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

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

Technical Field

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

Background

Compared with the traditional communication technology, the quantum communication has the advantages of large information transmission capacity, absolute safety of information transmission, high transmission rate and the like, and is the quantum secret communication technology based on quantum key distribution, which is the fastest in development and the strongest in practicability in the quantum communication, and is focused on industries such as military, national defense, aerospace, banks and the like in recent years. The quantum key distribution is based on the principle of the Hessenberg uncertainty in quantum mechanics, the basic principle of quantum state unclonability, a shared key is established between a sending end and a receiving end, and a one-time-pad encryption mode is utilized to realize the unconditional security characteristic in the real sense.

The existing quantum key distribution system mainly adopts a coding mode comprising polarization coding and phase coding, and the quantum key distribution system utilizing photon polarization coding has the advantage of high key generation efficiency, and the polarization coding mode generally uses two groups of light with orthogonal polarization states for coding, namely, horizontal polarization state |H >, vertical polarization state |V >, 45-degree polarization state|++, and 135-degree polarization state|- > for coding. In an ideal single-mode optical fiber, an optical signal exists in the form of mutually perpendicular linear polarization modes, the two mutually perpendicular polarization modes have the same transmission constant, the coupled polarization states are not affected in the transmission process, but because the common optical fiber is easy to generate a double refraction effect caused by stress, temperature, polarization effect or manufacturing defects of the optical fiber, the polarization states of communication photons transmitted in a channel can be randomly changed, for example, the signal source transmits light with horizontal polarization state |H >, the polarization state is easy to change after the light is transmitted through a common optical path, and the light received by a receiving end can not be in the horizontal polarization state any more, so that polarization information is lost.

Disclosure of Invention

In view of this, the purpose of the present application is to overcome the defects in the prior art, and provide a transmitting device and a receiving device of a wavelength division multiplexing polarization compensation system, which use a group of weak light narrow pulse conjugated polarized light with the same wavelength as a reference light, so as to avoid the problem that different wavelength reference light is affected differently by the channel to different polarization state changes, reduce the influence of the scattering noise of the reference light on the signal light detection, reduce the error rate of the system and realize real-time polarization compensation.

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

In an alternative embodiment, the polarization encoder comprises a transmitting-end beam splitter, an optical retarder, 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.

In an alternative embodiment, the method 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.

In a second aspect, the present invention provides a receiving apparatus of a wavelength division multiplexing polarization compensation system, including a demultiplexing 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;

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

In an alternative embodiment, the first receiving module includes a receiving-side first manual polarization controller, a receiving-side 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 receiving end 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.

In an alternative embodiment, the first polarizing beam splitter and the second polarizing beam splitter are 2 x 2 polarizing beam splitters of the same type, a second port of the first polarizing beam splitter is used for inputting fast axis aligned polarized light, and a fourth port of the first polarizing beam splitter is used for outputting the fast axis aligned 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.

In an alternative embodiment, the system further comprises an electric polarization controller, and the control module comprises 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.

In an alternative embodiment, the polarization compensation operation includes 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 one of two mutually perpendicular axes on a certain polarized light winding buna ball to rotate 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 the error rate threshold range, if not, calculating and 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 to carry out compensation again until the compensated total distance value reaches the error rate threshold range.

Step S6: 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 error rate threshold range.

In a third aspect, the present invention provides a wavelength division multiplexing polarization compensation system, comprising a transmitting device according to any one of the preceding embodiments and a receiving device according to any one of the preceding embodiments.

In a fourth aspect, the present invention provides a quantum key distribution system comprising a wavelength division multiplexing polarization compensation system according to the previous embodiments.

The transmitting device and the receiving device of the wavelength division multiplexing polarization compensation system provided by the invention have the beneficial effects that:

the transmitting device and the receiving device of the wavelength division multiplexing polarization compensation system of the invention avoid the problem that the reference light with different wavelengths is affected differently by the change of the polarization state in the optical fiber channel by adopting a group of conjugate state reference light with the same wavelength, and adopt a group of brand new output methods, namely a Faraday rotator and an optical delay device to prepare the conjugate state, adopt a weak light narrow pulse modulation mode to reduce the value of the reference light energy, reduce the influence of the scattering noise of the reference light on the detection of the signal light, and maintain high compensation rate by the detection compensation method in the receiving device, thereby realizing the real-time monitoring and compensation of the polarization state, and further reducing the error rate of the system to realize stable operation.

Drawings

In order to more clearly illustrate the technical solutions of the present invention, the drawings that are required for the embodiments will be briefly described, it being understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope of the present invention. Like elements are numbered alike in the various figures.

Fig. 1 shows a schematic diagram of a transmitting 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 Description

The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments.

The components of the embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of the embodiments of the invention, as presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be made by a person skilled in the art without making any inventive effort, are intended to be within the scope of the present invention.

The terms "comprises," "comprising," "including," or any other variation thereof, are intended to cover a specific feature, number, step, operation, element, component, or combination of the foregoing, which may be used in various embodiments of the present invention, and are not intended to first exclude the presence of or increase the likelihood of one or more other features, numbers, steps, operations, elements, components, or combinations of the foregoing.

Furthermore, the terms "first," "second," "third," and the like are used merely to distinguish between descriptions and should not be construed as indicating or implying relative importance.

Unless otherwise defined, all terms (including technical 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 invention belong. Terms such as those defined in commonly used dictionaries will be interpreted as having a meaning that is the same as the context of the relevant art and will not be interpreted as having an idealized or overly formal sense unless expressly so defined herein in connection with the various embodiments of the invention.

Example 1

Referring to fig. 1, the present embodiment provides a transmitting apparatus 10 of a wdm polarization compensation system, which includes a reference optical transmitting module 110, a signal optical transmitting module 120, and a wdm module 130.

In one embodiment, as shown in fig. 2, the reference light transmitting module 110 includes a laser LD, an intensity modulator IM, a polarization encoder 101, and an attenuator ATT, which are connected in this order; the laser LD is used for generating continuous polarized light, and the intensity modulator IM is used for modulating the amplitude of the continuous polarized light to obtain narrow pulse polarized light; the polarization encoder 101 is configured to process the narrow pulse horizontal polarized light and output a set of narrow pulse conjugated polarized light with the same wavelength; the attenuator ATT 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 120 is configured to transmit a signal light signal; the wavelength division multiplexing module 130 is configured to perform wavelength division multiplexing on the reference optical signal and the signal optical signal, so as to obtain a wavelength division multiplexed optical signal. The wavelength division multiplexed optical signal may be output to a receiving apparatus of the wavelength division multiplexed polarization compensation system through a fiber channel, and in general, the fiber channel may be a disk fiber of km class.

Due to the influence of experimental environment, a slight shift may occur when preparing the conjugate reference light, which affects the polarization compensation operation of the receiving device, and in order to more precisely adjust the conjugate state of the reference light, the polarization encoder 101 includes, for example, a transmitting-side beam splitter BS1, an optical retarder ODL, a transmitting-side manual polarization controller PC11, a transmitting-side faraday rotator FR1, and a coupler BS2. Illustratively, the optical signal passes through the transmitting-end manual polarization controller PC11 before entering the transmitting-end faraday rotator FR1, so that the conjugate state of the reference light can be more accurately adjusted, and the value received by the detector in the receiving device is more stable. Alternatively, the transmitter manual polarization controller PC11 and the transmitter faraday rotator FR1 may be connected by a fixed attenuation head.

The first end of the transmitting end beam splitter BS1 is connected to the output end of the intensity modulator IM, the second end of the transmitting end beam splitter BS1 is connected to the input end of the transmitting end manual polarization controller PC11, and the third end of the transmitting end beam splitter BS1 is connected to the input end of the optical delay device ODL. The output end of the transmitting-end manual polarization controller PC11 is connected to the first end of the coupler BS2 through the transmitting-end faraday rotator FR1, the second end of the coupler BS2 is connected to the output end of the optical delay device ODL, and the third end of the coupler BS2 is connected to the attenuator ATT.

The narrow pulse polarized light is split into a first reference light and a second reference light at the transmitting end by the transmitting end beam splitter BS 1: after the polarization state of the first reference light is adjusted by the transmitting-end manual polarization controller PC11, the polarization state of the first reference light is rotated by 45 degrees by the transmitting-end Faraday rotator FR1 and then enters 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 set of narrow pulse conjugated polarized light of the same wavelength through the coupler BS 2. Optionally, the polarization state of the first reference light is 45 °, and the optical delayer ODL delays the second reference light, that is, the 0 ° polarized light, where the first reference light and the second reference light are conjugate states (45 °, 0 °) that are distinguished in the time domain, and the 45 ° polarized light is the front 0 ° polarized light and the rear 0 ° polarized light. Alternatively, the second reference light may be delayed by a fixed polarizing fiber.

In one embodiment, the transmitting device 10 of the wdm polarization compensation system includes a pulse signal generator SS connected to the intensity modulator IM, for controlling the intensity modulator IM to amplitude modulate the continuous polarized light signal output from the laser LD, so as to obtain a narrow pulse polarized light signal.

The embodiment adopts a group of conjugate state reference lights with the same wavelength, avoids the problem that the reference lights with different wavelengths are affected differently by polarization state changes in the optical fiber channel, adopts a group of brand-new output methods, namely a manual polarization controller, a Faraday rotator and an optical delay device ODL to prepare the conjugate state, adopts a weak light narrow pulse modulation mode to reduce the reference light energy value, and reduces the influence of reference light scattering noise on signal light detection.

Example 2

Referring to fig. 2, the receiving device 20 of the wdm polarization compensation system includes a de-wdm 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 configured to perform wavelength division multiplexing on the wavelength division multiplexed optical signal from the transmitting device 10 of the polarization compensation system to obtain the reference optical signal and the signal optical 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 configured to split the reference light into a first reference light and a second reference light at a receiving end; the first receiving module 221 and the second receiving module 222 are respectively configured to detect and count the first reference light and the second reference light, and output the detection result to the control module.

The signal light receiving module 230 is configured to receive 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.

As shown in fig. 2, the first receiving module 221 includes a receiving end first manual polarization controller PC21, a receiving end faraday rotator FR2, a first polarization beam splitter PBS1, and a first single photon detector SPD1; the second receiving module 222 comprises a receiving end second manual polarization controller PC22, a second polarization beam splitter PBS2, and a second single photon detector SPD2; the first polarizing beam splitter PBS1 and the second polarizing beam splitter PBS2 each include a first port, a second port, a third port, and a fourth port.

The first end of the receiving-end beam splitter BS3 is configured to receive the reference optical signal output by the wavelength division demultiplexing module 210, the second end of the receiving-end beam splitter BS3 is connected to the input end of the receiving-end first manual polarization controller PC21, and the third end of the receiving-end beam splitter BS3 is connected to the input end of the receiving-end second manual polarization controller PC 22; the output end of the receiving end first manual polarization controller PC21 is connected with a second port a12 of the first polarization beam splitter through a receiving end Faraday rotator FR2, and a fourth port a14 of the first polarization beam splitter is connected with the first single photon detector SPD1; the output end of the receiving end second manual polarization controller PC22 is connected with the first port a21 of the second polarization beam splitter, and the third port a23 of the receiving end second polarization beam splitter is connected with the second single photon detector SPD 2.

The first reference light enters the second port a12 of the first polarization beam splitter after the polarization state of the first reference light is rotated by 45 ° through the first manual polarization controller PC21 at the receiving end and the faraday rotator FR2 at the receiving end, and the first single photon detector SPD1 is used for selecting and detecting and counting the optical signals output from the fourth port a14 of the first polarization beam splitter, so as to obtain a first detection result. After passing through the receiving end second manual polarization controller PC22, the second reference light enters the first port a21 of the second polarization beam splitter, and the second single photon detector SPD2 is configured to select and detect and count the optical signal output by the third port a23 of the second polarization beam splitter, so as 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.

For example, after the optical signal passes through the beam splitter BS3 at the receiving end, the upper path and the lower path are conjugate state reference light (45 ° and 0 °) distinguished in the time domain, the first reference light at the receiving end rotates the polarization state by 45 ° through the faraday rotator after the polarized light at the first 0 ° is polarized light at the first 0 °, the first reference light at the receiving end is polarized light at (90 ° and 45 °), and the second reference light at the receiving end is polarized light at (45 ° and 0 °). The first reference light enters the second port a12 of the first polarization beam splitter, 90 ° polarized light is transmitted and output from the fourth port a14 of the first polarization beam splitter, 45 ° polarized light is output from the third port and the fourth port of the first polarization beam splitter PBS1 respectively in a ratio of 1:1, the first single photon detector SPD1 scans two peaks in one period at the fourth port a14 of the first polarization beam splitter, the front peak represents the photon number of the light with larger photon number, namely 90 ° polarized light, the rear peak represents the photon number of the light with 45 ° polarized light, the detector can be arranged to select a 90 ° peak signal to output to the FPGA, and 90 ° polarized light photon number signal in the receiving device can be obtained as a first detection result, namely, 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 sweep two peaks from the third port a23 of the second polarization beam splitter in one period, the front peak represents the photon number of 45 ° polarized light, the back peak is the photon number of 0 ° polarized light, and the detector can be set to select a 0 ° polarized light peak signal, that is, the second detection result, to output to the FPGA.

Optionally, the first polarizing beam splitter PBS1 and the second polarizing beam splitter PBS2 are 2 x 2 polarizing beam splitters of the same type. Wherein the second port a12 of the first polarization beam splitter is used for inputting the fast axis alignment polarized light, and the fourth port a14 of the first polarization beam splitter is used for outputting the fast axis alignment polarized light; the first port a21 of the second polarization beam splitter is used for inputting the slow axis alignment polarized light, and the third port a23 of the second polarization beam splitter is used for outputting the slow axis alignment polarized light.

As shown in fig. 2, the receiving device 20 of the wavelength division multiplexing polarization compensation system optionally further comprises an electric polarization controller EPC, and the control module comprises a programmable gate array module FPGA.

The optical input end of the electric polarization controller EPC is used for receiving the wavelength division multiplexing optical signals, 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 data output ends of the first single photon detector SPD1 and the second single photon detector SPD 2. The single photon detector is in a gating mode, can realize time delay scanning and count received quantum optical signals in different time periods, and can transmit the counted value to the programmable gate array module in real time, and the FPGA internal program judges and controls the EPC to perform compensation operation.

And the programmable gate array module FPGA controls the electric polarization controller EPC to perform polarization compensation operation on the wavelength division multiplexing optical signals according to detection results output by the first single photon detector SPD1 and the second single photon detector SPD 2.

The polarization compensation operation illustratively includes the steps of:

step S1: the first single photon detector and the second single photon detector select photon number signals to be detected and send the photon number signals to a programmable gate array (FPGA) module, and the FPGA module selects the target photon number signals with accumulated counting period to obtain current photon number signals 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 FPGA performs difference between the current photon number signal and the intermediate value of the photon number obtained by testing when the polarization state of the selected reference light is correctly received to obtain a difference value, and the binary intermediate value corresponding to the data control bit of the programmable gate array module FPGA performs sum or difference with the difference value to obtain a binary value corresponding to the current photon number signal; the binary value corresponding to the current photon number signal and the binary value corresponding to the intermediate value are subjected to difference to obtain a distance value;

Typically, the FPGA may utilize a phase locked loop to provide a photon counting clock with a period of 1ms by means of an internal 50M clock, and it is understood that the FPGA may perform subsequent program operations based on the number of photons received from the single photon detector and transmitted for a cumulative length of 1 ms. The first preset threshold may be an intermediate 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 intermediate value of the number of photons tested when the polarization state is correctly received. For example, after the two paths of optical detection accumulate photon numbers for 1ms respectively, the corresponding photon numbers and the intermediate value of the photon numbers obtained by testing when the polarization state is correctly received can be respectively differentiated, alternatively, the FPGA can include 12-bit data control bits, and the binary value corresponding to the current two paths of photon numbers can be obtained according to the binary intermediate value corresponding to the FPGA.

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; and comparing the total distance value with an error rate threshold value by taking the sum of the first distance value and the second distance value as a total distance value, wherein if the total distance value is smaller than the error rate threshold value, compensation operation is not needed, and if the total distance value is larger than the error rate threshold value, the electric polarization controller EPC is controlled to carry out polarization compensation.

Step S4: the EPC has controllable voltages V1, V2, V3 and V4, wherein V1, V3, V2 and V4 respectively control one of two mutually perpendicular axes on a certain polarized light winding bungaz ball to rotate so as to obtain a required polarized light signal, and when compensating a selected group of reference lights, the FPGA 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 the error rate threshold range, if not, calculating and 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 to carry out compensation again until the compensated total distance value reaches the error rate threshold range.

Step S6: 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 error rate threshold range.

It will be appreciated that the polarization state may not be compensated within the required bit error rate after one dithering by the electric polarization controller EPC, and for example, when one dithering is performed, if the compensated polarization state is further from the preset threshold value, the polarization compensation operation needs to be performed again by replacing the axis controlled by the electric polarization controller EPC. In general, the reference light and the signal light have different wavelengths, and when the wavelengths differ by no more than 0.8nm, the polarization compensation of the reference light and the signal light in the channel output by the electric polarization controller EPC can be controlled according to the detection result of the single photon detector.

It should be noted that, in the present invention, the polarization control time set by the FPGA internal control program should be less than the polarization change time, and if the polarization control time is greater than the polarization change time, the system will continuously perform compensation control, so that the encoding cannot be performed.

Alternatively, the first single photon detector SPD1 and the second single photon detector SPD2 may be connected to a pulse signal generator SS in the transmitting device 10 of the wavelength division multiplexing polarization compensation system, where the pulse signal generator SS may be configured to provide clock frequencies for the first single photon detector and the second single photon detector. It will be appreciated that the pulse signal generator SS provides a frequency pulse signal to the intensity modulator IM to produce a frequency pulse light, and simultaneously provides a clock frequency to the single photon detector, so that the single photon detector can receive and select optical signals with different polarization states in one period when performing time-lapse scanning positioning while maintaining clock homology between the transmitting device and the receiving device.

For example, as shown in fig. 3, the signal generator SS may be connected to the intensity modulator IM in the transmitting device of the wdm polarization compensation system, and transmit a pulse signal of 250M for the intensity modulator IM, for modulating the laser LD continuously to pulse light of 250M, and the signal generator SS simultaneously transmits a signal of 10M to the first and second single photon detectors, and the detection frequency of the single photon detector is 1.25GHZ. Alternatively, the signal generator SS and the single photon detector may be connected by a cable. In another embodiment, it can be understood that, because the cable transmission distance is very short in practical application, it is preferable that the signal generator SS can be connected to the single photon detector through two photoelectric converters by using an optical cable, wherein the signal sent by the signal generator SS to the single photon detector is first converted into an optical signal by using the first photoelectric converter PT1, the signal is transmitted through an optical fiber, and then the optical signal is converted into an electrical signal by using the second photoelectric converter PT2 and sent to the detector.

In this embodiment, the polarization state compensation is performed on a group of conjugate reference lights with the same wavelength by the de-wavelength multiplexing module 210, the reference light receiving module 220, the signal light receiving module 230 and the control module, and by the electric polarization controller EPC, the problem that the different wavelength reference lights are affected differently by the change of the polarization state in the optical fiber channel is avoided, the high compensation rate can be maintained, the real-time monitoring and compensation of the polarization state can be realized, and thus the error rate of the system can be reduced to realize the stable operation of the system.

Referring to fig. 3, the present invention provides a polarization compensation system 1 for wavelength division multiplexing, which includes a transmitting device and a receiving device according to the foregoing embodiments.

The invention also provides a quantum key distribution system comprising the wavelength division multiplexing polarization compensation system 1 according to the previous embodiment.

In the several embodiments provided in this application, it should be understood that the disclosed apparatus and method may be implemented in other manners as well. The apparatus embodiments described above are merely illustrative, for example, of the flow diagrams and block diagrams in the figures, which illustrate the architecture, functionality, and operation of possible implementations of apparatus, methods and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). 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 shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems which perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.

In addition, functional modules or units in various embodiments of the invention may be integrated together to form a single part, or the modules may exist alone, or two or more modules may be integrated to form a single part.

The functions, if implemented in the form of software functional modules and sold or used as a stand-alone product, may be stored on a computer readable storage medium. Based on such understanding, the technical solution of the present invention may be embodied essentially or in a part contributing to the prior art or in a part of the technical solution in the form of a software product stored in a storage medium, comprising several instructions for causing a computer device (which may be a smart phone, a personal computer, a server, a network device, or the like) to perform all or part of the steps of the method of the embodiments of the present invention. And the aforementioned storage medium includes: a U-disk, a removable hard disk, a Read-Only Memory (ROM), a random access Memory (RAM, random Access Memory), a magnetic disk, or an optical disk, or other various media capable of storing program codes.

The foregoing is merely illustrative embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily think about variations or substitutions within the technical scope of the present invention, and the invention should be covered.

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.