An adaptive deviation correction and compensation polarization coding quantum key distribution system

Abstract

The present invention discloses a polarization-coded quantum key distribution system with adaptive deviation correction and compensation. The light source generates quantum light and deviation correction reference light respectively, and its output end is connected to a polarization coding module. The polarization coding module is used to perform polarization coding on the quantum light and reference light generated by the light source, and then transmit them through a quantum channel to the deviation correction module at the receiving end. The deviation correction module is a module for correcting the change of channel polarization, and its output end is connected to a polarization decoding module. The polarization decoding module is used for decoding the polarization state at the receiving end, and its output end is connected to a single photon detector. The single photon detector is used for detecting the reference light, and the detection count will be sent to a polarization control module. The polarization control module is used for counting and statistically analyzing the reference light, and performing deviation correction control on the deviation correction module in real time according to the statistical result. By setting a reference light at the sending end to provide a reference for deviation correction, the use of the reference light does not occupy the quantum key distribution time of the system.

Description

Technical Field

[0001] The present invention relates to the field of quantum communication, and particularly to a polarization encoding quantum key distribution system with adaptive deviation correction and compensation. Background Art

[0002] In long-distance optical fiber communication, due to defects of the optical fiber itself, external forces, twists, and the influence of the environment and temperature on the optical fiber, etc., the polarization state transmitted in the optical fiber will change, resulting in polarization mode dispersion, and its output will no longer be the required linear polarization state, but may be an elliptical polarization state. In a polarization encoding quantum key distribution system, the degree of consistency between the received polarization state and the locally detected polarization state directly affects the final result. Therefore, a special device, that is, a deviation correction module, is required to control and compensate the received polarization state so that it can reach the most ideal state. Currently, deviation correction mainly uses the counting of quantum light or occupies the system operation time, both of which will affect the final generation of the secure key rate of the polarization encoding quantum key distribution system. Summary of the Invention

[0003] The purpose of the present invention is to overcome the deficiencies of the prior art, provide a polarization encoding quantum key distribution system with adaptive deviation correction and compensation, solve the defect that the deviation correction of the prior art will occupy the system time or use the counting of quantum light, and provide a new solution.

[0004] To achieve the above purpose, the technical solution adopted by the present invention is: a polarization encoding quantum key distribution system with adaptive deviation correction and compensation, including a sending end and a receiving end. The sending end includes a light source and a polarization encoding module; the receiving end includes a deviation correction module, a polarization decoding module, a single-photon detector, a polarization control module, and a quantum state measurement module; the light source generates quantum light and deviation correction reference light respectively, and its output end is connected to the polarization encoding module; the polarization encoding module is used to perform polarization encoding on the quantum light and reference light generated by the light source and then transmit them to the deviation correction module at the receiving end through a quantum channel;

[0005] The deviation correction module is a module for correcting the change of channel polarization, and its output end is connected to the polarization decoding module; the polarization decoding module is used for decoding the polarization state at the receiving end, and its output end is connected to the single-photon detector. The single-photon detector is used for detecting the reference light, and the detection count will be sent to the polarization control module;

[0006] The polarization control module is used for counting and statistically analyzing the reference light, and performing deviation correction control on the deviation correction module in real time according to the statistical result.

[0007] The light source uses time-division multiplexing to alternately generate quantum light and reference light in the time domain and alternately enter the subsequent polarization encoding module in the time domain.

[0008] The polarization encoding module adopts the return-to-zero code encoding method to ensure the consistency of the polarization state of the reference light; it is connected to the return-to-zero code encoding drive module, which is used to convert the encoding information into a return-to-zero code and modulate it to the corresponding voltage to drive the polarization encoding module to perform encoding.

[0009] The deviation correction control module monitors the polarization and channel attenuation changes of the channel according to the count of the reference light, and then corrects and compensates for the attenuation through the deviation correction module.

[0010] The polarization control module is connected to the light source, and is used to set and adjust the light intensity of the reference light according to the channel distance.

[0011] The light source generates the reference light and the quantum light through the reference light laser and the quantum light laser respectively. The reference light laser is connected to the optical beam splitter BS through the delay line, and the quantum light laser is connected to the optical beam splitter BS. The quantum light and the reference light are combined through BS; the delay line is used to delay the reference light to achieve time-domain multiplexing with quantum time division.

[0012] Both the quantum light and the reference light are realized by the quantum light laser. The distinction between the quantum light and the reference light is achieved by changing the driving amplitude; at the same time, the triggering frequency of the quantum light laser is doubled. Here, it refers to twice the generation frequency of the quantum light, with 1 part being the quantum light and 1 part being the reference light.

[0013] The quantum light and the reference light are realized by using the quantum light laser. The outputs of the quantum lasers are all connected to the intensity modulator, and the output end of the intensity modulator outputs the reference light and the quantum light; the intensity modulator is used to drive the intensity modulator to output the reference light and the quantum light through the alternating change of the driving amplitude.

[0014] The quantum light after being corrected by the deviation correction module is input into the optical beam splitter BS for splitting and then enters the upper and lower arms. The upper arm passes through the polarization beam splitter PBS and is then measured by the single-photon detector for the quantum light of the corresponding polarization state; the single-photon detector for reference light detection is a single-photon detector with a doubled gating frequency. The reference light detection count is time-shared and transmitted to the polarization control module, and the polarization control module implements polarization control and reference light intensity control. The detection count of the other half of the time of this single-photon detector will be used as the test result of the quantum light polarization state and enter the subsequent processing;

[0015] The lower arm passes through the quarter-wave plate and PBS and is then measured by the single-photon detector for the quantum light of the corresponding polarization state. In the polarization encoding protocol, different polarization information is loaded, and the serial numbers of the single-photon detectors reached are different. Therefore, for a randomly polarized encoded QKD system, among the four detectors at the receiving end, when the detector indicators are similar, the counting rates should also be similar. Therefore, the lower arm also needs to have detection.

[0016] When using return-to-zero coding, the polarization state of the quantum light is encoded, the polarization state of the reference light is not modulated, and the polarization state of the quantum light is kept consistent with that of the reference light.

[0017] The advantages of the present invention are as follows: In the process of quantum key distribution, a reference light with adjustable intensity is introduced, and the time-division multiplexing technology is adopted. Without occupying the system quantum key distribution time, the reference light intensity can be configured according to the single-photon counting rate at the receiving end, improving the accuracy and speed of deviation correction; in addition, the advantages of this scheme can be realized by only increasing the emission frequency of the quantum light and the gating frequency of the single-photon detector, without increasing other costs, and it is easier to promote the practical application. Brief Description of the Drawings

[0018] The following briefly describes the content expressed in each drawing of the present invention specification and the marks in the drawings:

[0019] Figure 1 It is the overall architecture diagram of the present invention scheme;

[0020] Figure 2 It is the composition diagram of the light source of the present invention;

[0021] Figure 3 It is the embodiment diagram of the light source of the present invention;

[0022] Figure 4 It is the optimal embodiment diagram of the light source of the present invention;

[0023] Figure 5 It is the optimal embodiment diagram of the light source of the present invention;

[0024] Figure 6 It is the optimal embodiment diagram of polarization decoding and measurement of the present invention;

[0025] Figure 7 It is the non-return-to-zero coding timing diagram of the present invention. Detailed Embodiment

[0026] The following further details the specific embodiments of the present invention by describing the optimal embodiments with reference to the drawings.

[0027] This patent introduces a reference light through time division. The deviation correction process not only does not occupy the system operation time, but also can adjust the reference light according to the transmission distance to achieve a better deviation correction effect. In addition, in the optimal embodiment, the system does not need to increase the hardware cost and can be directly upgraded and transformed in the existing system.

[0028] As Figure 1 shown, a polarization coding quantum key distribution scheme with adaptive deviation correction compensation in this scheme includes: a sending end and a receiving end;

[0029] The transmitting end includes a light source, a polarization encoding module, and a return-to-zero (RZ) code encoding and driving module; the receiving end includes a polarization correction module, a polarization decoding module, a single-photon detector, a polarization control module, and a quantum state measurement module.

[0030] The quantum optical signal is transmitted between the receiving end and the transmitting end through a quantum channel. The quantum channel refers to an optical fiber channel, which is used to send the encoded quantum light to the receiving end.

[0031] The light source generates quantum light and polarization correction reference light and is connected to the polarization encoding module; the polarization encoding module is connected to the RZ code encoding and driving module and the quantum channel; the RZ code encoding and driving module is connected to the polarization encoding module; the quantum channel is used to connect the transmitting end and the receiving end; the polarization correction module is connected to the quantum channel and the polarization decoding module; the polarization control module is connected to the polarization correction module and the single-photon detector; the polarization decoding module is connected to the polarization correction module, the quantum state measurement module, and the single-photon detector; the quantum state measurement module is connected to the polarization decoding module; the single-photon detector is connected to the polarization decoding module and the polarization control module;

[0032] The light source refers to the module that generates quantum light and polarization correction reference light. In a time-division manner, they enter the subsequent modules alternately in the time domain; the polarization encoding module is used for polarization state encoding at the transmitting end. In the solution, in order not to affect the polarization state of the reference light, the RZ code encoding method is adopted to ensure the consistency of the polarization state of the reference light and the counting stability of the single-photon detector used for polarization correction at the receiving end.

[0033] The RZ code encoding and driving module is used to convert the encoded information into an RZ code and modulate it to the corresponding voltage to drive the polarization encoding module; the polarization correction module refers to the module used to correct the polarization change of the channel; the polarization decoding module is used for polarization state decoding at the receiving end; the single-photon detector is a gated-mode single-photon detector, which is used for the detection of the reference light, and the detection count will be sent to the polarization control module; the polarization control module is used for counting statistics of the reference light, and based on the statistical results, it controls the polarization correction module in real time and controls the intensity of the reference light at the transmitting end. The quantum state measurement module is used for detecting the quantum light after polarization decoding and sending the detection results to the subsequent stage for key extraction.

[0034] The working principle of this application is as follows: At the light source, the quantum light and the reference light are combined in a time-division multiplexing manner and then received by the receiving end. The receiving end receives the count of the corresponding reference light, and the polarization correction control module controls the parameters of the polarization correction module according to the count quantity, so as to realize polarization correction control.

[0035] In a quantum key distribution (QKD) system based on polarization coding, due to factors such as the bending of transmission fibers, changes in ambient temperature, and uneven stress on the fibers, the polarization state of light is extremely likely to change during the transmission of quantum light. This leads to an increase in the bit error rate at the receiving end and affects the generation of the final key. This effect is more obvious in long-distance QKD systems. In the quantum channel of the QKD system, a polarization controller needs to be introduced to calibrate, i.e., correct, the polarization state of light and overcome the polarization state jitter caused by various factors during the transmission process.

[0036] The process of correcting the polarization can be regarded as an optimization process of the polarization state under the influence of multiple variables. Optimal search algorithms such as genetic algorithms, simulated annealing algorithms, ant colony algorithms, and gradient algorithms can be used.

[0037] The present invention proposes a polarization coding quantum key distribution scheme with adaptive correction compensation, which can dynamically adjust the reference light intensity and adjust the polarization of the channel in real time through a correction module. By monitoring the polarization and channel attenuation changes of the channel with time-division reference light, on the one hand, it is no longer necessary to occupy the time or counting overhead of quantum light for correction counting, and on the other hand, it can adjust the correction distortion caused by the saturation of the single-photon detector due to the small attenuation of the fiber channel and the low correction accuracy caused by the low counting of the single-photon detector due to the large attenuation of the fiber channel.

[0038] The present invention proposes a polarization coding quantum key distribution scheme with adaptive correction compensation. Due to the fiber birefringence effect, the polarization coding quantum key distribution system has poor self-adaptability to the signal environment. In the actual use of the polarization coding quantum key distribution system, in order to generate a secure key normally, a correction control needs to be added to the channel. Since the attenuation of the channel fiber varies greatly in different application scenarios and the correction process also consumes the time of the system's quantum key distribution, to solve the above problems, the present invention introduces a reference light with adjustable intensity in the process of quantum key distribution and adopts the time-division multiplexing technology. Without occupying the time of the system's quantum key distribution, the reference light intensity can be configured according to the single-photon counting rate at the receiving end, improving the accuracy and speed of correction; in addition, the advantage of this scheme is that it can be promoted for practical applications more easily without increasing other costs based on only increasing the emission frequency of quantum light and the gating frequency of the single-photon detector.

[0039] Such as Figure 1As shown in the figure, it is the overall architecture diagram of a polarization coding quantum key distribution scheme with adaptive deviation correction and compensation. The light source generates quantum light and reference light through time division multiplexing, drives the polarization coding module through return-to-zero code encoding, completes polarization coding of the quantum light, and the polarization state of the reference light remains unchanged and is consistent with one of the polarization coding states. The modulated quantum light is output from the sending end and reaches the receiving end through the quantum channel. After passing through the deviation correction module, it enters the polarization decoding module. On the one hand, the reference light is detected by a single-photon detector, and the detection result is sent to the polarization control module, which controls the polarization direction of the deviation correction module and the intensity of the reference light. On the other hand, the decoded quantum light outputs the measurement result through quantum state measurement.

[0040] As Figure 2 shown in the figure, it is the schematic diagram of the light source composition. The light source includes quantum light and reference light. The reference light is used for deviation correction at the receiving end, and the quantum light is used for secure key distribution. There is no requirement for the consistency of the intensities of the two lights. The deviation correction control module can control the intensity of the reference light emitted by the light source. Because if the channel transmission distance is long and the intensity of the reference light is weak, it will cause defects such as few counts and low deviation correction rate. Therefore, in this application, according to the distance between the receiving end and the sending end, the intensity of the reference light can be adjusted to achieve more detection counts of the reference light and improve the deviation correction efficiency.

[0041] As Figure 3 shown in the figure, it is an embodiment of the light source. The quantum light and the reference light are respectively realized by two lasers, and the purpose of time sharing is achieved through a delay line. After the quantum light and the reference light are combined by a BS, the optical pulse enters the subsequent optical device. The BS is an optical beam splitter used to achieve optical intensity splitting.

[0042] As Figure 4 shown in the figure, it is an optimal embodiment of the light source. The quantum light and the reference light are respectively realized by one laser, and the distinction between the quantum light and the reference light is achieved through the change of the driving amplitude. Moreover, in this embodiment, the triggering frequency of the laser is doubled, and the quantum light and the reference light are generated alternately. The advantage of this embodiment is that no additional devices are added and the cost is low.

[0043] As Figure 5 shown in the figure, it is an optimal embodiment of the light source. The quantum light and the reference light are respectively realized by one laser, and the triggering frequency of the laser is doubled in this embodiment, and the quantum light and the reference light are generated alternately. The distinction between the quantum light and the reference light is achieved through the change of the driving amplitude by an intensity modulator. Since the intensity modulator is usually used to modulate the decoy state in quantum key distribution, the advantage of this embodiment is also that no additional devices are added and the cost is low.

[0044] As Figure 6As shown, it is an optimal embodiment of polarization decoding and measurement. The quantum light after polarization correction at the receiving end is input into the BS. After being split, it enters the upper and lower arms. The upper arm passes through the PBS and is measured by a single-photon detector for the quantum light of the corresponding polarization state. The PBS is a polarization beam splitter. The single-photon detector (reference) is a single-photon detector with a doubled gating frequency. Since the polarization state of the reference light at the sending end is the same as that of the quantum light measured by this single-photon detector, the reference light is only detected by this single-photon detector. When the reference light detection count is distributed to the polarization control module, the polarization control and reference light intensity control are implemented by the polarization control module. The detection count of this single-photon detector in the other half of the time will enter the post-processing as the test result of the quantum light polarization state. The upper arm passes through a quarter-wave plate and a PBS and is measured by a single-photon detector for the quantum light of the corresponding polarization state. The quarter-wave plate is a birefringent single-crystal wave plate with a certain thickness. When light is incident vertically and passes through, the phase difference between the ordinary light and the extraordinary light emerging is 1 / 4 wavelength. In the optical path, it is often used to change linearly polarized light into circularly polarized light or elliptically polarized light, or vice versa. In the polarization coding protocol, different polarization information is loaded, and the serial numbers of the single-photon detectors reached are different. Therefore, for a randomly polarized-coded QKD system, among the four detectors at the receiving end, when the detector indicators are similar, the counting rates should also be similar. Therefore, the lower arm also needs to have detections.

[0045] As Figure 7 shown, it is a timing diagram of non-return-to-zero coding. The polarization state of the quantum light is encoded, and the polarization state of the reference light is not modulated. Moreover, one polarization state of the quantum light is kept the same as the polarization state of the reference light to ensure that the reference light and the quantum light of this polarization state can be detected by a single path of single-photon detector, which is convenient for the counting of the reference light.

[0046] Obviously, the specific implementation of the present invention is not limited by the above methods. As long as various non-substantive improvements are made by adopting the method concept and technical solution of the present invention, they are all within the protection scope of the present invention.

Claims

1. An adaptive deviation correction and compensation polarization-coded quantum key distribution system, characterized in that: It includes a transmitting end and a receiving end. The transmitting end includes a light source and a polarization encoding module. The receiving end includes a polarization correction module, a polarization decoding module, a single-photon detector, a polarization control module, and a quantum state measurement module. The light source generates quantum light and polarization correction reference light respectively, and its output end is connected to the polarization encoding module. The polarization encoding module is used to perform polarization encoding on the quantum light and reference light generated by the light source and then transmit them through the quantum channel to the polarization correction module at the receiving end. The polarization correction module is used to correct the change of channel polarization, and its output end is connected to the polarization decoding module. The polarization decoding module is used for polarization state decoding at the receiving end, and its output end is connected to the single-photon detector. The single-photon detector is used for the detection of the reference light, and the detection count will be sent to the polarization control module. The polarization control module is used for counting and statistics of the reference light, and performs polarization correction control on the polarization correction module in real time according to the statistical result. The polarization control module is connected to the light source, and the polarization control module is used to set and adjust the light intensity of the reference light according to the channel distance.

2. The adaptive deviation correction and compensation polarization-coded quantum key distribution system according to claim 1, characterized in that: The light source uses time-division multiplexing to alternately generate quantum light and reference light in the time domain and enter the next-stage polarization encoding module alternately in the time domain.

3. The adaptive deviation correction and compensation polarization-coded quantum key distribution system according to claim 2, characterized in that: The polarization encoding module adopts the return-to-zero code encoding method to ensure the consistency of the polarization state of the reference light. It is connected to the return-to-zero code encoding driving module, and the return-to-zero code encoding driving module is used to convert the encoding information into a return-to-zero code and modulate it to the corresponding voltage to drive the polarization encoding module to perform encoding.

4. The adaptive deviation correction and compensation polarization-coded quantum key distribution system according to any one of claims 1-3, characterized in that: The polarization control module monitors the polarization and channel attenuation changes of the channel according to the count of the reference light, and then corrects and compensates the attenuation through the polarization correction module.

5. The adaptive deviation correction and compensation polarization-coded quantum key distribution system according to any one of claims 1-3, characterized in that: The light source generates reference light and quantum light respectively through a reference light laser and a quantum light laser. The reference light laser is connected to an optical beam splitter BS through a delay line, and the quantum light laser is connected to the optical beam splitter BS. The quantum light and the reference light are combined through the BS. The delay line is used to delay the reference light so as to realize time-domain multiplexing with quantum time division.

6. The adaptive deviation correction and compensation polarization-coded quantum key distribution system according to any one of claims 1-3, characterized in that: Both the quantum light and the reference light are realized through a quantum light laser, and the distinction between the quantum light and the reference light is realized by the change of the driving amplitude. At the same time, the triggering frequency of the quantum light laser is doubled.

7. The adaptive deviation correction and compensation polarization-coded quantum key distribution system according to claim 6, characterized in that: A quantum light laser is used to realize the quantum light and the reference light. The output end of the quantum light laser is connected to an intensity modulator, and the output end of the intensity modulator outputs the reference light and the quantum light. The intensity modulator is used to realize the output of the reference light and the quantum light by alternately changing the driving amplitude.

8. The adaptive deviation correction and compensation polarization-coded quantum key distribution system according to any one of claims 1-3, characterized in that: The quantum light after being corrected by the polarization correction module enters the optical beam splitter BS for splitting and then enters the upper and lower arms. The upper arm passes through a polarization beam splitter PBS and then the single-photon detector measures the quantum light with the corresponding polarization state. The single-photon detector for reference light detection is a gated single-photon detector with a doubled frequency. The reference light detection count is time-division transmitted to the polarization control module, and the polarization control module implements polarization control and reference light intensity control. The detection count of the other half of the time of this single-photon detector will enter the post-stage processing as the test result of the quantum light polarization state. The lower arm passes through a quarter-wave plate and a PBS, and then the single-photon detector measures the quantum light with the corresponding polarization state.

9. The adaptive deviation correction and compensation polarization-coded quantum key distribution system according to any one of claims 1-3, characterized in that: When using return-to-zero coding, the polarization state of the quantum light is encoded, the polarization state of the reference light is not modulated, and the polarization state of the quantum light is kept consistent with that of the reference light.

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