A QKD system and a method for improving QKD coding rate

Abstract

The present invention relates to the technical field of quantum key distribution, and discloses a QKD system and a method for improving the QKD coding rate. The transmitting end of the system measures a first optical power measurement value after splitting the synchronous light beam, and sends it to the receiving end through a classical channel and performs quantum optical sequence synchronization with the receiving end through a quantum channel; the receiving end measures a second optical power measurement value after splitting the received synchronous light beam through a classical channel and calculates the difference between the two, obtains the single photon level currently entering the single photon detector based on the difference and the nominal single photon level, obtains the dead time parameter according to the single photon level and the corresponding relationship between the single photon level and the dead time parameter, and closes the gate signal within the range of the dead time parameter after each response photon detection. The present invention can automatically and accurately adjust the dead time parameter of the single photon detector of the QKD receiving end in real time, so that the QKD system can adapt to the change of channel attenuation and always maintain high coding rate performance.

Description

Technical Field

[0001] The present invention relates to the technical field of quantum key distribution, and in particular to a QKD system and a method for improving the QKD coding rate. Background Art

[0002] Existing single-photon detectors often use a dead time setting method to suppress dark counts caused by the back-pulse effect. However, if the dead time is set too large, the detection efficiency of the detector will be reduced, thereby reducing the coding rate of the QKD (quantum key distribution) system; if the dead time is set too small, the effect of suppressing the back pulse of the detector will be reduced, a large number of detector dark counts will be increased, and the bit error rate of the QKD system will increase, which will also reduce the coding rate of the QKD system. Therefore, the setting of the dead time has a great impact on the coding rate of the QKD system.

[0003] In the operating environment of a standard QKD system, a fixed intensity (single-photon level intensity) of quantum light is output from the QKD transmitter, which enters the QKD receiver after passing through the optical fiber channel and is detected and counted by the single-photon detector at the QKD receiver. In the environment of optical fiber channels with different attenuation, such as ice-covered power lines and when some lines are disturbed by external forces, the quantum light intensity entering the single-photon detector at the QKD receiver in different time periods will vary greatly due to the change in the attenuation of the optical fiber channel. Summary of the invention

[0004] In view of this, in order to solve the defect of low coding rate caused by reduced detection efficiency of the QKD system detector in the prior art, the present invention provides a QKD system and a method for improving the QKD coding rate.

[0005] In a first aspect, the present invention provides a method for improving a QKD coding rate, comprising:

[0006] The QKD transmitter is used to measure the optical power after splitting the synchronization light to obtain a first optical power measurement value, and send the first optical power measurement value to the QKD receiver through a classical channel, and synchronize the sequence number of the quantum light with the QKD receiver through a quantum channel;

[0007] The QKD receiving end is used to measure the optical power after splitting the received synchronization light through the classical channel to obtain a second optical power measurement value, calculate the difference between the second optical power measurement value and the first optical power measurement value, and obtain the single photon level currently entering the single photon detector based on the difference between the second optical power measurement value and the first optical power measurement value and the preset nominal single photon level, obtain the dead time parameter according to the single photon level currently entering the single photon detector and the preset correspondence between the single photon level and the dead time parameter, and after each response photon detection, close the gate signal within a time range of the dead time parameter.

[0008] The QKD system provided by the embodiment of the present invention can detect changes in channel attenuation in real time without the need for manual debugging and configuration of QKD system parameters, and automatically and accurately adjust the dead time parameters of the single-photon detector at the QKD receiving end, so that the QKD system can adapt to changes in channel attenuation and always maintain high coding rate performance. It can fully automatically complete the process of "status monitoring-detecting state changes-automatically adjusting to the optimal state", which can save maintenance manpower investment and reduce the professional requirements for users.

[0009] In an optional implementation, the QKD transmitter includes: a quantum light laser, a decoy state debugging module, a coding module, a quantum light attenuation module, a first optical beam splitter, a first light intensity monitoring unit, a transmitter control module, a synchronous light laser, a synchronous attenuation module and a first wavelength division multiplexing module, wherein:

[0010] The quantum light laser is a light source for generating quantum light;

[0011] The decoy state debugging module is used to perform random decoy state modulation on the quantum light generated by the quantum light laser to form quantum light with different light intensities;

[0012] The encoding module is used to load encoding information on quantum lights of different light intensities;

[0013] The quantum light attenuation module is used to attenuate the quantum light output by the encoding module to a level within the intensity of a single photon;

[0014] The synchronous light laser is a light source for generating synchronous light for time synchronization of quantum light;

[0015] The first optical beam splitter is located between the synchronous optical laser and the synchronous optical attenuation module, and is used to output the synchronous light generated by the first synchronous optical laser in two parts according to a preset ratio of light intensity;

[0016] The synchronous optical attenuation module is used to attenuate the output light intensity of one of the paths after the first optical beam splitter performs beam splitting, so that the number of pulses detected by the synchronous optical detector at the QKD receiving end is consistent with the operating frequency of the QKD receiving end;

[0017] The first light intensity monitoring unit is used to measure the optical power of another path after the first optical beam splitter splits the light to obtain a first optical power measurement value;

[0018] The transmitting end control module is used to obtain the first optical power measurement value and send it to the QKD receiving end through the classical channel, and synchronize the sequence number of the quantum light with the QKD receiving end through the quantum channel;

[0019] The first wavelength division multiplexing module is used to combine the optical signals of different wavelengths of the two lasers of synchronization light and quantum light at the QKD transmitting end into the same optical fiber for transmission in the quantum channel.

[0020] In an optional implementation, the transmitting end control module includes: a first light intensity acquisition unit and a first main control unit, wherein:

[0021] The first light intensity acquisition unit is used to acquire a first optical power measurement value from the first light intensity monitoring unit;

[0022] The first main control unit is used to obtain a first optical power measurement value from the first optical intensity monitoring unit and send it to the QKD receiving end through a classical channel.

[0023] In the embodiment of the present invention, the first light intensity monitoring unit is provided to monitor the optical power value of the transmitting end and send it to the receiving end for reference to achieve dead time adjustment.

[0024] In an optional implementation, the QKD receiving end includes: a second wavelength division multiplexing module, a decoding module, a single photon detector, a synchronous light detector, a second optical beam splitter, a second light intensity monitoring unit and a receiving end control module, wherein:

[0025] The second wavelength division multiplexing module is used to divide the optical signal entering the QKD receiving end through the quantum channel according to different wavelengths, separate the quantum light and the synchronization light, and enter the single photon detector and the synchronization light detector for detection respectively;

[0026] The decoding module is used to decode the quantum state carrying the encoded information from the QKD receiving end through the quantum channel;

[0027] The single photon detector is used to detect and count the decoded quantum states output from the decoding module to obtain the original key information;

[0028] A second synchronous light detector, used for detecting the synchronous light and using the detected electrical signal as a clock signal for operation of the receiving end;

[0029] The second optical beam splitter is used to split the intensity of the received synchronization light according to the preset ratio into two outputs;

[0030] The second light intensity monitoring unit is used to measure the optical power of one of the split synchronization lights to obtain a second optical power measurement value;

[0031] The receiving end control module is used to obtain a second optical power measurement value and receive the first optical power measurement value sent from the QKD transmitting end through a classical channel, and calculate the difference between the two, and based on the difference between the second optical power measurement value and the first optical power measurement value and the preset nominal single photon level, obtain the single photon level currently entering the single photon detector, obtain the dead time parameter according to the single photon level currently entering the single photon detector and the preset correspondence between the single photon level and the dead time parameter, and after each response to photon detection, close the gate signal within a time length range of the dead time parameter.

[0032] The QKD transmitting end provided by the embodiment of the present invention can monitor the optical power value of the transmitting end and send it to the receiving end for automatic dead time adjustment by setting a first optical beam splitter, a first light intensity monitoring unit and a first light intensity acquisition module.

[0033] In an optional implementation, the receiving end control module includes: a second light intensity acquisition unit, a second main control unit and a dead time adjustment unit, wherein:

[0034] The second light intensity acquisition unit is used to obtain a second optical power measurement value from the second light intensity monitoring unit and receive the first optical power measurement value and calculate the difference between the two;

[0035] The dead time adjustment unit is used to obtain the single photon level currently entering the single photon detector based on the difference between the second optical power measurement value and the first optical power measurement value and the preset nominal single photon level;

[0036] The second main control unit is used to obtain the dead time parameter based on the current single photon level entering the single photon detector and the preset correspondence between the single photon level and the dead time parameter, and control the dead time adjustment unit to close the gate signal within a time length range of the dead time parameter after each response to photon detection.

[0037] The receiving end control module provided in the embodiment of the present invention controls the dead time adjustment unit through the second main control unit, and can automatically and accurately adjust the dead time parameters of the single photon detector, so that the QKD system can adapt to changes in channel attenuation and always maintain a relatively high coding rate performance.

[0038] In an optional embodiment, the first main control unit is also used to provide electrical signal control to the quantum light laser, the entangled state modulation module, the encoding module, the quantum light attenuation module, the synchronous light laser, and the synchronous light attenuation module, and to adjust their working modes and parameters.

[0039] The first main control unit provided by the embodiment of the present invention, on the one hand, provides electrical signal control for the quantum light laser, the entangled state modulation module, the encoding module, the quantum light attenuation module, the synchronous light laser, and the synchronous light attenuation module, and adjusts their working modes and parameters; on the other hand, transmits the light intensity monitoring value transmitted by the first light intensity acquisition module and some synchronization information of the system operation to the QKD receiving end main control unit through the classical channel.

[0040] In an optional implementation, the first optical beam splitter and the second optical beam splitter are both optical beam splitting devices with a large splitting ratio of 1:99 or 1:9.

[0041] The embodiment of the present invention sets the ratio of the first optical beam splitter to the second optical beam splitter so that the optical signal output to the receiving end can be accurately detected by the synchronous optical detector of the receiving end and the clock signal can be recovered, and the light intensity is not lower than the light intensity required for recovering the clock signal.

[0042] In an optional embodiment, the single-photon level is: N photons / pulse, where N is the number of photons, which is stored in the first main control unit and sent to the dead time adjustment unit through a quantum channel.

[0043] In the embodiment of the present invention, the first main control unit at the transmitting end sends the single photon level currently entering the single photon detector to the dead time adjustment unit through the quantum channel.

[0044] In an optional implementation, the preset correspondence between the single photon level and the dead time parameter is a correspondence table between the number of photons and the dead time, which is stored in the second main control unit.

[0045] The embodiment of the present invention obtains the dead time parameter by querying the correspondence table of the number of photons and the dead time prefabricated in the second main control unit, which is convenient and quick.

[0046] In an optional embodiment, the single photon level is calculated by the following formula:

[0047] M=N*△P*ATT

[0048] Wherein, M is the single photon level, N is the number of photons, ΔP is the difference between the second optical power measurement value and the first optical power measurement value, and ATT is the sum of the inherent attenuation of all optical devices in the quantum optical path at the receiving end.

[0049] In an optional implementation, the dead time adjustment unit is software or logic code on a receiving end control module, or a processor chip or circuit capable of data acquisition and storage.

[0050] In an optional implementation, the first light intensity monitoring unit and the second light intensity monitoring unit are photodetectors or PIN diodes.

[0051] In an optional implementation, the encoding module encodes quantum light in a manner including phase encoding and polarization encoding.

[0052] In a second aspect, the present invention provides a method for improving the QKD coding rate, which is applied to the QKD system described in any embodiment of the first aspect, comprising:

[0053] Real-time monitoring of a first optical power measurement value of the synchronization light outputted by the QKD transmitting end and a second optical power measurement value of the synchronization light received by the QKD receiving end;

[0054] Obtaining a real-time optical fiber line attenuation between a QKD transmitting end and a QKD receiving end according to a difference between the second optical power measurement value and the first optical power measurement value;

[0055] Based on the obtained optical fiber line attenuation and the inherent optical path attenuation in the QKD receiving end, the intensity of the quantum light entering the single-photon detector at the receiving end is obtained;

[0056] The QKD receiving end adjusts the dead time of the single photon detector at the QKD receiving end according to the different light intensities entering the single photon detector.

[0057] In an optional embodiment, the parameters corresponding to the dead time of the single-photon detector need to be calibrated in advance, and the calibration content includes: the dead time value corresponding to the single-photon detector when maintaining the nominal detection efficiency and dark count rate under input light conditions of different single-photon levels.

[0058] The method for improving the QKD coding rate provided by the embodiment of the present invention can adaptively detect changes in channel attenuation without the need for manual debugging and configuration of QKD system parameters, and automatically and accurately adjust the dead time parameters of the single-photon detector at the QKD receiving end, so that the QKD system can adapt to changes in channel attenuation and always maintain a relatively high coding rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0060] Figure 1 is a structural block diagram of a QKD system provided by an embodiment of the present invention;

[0061] Figure 2 It is a flowchart of a method for improving the QKD coding rate provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0062] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0063] According to an embodiment of the present invention, a QKD system is provided, characterized in that it includes: a QKD transmitter and a QKD receiver, wherein:

[0064] The QKD transmitter is used to measure the optical power after splitting the synchronization light to obtain a first optical power measurement value, and send the first optical power measurement value to the QKD receiver through a classical channel, and synchronize the sequence number of the quantum light with the QKD receiver through a quantum channel;

[0065] The QKD receiving end is used to measure the optical power after splitting the received synchronization light through the classical channel to obtain a second optical power measurement value, calculate the difference between the second optical power measurement value and the first optical power measurement value, and obtain the single photon level currently entering the single photon detector based on the difference between the second optical power measurement value and the first optical power measurement value and the preset nominal single photon level, obtain the dead time parameter according to the single photon level currently entering the single photon detector and the preset correspondence between the single photon level and the dead time parameter, and after each response photon detection, close the gate signal within a time range of the dead time parameter.

[0066] The QKD system provided by the embodiment of the present invention can detect changes in channel attenuation in real time without the need for manual debugging and configuration of QKD system parameters, and automatically and accurately adjust the dead time parameters of the single-photon detector at the QKD receiving end, so that the QKD system can adapt to changes in channel attenuation and always maintain high coding rate performance. It can fully automatically complete the process of "status monitoring-detecting state changes-automatically adjusting to the optimal state", which can save maintenance manpower investment and reduce the professional requirements for users.

[0067] Specifically, Figure 1 As shown, the QKD transmitter includes: a quantum light laser, a decoy state debugging module, a coding module, a quantum light attenuation module, a first optical beam splitter, a first light intensity monitoring unit, a transmitter control module, a synchronous light laser, a synchronous attenuation module and a first wavelength division multiplexing module, wherein:

[0068] The quantum light laser is a light source for generating quantum light; the decoy state debugging module is used to perform random decoy state modulation on the quantum light generated by the quantum light laser to form quantum light of different light intensities; the encoding module is used to load encoded information on quantum light of different light intensities; the quantum light attenuation module is used to attenuate the quantum light output by the encoding module to make it attenuate to within the intensity of the single photon level; after passing through the decoy state modulation module, the encoding module and the quantum light attenuation module, the preparation of the quantum state is completed, and the encoded information is carried through the quantum channel to enter the QKD receiving end; the synchronous light laser is a light source for generating synchronous light for time synchronization of quantum light; the first optical beam splitter is located between the synchronous light laser and the synchronous light attenuation module, and is used to divide the synchronous light generated by the first synchronous light laser into synchronous light according to the predetermined The light intensity of the ratio is divided into two outputs; the synchronous light attenuation module is used to attenuate the output light intensity of one of the paths after the first optical beam splitter is split, so that the number of pulses detected by the synchronous light detector at the QKD receiving end is consistent with the working frequency of the QKD receiving end; the first light intensity monitoring unit is used to measure the light power of the other path after the first optical beam splitter is split to obtain a first light power measurement value; the transmitting end control module is used to obtain the first light power measurement value and send it to the QKD receiving end through the classical channel, and synchronize the sequence number of quantum light with the QKD receiving end through the quantum channel; the first wavelength division multiplexing module is used to combine the optical signals of different wavelengths of the synchronous light and quantum light lasers of the QKD transmitting end into the same optical fiber for transmission in the quantum channel.

[0069] The original key is the original data obtained after the quantum state is measured by the receiving end. At this time, the original keys of the sender and the receiver are not the same. They need to go through the post-processing process of the QKD protocol (including basis, error correction and security enhancement), that is, after passing through the encoding module and the decoding module, the sender and the receiver can have the same quantum key, thus completing the complete quantum key distribution process. Practical quantum communication now refers to quantum key distribution, that is, to share keys based on the principles of quantum mechanics, and realize a new, non-mathematical (computational complexity) password sharing technology. Quantum key distribution technology combined with classical cryptography technology can achieve security and confidentiality of information communication.

[0070] In one embodiment, the above-mentioned transmitting end control module includes: a first light intensity acquisition unit and a first main control unit, wherein:

[0071] The first light intensity acquisition unit is used to acquire the first optical power measurement value from the first light intensity monitoring unit; in one implementation, the first light intensity acquisition unit is a software code or logic code of a transmitting end control module.

[0072] The first main control unit is used to obtain a first optical power measurement value from the first optical intensity monitoring unit and send it to the QKD receiving end through a classical channel.

[0073] The first main control unit provided by the implementation of the present invention is also used to provide electrical signal control to the quantum light laser, the decoy state modulation module, the coding module, the quantum light attenuation module, the synchronous light laser, and the synchronous light attenuation module, and adjust their working modes and parameters. That is, the first main control unit, on the one hand, provides electrical signal control to the quantum light laser, the decoy state modulation module, the coding module, the quantum light attenuation module, the synchronous light laser, and the synchronous light attenuation module, and adjusts their working modes and parameters; on the other hand, transmits the light intensity monitoring value transmitted from the first light intensity acquisition module and some synchronization information of the system operation to the QKD receiving end main control unit through the classical channel.

[0074] like Figure 1 As shown, the QKD receiving end in the embodiment of the present invention includes: a second wavelength division multiplexing module, a decoding module, a single photon detector, a synchronous light detector, a second optical beam splitter, a second light intensity monitoring unit and a receiving end control module, wherein:

[0075] The second wavelength division multiplexing module is used to divide the optical signal entering the QKD receiving end through the quantum channel according to different wavelengths, separate the quantum light and the synchronization light, and enter the single photon detector and the synchronization light detector for detection respectively; the decoding module is used to decode the quantum state carrying the coded information from the QKD receiving end through the quantum channel; the single photon detector is used to detect and count the decoded quantum state output from the decoding module to obtain the original key information; the second synchronization light detector is used to detect the synchronization light and use the detected electrical signal as the clock signal for the receiving end to operate; the second optical beam splitter is used to output the received synchronization light in two according to the preset ratio of light intensity; the second optical The strong monitoring unit is used to measure the optical power of one of the split synchronization lights to obtain a second optical power measurement value; the receiving end control module is used to obtain the second optical power measurement value and receive the first optical power measurement value sent from the QKD transmitting end through the classical channel, and calculate the difference between the two, and based on the difference between the second optical power measurement value and the first optical power measurement value and the preset nominal single photon level, obtain the single photon level currently entering the single photon detector, obtain the dead time parameter according to the single photon level currently entering the single photon detector and the preset correspondence between the single photon level and the dead time parameter, and after each response photon detection, close the gate signal within the time length range of the dead time parameter.

[0076] In one embodiment, the above-mentioned receiving end control module includes: a second light intensity acquisition unit, a second main control unit and a dead time adjustment unit, wherein:

[0077] The second light intensity acquisition unit is used to obtain the second optical power measurement value from the second light intensity monitoring unit and receive the first optical power measurement value and calculate the difference between the two; the dead time adjustment unit is used to obtain the single photon level currently entering the single photon detector based on the difference between the second optical power measurement value and the first optical power measurement value and the preset nominal single photon level; the second main control unit is used to obtain the dead time parameter according to the single photon level currently entering the single photon detector and the preset correspondence between the single photon level and the dead time parameter, and control the dead time adjustment unit to close the gate signal within the time length of the dead time parameter after each response to photon detection. The second light intensity acquisition unit is the software code or logic code of the receiving end control module, and the dead time adjustment unit is the software or logic code on the receiving end control module, or a processor chip or circuit with data acquisition and storage.

[0078] In the embodiment of the present invention, the single photon level is referred to as: N photons / pulse, where N is the number of photons, which can be pre-set by the administrator in the first main control unit of the transmitting end when the QKD device leaves the factory, and sent to the dead time adjustment unit through the quantum channel. The preset correspondence between the single photon level and the dead time parameter is a correspondence table between the number of photons and the dead time, which is stored in the second main control unit. The single photon level is calculated by the following formula:

[0079] M=N*△P*ATT

[0080] Wherein, M is the single photon level, N is the number of photons, △P is the difference between the second optical power measurement value and the first optical power measurement value, in dB, and ATT is the sum of the inherent attenuation of all optical devices in the quantum optical path at the receiving end.

[0081] Generally, the beam splitters with a beam splitting ratio of 1:9, 1:99, and 50:50 are common, because the optical signal output to the receiving end is to be accurately detected by the synchronous optical detector at the receiving end and the clock signal is recovered. The light intensity should not be lower than the light intensity required to recover the clock signal. In the embodiment of the present invention, the first optical beam splitter and the second optical beam splitter are both optical beam splitters with a large beam splitting ratio of 1:99 or 1:9. The output light of port 1 is input to the first light intensity monitoring unit and the second light intensity monitoring unit for optical power measurement, and the output light of port 9 (or port 99) is output to the synchronous optical detector of the QKD receiving end through the synchronous optical attenuation module for quantum light sequence synchronization.

[0082] According to an embodiment of the present invention, a method embodiment for improving the QKD coding rate is provided. It should be noted that the steps shown in the flowchart of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and although a logical order is shown in the flowchart, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0083] In this embodiment, a method for improving the QKD coding rate is provided, which can be used in the above-mentioned QKD system. Figure 2 is a flow chart of a method for improving the QKD coding rate according to an embodiment of the present invention. Figure 2 As shown, the process includes the following steps:

[0084] S101, real-time monitoring of a first optical power measurement value of the output of the synchronization light of the QKD transmitting end and a second optical power measurement value of the received synchronization light of the QKD receiving end.

[0085] S102, obtaining the real-time attenuation of the optical fiber line between the QKD transmitting end and the QKD receiving end according to the difference between the second optical power measurement value and the first optical power measurement value.

[0086] S103, based on the obtained optical fiber line attenuation and combined with the inherent optical path attenuation in the QKD receiving end, the light intensity of the quantum light entering the single-photon detector at the receiving end, that is, the average number of photons per pulse, is obtained.

[0087] S104, the QKD receiving end adjusts the dead time of the single photon detector of the QKD receiving end according to the different light intensities entering the single photon detector. In the embodiment of the present invention, the parameters corresponding to the dead time of the single photon detector need to be calibrated in advance, and the calibration content includes: the dead time value corresponding to the single photon detector when maintaining the nominal detection efficiency and dark count rate under the input light conditions of different single photon levels, that is, the corresponding relationship table between the number of photons and the dead time stored in the second main control unit.

[0088] The method for improving the QKD coding rate provided by the embodiment of the present invention can adaptively detect changes in channel attenuation without the need for manual debugging and configuration of QKD system parameters, and automatically and accurately adjust the dead time parameters of the single-photon detector at the QKD receiving end, so that the QKD system can adapt to changes in channel attenuation and always maintain a relatively high coding rate performance.

[0089] Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A QKD system, characterized in that: include: QKD transmitter and QKD receiver, where: The QKD transmitter is used to measure the optical power after splitting the synchronization light to obtain a first optical power measurement value, and send the first optical power measurement value to the QKD receiver through a classical channel, and synchronize the sequence number of the quantum light with the QKD receiver through a quantum channel; The QKD receiving end is used to measure the optical power after splitting the received synchronization light through the classical channel to obtain a second optical power measurement value, calculate the difference between the second optical power measurement value and the first optical power measurement value, and obtain the single photon level currently entering the single photon detector based on the difference between the second optical power measurement value and the first optical power measurement value and the preset nominal single photon level, obtain the dead time parameter according to the single photon level currently entering the single photon detector and the preset correspondence between the single photon level and the dead time parameter, and after each response photon detection, close the gate signal within a time range of the dead time parameter.

2. The QKD system according to claim 1, characterized in that: The QKD transmitter includes: a quantum light laser, a decoy state debugging module, a coding module, a quantum light attenuation module, a first optical beam splitter, a first light intensity monitoring unit, a transmitter control module, a synchronous light laser, a synchronous attenuation module and a first wavelength division multiplexing module, wherein: The quantum light laser is a light source for generating quantum light; The decoy state debugging module is used to perform random decoy state modulation on the quantum light generated by the quantum light laser to form quantum light with different light intensities; The encoding module is used to load encoding information into quantum lights of different light intensities; The quantum light attenuation module is used to attenuate the quantum light output by the encoding module to a level within the intensity of a single photon; The synchronous light laser is a light source for generating synchronous light for time synchronization of quantum light; The first optical beam splitter is located between the synchronous optical laser and the synchronous optical attenuation module, and is used to output the synchronous light generated by the first synchronous optical laser in two parts according to a preset ratio of light intensity; The synchronous optical attenuation module is used to attenuate the output light intensity of one of the paths after the first optical beam splitter performs beam splitting, so that the number of pulses detected by the synchronous optical detector at the QKD receiving end is consistent with the operating frequency of the QKD receiving end; The first light intensity monitoring unit is used to measure the optical power of another path after the first optical beam splitter splits the light to obtain a first optical power measurement value; The transmitting end control module is used to obtain the first optical power measurement value and send it to the QKD receiving end through the classical channel, and synchronize the sequence number of the quantum light with the QKD receiving end through the quantum channel; The first wavelength division multiplexing module is used to combine the optical signals of different wavelengths of the two lasers of synchronization light and quantum light at the QKD transmitting end into the same optical fiber for transmission in the quantum channel.

3. The QKD system according to claim 2, characterized in that: The transmitting end control module includes: a first light intensity acquisition unit and a first main control unit, wherein: The first light intensity acquisition unit is used to acquire a first optical power measurement value from the first light intensity monitoring unit; The first main control unit is used to obtain a first optical power measurement value from the first optical intensity monitoring unit and send it to the QKD receiving end through a classical channel.

4. The QKD system according to claim 2 or 3, characterized in that: The QKD receiving end includes: a second wavelength division multiplexing module, a decoding module, a single photon detector, a synchronous light detector, a second optical beam splitter, a second light intensity monitoring unit and a receiving end control module, wherein: The second wavelength division multiplexing module is used to divide the optical signal entering the QKD receiving end through the quantum channel according to different wavelengths, separate the quantum light and the synchronization light, and enter the single photon detector and the synchronization light detector for detection respectively; The decoding module is used to decode the quantum state carrying the encoded information from the QKD receiving end through the quantum channel; The single photon detector is used to detect and count the decoded quantum states output from the decoding module to obtain the original key information; The second optical beam splitter is used to split the intensity of the received synchronization light according to the preset ratio into two outputs; The second light intensity monitoring unit is used to measure the optical power of one of the split synchronization lights to obtain a second optical power measurement value; A synchronous light detector is used to detect the other path of the split synchronous light and use the detected electrical signal as a clock signal for the receiving end to operate; The receiving end control module is used to obtain a second optical power measurement value and receive the first optical power measurement value sent from the QKD transmitting end through a classical channel, and calculate the difference between the two, and based on the difference between the second optical power measurement value and the first optical power measurement value and the preset nominal single photon level, obtain the single photon level currently entering the single photon detector, obtain the dead time parameter according to the single photon level currently entering the single photon detector and the preset correspondence between the single photon level and the dead time parameter, and after each response to photon detection, close the gate signal within a time length range of the dead time parameter.

5. The QKD system according to claim 4, characterized in that: The receiving end control module includes: a second light intensity acquisition unit, a second main control unit and a dead time adjustment unit, wherein: The second light intensity acquisition unit is used to obtain a second optical power measurement value from the second light intensity monitoring unit and receive the first optical power measurement value and calculate the difference between the two; The dead time adjustment unit is used to obtain the single photon level currently entering the single photon detector based on the difference between the second optical power measurement value and the first optical power measurement value and the preset nominal single photon level; The second main control unit is used to obtain the dead time parameter based on the single photon level currently entering the single photon detector and the preset correspondence between the single photon level and the dead time parameter, and controls the dead time adjustment unit to close the gate signal within a time length range of the dead time parameter after each response to photon detection.

6. The QKD system according to claim 3, characterized in that: The first main control unit is also used to provide electrical signal control to the quantum light laser, the entrapped state modulation module, the encoding module, the quantum light attenuation module, the synchronous light laser, and the synchronous light attenuation module, and to adjust their working modes and parameters.

7. The QKD system according to claim 4, characterized in that: The first optical beam splitter and the second optical beam splitter are both optical beam splitting devices with a large splitting ratio of 1:99 or 1:

9.

8. The QKD system according to claim 5, characterized in that: The preset nominal single photon level is: N photons / pulse, where N is the number of photons, which is stored in the first main control unit and sent to the dead time adjustment unit through the quantum channel.

9. The QKD system according to claim 5, characterized in that: The preset correspondence between the single photon level and the dead time parameter is a correspondence table between the number of photons and the dead time, which is stored in the second main control unit.

10. The QKD system according to claim 1, characterized in that: The single photon level is calculated by the following formula: M=N*△P*ATT Wherein, M is the single photon level, N is the number of photons, ΔP is the difference between the second optical power measurement value and the first optical power measurement value, and ATT is the sum of the inherent attenuation of all optical devices in the quantum optical path at the receiving end.

11. The QKD system according to claim 5, characterized in that: The dead time adjustment unit is software or logic code on the receiving end control module, or a processor chip or circuit with data acquisition and storage.

12. The QKD system according to claim 4, characterized in that: The first light intensity monitoring unit and the second light intensity monitoring unit are photodetectors or PIN diodes.

13. The QKD system according to claim 2, characterized in that: The encoding module encodes quantum light in the following ways: phase encoding and polarization encoding.

14. A method for improving QKD coding rate, applied to the QKD system according to any one of claims 1 to 13, characterized in that: include: Real-time monitoring of a first optical power measurement value of the synchronization light outputted by the QKD transmitting end and a second optical power measurement value of the synchronization light received by the QKD receiving end; Obtaining the real-time attenuation of the optical fiber line between the QKD transmitting end and the QKD receiving end according to the difference between the second optical power measurement value and the first optical power measurement value; Based on the obtained optical fiber line attenuation and the inherent optical path attenuation in the QKD receiving end, the intensity of the quantum light entering the single-photon detector at the receiving end is obtained; The QKD receiving end adjusts the dead time of the single photon detector at the QKD receiving end according to the different light intensities entering the single photon detector.

15. The method for improving QKD coding rate according to claim 14, characterized in that: The parameters corresponding to the dead time of the single-photon detector need to be calibrated in advance, and the calibration content includes: the dead time value corresponding to the single-photon detector when maintaining the nominal detection efficiency and dark count rate under the input light conditions of different single-photon levels.

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