Signal synchronization method and system based on free-space quantum key distribution system

Abstract

The present application discloses a signal synchronization method and system based on a free-space quantum key distribution system, which belongs to the field of key transmission technology. The method includes: for a free channel that is prone to photon loss, a high-power synchronization laser is used as a synchronization light source, a preset frame recognition head is used to modulate the synchronization light signal, and then the synchronization light signal is sent to the receiving end as a reference light, and then the synchronization signal received by the synchronization detector at the receiving end is synchronously encoded, and the position information of the synchronization signal is generated and sent to the single-photon detector at the receiving end; thereby, the quantum signal received by the single-photon detector at the receiving end is sequenced with the synchronization signal according to the position information to complete signal synchronization. Frame synchronization is achieved through the synchronization laser, and bit synchronization is achieved through synchronization coding and sequence correspondence, which can effectively resist the interference of the atmospheric channel and reduce the bit error rate of the system.

Description

Technical Field

[0001] The present application relates to the field of optical measurement technology, and more specifically, to a signal synchronization method and system based on a free-space quantum key distribution system. Background Art

[0002] Quantum key distribution (QKD) systems can be categorized as fiber-based QKD systems and free-space QKD systems, depending on the channel used for key transmission. Key transmission channels primarily involve fiber and space. Due to the inherent fixed attenuation of light by optical fibers, the transmission distance of QKD based on fiber-based channels is limited. However, fiber-based channels are stable, making them advantageous for short distances. Space channels encompass a wider range, encompassing both the atmosphere and outer space. Compared to fiber-based channels and surface space channels, outer space channels experience minimal attenuation, making them advantageous for long-distance transmission. Furthermore, QKD systems based on space channels offer superior mobility.

[0003] The biggest difference between free-space QKD and fiber-optic QKD is the channel. The beam attenuation caused by the spatial channel will lead to the loss of optical pulses. Therefore, the synchronization problem is the key issue that determines the bit error rate of the free-space QKD system. Summary of the Invention

[0004] In response to at least one defect or improvement need in the prior art, the present invention provides a signal synchronization method and system based on a free-space quantum key distribution system, which solves the technical defect of high bit error rate of the free-space QKD system, resists interference from the atmospheric channel, and effectively reduces the bit error rate of the quantum key distribution system.

[0005] The point spread function of each point in the slit can be measured, thereby improving the convenience and comprehensiveness of the point spread function measurement.

[0006] To achieve the above objectives, according to a first aspect of the present invention, a signal synchronization method based on a free-space quantum key distribution system is provided, comprising:

[0007] Turning on the synchronization light source at the transmitting end to enable it to send a synchronization signal to the receiving end; wherein the synchronization signal is a synchronization reference light corresponding to the frame data generated by the synchronization light source after performing signal modulation according to a preset frame identification header;

[0008] Turning on the signal light source at the transmitting end to transmit a quantum signal to the receiving end; wherein the quantum signal is quantum light corresponding to the quantum key generated after encrypting the target data;

[0009] Perform frame header recognition on the synchronization signal received by the synchronization detector at the receiving end, generate coding information of the synchronization signal and send it to the single photon detector at the receiving end;

[0010] The quantum signal received by the single-photon detector at the receiving end is matched with the synchronization signal in sequence according to the coding information to complete signal synchronization.

[0011] In an exemplary embodiment, the modulation mode of the synchronization signal includes pulse width modulation, frequency modulation and phase modulation.

[0012] In an exemplary embodiment, performing frame header recognition on a synchronization signal received by a synchronization detector at a receiving end and generating coding information of the synchronization signal includes:

[0013] Decode the synchronization signal to obtain frame data;

[0014] Based on the frame data, the signal is synchronously encoded using a timestamp and signal strength encoding method to generate encoding information of the synchronization signal; wherein the encoding information is a serial number corresponding to the time point when the synchronization signal arrives at the receiving end.

[0015] In an exemplary embodiment, decoding the synchronization signal to obtain frame data includes:

[0016] Scan the frame identification header corresponding to each frame data in the synchronization signal;

[0017] When any code in the frame identification header is scanned, the duration of each code chip is adjusted to align with the center of the current code chip;

[0018] Based on the clock of the receiving end and according to the frame synchronization theory, the frame tail corresponding to the frame identification header is restored.

[0019] In an exemplary embodiment, the sequence correspondence adopts a cross-correlation algorithm based on fast Fourier transform.

[0020] According to a second aspect of the present invention, there is also provided a signal synchronization system based on a free-space quantum key distribution system, comprising a first optical module and a second optical module, a delay module, a synchronization optical detector and a quantum optical detector;

[0021] The first optical module is used to generate a synchronization signal and send it to the receiving end, wherein the synchronization signal is a synchronization reference light corresponding to the frame data generated by the synchronization light source after signal modulation according to the preset frame identification header;

[0022] The second optical module is used to generate a quantum signal and send it to the receiving end, wherein the quantum signal is quantum light corresponding to the quantum key generated after encrypting the target data;

[0023] The delay module is used to identify the frame header of the synchronization signal received by the synchronization detector at the receiving end, generate the coding information of the synchronization signal and send it to the single photon detector at the receiving end;

[0024] The quantum light detector is used to sequence the quantum signal received by the single-photon detector at the receiving end with the synchronization signal according to the coding information to complete signal synchronization.

[0025] In one exemplary embodiment, a quantum light detector includes a gated single photon detector and a synchronization module;

[0026] A gated single-photon detector is used to use the synchronization signal as a gate signal to receive the quantum signal corresponding to the scanning period;

[0027] The synchronization module is used to perform sequence correspondence between the received quantum signal and the synchronization signal according to the coding information to complete signal synchronization.

[0028] In an exemplary embodiment, the delay module includes: an analysis unit and a processing unit;

[0029] An analysis unit, configured to decode the synchronization signal to obtain frame data;

[0030] A processing unit is used to synchronously encode the signal based on the frame data using a timestamp and signal strength encoding method to generate encoding information of the synchronization signal; wherein the encoding information is a serial number corresponding to the time point when the synchronization signal arrives at the receiving end.

[0031] In an exemplary embodiment, a coupling module is further included, wherein the input end of the coupling module is connected to the output end of the first optical module and the output end of the second optical module respectively, and is used to couple the synchronization signal and the quantum signal using wavelength division multiplexing technology to obtain a coupled signal and output it to the atmospheric channel through optical fiber.

[0032] In an exemplary embodiment, a decomposition module is further included, wherein the output end of the decomposition module is connected to the input end of the synchronous detector and the input end of the quantum light detector respectively, and is used to receive the coupled signal, separate the synchronous signal and the quantum signal using WDM technology, and input them into the synchronous detector and the quantum light detector respectively.

[0033] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects compared with the prior art:

[0034] (1) The present invention provides a signal synchronization method based on a free-space quantum key distribution system. For free channels that are prone to photon loss, a high-power synchronization laser is used as a synchronization light source. Its function is to be captured by a high-sensitivity synchronization light detector after long-distance atmospheric attenuation, and then the synchronization signal received by the synchronization detector at the receiving end is synchronously encoded, and the position information of the synchronization signal is generated and sent to the single-photon detector at the receiving end; thereby, the quantum signal received by the single-photon detector at the receiving end is sequenced with the synchronization signal according to the position information to complete signal synchronization. Frame synchronization is achieved through the synchronization laser, and bit synchronization is achieved through synchronization coding and sequence correspondence, which can effectively resist the interference of the atmospheric channel and reduce the bit error rate of the system.

[0035] (2) In the extreme case where part of the synchronization light is lost, a delay is generated based on the synchronization light counter to record the position information of the quantum signal relative to the synchronization signal; then, the position information of the synchronization signal is generated based on the delay and the number of codes of the frame identification header corresponding to each frame data in the synchronization signal received by the synchronization detector. The synchronization light detector also only needs to obtain part of the photons at the frame head and the frame tail. The sampling clock of the high-precision FPGA at the receiving end can exit the start and end of each frame according to the photon period.

[0036] (3) The present invention uses a gated single-photon detector as the quantum detector on the receiving side, and its gate signal comes from the trigger signal output by the synchronous light detector; a delayed scanning module is used to count the pulse counts in each scanning cycle. When the pulse count is the maximum, the scan ends. At this time, it is considered that the electrical pulse output by the synchronous detector and the electrical pulse output by the quantum detector are synchronized in time sequence. Combined with the synchronous light pulse counter, the synchronous light and the quantum light are sequenced to achieve the purpose of bit synchronization. When using a gated single-photon detector, the detected signal is considered to be a signal photon only when the synchronous signal is turned on as a gate signal. This method effectively avoids the influence of dark technology, false triggering, etc. on the system. When the photons of each polarization direction and each signal state are emitted by the sender, they need to be adjusted to coincide with the position of the synchronous light, so that they can be correctly collected by the single-photon detector on the receiving side. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0038] Figure 1A schematic flow chart of an optional signal synchronization method based on a free-space quantum key distribution system provided in an embodiment of the present application;

[0039] Figure 2 A schematic structural diagram of an optional signal synchronization system based on a free-space quantum key distribution system provided in an embodiment of the present application. DETAILED DESCRIPTION

[0040] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0041] The terms "first," "second," "third," and the like in the specification and claims of this application and the accompanying drawings are used to distinguish between different objects, not to describe a particular order. Furthermore, the terms "including," "having," and any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus comprising a series of steps or elements is not limited to the listed steps or elements, but may optionally include steps or elements not listed, or may optionally include other steps or elements inherent to the process, method, product, or apparatus.

[0042] According to one aspect of the embodiments of the present application, a signal synchronization method based on a free space quantum key distribution system is provided. Figure 1 The present invention describes a signal synchronization method based on a free-space quantum key distribution system provided in an embodiment of the present application.

[0043] Figure 1 This is a flow chart of an optional signal synchronization method based on a free-space quantum key distribution system provided in an embodiment of the present application, such as Figure 1 As shown, the process of the method may include the following steps:

[0044] S102, turning on the synchronization light source of the transmitting end to send a synchronization signal to the receiving end.

[0045] The synchronization signal is a synchronization reference light corresponding to frame data generated by a synchronization light source after performing signal modulation according to a preset frame recognition header.

[0046] S104, turning on the signal light source at the transmitting end to send the quantum signal to the receiving end.

[0047] The quantum signal is the quantum light corresponding to the quantum key generated after encrypting the target data;

[0048] S106, performing frame header recognition on the synchronization signal received by the synchronization detector at the receiving end, generating coding information of the synchronization signal and sending it to the single photon detector at the receiving end;

[0049] S108 , according to the coding information, the quantum signal received by the single-photon detector at the receiving end is matched with the synchronization signal in sequence to complete signal synchronization.

[0050] Specifically, the transmitting end synchronization light source is turned on to transmit a synchronization signal to the receiving end. The system control module drives the synchronization light to generate the synchronization signal and drives the synchronization laser to generate the synchronization signal. The synchronization signal is the synchronization reference light corresponding to the frame data generated by the synchronization light source after signal modulation according to a preset frame identification header. The preset frame identification header has a unique encoding format for distinguishing different frame data. For example, the frame identification headers AA, BB, CC, DD, EE, and FF are modulated into the synchronization light emission. The modulation method of the synchronization light source can include but is not limited to pulse width modulation, frequency modulation, and phase modulation.

[0051] The transmitter's signal light source is turned on to transmit a quantum signal to the receiver. The quantum signal is quantum light corresponding to the quantum key generated by encrypting the target data, using, for example, the BB84 encryption algorithm. The target data on the transmitter is the original encrypted information used to generate the quantum key.

[0052] In one embodiment, the BB84 encryption algorithm is used to encrypt data using the polarization state of photons. The target data is first converted into binary format. Then, according to the rules of the BB84 algorithm, the polarization state of each binary bit is encoded to generate quantum light corresponding to the quantum key as a quantum signal, which is then sent to the receiving end.

[0053] The synchronous detector at the receiving end decodes the received synchronization signal to obtain frame data; then, based on the frame data, the signal is synchronously encoded using a timestamp and signal strength encoding method to generate encoding information of the synchronization signal.

[0054] The coded information is the sequence number corresponding to the time point when the synchronization signal arrives at the receiving end. Finally, the coded information is sent to the single photon detector at the receiving end.

[0055] After receiving the quantum signal, the single-photon detector at the receiving end uses the private key to decrypt it and obtain the original target data. Simultaneously, the synchronization detector at the receiving end also receives the synchronization signal and, based on its positional information, aligns the quantum signal with the synchronization signal. This ensures the temporal and sequential consistency of the quantum signal and the synchronization signal, thereby achieving signal synchronization in the free-space quantum key distribution system and ensuring the accuracy and reliability of the quantum key distribution process.

[0056] The synchronization detector at the receiving end decodes the received synchronization signal to obtain frame data.

[0057] Based on the contents of the above embodiments, the signal synchronization method based on the free-space quantum key distribution system proposed by the present invention performs frame header recognition on the synchronization signal received by the synchronization detector at the receiving end, and generates coding information of the synchronization signal, including: decoding the synchronization signal to obtain frame data; based on the frame data, synchronously encoding the signal using a timestamp and signal strength encoding method to generate coding information of the synchronization signal; wherein the coding information is a serial number corresponding to the time point when the synchronization signal arrives at the receiving end.

[0058] Specifically, the signal is synchronously encoded based on the frame data using a timestamp and signal strength encoding method to generate encoded information of the synchronization signal. The encoded information is a sequence number corresponding to the time point when the synchronization signal arrives at the receiving end. Finally, this encoded information is sent to the single-photon detector at the receiving end.

[0059] In one embodiment, performing frame header identification on a synchronization signal received by a synchronization detector at a receiving end and generating coding information of the synchronization signal includes: decoding the synchronization signal to obtain frame data; performing synchronization encoding on the signal based on the frame data using a timestamp and signal strength encoding method to generate coding information of the synchronization signal; wherein the coding information is a serial number corresponding to the time point when the synchronization signal arrives at the receiving end.

[0060] Furthermore, decoding the synchronization signal to obtain frame data includes: scanning the frame identification header corresponding to each frame data in the synchronization signal; when scanning any code in the frame identification header, adjusting the duration of each code piece to align with the center of the current code piece; and restoring the frame tail corresponding to the frame identification header based on the clock of the receiving end and the frame synchronization theory.

[0061] Specifically, after the synchronization detector at the receiving end receives the synchronization signal, it starts frame header recognition. For the decoding process, taking a scanned data frame as an example, its frame identification header is "AA, BB, CC, DD, EE and FF". When any of the codes is identified, the duration of each code piece is adjusted. Assuming that the original duration of the code piece is 1ns, the adjustment is made to align its center. According to the clock of the receiving end (assuming the clock accuracy is 1ps) and frame synchronization theory, the frame tail is restored. After that, synchronization encoding is performed, and the time point when the synchronization signal arrives at the receiving end is recorded. Assuming that the time at this time is 100.5ms, it is converted into the corresponding serial number (for example, through a certain time-serial number mapping rule) as the coding information.

[0062] The frame header of the synchronization signal received by the synchronous detector at the receiving end is identified, and the position information of the synchronization signal is generated and sent to the single-photon detector at the receiving end. The encoding rules of the synchronization encoding follow, for example, encoding rules based on time marks and signal phase characteristics. A high-speed encoding chip of model XYZ-123 can be used in the synchronization encoding process, and its encoding efficiency can reach 1000 encoding operations to 5000 encoding operations per second.

[0063] The quantum signal received by the single-photon detector at the receiving end is sequenced with the synchronization signal according to the position information to complete signal synchronization. The sequence correspondence can adopt, for example, a cross-correlation algorithm based on fast Fourier transform.

[0064] The signal synchronization method of the present invention effectively improves the accuracy and efficiency of signal synchronization in the free-space quantum key distribution system through precise frame header recognition, encoding and sequence correspondence algorithms, ensures the reliability of the quantum key distribution process, reduces errors caused by signal asynchrony, and improves the performance of the entire quantum communication system.

[0065] Furthermore, after the synchronization light source at the transmitting end is turned on to transmit the synchronization signal to the receiving end, the method further includes: generating a delay amount according to a synchronization light counter to record position information of the quantum signal relative to the synchronization signal.

[0066] The following is a specific example to further illustrate this. During synchronization, the sender needs to prepare signal light in four polarization states, labeled H / V / P / N. These four polarizations are generated separately by eight lasers on the light source board. Preferably, the eight lasers are combined using polarization-maintaining fiber to form a time-division multiplexed optical channel, ensuring that only one polarization is emitted at a time.

[0067] Turn on the test mode. First, the transmitter sends a synchronous light source to continuously output in the free space channel. In order to reduce the system false triggering and after pulses that affect the single photon detector's correct detection of the signal light,

[0068] Preferably, the single-photon detector is a gated single-photon detector, and the detected signal light is effective only when the gate signal is turned on.

[0069] At the receiving end, the synchronization signal needs to be photoelectrically converted, and the converted synchronization signal is output to the detector as the gating signal of the single-photon detector.

[0070] During the transmission process from the sender to the receiver, the beam of light in the atmospheric channel sometimes widens, causing a certain phase difference between the signal light and the synchronization light during transmission. In this case, a delay chip is required at the receiving end to control the phase difference within a quantum emission cycle so that the signal light can be detected without confusion.

[0071] When the working mode is turned on, the system control module drives the synchronization light to generate a synchronization signal, and drives the quantum laser to generate a quantum signal, modulating the frame identification header AA, BB, CC, DD, EE and FF into the synchronization light emission, and when the last bit of FF is modulated and output;

[0072] When the system control module uses random numbers to generate electric drive signals, it is necessary to encode and store the drive signals so as to be used for comparison during the basis vector comparison process.

[0073] During encoding, it is necessary to record not only the basis vector information and state information of the signal but also the position information of the signal, that is, the position information relative to which synchronization light the signal is emitted.

[0074] Therefore, during the transmission of the system synchronization light, a synchronization light counter is generated to record the number of synchronization light emissions of different quantum lights. After the quantum light emits 1018 valid data, the quantum light stops emitting, and the synchronization light modulation encoding data is the synchronization light output of FF, AA, FA, OO;

[0075] After the synchronization light has finished outputting the frame tail, the synchronization light and quantum light are turned off, and after waiting for 12 clock cycles, the synchronization light is turned on to send the frame header, and the cycle is repeated.

[0076] On the receiving side, the detector collects photons of four polarization directions and sends them to the signal collection and encoding module of the key generation and control board. Simultaneously, the delay board converts the receiver's synchronous optical signal into a synchronous electrical signal, which is then sent to the key generation and control board via the backplane.

[0077] The signal acquisition and encoding module recovers the position of the synchronization frame based on the received synchronization signal. Due to the nonlinear effect of the atmospheric channel on the light beam, the first data AA of the synchronization header is lost. According to frame synchronization theory, as long as the synchronization detector detects any one of the data BB, CC, DD, EE, and FF, the end of the frame header can be recovered based on the clock used by the receiving end, ensuring the bit synchronization relationship between the quantum light and the synchronization light.

[0078] Similarly, the end of the frame can be calculated based on the sampling clock of the FPGA at the receiving end by detecting any one of the data FF, AA, FA, and OO.

[0079] This method effectively resists the interference of atmospheric channels and can effectively reduce the bit error rate of the system;

[0080] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects compared with the prior art:

[0081] The present invention provides two ideas: frame synchronization and bit synchronization.

[0082] On the one hand, for free channels that are prone to photon loss, high-power synchronous lasers are used as synchronous light sources. Their function is to be captured by high-sensitivity synchronous light detectors even after long-distance atmospheric attenuation. In extreme cases, if part of the synchronous light is lost, the synchronous light detector only needs to obtain some photons at the frame head and tail. At the receiving end, a high-precision FPGA sampling clock is used to exit the start and end of each frame according to the photon period.

[0083] On the other hand, the quantum detector uses a gated single-photon detector, whose gating signal comes from the trigger signal output by the synchronous light detector; a high-precision delay chip is used as hardware, and a delay scanning module is used in software to count the pulses in each scanning cycle. When the pulse count is the largest, the scan ends. At this time, it is considered that the electrical pulses output by the synchronous detector and the electrical pulses output by the quantum detector are synchronized in time sequence. Combined with the synchronous light pulse counter, the synchronous light and the quantum light are sequenced to achieve the purpose of bit synchronization.

[0084] According to another aspect of the embodiments of the present application, a signal synchronization system for implementing the above-mentioned free-space quantum key distribution system is also provided. Figure 2 is a schematic structural diagram of an optional signal synchronization system based on a free-space quantum key distribution system according to an embodiment of the present application, such as Figure 2 As shown, the system may include: a first optical module and a second optical module, a delay module, a synchronous optical detector and a quantum optical detector;

[0085] The first optical module is used to generate a synchronization signal and send it to the receiving end, wherein the synchronization signal is a synchronization reference light corresponding to the frame data generated by the synchronization light source after signal modulation according to the preset frame identification header;

[0086] The second optical module is used to generate a quantum signal and send it to the receiving end, wherein the quantum signal is quantum light corresponding to the quantum key generated after encrypting the target data;

[0087] The delay module is used to identify the frame header of the synchronization signal received by the synchronization detector at the receiving end, generate the coding information of the synchronization signal and send it to the single photon detector at the receiving end;

[0088] The quantum light detector is used to sequence the quantum signal received by the single-photon detector at the receiving end with the synchronization signal according to the coding information to complete signal synchronization.

[0089] Furthermore, the quantum light detector includes a gated single photon detector and a synchronization module;

[0090] A gated single-photon detector is used to use the synchronization signal as a gate signal to receive the quantum signal corresponding to the scanning period;

[0091] The synchronization module is used to perform sequence correspondence between the received quantum signal and the synchronization signal according to the coding information to complete signal synchronization.

[0092] In addition, the sender also needs a laser source module to generate a corresponding optical signal based on the driving signal of the light source. At the same time, an optical system is required to process the optical signal and couple light with different polarization directions and synchronous light into an optical fiber for transmission.

[0093] The signal detected by the quantum light detector at the receiving end of the system must be a photon synchronized with the synchronization light signal to be considered as the photon emitted by the sender. Therefore, a gated single-photon detector is required. Only when the synchronization signal is turned on as the gate signal, the detected signal is considered as a signal photon.

[0094] This approach effectively avoids the impact of dark technology, false triggering, etc. on the system. When photons of various polarization directions and signal states are emitted by the sender, they need to be adjusted to coincide with the position of the synchronization light, so that they can be correctly collected by the single-photon detector at the receiver. At the receiver, the synchronization light needs to be photoelectrically converted to generate a path synchronization signal to serve as the gating signal of the detector. Due to circuit errors, differences in the length of the gating signal output cable, and differences in the length of the optical fiber of the path polarization light, the path synchronization signal needs to be delayed by different amounts to ensure that it coincides with the position of the photon in the corresponding path polarization state. Therefore, the receiver needs to design a synchronous acquisition and controllable delay module. In addition, based on the synchronization signal, the receiver also needs to synchronously encode the signal output by the detector to perform the basis vector comparison process for key extraction.

[0095] Preferably, the delay module includes: an analysis unit and a processing unit;

[0096] An analysis unit, configured to decode the synchronization signal to obtain frame data;

[0097] A processing unit is used to synchronously encode the signal based on the frame data using a timestamp and signal strength encoding method to generate encoding information of the synchronization signal; wherein the encoding information is a serial number corresponding to the time point when the synchronization signal arrives at the receiving end.

[0098] Specifically, in a quantum key distribution system, the photon information measured by the receiver correctly corresponds to the photon information emitted by the sender. A fixed-frequency synchronization light signal needs to be emitted, and the synchronization signal is used to synchronously encode the transmitted and received photon information, that is, to record the position of the photon relative to the synchronization light. This allows the photon measured by the receiver to be synchronized with the position of the emitted photon by corresponding to the position of the synchronization light.

[0099] Preferably, the second optical module includes at least four lasers for generating quantum light of at least four corresponding polarization states, wherein the lasers are combined into time-division multiplexed optical channels using polarization-maintaining optical fibers.

[0100] Based on the contents of the above embodiments, the signal synchronization system based on the free-space quantum key distribution system provided by the present invention further includes a coupling module, wherein the input end of the coupling module is respectively connected to the output end of the first optical module and the output end of the second optical module, and is used to couple the synchronization signal and the quantum signal using wavelength division multiplexing technology to obtain a coupled signal and output it to the atmospheric channel through optical fiber.

[0101] Based on the contents of the above embodiments, the signal synchronization system based on the free-space quantum key distribution system provided by the present invention further includes a decomposition module, the output end of which is respectively connected to the input end of the synchronization detector and the input end of the quantum light detector, and is used to receive the coupled signal and use WDM technology to separate the synchronization signal and the quantum signal, and input them into the synchronization detector and the quantum light detector respectively.

[0102] It should be noted that for the aforementioned method embodiments, for the sake of simplicity, they are all expressed as a series of action combinations, but those skilled in the art should be aware that this application is not limited by the order of the actions described, because according to this application, certain steps can be performed in other orders or simultaneously. Secondly, those skilled in the art should also be aware that the embodiments described in the specification are all preferred embodiments, and the actions and modules involved are not necessarily required by this application.

[0103] In the above embodiments, the description of each embodiment has its own focus. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0104] In the several embodiments provided in this application, it should be understood that the disclosed devices can be implemented in other ways. For example, the device embodiments described above are merely schematic. For example, the division of the units is merely a logical function division. In actual implementation, there may be other division methods, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some service interface, and the indirect coupling or communication connection of the device or unit can be electrical or other forms.

[0105] The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of these units may be selected to achieve the purpose of this embodiment according to actual needs.

[0106] In addition, the functional units in the various embodiments of the present application may be integrated into a single processing unit, or each unit may exist physically separately, or two or more units may be integrated into a single unit. The aforementioned integrated units may be implemented in the form of hardware or software functional units.

[0107] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable memory. Based on this understanding, the technical solution of the present application is essentially or the part that contributes to the prior art or all or part of the technical solution can be embodied in the form of a software product, and the computer software product is stored in a memory, including a number of instructions for enabling a computer device (which can be a personal computer, server or network device, etc.) to execute all or part of the steps of the method described in each embodiment of the present application. The aforementioned memory includes: various media that can store program codes, such as a USB flash drive, a read-only memory (ROM), a random access memory (RAM), a mobile hard disk, a magnetic disk or an optical disk.

[0108] Those skilled in the art will understand that all or part of the steps in the various methods of the above embodiments can be completed by instructing related hardware through a program, and the program can be stored in a computer-readable memory, which may include: a flash drive, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk, etc.

[0109] The above is only an exemplary embodiment of the present disclosure and cannot be used to limit the scope of the present disclosure. That is, any equivalent changes and modifications made according to the teachings of the present disclosure are still within the scope of the present disclosure. After considering the specification and practicing the disclosure herein, those skilled in the art will easily think of the implementation scheme of the present disclosure. This application is intended to cover any variation, use or adaptation of the present disclosure, which follows the general principles of the present disclosure and includes common knowledge or customary technical means in the art that are not recorded in the present disclosure. The description and examples are to be regarded as exemplary only, and the scope and spirit of the present disclosure are defined by the claims.

[0110] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0111] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A signal synchronization method based on a free-space quantum key distribution system, characterized in that: include: Turning on the synchronization light source at the transmitting end to enable it to send a synchronization signal to the receiving end; wherein the synchronization signal is a synchronization reference light corresponding to the frame data generated by the synchronization light source after performing signal modulation according to a preset frame identification header; Turning on the signal light source at the transmitting end to transmit a quantum signal to the receiving end; wherein the quantum signal is quantum light corresponding to the quantum key generated after encrypting the target data; Performing frame header recognition on the synchronization signal received by the synchronous detector at the receiving end, generating coding information of the synchronization signal and sending it to the single-photon detector at the receiving end; performing frame header recognition on the synchronization signal received by the synchronous detector at the receiving end and generating coding information of the synchronization signal includes: decoding the synchronization signal to obtain frame data; synchronously encoding the signal based on the frame data using a timestamp and signal strength coding method to generate coding information of the synchronization signal; wherein the coding information is a sequence number corresponding to the time point when the synchronization signal arrives at the receiving end; The quantum signal received by the single-photon detector at the receiving end is matched with the synchronization signal in sequence according to the coding information to complete signal synchronization.

2. The signal synchronization method based on the free-space quantum key distribution system according to claim 1, characterized in that: The modulation mode of the synchronization signal includes pulse width modulation, frequency modulation and phase modulation.

3. The signal synchronization method based on the free-space quantum key distribution system according to claim 1, characterized in that: Decoding the synchronization signal to obtain frame data includes: Scan the frame identification header corresponding to each frame data in the synchronization signal; When any code in the frame identification header is scanned, the duration of each code chip is adjusted to align with the center of the current code chip; Based on the clock of the receiving end and according to the frame synchronization theory, the frame tail corresponding to the frame identification header is restored.

4. The signal synchronization method based on the free-space quantum key distribution system according to claim 1, characterized in that: The sequence correspondence adopts a cross-correlation algorithm based on fast Fourier transform.

5. A signal synchronization system based on a free-space quantum key distribution system, characterized in that: It includes a first optical module and a second optical module, a delay module, a synchronous optical detector and a quantum optical detector; The first optical module is used to generate a synchronization signal and send it to the receiving end, wherein the synchronization signal is a synchronization reference light corresponding to the frame data generated by the synchronization light source after signal modulation according to the preset frame identification header; The second optical module is used to generate a quantum signal and send it to the receiving end, wherein the quantum signal is quantum light corresponding to the quantum key generated after encrypting the target data; A delay module is configured to perform frame header recognition on the synchronization signal received by the synchronization detector at the receiving end, generate coded information of the synchronization signal, and send it to the single-photon detector at the receiving end. The delay module includes: an analysis unit and a processing unit; the analysis unit is configured to decode the synchronization signal to obtain frame data; the processing unit is configured to synchronously encode the signal using a timestamp and signal strength encoding method based on the frame data to generate coded information of the synchronization signal; wherein the coded information is a sequence number corresponding to the time point when the synchronization signal arrives at the receiving end; The quantum light detector is used to sequence the quantum signal received by the single-photon detector at the receiving end with the synchronization signal according to the coding information to complete signal synchronization.

6. The signal synchronization system based on the free-space quantum key distribution system according to claim 5, characterized in that: The quantum light detector includes a gated single-photon detector and a synchronization module; A gated single-photon detector is used to use the synchronization signal as a gate signal to receive the quantum signal corresponding to the scanning period; The synchronization module is used to perform sequence correspondence between the received quantum signal and the synchronization signal according to the coding information to complete signal synchronization.

7. The signal synchronization system based on the free-space quantum key distribution system according to claim 5, characterized in that: It also includes a coupling module, the input end of which is connected to the output end of the first optical module and the output end of the second optical module respectively, and is used to couple the synchronization signal and the quantum signal using wavelength division multiplexing technology to obtain a coupled signal and output it to the atmospheric channel through optical fiber.

8. The signal synchronization system based on the free-space quantum key distribution system according to claim 7, characterized in that: It also includes a decomposition module, the output end of which is connected to the input end of the synchronous detector and the input end of the quantum light detector respectively, for receiving the coupled signal, separating the synchronous signal and the quantum signal using WDM technology, and inputting them into the synchronous detector and the quantum light detector respectively.

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