influence of the reference light scattering noise on the signal light detection.

Example 2

Referring to FIG. 2 , the present invention provides a receiving device 20 of a wavelength division multiplexing polarization compensation system, including a wavelength division multiplexing module 210 , a reference light receiving module 220 , a signal light receiving module 230 and a control module.

In one embodiment, the demultiplexing module 210 is used to demultiplex the wavelength division multiplexed optical signal from the transmitting device 10 of the wavelength division multiplexed polarization compensation system to obtain the reference optical signal and the signal light Signal.

The reference light receiving module 220 includes a receiving end beam splitter BS3, a first receiving module 221 and a second receiving module 222; the receiving end beam splitter BS3 is used to divide the reference light into the first reference light and the second reference light at the receiving end; The first receiving module 221 and the second receiving module 222 are used to detect and count the first and second reference lights respectively, and output the detection results to the control module.

The signal light receiving module 230 is used for receiving the signal light signal; the control module is used for performing polarization compensation operation on the reference light signal according to the detection result.

Wherein, as shown in Figure 2, the first receiving module 221 includes the first manual polarization controller PC21 at the receiving end, the Faraday rotator FR2 at the receiving end, the first polarization beam splitter PBS1, and the first single photon detector SPD1; Module 222 includes a second manual polarization controller PC22 at the receiving end, a second polarization beam splitter PBS2, and a second single photon detector SPD2; both the first polarization beam splitter PBS1 and the second polarization beam splitter PBS2 include a first port , the second port, the third port, and the fourth port.

The first end of the beam splitter BS3 at the receiving end is used to receive the reference optical signal output by the demultiplexing module 210, and the second end of the beam splitter BS3 at the receiving end is connected to the input end of the first manual polarization controller PC21 at the receiving end , the third end of the beam splitter BS3 at the receiving end is connected to the input end of the second manual polarization controller PC22 at the receiving end; the output end of the first manual polarization controller PC21 at the receiving end passes through the Faraday rotator FR2 at the receiving end and connects The second port a12 of the beam splitter is connected, and the fourth port a14 of the first polarization beam splitter is connected with the first single photon detector SPD1; the output end of the second manual polarization controller PC22 at the receiving end is connected with the second polarization beam splitter connected to the first port a21 of the polarizing beam splitter, and the third port a23 of the second polarization beam splitter at the receiving end is connected to the second single photon detector SPD2.

Exemplarily, the first reference light passes through the first manual polarization controller PC21 at the receiving end and the Faraday rotator FR2 at the receiving end, rotates the polarization state of the first reference light by 45°, and then enters the second port of the first polarization beam splitter a12, the first single photon detector SPD1 is used to select and detect and count the optical signal output by the fourth port a14 of the first polarization beam splitter, and obtain a first detection result. After the second reference light passes through the second manual polarization controller PC22 at the receiving end, it enters the first port a21 of the second polarization beam splitter, and the second single photon detector SPD2 is used for the third port of the second polarization beam splitter The optical signal output by a23 is selected and detected and counted to obtain a second detection result. The control module is used to perform a polarization compensation operation on the reference optical signal according to the first detection result and the second detection result.

For example, after the optical signal passes through the beam splitter BS3 at the receiving end, the uplink and downlink are conjugate reference lights (45°, 0°) distinguished in the time domain, and the 45° polarized light is in the front and the 0° polarized light is behind. The polarization state of the first reference light at the receiving end is rotated by 45° through the Faraday rotator, the polarization state of the first reference light at the receiving end is (90°, 45°), and the polarization state of the second reference light at the receiving end is (45°, 0° ). The first reference light enters the second port a12 of the first polarizing beam splitter, the 90° polarized light will be transmitted and output from the fourth port a14 of the first polarizing beam splitter, and the 45° polarized light will be transmitted from The third and fourth port outputs of the first polarization beam splitter PBS1, the first single photon detector SPD1 will scan to two peaks in one cycle at the fourth port a14 of the first polarization beam splitter, the front peak Represents the larger number of photons, that is, the number of photons of 90° polarized light, and the later peak is the number of photons of 45° polarized light. The detector can be set to select the 90° peak signal to output to the FPGA, and the photons of 90° polarized light in the receiving device can be obtained. By taking the number signal as the first detection result, the photon number signal of the 45° polarized light sent from the sending device can be obtained. Similarly, the second single-photon detector SPD2 can scan to two peaks in one cycle from the third port a23 of the second polarization beam splitter, the front peak represents the number of photons of 45° polarized light, and the rear peak That is, the number of photons of the 0° polarized light, the detector can be set to select the peak signal of the 0° polarized light, that is, the second detection result, and output it to the FPGA.

Optionally, the first polarization beam splitter PBS1 and the second polarization beam splitter PBS2 are 2*2 polarization beam splitters of the same type. Wherein, the second port a12 of the first polarization beam splitter is used to input the fast axis aligned polarized light, and the fourth port a14 of the first polarized beam splitter is used to output the fast axis aligned polarized light; the second polarized beam splitter The first port a21 of the second polarization beam splitter is used for inputting the polarized light aligned with the slow axis, and the third port a23 of the second polarization beam splitter is used for outputting the polarized light aligned with the slow axis.

As shown in FIG. 2 , optionally, the receiving device 20 of the WDM polarization compensation system further includes an electric polarization controller EPC, and the control module includes a programmable gate array module FPGA.

Among them, the optical input end of the electric polarization controller EPC is used to receive the wavelength division multiplexing optical signal, and the electric signal input end of the electric polarization controller EPC is connected with the programmable gate array module FPGA; the programmable gate array module FPGA is respectively connected with the first The data output ends of the single photon detector SPD1 and the second single photon detector SPD2 are connected. Exemplarily, the single photon detector is in the gate control mode, which can realize time-delay scanning and count the received quantum optical signals in different time periods, and the single photon detector can transmit the count value to the programmable gate array module in real time, and the The internal program of FPGA judges and controls the electric polarization controller EPC to perform compensation operation.

According to the detection results output by the first single photon detector SPD1 and the second single photon detector SPD2, the programmable gate array module FPGA controls the electric polarization controller EPC to perform polarization compensation operation on the wavelength division multiplexed optical signal.

Exemplarily, the polarization compensation operation includes the following steps:

Step S1: Both the first and second single photon detectors select the photon number signal to be detected and send it to the programmable gate array module FPGA, and the programmable gate array module FPGA selects the target photon number signal of the cumulative counting cycle to obtain the current photon digital signal to operate.

Step S2: The operation includes, when selecting the above-mentioned current photon number signal of a set of reference light for operation, the programmable gate array module FPGA will test the current photon number signal and the polarization state of the selected reference light to obtain the photon number The difference is obtained by making a difference between the median value of the programmable gate array module FPGA, and the binary number median value corresponding to the data control bit of the programmable gate array module FPGA is summed or differenced with the difference value to obtain the binary value corresponding to the current photon number signal; the current photon number signal The binary value corresponding to the signal is subtracted from the binary value corresponding to the intermediate value to obtain the distance value;

Generally, the FPGA can use the phase-locked loop to use the internal 50M clock to provide a photon counting clock with a period of 1ms for polarization detection. It can be understood that the FPGA can perform follow-up based on the number of photons received by the single-photon detector with a cumulative length of 1ms. Program operation. Exemplarily, the above-mentioned first preset threshold may be the median value of the number of photons tested when the polarization state is correctly received, and the second preset threshold may be a binary value corresponding to the median value of the photon number tested when the polarization state is correctly received. . For example, after the two optical detections respectively accumulate the number of photons for 1 ms, the corresponding photon number can be compared with the median value of the photon number obtained when the polarization state is correctly received. Optionally, the FPGA can contain 12 data control bits , the binary value corresponding to the current two photon numbers can be obtained according to the corresponding intermediate value of the binary number.

Step S3: Carry out the above operations on the above-mentioned current photon number signals of the two groups of reference lights respectively, to obtain the first distance value and the second distance value; use the sum of the above-mentioned first distance value and the above-mentioned second distance value as the total distance value, and compare For the total distance value and the BER threshold value, if the total distance value is less than the BER threshold value, no compensation operation is required; if the total distance value is greater than the BER threshold value, the electric polarization controller EPC is controlled to perform polarization compensation.

Step S4: The motorized polarization controller EPC has controllable voltages V1, V2, V3, and V4, wherein V1, V3, V2, and V4 respectively control a certain polarized light to rotate around one of two mutually perpendicular axes on the Poincare sphere In order to obtain the required polarization state optical signal, when compensating the selected set of reference lights, the programmable gate array module FPGA controls by selecting two voltages corresponding to one axis, and the selected set of reference lights according to the calculation Set the jitter value corresponding to the distance value, and try jitter on different axes.

Step S5: Determine whether the total distance value after compensation reaches the threshold range of the bit error rate, if not, calculate the distance value after compensation corresponding to the selected set of reference lights, and compare the compensation The size of the distance after compensation and the distance value before compensation, if the distance value after the compensation is greater, then replace the axis described in step S4 and re-compensate until the total distance value after compensation reaches the bit error rate threshold range.

Step S6: Repeat steps S1-S5 until the polarization states of the signal light and the reference light in the wavelength division multiplexed optical signal reach the range of the bit error rate threshold.

It can be understood that the polarization state may not be compensated to the required bit error rate range after one jitter is controlled by the electric polarization controller EPC. If it is further away, it is necessary to replace the axis controlled by the electric polarization controller EPC and then perform polarization compensation operation. Generally, the reference light and signal light use different wavelengths. When the wavelength difference is not large, such as 0.8nm, the electric polarization controller EPC can be controlled to polarize the reference light and signal light in the channel output according to the detection result of the single photon detector. compensate.

It should be noted that the polarization control time set by the internal control program of the FPGA in the present invention should be less than the polarization change time. If it is greater than the polarization change time, the system will continue to perform compensation control, resulting in failure to code.

Optionally, the above-mentioned first single-photon detector SPD1 and second single-photon detector SPD2 can be connected with the pulse signal generator SS in the sending device 10 of the wavelength division multiplexing polarization compensation system, and the pulse signal generator SS can be used for Clock frequency is provided for the first and second single photon detectors. It can be understood that the pulse signal generator SS provides a pulse signal of a frequency to the intensity modulator IM to prepare a pulse light of a certain frequency, and at the same time provides a clock frequency to the single photon detector. When the sending device and the receiving device maintain the same clock source , the single-photon detector can receive and select optical signals of different polarization states in one cycle when performing time-lapse scanning positioning.

For example, as shown in Figure 3, the signal generator SS can be connected to the intensity modulator IM in the sending device of the wavelength division multiplexing polarization compensation system to send a pulse signal of 250M for the intensity modulator IM, which is used to convert the continuous pulse signal of the laser LD The light is modulated into 250M pulsed light, and the signal generator SS simultaneously sends 10M signals to the first and second single photon detectors, and the detection frequency of the single photon detectors is 1.25GHZ. Optionally, a cable can be used to connect the signal generator SS and the single photon detector. In another embodiment, it can be understood that since the cable transmission distance is very short in practical applications, preferably, the signal generator SS can be connected to the single photon detector through two photoelectric converters through an optical cable, wherein the signal generation The signal sent by the detector SS to the single photon detector is first converted into an optical signal by the first photoelectric converter PT1, transmitted through the optical fiber, and then converted into an electrical signal by the second photoelectric converter PT2 and sent to the detector.

In this embodiment, the polarization state compensation is performed on a group of conjugate state reference lights with the same wavelength through the demultiplexing module 210, the reference light receiving module 220, the signal light receiving module 230 and the control module, and the electric polarization controller EPC. It avoids the problem that reference lights of different wavelengths are affected differently by changes in the polarization state in the fiber channel, can maintain a high compensation rate, and realize real-time monitoring and compensation of the polarization state, thereby reducing the bit error rate of the system and realizing stable operation of the system.

Referring to FIG. 3 , the present invention provides a wavelength division multiplexing polarization compensation system 1 , including the sending device and the receiving device according to the foregoing embodiments.

The present invention also provides a quantum key distribution system, including the wavelength division multiplexing polarization compensation system 1 according to the foregoing embodiments.

In the several embodiments provided in this application, it should be understood that the disclosed devices and methods may also be implemented in other ways. The device embodiments described above are only illustrative. For example, the flowcharts and structural diagrams in the accompanying drawings show the possible implementation architecture and functions of devices, methods and computer program products according to multiple embodiments of the present invention. and operation. In this regard, each block in a flowchart or block diagram may represent a module, program segment, or portion of code that contains one or more executable instruction. It should also be noted that, in alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks in succession may, in fact, be executed substantially concurrently, or they may sometimes be executed in the reverse order, depending upon the functionality involved. It is also to be noted that each block of the block diagrams and/or flow diagrams, and combinations of blocks in the block diagrams and/or flow diagrams, can be implemented by a dedicated hardware-based system that performs the specified function or action may be implemented, or may be implemented by a combination of special purpose hardware and computer instructions.

In addition, each functional module or unit in each embodiment of the present invention can be integrated together to form an independent part, or each module can exist independently, or two or more modules can be integrated to form an independent part.

If the functions are implemented in the form of software function modules and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the essence of the technical solution of the present invention or the part that contributes to the prior art or the part of the technical solution can be embodied in the form of a software product, and the computer software product is stored in a storage medium, including Several instructions are used to make a computer device (which may be a smart phone, a personal computer, a server, or a network device, etc.) execute all or part of the steps of the methods in various embodiments of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), magnetic disk or optical disk and other media that can store program codes. .

The above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Anyone familiar with the technical field can easily think of changes or replacements within the technical scope disclosed in the present invention, and should cover all Within the protection scope of the present invention.

Claims (9)

1. A receiving device of a wavelength division multiplexing polarization compensation system is characterized by comprising a wavelength division multiplexing module, a reference light receiving module, a signal light receiving module and a control module,

the de-wavelength division multiplexing module is used for performing de-wavelength division multiplexing on the wavelength division multiplexing optical signals from the transmitting device of the wavelength division multiplexing polarization compensation system to obtain reference optical signals and signal optical signals;

the reference light receiving module comprises a receiving end beam splitter, a first receiving module and a second receiving module; the receiving end beam splitter is used for dividing the reference light into a first reference light and a second reference light of a receiving end; the first receiving module and the second receiving module are respectively used for detecting and counting the first reference light and the second reference light and outputting detection results to the control module;

the signal light receiving module is used for receiving a signal light signal;

the control module is used for carrying out polarization compensation operation on the reference light signal according to the detection result;

the first receiving module comprises a receiving end first manual polarization controller, a receiving end Faraday rotator, a first polarization beam splitter and a first single photon detector; the second receiving module comprises a receiving end second manual polarization controller, a second polarization beam splitter and a second single photon detector; the first polarizing beam splitter and the second polarizing beam splitter each comprise a first port, a second port, a third port and a fourth port;

The first end of the receiving end beam splitter is used for receiving the reference light signal output by the wavelength division demultiplexing module, the second end of the receiving end beam splitter is connected with the input end of the first manual polarization controller of the receiving end, and the third end of the receiving end beam splitter is connected with the input end of the second manual polarization controller of the receiving end; the output end of the first manual polarization controller at the receiving end is connected with the second port of the first polarization beam splitter through the Faraday rotator at the receiving end, and the fourth port of the first polarization beam splitter is connected with the first single photon detector;

the output end of the receiving end second manual polarization controller is connected with the first port of the second polarization beam splitter, and the third port of the second polarization beam splitter is connected with the second single photon detector;

the first reference light enters the second port of the first polarization beam splitter after the polarization state of the first reference light is rotated by 45 degrees through the first manual polarization controller at the receiving end and the Faraday rotator at the receiving end, and the first single photon detector is used for selecting and detecting and counting optical signals output by the fourth port of the first polarization beam splitter to obtain a first detection result;

The second reference light enters the first port of the second polarization beam splitter after passing through the second manual polarization controller at the receiving end, and the second single photon detector is used for selecting and detecting and counting optical signals output by the third port of the second polarization beam splitter to obtain a second detection result;

the control module is used for carrying out polarization compensation operation on the reference light signal according to the first detection result and the second detection result.

2. The receiving apparatus of the polarization compensation system for wavelength division multiplexing according to claim 1, wherein:

the first polarization beam splitter and the second polarization beam splitter are 2 x 2 polarization beam splitters of the same type, a second port of the first polarization beam splitter is used for inputting fast axis alignment polarized light, and a fourth port of the first polarization beam splitter is used for outputting the fast axis alignment polarized light;

the first port of the second polarizing beam splitter is used for inputting slow axis alignment polarized light, and the third port of the second polarizing beam splitter is used for outputting the slow axis alignment polarized light.

3. The apparatus of claim 1, further comprising an electric polarization controller, the control module comprising a programmable gate array module:

The optical input end of the electric polarization controller is used for receiving the wavelength division multiplexing optical signal, and the electric signal input end of the electric polarization controller is connected with the programmable gate array module; the programmable gate array module is respectively connected with the data output ends of the first single photon detector and the second single photon detector;

and the programmable gate array module controls the electric polarization controller to perform polarization compensation operation on the wavelength division multiplexing optical signals according to detection results output by the first single photon detector and the second single photon detector.

4. A receiving device of a wavelength division multiplexing polarization compensation system according to claim 3, wherein the polarization compensation operation comprises the steps of:

step S1: the first single photon detector and the second single photon detector respectively select a target photon number signal to be sent to the programmable gate array module, and the programmable gate array module selects the target photon number signal with the accumulated counting period to obtain a current photon number signal for operation;

step S2: when the current photon number signal of a group of reference light is selected for operation, the programmable gate array module makes a difference between the current photon number signal and a binary number intermediate value obtained by testing when the polarization state of the selected reference light is correctly received to obtain a difference value, and makes a sum or a difference between the binary number intermediate value corresponding to a data control bit of the programmable gate array module and the difference value to obtain a binary number value corresponding to the current photon number signal; the binary value corresponding to the current photon number signal is differenced with the binary value corresponding to the intermediate value to obtain a distance value;

Step S3: respectively carrying out the operation on the current photon number signals of the two groups of reference light to obtain a first distance value and a second distance value; taking the sum of the first distance value and the second distance value as a total distance value, comparing the total distance value with an error rate threshold value, if the total distance value is smaller than the error rate threshold value, no compensation operation is needed, and if the total distance value is larger than the error rate threshold value, controlling the electric polarization controller to perform polarization compensation;

step S4: the electric polarization controller is provided with controllable voltages V1, V2, V3 and V4, wherein V1, V3, V2 and V4 respectively control any polarized light to rotate around one of two mutually perpendicular axes on the bungaz ball so as to obtain a required polarized light signal, and when compensating a selected group of reference lights, the programmable gate array module controls the selected group of reference lights by selecting two voltages corresponding to one axis, sets a jitter value according to a distance value corresponding to the calculated selected group of reference lights, and tries to shake on different axes;

step S5: judging whether the compensated total distance value reaches an error rate threshold range, if not, calculating a group of compensated distance values corresponding to the selected reference light, comparing the distance after compensation with the distance value before compensation, and if the distance value after compensation is larger, replacing the shaft in the step S4 for compensation until the compensated total distance value reaches the error rate threshold range;

Step S6: and replacing the selected group of reference light, and repeating the steps S1-S5 until the polarization states of the signal light and the reference light in the wavelength division multiplexing optical signal reach the bit error rate threshold range.

5. A wavelength division multiplexing polarization compensation system comprising a receiving device of the wavelength division multiplexing polarization compensation system according to any one of claims 1 to 4 and a transmitting device of the wavelength division multiplexing polarization compensation system.

6. The polarization compensation system of claim 5, wherein the transmission means of the polarization compensation system comprises a reference light transmission module, a signal light transmission module, and a wavelength division multiplexing module;

the reference light transmitting module comprises a laser, an intensity modulator, a polarization encoder and an attenuator which are connected in sequence; the laser is used for generating continuous polarized light, and the intensity modulator is used for modulating the amplitude of the continuous polarized light to obtain narrow pulse polarized light; the polarization encoder is used for processing the narrow pulse polarized light and then outputting a group of narrow pulse conjugated polarized light with the same wavelength; the attenuator is used for attenuating the narrow-pulse conjugated polarized light to a single photon magnitude to obtain a group of weak light narrow-pulse conjugated polarized light serving as a reference light signal;

The signal light transmitting module is used for transmitting a signal light signal;

the wavelength division multiplexing module is used for performing wavelength division multiplexing on the reference optical signal and the signal optical signal to obtain a wavelength division multiplexing optical signal.

7. The wdm polarization compensation system of claim 6, wherein:

the polarization encoder comprises a transmitting end beam splitter, an optical delay device, a transmitting end manual polarization controller, a transmitting end Faraday rotator and a coupler;

the first end of the transmitting end beam splitter is connected with the output end of the intensity modulator, the second end of the transmitting end beam splitter is connected with the input end of the transmitting end manual polarization controller, and the third end of the transmitting end beam splitter is connected with the input end of the optical delay device;

the output end of the transmitting end manual polarization controller is connected with the first end of the coupler through the transmitting end Faraday rotator, the second end of the coupler is connected with the output end of the optical delay device, and the third end of the coupler is connected with the attenuator;

the narrow pulse polarized light is divided into a first reference light and a second reference light of a transmitting end through the transmitting end beam splitter, the polarization state of the first reference light is rotated by 45 degrees through the transmitting end Faraday rotator after the polarization state of the first reference light is adjusted through the transmitting end manual polarization controller, and then the first reference light enters the coupler;

The second reference light enters the coupler after passing through the optical delay device; the first reference light and the second reference light output a group of the narrow pulse conjugated polarized light with the same wavelength through the coupler.

8. The wdm polarization compensation system of claim 6, wherein the means for transmitting the wdm polarization compensation system further comprises:

and the pulse signal generator is used for controlling the intensity modulator to carry out amplitude modulation on the continuous polarized light signals output by the laser so as to obtain narrow pulse polarized light signals.

9. A quantum key distribution system comprising a wavelength division multiplexed polarization compensation system according to any one of claims 5 to 8.