Quantum key distribution method, device and system

Abstract

The invention discloses a quantum key distribution method, device and system, and belongs to the technical field of networks. The first quantum device generates a modulated optical signal carrying quantum information and classic information. The classic information and the quantum information are simultaneously modulated on at least one polarization of the modulated optical signal. The modulated optical signal includes a plurality of subcarriers at different frequency bands. The classic information and the quantum information are located within different ones of the plurality of subcarriers. The classical information comprises quantum key negotiation information. The first quantum device sends the modulated optical signal to the second quantum device over the optical fiber link. Quantum information and classical information are modulated on the same polarization of an optical signal, and the system capacity is high. The quantum information and the classical information are respectively modulated on subcarriers in different frequency bands in the optical signal, so that respective modulation precision requirements of the classical signal and the quantum signal can be met. And quantum information and classical information are transmitted simultaneously by multiplexing a set of devices, so that the hardware cost is saved.

Description

Technical Field

[0001] The present application relates to the field of network technology, and in particular to a quantum key distribution method, device and system. Background Art

[0002] With the development of quantum computing, quantum attacks pose a huge threat to the currently widely used cryptographic systems. Quantum attacks are attack algorithms running on quantum computers, which can crack many key negotiation algorithms currently used, such as the RSA algorithm (a public key encryption algorithm proposed by Ron Rivest, Adi Shamir and Leonard Adleman) and the Diffie-Hellman key exchange (DH) algorithm used in conjunction with the Advanced Encryption Standard (AES) algorithm and the SM4 block cipher algorithm. Quantum computers are expected to be available in the next few decades. If an eavesdropper intercepts and saves data encrypted using the current encryption algorithm and transmitted over the network, and then uses a quantum attack to crack the encryption algorithm used by the saved data after quantum computers are available, the decrypted plaintext data can be obtained. This is a huge threat to confidential information that needs to be stored for a long time. Therefore, it is urgent to design cryptographic technology that can resist quantum attacks.

[0003] Quantum key distribution (QKD) is a secure key distribution technology that can achieve secure transmission of quantum keys (QK) between two distant communication terminals. The security of quantum key distribution is guaranteed by the basic principles of quantum mechanics. In a quantum network, the transmission of quantum keys is theoretically unconditionally secure.

[0004] In the related art, when implementing quantum key distribution, the transmitter (transmitter, Tx) needs to transmit quantum light signals to the receiver (receiver, Rx) through an optical fiber link to transmit quantum information, and the transmitter and the receiver need to transmit classical information used to negotiate quantum keys through a classical network, so that the transmitter and the receiver can jointly generate the same quantum key. How to complete the transmission of quantum information and classical information between the transmitter and the receiver is the key to realizing quantum key distribution. Summary of the invention

[0005] The present application provides a quantum key distribution method, device and system.

[0006] In a first aspect, a quantum key distribution method is provided. The method includes: a first quantum device generates a modulated optical signal, and the modulated optical signal carries quantum information and classical information. The classical information and the quantum information are simultaneously modulated on at least one polarization of the modulated optical signal. The modulated optical signal includes multiple subcarriers in different frequency bands. The classical information and the quantum information are located in different subcarriers among the multiple subcarriers. The classical information includes quantum key negotiation information. The first quantum device sends a modulated optical signal to the second quantum device via an optical fiber link. The quantum information and the quantum key negotiation information are used by the first quantum device and the second quantum device to jointly generate the same quantum key.

[0007] In this application, quantum information and classical information including quantum key negotiation information are modulated on the same polarization of the optical signal for transmission at the transmitting end. Compared with the scheme of modulating quantum information and classical information on different polarizations of the optical signal for transmission, one polarization degree of freedom is saved, which can double the capacity of the system. Since quantum information and classical information in this application are modulated on subcarriers in different frequency bands in the optical signal, that is, frequency division multiplexing of the optical signal is performed, the receiving end can obtain quantum information and classical information respectively by demodulating different subcarriers, and the demodulation of quantum information is less affected by the signal receiving power of the classical information, so that a higher signal-to-noise ratio of the classical signal and a higher signal-to-noise ratio of the quantum signal can be achieved at the receiving end, while meeting the modulation accuracy requirements of the classical signal and the quantum signal. In addition, a set of devices is reused to transmit quantum information and classical information at the same time, saving hardware costs.

[0008] Optionally, the quantum key agreement information includes one or more of random sampling data, error correction auxiliary information, confidentiality enhancement parameters, basis comparison information, or consistency verification parameters. The quantum key agreement information is information that the first quantum device and the second quantum device need to exchange when performing data processing in the process of generating a quantum key.

[0009] Optionally, the classic information also includes business communication data.

[0010] In this application, the classical information includes not only the quantum key negotiation information between the first quantum device and the second quantum device, but also business communication data. In other words, one optical fiber can be used to simultaneously transmit information for generating quantum keys and business communication data, which can maximize the use of optical fiber links and thus improve bandwidth utilization.

[0011] Optionally, the business communication data includes encrypted data. The encrypted data may be encrypted using a quantum key generated by the first quantum device, or the encrypted data may be encrypted using a session key (or encryption key) fused or derived based on the quantum key.

[0012] Optionally, an implementation method for the first quantum device to generate a modulated optical signal includes: the first quantum device generates an analog modulated signal based on quantum information and classical information, the analog modulated signal includes a quantum signal frequency band obtained based on quantum information modulation and a classical signal frequency band obtained based on classical information modulation, and there is no overlapping frequency between the quantum signal frequency band and the classical signal frequency band. The first quantum device performs signal adjustment processing on the analog modulated signal to obtain a target modulated signal. The difference between the average amplitude of the classical signal frequency band in the target modulated signal and the average amplitude of the quantum signal frequency band is greater than a first amplitude threshold. The first quantum device performs electro-optical modulation on the target modulated signal to obtain a modulated optical signal. Each subcarrier in the modulated optical signal corresponds to a quantum signal frequency band or a classical signal frequency band.

[0013] In this implementation, by performing signal adjustment processing on the analog modulation signal including the quantum signal frequency band and the classical signal frequency band, the average amplitude difference between the quantum signal frequency band and the classical signal frequency band in the target modulation signal obtained after adjustment reaches the set requirement, so that the power intensity of the quantum light signal in the modulated light signal obtained based on the modulation of the target modulation signal can be much weaker than the power intensity of the classical light signal, thereby meeting the transmission performance requirements of the quantum light signal and the classical light signal. As the transmitting end of quantum key distribution, the first quantum device can use a laser to emit an optical signal, and use a digital-to-analog converter (DAC) to generate an analog modulation signal, and finally use an electro-optical modulator to modulate the analog modulation signal after signal modulation processing on the optical signal emitted by the laser to obtain the modulated light signal to be transmitted. The number of lasers, the number of DACs, and the number of electro-optical modulators required for the first quantum device to generate a modulated light signal are all one, and the hardware cost is low.

[0014] Optionally, the difference between the average amplitude of the classical signal frequency band and the average amplitude of the quantum signal frequency band in the analog modulation signal is less than a second amplitude threshold, and the second amplitude threshold is less than the first amplitude threshold.

[0015] In the present application, by making the difference between the average amplitude of the classical signal frequency band and the average amplitude of the quantum signal frequency band in the generated analog modulation signal smaller, the sampling accuracy of the DAC can be guaranteed, so that both the classical signal and the quantum signal have a higher signal-to-noise ratio.

[0016] Optionally, the first quantum device performs signal adjustment processing on the analog modulated signal to obtain a target modulated signal, including: the first quantum device uses a filter to filter the analog modulated signal to obtain the target modulated signal, wherein the quantum signal frequency band is located in a first frequency band of the filter, the classical signal frequency band is located in a second frequency band of the filter, and the frequency attenuation of the first frequency band is greater than the frequency attenuation of the second frequency band.

[0017] This implementation adopts a filter to realize signal adjustment processing of analog modulation signal. By designing the frequency response function of the filter to be related to the distribution of quantum signal frequency band and classical signal frequency band in the analog modulation signal, the frequency attenuation of the frequency band formed by the filter in the quantum signal frequency band is large, and the function of this frequency band is similar to the stop band of the filter, and the frequency attenuation of the frequency band formed by the filter in the classical signal frequency band is small, and the function of this frequency band is similar to the pass band of the filter. Thus, the average amplitude difference between the classical signal frequency band and the quantum signal frequency band in the modulation signal after filtering processing meets the set requirements.

[0018] Optionally, the first quantum device performs signal adjustment processing on the analog modulated signal to obtain another implementation method of the target modulated signal, including: the first quantum device performs branch processing on the analog modulated signal according to the distribution area of ​​the quantum signal frequency band and the classical signal frequency band in the analog modulated signal to obtain multiple branch signals. The first quantum device uses multiple filters to filter the multiple branch signals respectively to obtain one or more quantum filtered signals and one or more classical filtered signals, each quantum filtered signal includes one or more adjacent quantum signal frequency bands, and each classical filtered signal includes one or more adjacent classical signal frequency bands. The first quantum device performs attenuation processing on one or more quantum filtered signals. The first quantum device combines all classical filtered signals and all quantum filtered signals that have been attenuated to obtain the target modulated signal.

[0019] This implementation adopts shunt filtering to achieve signal adjustment processing of analog modulated signals. The shunt filtering method can more easily form a flatter frequency response in the passband and stopband, which can reduce the difficulty of digital signal processing.

[0020] Optionally, another implementation method for the first quantum device to generate a modulated optical signal includes: the first quantum device generates a first analog modulation signal according to quantum information, and generates a second analog modulation signal according to classical information. The first analog modulation signal includes one or more quantum signal frequency bands, the second analog modulation signal includes one or more classical signal frequency bands, and there is no overlapping frequency between the quantum signal frequency band and the classical signal frequency band. The first quantum device attenuates the first analog modulation signal so that the difference between the average amplitude of the classical signal frequency band in the second analog modulation signal and the average amplitude of the quantum signal frequency band in the attenuated first analog modulation signal is greater than a third amplitude threshold. The first quantum device generates a modulated optical signal based on the second analog modulation signal and the attenuated first analog modulation signal. Each subcarrier in the modulated optical signal corresponds to a quantum signal frequency band or a classical signal frequency band.

[0021] In this implementation, by attenuating the first analog modulation signal including the quantum signal frequency band, the average amplitude difference between the quantum signal frequency band in the attenuated first analog modulation signal and the classical signal frequency band in the second analog modulation signal can reach the set requirement, thereby making the power intensity of the quantum light signal in the modulated light signal finally modulated much weaker than the power intensity of the classical light signal, thereby meeting the transmission performance requirements of the quantum light signal and the classical light signal.

[0022] Optionally, an implementation manner in which the first quantum device generates a modulated optical signal based on the second analog modulation signal and the attenuated first analog modulation signal includes: the first quantum device combines the second analog modulation signal and the attenuated first analog modulation signal to obtain a combined analog modulation signal. The first quantum device electro-optically modulates the combined analog modulation signal to obtain a modulated optical signal.

[0023] In this implementation, the first quantum device, as the transmitting end of quantum key distribution, can use a laser to emit an optical signal, and use two DACs to generate two analog modulation signals respectively, and then attenuate one analog modulation signal containing the quantum signal frequency band, and then combine it with another analog modulation signal containing the classical signal frequency band, and finally use an electro-optical modulator to modulate the combined analog modulation signal on the optical signal emitted by the laser to obtain the modulated optical signal to be transmitted. The number of lasers and electro-optical modulators required for the first quantum device to generate a modulated optical signal is one, and the number of DACs is two, so the hardware cost is low.

[0024] Optionally, another implementation of the first quantum device generating a modulated optical signal based on the second analog modulation signal and the attenuated first analog modulation signal includes: the first quantum device uses a first electro-optical modulator to electro-optically modulate the attenuated first analog modulation signal to obtain a first optical signal. The first quantum device uses a second electro-optical modulator to electro-optically modulate the second analog modulation signal to obtain a second optical signal. The first quantum device combines the first optical signal and the second optical signal to obtain a modulated optical signal.

[0025] In this implementation, the first quantum device, as the transmitting end of quantum key distribution, can use a laser to emit an optical signal, and use an optical beam splitter to split the optical signal into two paths, and use two DACs to generate two analog modulation signals respectively, and then use an electro-optical modulator to modulate the analog modulation signal containing the quantum signal frequency band on one optical signal of the laser after attenuation, and use another electro-optical modulator to modulate the other analog modulation signal containing the classical signal frequency band on another optical signal of the laser, and finally use an optical combiner to combine the two modulated optical signals to obtain the modulated optical signal to be transmitted. The number of lasers required for the first quantum device to generate a modulated optical signal is one, and the number of DACs and electro-optical modulators are both two, so the hardware cost is low.

[0026] Optionally, the first analog modulation signal and the second analog modulation signal are generated by different digital-to-analog converters respectively.

[0027] Optionally, the modulated optical signal comes from the same laser.

[0028] In a second aspect, a quantum key distribution method is provided. The method includes: a second quantum device receives a modulated optical signal sent by a first quantum device through an optical fiber link, and the modulated optical signal carries quantum information and classical information. The classical information and the quantum information are simultaneously modulated on at least one polarization of the modulated optical signal. The modulated optical signal includes a plurality of subcarriers in different frequency bands, and the classical information and the quantum information are located in different subcarriers among the plurality of subcarriers. The classical information includes quantum key negotiation information. The second quantum device obtains quantum information and classical information based on the modulated optical signal. The quantum information and the quantum key negotiation information are used by the first quantum device and the second quantum device to jointly generate the same quantum key.

[0029] Since the quantum information and classical information in this application are modulated on subcarriers in different frequency bands in the optical signal, that is, the optical signal is frequency-division multiplexed, so that the receiving end can obtain quantum information and classical information respectively by demodulating different subcarriers, and the demodulation of quantum information is less affected by the signal receiving power of classical information, so that a higher signal-to-noise ratio of the classical signal and a higher signal-to-noise ratio of the quantum signal can be achieved at the receiving end, while meeting the modulation accuracy requirements of the classical signal and the quantum signal. In addition, multiplexing a set of devices to transmit quantum information and classical information at the same time saves hardware costs.

[0030] Optionally, the quantum key agreement information includes one or more of random sampling data, error correction auxiliary information, confidentiality enhancement parameters, basis comparison information or consistency verification parameters.

[0031] Optionally, the classic information also includes business communication data.

[0032] Optionally, the business communication data includes encrypted data.

[0033] Optionally, an implementation method for the second quantum device to obtain quantum information and classical information based on a modulated optical signal includes: the second quantum device uses a coherent detector to convert the received modulated optical signal into an analog signal, the analog signal includes a quantum signal frequency band and a classical signal frequency band, there is no overlapping frequency between the quantum signal frequency band and the classical signal frequency band, the quantum signal frequency band corresponds to a subcarrier carrying quantum information in the modulated optical signal, and the classical signal frequency band corresponds to a subcarrier carrying classical information in the modulated optical signal. The second quantum device performs a received signal adjustment process on the analog signal to obtain a target signal, wherein the difference between the average amplitude of the classical signal frequency band in the target signal and the average amplitude of the quantum signal frequency band is less than an amplitude threshold. The second quantum device uses an analog-to-digital converter to sample the classical signal frequency band and the quantum signal frequency band of the target signal respectively to obtain classical information and quantum information.

[0034] In this implementation, the receiving end only needs one analog-to-digital converter to complete the sampling of the analog signal, and the hardware cost is low.

[0035] Optionally, the second quantum device performs a received signal adjustment process on the analog signal to obtain a target signal, including: the second quantum device uses a filter to filter the analog signal to obtain the target signal, wherein the quantum signal frequency band is located in a first frequency band of the filter, the classical signal frequency band is located in a second frequency band of the filter, and the frequency attenuation of the first frequency band is less than the frequency attenuation of the second frequency band.

[0036] This implementation adopts a filter to implement signal adjustment processing of analog signals. By designing the frequency response function of the filter to be related to the distribution of the quantum signal frequency band and the classical signal frequency band in the analog signal, the frequency attenuation of the frequency band formed by the filter in the quantum signal frequency band is small, and the function of this frequency band is similar to the passband of the filter, and the frequency attenuation of the frequency band formed by the filter in the classical signal frequency band is large, and the function of this frequency band is similar to the stopband of the filter. As a result, the average amplitudes of the classical signal frequency band and the quantum signal frequency band in the target signal after filtering are similar.

[0037] Optionally, another implementation method of the second quantum device performing a received signal adjustment process on the analog signal to obtain a target signal includes:

[0038] The second quantum device performs branch processing on the analog signal according to the distribution area of ​​the quantum signal frequency band and the classical signal frequency band in the analog signal to obtain multiple branch signals. The second quantum device uses multiple filters to filter the multiple branch signals respectively to obtain one or more quantum filter signals and one or more classical filter signals, each quantum filter signal includes one or more adjacent quantum signal frequency bands, and each classical filter signal includes one or more adjacent classical signal frequency bands. The second quantum device performs attenuation processing on one or more classical filter signals. The second quantum device combines all quantum filter signals and all classical filter signals that have been attenuated to obtain a target signal.

[0039] This implementation adopts shunt filtering to achieve signal adjustment processing of analog signals. The shunt filtering method is more likely to form a flatter frequency response in the passband and stopband, which can reduce the difficulty of digital signal processing.

[0040] Optionally, another implementation method for the second quantum device to obtain quantum information and classical information based on the modulated optical signal includes: the second quantum device uses a coherent detector to convert the received modulated optical signal into an analog signal, the analog signal includes a quantum signal frequency band and a classical signal frequency band, there is no overlapping frequency between the quantum signal frequency band and the classical signal frequency band, the quantum signal frequency band corresponds to the subcarrier carrying quantum information in the modulated optical signal, and the classical signal frequency band corresponds to the subcarrier carrying classical information in the modulated optical signal. The second quantum device uses the first analog-to-digital converter to sample the classical signal frequency band of the analog signal to obtain classical information. The second quantum device uses the second analog-to-digital converter to sample the quantum signal frequency band of the analog signal to obtain quantum information.

[0041] In this implementation, the receiving end uses two analog-to-digital converters to sample the classical signal frequency band and the quantum signal frequency band of the analog signal respectively to meet the respective sampling accuracy requirements.

[0042] In a third aspect, a quantum key distribution device is provided. The device includes multiple functional modules, and the multiple functional modules interact with each other to implement the method in the first aspect and its embodiments. The multiple functional modules can be implemented based on software, hardware, or a combination of software and hardware, and the multiple functional modules can be arbitrarily combined or divided based on the specific implementation.

[0043] In a fourth aspect, a quantum key distribution device is provided. The device includes multiple functional modules, and the multiple functional modules interact with each other to implement the method in the above second aspect and its various embodiments. The multiple functional modules can be implemented based on software, hardware, or a combination of software and hardware, and the multiple functional modules can be arbitrarily combined or divided based on the specific implementation.

[0044] In a fifth aspect, a quantum key distribution system is provided, including: a first quantum device and a second quantum device, the first quantum device and the second quantum device are connected via an optical fiber link, the first quantum device is used to implement the method in the above-mentioned first aspect and its various embodiments, and the second quantum device is used to implement the method in the above-mentioned second aspect and its various embodiments.

[0045] In a sixth aspect, a quantum device is provided, comprising: a processor and a memory. The memory is used to store a computer program, and the computer program includes program instructions. The processor is used to call the computer program to implement the method in the first aspect and its various embodiments or the method in the second aspect and its various embodiments.

[0046] In the seventh aspect, a computer-readable storage medium is provided, on which instructions are stored. When the instructions are executed by a processor, the method of the above-mentioned first aspect and its various embodiments is implemented, or the method of the above-mentioned second aspect and its various embodiments is implemented.

[0047] In an eighth aspect, a computer program product is provided, comprising a computer program, which, when executed by a processor, implements the method of the above-mentioned first aspect and its various embodiments, or implements the method of the above-mentioned second aspect and its various embodiments.

[0048] In the ninth aspect, a chip is provided, which includes a programmable logic circuit and / or program instructions. When the chip is running, it implements the method in the above-mentioned first aspect and its various embodiments, or implements the method in the above-mentioned second aspect and its various embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 This is a schematic diagram of an implementation process of quantum key distribution provided by an embodiment of the present application;

[0050] Figure 2 It is a schematic diagram of a quantum key generation system provided by the related technology;

[0051] Figure 3 It is a schematic diagram of transmission of classical information and quantum information provided by relevant technologies;

[0052] Figure 4 It is a modulation diagram of classical information and quantum information provided by related technologies;

[0053] Figure 5 It is a schematic diagram of the structure of a quantum key distribution system provided in an embodiment of the present application;

[0054] Figure 6It is a flowchart of a quantum key distribution method provided in an embodiment of the present application;

[0055] Figure 7 This is a schematic diagram of an implementation process of a first quantum device generating a modulated optical signal provided in an embodiment of the present application;

[0056] Figure 8 It is a schematic diagram of performing signal adjustment processing on an analog modulation signal provided by an embodiment of the present application;

[0057] Fig. 9 is another schematic diagram of performing signal adjustment processing on an analog modulation signal provided in an embodiment of the present application;

[0058] Fig.10 It is a schematic diagram of another signal adjustment process for an analog modulation signal provided in an embodiment of the present application;

[0059] Fig.11 It is a schematic diagram of another signal adjustment process for an analog modulation signal provided in an embodiment of the present application;

[0060] Fig.12 It is a schematic diagram of another signal adjustment process for an analog modulation signal provided in an embodiment of the present application;

[0061] Fig.13 It is a schematic diagram of a generation process of a modulated optical signal provided in an embodiment of the present application;

[0062] Fig.14 It is a schematic diagram of another implementation process of generating a modulated optical signal by a first quantum device provided in an embodiment of the present application;

[0063] Fig.15 is a schematic diagram of another process of generating a modulated optical signal provided in an embodiment of the present application;

[0064] Fig.16 This is a schematic diagram of another process of generating a modulated optical signal provided in an embodiment of the present application;

[0065] Fig.17 is a structural schematic diagram of a coherent receiver provided in an embodiment of the present application;

[0066] Fig.18 is a structural schematic diagram of a single polarization receiver provided in an embodiment of the present application;

[0067] Fig.19 is a schematic diagram of the structure of a coherent detector provided in an embodiment of the present application;

[0068] Fig. 20 It is a schematic diagram of performing a received signal adjustment process on an analog signal provided by an embodiment of the present application;

[0069] Fig.21 It is a schematic diagram of another embodiment of the present application providing a received signal adjustment process for an analog signal;

[0070] Fig. 22 It is a structural schematic diagram of a quantum key distribution device provided in an embodiment of the present application;

[0071] Fig.23 is a schematic diagram of the structure of another quantum key distribution device provided in an embodiment of the present application;

[0072] Fig.24 It is a schematic diagram of the hardware structure of a quantum device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0073] In order to make the objectives, technical solutions and advantages of the present application clearer, the implementation methods of the present application will be further described in detail below with reference to the accompanying drawings.

[0074] With the rapid development of information technology, people have higher and higher requirements for the security of communication. Quantum communication is a technology developed on the basis of quantum mechanics and classical information theory. It uses the basic principles of quantum mechanics to ensure the security of communication. In quantum communication technology, quantum key distribution is the most mature technology. It realizes the unconditional and secure distribution of symmetric keys between legal senders and receivers on the premise that some security keys have been shared. Unconditional security means that there are no restrictions on the computing resources of eavesdroppers in the channel.

[0075] There are many kinds of quantum key distribution protocols and systems. The two mainstream applications are discrete-variable quantum key distribution (DVQKD) and continuous-variable quantum key distribution (CVQKD). DVQKD requires encoding of single-photon signals, and single-photon detectors need to work in a low-temperature environment. CVQKD encodes coherent light and uses a low-noise coherent receiver (also called a coherent detector) for detection. It does not require a single-photon source and a single-photon detector, and can reuse the existing industrial chain in the field of communications to a great extent. Therefore, CVQKD has the potential advantages of high integration and low cost.

[0076] CVQKD uses a coherent state as a light source at the transmitting end, and modulates the center position of the coherent state through a modulator. After the modulated quantum light signal is transmitted through an optical fiber, it is detected by a homodyne detector or a heterodyne detector at the receiving end. The analog electrical signal output by the detector is sampled by analog-to-digital conversion (ADC) and then enters the data processing module, which performs corresponding data processing and evaluation to finally obtain a secure quantum key.

[0077] For example, Figure 1 Schematic diagram of the implementation process of quantum key distribution provided by the embodiment of the present application. Figure 1 As shown, the transmitter first generates quantum random numbers as the original coding information, and then encodes the coherent state according to the generated quantum random numbers (i.e., performs quantum state preparation), and then transmits the encoded coherent state signal (i.e., quantum light signal) to the receiver through the quantum channel. Correspondingly, the receiver generates quantum random numbers as the original key information, and uses a homodyne detector or a heterodyne detector to randomly measure the X or P regular component of the coherent state according to the generated quantum random numbers (i.e., performs quantum state measurement). Afterwards, the transmitter and the receiver perform data processing and evaluation respectively through the data processing module to generate the same quantum key. See Figure 1 ,The functions of the data processing module usually include signal ,processing, parameter estimation, data error correction and privacy amplification (PA).

[0078] Signal processing usually refers to the digital signal processing of the sampled signal at the receiving end to obtain reasonable regular component measurement results.

[0079] Parameter estimation refers to the process in which the sender and receiver randomly compare some data to determine the amount of information stolen by the eavesdropper in the channel, and determine whether the current distribution process can still generate a secure quantum key. If a secure quantum key cannot be generated, the system will usually choose to terminate the processing flow and wait for the accumulation of data in the next round of distribution. If a secure quantum key can be generated, the subsequent processing flow will continue. In this process, a classical channel is required so that the sender and receiver can synchronize information losslessly, and the synchronized information is the randomly sampled data.

[0080] Data error correction refers to the process of sharing the syndrome or other error correction auxiliary information through a lossless classical channel between the sender and the receiver to complete the key data synchronization between the sender and the receiver. The key after error correction can be referred to as the corrected key. In this process, a classical channel is also required so that the sender and the receiver can synchronize information losslessly, and the information synchronized is the error correction auxiliary information.

[0081] Confidentiality enhancement means that the sender and receiver perform the same hash operation, compress the corrected keys of both parties, and output the final quantum key. In this process, a classical channel is also required so that the sender and receiver can synchronize information losslessly. The key parameters of the hash operation (referred to as confidentiality enhancement parameters) are synchronized.

[0082] Optionally, see Figure 1 The function of the data processing module also includes basis comparison. In some protocols, since the receiving end randomly measures a certain canonical component of the coherent state, it does not have information about the two components at the same time. Therefore, a comparison process is required between signal processing and parameter estimation, that is, the receiving end discloses to the transmitting end which specific canonical component it has measured, and the transmitting end only retains the information of the canonical component for generating quantum keys. In this process, a classical channel is also required so that the sender and receiver can synchronize information losslessly. What is synchronized is the relevant information of the measurement basis used by the receiving end (referred to as basis comparison information).

[0083] Optionally, see Figure 1 The function of the data processing module also includes consistency verification. In order to ensure the consistency of the quantum keys generated by the sender and receiver, and avoid some small probability errors in logic or protocol. Usually, a key consistency verification process is also required. This process can be added after the data error correction step, or it can also be added after the confidentiality enhancement step, or later, when the application end uses the key. In this process, a classical channel is also required so that the sender and receiver can synchronize information losslessly. What is synchronized is the key parameters of the consistency verification operation (referred to as the consistency verification parameters).

[0084] It is not difficult to see from the data processing module introduced above that in the process of quantum key distribution, the transmitter and the receiver need to frequently use classical channel communication to losslessly transmit information related to each step of data processing. The traditional solution is to use another set of classical communication systems to transmit this part of information. For example, the data processing module of the QKD device transmits the classical information to be sent to the router, and the router transmits the classical information to be sent to the receiving end through the communication network according to the communication routing protocol. The router at the receiving end receives the information and parses it and transmits it to the data processing module at the receiving end. Considering that the transmitter and the receiver are connected by an optical fiber link in order to transmit quantum optical signals, this optical fiber link can also be used to carry classical channels. That is, the quantum channel and the classical channel are in the same optical fiber, but use different wavelengths, and the two are wavelength division multiplexed. This is also a commonly used solution in the industry. For example, Figure 2 This is a schematic diagram of a quantum key generation system provided by the relevant technology. Figure 2As shown in the figure, the classical communication system and the quantum key distribution system are two separate systems. The data processing module of the quantum key distribution system transmits the classical information it needs to send to the classical communication system, and the classical communication system completes the two-way communication between the sender and the receiver through the classical channel. Among them, the classical channel does not necessarily require a direct connection between the sender and the receiver, and information transmission can also be achieved through a classical communication network. For the case where the classical channel is a direct optical fiber connection between the sender and the receiver, it is possible to consider selecting a classical communication module with a different wavelength from the quantum optical signal, and the two use the same optical fiber in a wavelength division multiplexing manner to save optical fiber resources.

[0085] However, considering that the traditional solution requires an independent classical communication system and has a high implementation cost, related technologies have proposed a solution to modulate quantum information and classical information into the same optical signal for joint transmission. The following two implementation solutions are common.

[0086] The first implementation, such as Figure 3 As shown, the transmitter uses a laser, and its output light enters a dual-polarization (DP) modulator. Different arbitrary waveform generators (AWG) are used to generate the signal waveform of quantum information and the signal waveform of classical information respectively, and then the quantum signal and the classical signal are modulated on different polarization states of the optical signal in the dual polarization modulator. A common dual polarization modulator is a dual polarization in-phase and quadrature (IQ) modulator (DP-IQ modulator), which is a commonly used device in optical communications. For example, see Figure 3 , AWG1 is used to generate a signal waveform of quantum information, and then the quantum signal is modulated on one polarization state of the optical signal, such as X polarization; AWG2 is used to generate a signal waveform of classical information, and then the classical signal is modulated on another polarization state of the optical signal, such as Y polarization. In this way, the output light of the dual polarization modulator contains both quantum optical signals and classical optical signals, and the two are in a polarization multiplexed state. At the receiving end, a polarization controller is first used to restore the polarization crosstalk of the optical fiber channel noise, and then the quantum optical signal and the classical optical signal are separated by a polarization demultiplexing device and sent to different polarization detectors respectively, such as sending the separated quantum optical signal to an X polarization detector, and sending the separated classical optical signal to a Y polarization detector. The polarization demultiplexing device can be, for example, a polarization diversity coherent receiver. In this way, the common transmission of classical information and quantum information is achieved. Compared with the traditional solution, it is more integrated and saves a laser.

[0087] However, the first implementation is essentially equivalent to merging the classical channel and the quantum channel through polarization multiplexing. At the receiving end, the polarization controller needs to first restore the polarization change in the channel, which has a high hardware cost. In addition, since the classical information occupies one polarization, the quantum information can only use the other polarization. For the quantum channel, it is equivalent to losing half of the bandwidth, which affects the transmission efficiency of quantum information.

[0088] The second implementation scheme is Figure 4 As shown in the figure, the transmitter adds a quantum signal modulation on the basis of the classical signal modulation result. Taking the binary phase shift keying (BPSK) signal as an example, the classical signal originally has only two points on the phase plane, that is, the lower left point represents the classical information 0, and the upper right point represents the classical information 1. Taking Gaussian modulation as an example, the quantum signal is a two-dimensional quasi-continuous Gaussian distribution on the phase plane. The superposition of the two is equivalent to superimposing a two-dimensional quasi-continuous Gaussian distribution on the BPSK modulation result. Since the amplitude of the quantum signal is much weaker than that of the classical signal, even if the quantum modulation is superimposed on the BPSK modulation result of the classical signal, the signal-to-noise ratio of the BPSK signal is hardly affected. This realizes the simultaneous generation and transmission of classical information and quantum information.

[0089] Although the second implementation scheme can realize the simultaneous generation of classical signals and quantum signals on the same polarization, its modulation and demodulation are very difficult and it is very difficult to implement in practice. In terms of modulation, due to the large difference in amplitude between classical and quantum signals, simultaneous modulation is difficult. In terms of reception, changes in the received power of the classical signal caused by slight fluctuations in the channel will have a great impact on the demodulation of the quantum signal, resulting in a degradation of the signal-to-noise ratio of the quantum signal, and therefore it is usually unable to meet the modulation accuracy requirements of the quantum signal.

[0090] Based on this, the present application provides a technical solution that can solve the problem of signal-to-noise ratio degradation of quantum signals with weaker amplitudes due to the large difference in amplitudes between classical signals and quantum signals when quantum signals and classical signals are generated simultaneously on the same polarization. The specific technical solution is as follows: a first quantum device generates a modulated optical signal, which carries quantum information and classical information, and the classical information and the quantum information are simultaneously modulated on at least one polarization of the modulated optical signal. Here, the simultaneous modulation of classical information and quantum information on at least one polarization of the modulated optical signal means that at least one polarization of the modulated optical signal carries classical information and quantum information at the same time, and the classical information and quantum information can also be simultaneously modulated on multiple polarizations of the modulated optical signal, that is, multiple polarizations of the modulated optical signal can carry classical information and quantum information at the same time. For example, the X polarization of the modulated optical signal can carry classical information and quantum information, and the Y polarization can carry classical information or quantum information, or the Y polarization of the modulated optical signal can carry classical information and quantum information, and the X polarization can carry classical information or quantum information, or, the X polarization and Y polarization of the modulated optical signal both carry classical information and quantum information. In addition, the modulated optical signal generated by the first quantum device includes multiple subcarriers in different frequency bands, and the classical information and the quantum information are located in different subcarriers among the multiple subcarriers, that is, the quantum information and the classical information in the modulated optical signal are modulated on subcarriers in different frequency bands, respectively. Among them, the classical information includes quantum key negotiation information. The first quantum device sends a modulated optical signal to the second quantum device through an optical fiber link, and the quantum information carried by the modulated optical signal and the quantum key negotiation information in the classical information are used by the first quantum device and the second quantum device to jointly generate the same quantum key. The present application realizes the transmission of quantum information and classical information modulated on the same polarization of the optical signal. Compared with the first implementation scheme mentioned above, it saves one polarization degree of freedom and can double the capacity of the system. Compared with the second implementation scheme mentioned above, it is different from superimposing and modulating quantum signals on the modulation results of classical signals for transmission. Since the quantum information and classical information in this application are modulated on subcarriers in different frequency bands in the optical signal, that is, frequency division multiplexing of the optical signal, the receiving end can obtain quantum information and classical information respectively by demodulating different subcarriers, and the demodulation of quantum information is less affected by the signal receiving power of classical information, so that a higher signal-to-noise ratio of classical signals and a higher signal-to-noise ratio of quantum signals can be achieved at the receiving end, while meeting the modulation accuracy requirements of classical signals and quantum signals. The quantum device involved in this application can be a quantum key distribution device.

[0091] Optionally, the quantum key agreement information includes one or more of random sampling data, error correction auxiliary information, confidentiality enhancement parameters, basis comparison information or consistency verification parameters. Among them, the random sampling data refers to the information that the first quantum device and the second quantum device need to synchronize when performing the parameter estimation step. Error correction auxiliary information refers to the information that the first quantum device and the second quantum device need to synchronize when performing the data error correction step. Confidentiality enhancement parameters refer to the information that the first quantum device and the second quantum device need to synchronize when performing the confidentiality enhancement step. Basis comparison information refers to the information that the first quantum device and the second quantum device need to synchronize when performing the basis comparison step. Consistency verification parameters refer to the information that the first quantum device and the second quantum device need to synchronize when performing the consistency verification step. The specific implementation methods of the parameter estimation step, the data error correction step, the confidentiality enhancement step, the basis comparison step and the consistency verification step can be referred to. Figure 1 The quantum key distribution process shown in the figure will not be repeated in detail in the embodiments of the present application.

[0092] In the embodiment of the present application, the classical information may include business communication data in addition to the quantum key negotiation information between the first quantum device and the second quantum device. In other words, one optical fiber can be used to simultaneously transmit information for generating quantum keys and business communication data, which can maximize the use of optical fiber links and thus improve bandwidth utilization.

[0093] Optionally, the business communication data includes encrypted data. The encrypted data may be encrypted using a quantum key generated by the first quantum device, or the encrypted data may be encrypted using a session key (or encryption key) fused or derived based on the quantum key.

[0094] The technical solution provided in the embodiments of the present application is described in detail below.

[0095] The embodiments of the present application can be applied to quantum key distribution systems. For example, Figure 5 Schematic diagram of a quantum key distribution system provided by an embodiment of the present application. Figure 5 As shown, the quantum key distribution system 500 includes a first quantum device and a second quantum device. The first quantum device and the second quantum device are connected via an optical fiber link. Optionally, the quantum key distribution system 500 can be a CVQKD system, or a CVQKD module, or a coherent system that combines CVQKD with classical communication.

[0096] In the embodiment of the present application, the first quantum device is used as the transmitting end of the quantum key distribution system, and the second quantum device is used as the receiving end of the quantum key distribution system. The steps performed by the first quantum device and the second quantum device in the quantum key distribution process are detailed in the following method embodiment. For example, Figure 6Schematic diagram of a quantum key distribution method provided by an embodiment of the present application. Figure 6 As shown, the method includes but is not limited to the following steps 601 to 603.

[0097] Step 601: A first quantum device generates a modulated optical signal, which carries quantum information and classical information. The classical information and the quantum information are simultaneously modulated on at least one polarization of the modulated optical signal. The modulated optical signal includes multiple subcarriers in different frequency bands. The classical information and the quantum information are located in different subcarriers among the multiple subcarriers. The classical information includes quantum key negotiation information.

[0098] Optionally, the modulated optical signal comes from the same laser, that is, the modulated optical signal is obtained by modulating the laser emitted by a laser. The frequency band spacing of multiple subcarriers in the modulated optical signal does not exceed one optical communication channel to meet the maximum modulation bandwidth requirement of the laser. For example, an optical communication channel is 100 gigahertz (GHz), and the frequency band spacing of multiple subcarriers does not exceed one optical communication channel, that is, the difference between the maximum frequency and the minimum frequency of the multiple subcarriers is less than or equal to 100 GHz. Of course, the optical communication channel can also be greater than 100 GHz, and the embodiment of the present application does not limit the size of the optical communication channel. Quantum key negotiation information can be a quantum key distribution system (such as Figure 1 The classical information that needs to be transmitted in the data processing module of CVQKD) is shown.

[0099] Optionally, the general process of the first quantum device generating a modulated optical signal is as follows: first, the acquired quantum information and classical information are generated into a digital modulation signal according to a preset format, then the generated digital modulation signal is converted into a digital-to-analog format to obtain an analog modulation signal, then the analog modulation signal is subjected to signal adjustment processing, and finally the analog modulation signal subjected to signal adjustment processing is subjected to electro-optical modulation to obtain a modulated optical signal. Among them, the preset format used when generating the digital modulation signal includes but is not limited to the preset frequency interval of the quantum information, the preset frequency interval of the classical information, and the digital modulation format used by the quantum information and the classical information. The embodiment of the present application does not limit the digital modulation format used by the quantum information and the classical information. There is no overlapping frequency between the preset frequency interval of the quantum information and the preset frequency interval of the classical information. In the embodiment of the present application, the frequency interval where the quantum information in the generated analog modulation signal is located is called the quantum signal frequency band, which is obtained based on the modulation of the quantum information. The frequency interval where the classical information in the analog modulation signal is located is called the classical signal frequency band, which is obtained based on the modulation of the classical information. Since quantum information and classical information are modulated in different preset frequency ranges when they are digitally modulated, there is no overlapping frequency between the quantum signal frequency band and the classical signal frequency band in the analog modulation signal.

[0100] Optionally, the first quantum device may use a DAC to perform digital-to-analog conversion on the digital modulation signal to obtain an analog modulation signal that includes both the quantum signal frequency band and the classical signal frequency band, and then further process the analog modulation signal to obtain a modulated optical signal. Alternatively, the first quantum device may also use two digital-to-analog converters to perform a DAC conversion on the digital modulation signal respectively to obtain an analog modulation signal that includes the quantum signal frequency band (hereinafter referred to as the first analog modulation signal) and an analog modulation signal that includes the classical signal frequency band (hereinafter referred to as the second analog modulation signal), and then further process the first analog modulation signal and the second analog modulation signal to obtain a modulated optical signal. These two implementation methods are described below.

[0101] In the first implementation, the implementation process of the first quantum device generating a modulated optical signal is as follows: Figure 7 As shown, including but not limited to the following steps A1 to A3.

[0102] Step A1: A first quantum device generates an analog modulation signal according to quantum information and classical information, where the analog modulation signal includes a quantum signal frequency band and a classical signal frequency band.

[0103] Optionally, the analog modulated signal includes one or more quantum signal frequency bands and one or more classical signal frequency bands. There is no overlapping frequency between the quantum signal frequency band and the classical signal frequency band in the analog modulated signal. At least one of the classical signal frequency bands carries quantum key negotiation information. There are many possible distribution positions of the quantum signal frequency band and the classical signal frequency band in the analog modulated signal. The embodiments of the present application are described by taking the following four possible situations as examples.

[0104] In the first possible case, the quantum signal frequency band in the analog modulation signal is in the low frequency band, and the classical signal frequency band is in the high frequency band. Optionally, the analog modulation signal includes one quantum signal frequency band and two classical signal frequency bands, wherein the quantum signal frequency band is 10 megahertz (MHz) to 1GHz, one classical signal frequency band is 1.1GHz to 10GHz, and the other classical signal frequency band is 11GHz to 20Hz; or, the quantum signal frequency band is 10MHz to 10GHz, one classical signal frequency band is 10.1GHz to 20GHz, and the other classical signal frequency band is 21GHz to 80Hz; and so on.

[0105] For example, Figure 8 Figure 2 shows a distribution method of quantum signal frequency band and classical signal frequency band in analog modulation signal. Figure 8 As shown, the analog modulation signal includes a quantum signal frequency band Q and three classical signal frequency bands C1-C3. The quantum signal frequency band Q is in the low frequency band, and the classical signal frequency bands C1-C3 are in the high frequency band.

[0106] In the second possible case, the quantum signal frequency band in the analog modulation signal is in the high frequency band, and the classical signal frequency band is in the low frequency band. Optionally, the analog modulation signal includes a quantum signal frequency band and a classical signal frequency band, wherein the quantum signal frequency band is 10.1 GHz to 11 GHz, and the classical signal frequency band is 100 MHz to 10 GHz; or the quantum signal frequency band is 50 GHz to 60 GHz, and the classical signal frequency band is 100 MHz to 40 GHz; and so on.

[0107] For example, Fig. 9 Another distribution method of quantum signal frequency band and classical signal frequency band in analog modulation signal is shown. Fig. 9 As shown, the analog modulation signal includes a quantum signal frequency band Q and three classical signal frequency bands C1-C3. The quantum signal frequency band Q is in the high frequency band, and the classical signal frequency bands C1-C3 are in the low frequency band.

[0108] In the third possible case, the analog modulation signal includes multiple classical signal frequency bands, and the quantum signal frequency band is between the multiple classical signal frequency bands. Fig.10 Another distribution mode of quantum signal frequency band and classical signal frequency band in analog modulation signal is shown. Fig.10 As shown, the analog modulation signal includes a quantum signal frequency band Q and three classical signal frequency bands C1-C3. The quantum signal frequency band Q is between the classical signal frequency band C1 and the classical signal frequency band C2.

[0109] In the fourth possible case, the analog modulation signal includes multiple classical signal frequency bands and multiple quantum signal frequency bands, and the multiple quantum signal frequency bands and the multiple classical signal frequency bands are alternately distributed. For example, Fig.11 Another distribution mode of quantum signal frequency band and classical signal frequency band in analog modulation signal is shown. Fig.11 As shown, the analog modulation signal includes two quantum signal frequency bands Q1-Q2 and three classical signal frequency bands C1-C3. Among them, the classical signal frequency band C1, quantum signal frequency band Q1, classical signal frequency band C2, classical signal frequency band C3, and quantum signal frequency band Q2 are arranged in order from low frequency to high frequency.

[0110] Above Figures 8 to 11The abscissa in the signal shown is the frequency, and the ordinate is the average amplitude of the signal frequency band. In the embodiment of the present application, the amplitude of the analog modulated signal is mainly used to indicate the average power or average energy of the corresponding frequency band subcarrier converted to the optical signal. Optionally, the average amplitude of a signal frequency band in the analog modulated signal can be the mean (average power density) or integral (average power sum in the frequency band) of the corresponding frequency band of the signal frequency band in the power spectrum density of the analog modulated signal. Amplitude can also refer to the average signal energy in a modulation cycle, or the average energy of a symbol. If it is understood as the average amplitude of an analog electrical signal, it is often proportional to the square root of the aforementioned expression values. Or when the numerical value is not accurately required and only the trend of size is identified, the average amplitude of a signal frequency band in the analog modulated signal can also be simply regarded as the square mean of the voltage when the signal in the signal frequency band is converted back to voltage, or the voltage root mean square value, or the mean of the absolute value of the voltage. When comparing the amplitudes of two signals, if the average power difference of the two signals is too large, such as a difference of several orders of magnitude, the signal amplitude is usually converted to decibels (dB) for expression. At this time, the difference in dB values ​​of the two signal amplitudes has a direct conversion relationship with the difference in the amplitudes of the two signals. This is a common representation method in the field of electrical signals and optical signals.

[0111] Step A2: The first quantum device performs signal adjustment processing on the analog modulation signal to obtain a target modulation signal, wherein the difference between the average amplitude of the classical signal frequency band and the average amplitude of the quantum signal frequency band in the target modulation signal is greater than a first amplitude threshold.

[0112] Optionally, when dB is used as the signal amplitude unit, when the signal amplitude is described by using numerical values ​​such as average power and or average power density, the ratio of the average amplitude of the classical signal frequency band to the average amplitude of the quantum signal frequency band can be selected as the first amplitude threshold. The first amplitude threshold is, for example, 10 dB. Optionally, the difference between the average amplitude of the classical signal frequency band in the analog modulated signal and the average amplitude of the quantum signal frequency band (for example, in dB) is less than the second amplitude threshold, and the second amplitude threshold is less than the first amplitude threshold. In an embodiment of the present application, by making the difference between the average amplitude of the classical signal frequency band and the average amplitude of the quantum signal frequency band in the generated analog modulated signal smaller, the sampling accuracy of the DAC can be guaranteed, so that both the classical signal and the quantum signal have a higher signal-to-noise ratio. When the sampling accuracy of the DAC allows, the average amplitude of the quantum signal frequency band in the analog modulated signal can be reduced.

[0113] See also Figures 8 to 11, which respectively show schematic diagrams of signal adjustment processing for multiple analog modulation signals with different signal frequency band distributions, the signal adjustment processing includes filtering processing, wherein the filtering frequency response is determined according to the distribution of the quantum signal frequency band and the classical signal frequency band. The average amplitude difference between the classical signal frequency band and the quantum signal frequency band in the target modulation signal is significantly greater than the average amplitude difference between the classical signal frequency band and the quantum signal frequency band in the analog modulation signal.

[0114] In an embodiment of the present application, two electrical modulation signals that originally had similar amplitudes and similar signal-to-noise ratios but were in different frequency bands are converted into electrical modulation signals with one high amplitude and one low amplitude by filtering. Specifically, an analog modulation signal including a quantum signal frequency band and a classical signal frequency band is generated by a DAC, and then the analog modulation signal is filtered so that the average amplitude of the quantum signal frequency band is significantly lower than the average amplitude of the classical signal frequency band. Generally speaking, there will be significant differences in the average amplitudes of the quantum signal frequency band and the classical signal frequency band after filtering, and the maximum difference can even exceed 50dB.

[0115] Optionally, one implementation of step A2 is that the first quantum device uses a filter to filter the analog modulation signal to obtain a target modulation signal, wherein the quantum signal frequency band is located in a first frequency band of the filter, the classical signal frequency band is located in a second frequency band of the filter, and the frequency attenuation of the first frequency band is greater than the frequency attenuation of the second frequency band.

[0116] This implementation adopts a filter to realize signal adjustment processing of analog modulation signal. By designing the frequency response function of the filter to be related to the distribution of quantum signal frequency band and classical signal frequency band in the analog modulation signal, the frequency attenuation of the frequency band formed by the filter in the quantum signal frequency band is large, and the function of this frequency band is similar to the stop band of the filter, and the frequency attenuation of the frequency band formed by the filter in the classical signal frequency band is small, and the function of this frequency band is similar to the pass band of the filter. The frequency attenuation of each frequency band in the filter can be set according to actual needs, as long as the average amplitude difference between the classical signal frequency band and the quantum signal frequency band in the modulation signal after filtering processing meets the set requirements.

[0117] Optionally, in addition to the above-mentioned method of directly designing a filter to perform signal adjustment processing on the analog modulated signal, the signal adjustment effect can also be achieved by first splitting, then filtering and attenuating respectively, and then combining, so that the difference between the average amplitude of the classical signal frequency band and the average amplitude of the quantum signal frequency band in the target modulated signal obtained in the end is greater than the first amplitude threshold. The split filtering method is more likely to form a flatter frequency response in the passband and stopband, which can reduce the difficulty of digital signal processing. Specifically, another implementation method of the above step A2 includes the following steps A21 to A24.

[0118] In step A21, the first quantum device performs branching processing on the analog modulation signal according to the distribution areas of the quantum signal frequency band and the classical signal frequency band in the analog modulation signal to obtain multiple branched signals.

[0119] The number of branched signals may be the sum of the number of distribution areas of the quantum signal frequency band and the number of distribution areas of the classical signal frequency band. A distribution area of ​​the quantum signal frequency band may include one or more adjacent quantum signal frequency bands. A distribution area of ​​the classical signal frequency band may include one or more adjacent classical signal frequency bands. For example, Figure 8 , the number of distribution areas of the quantum signal frequency band in the analog modulation signal is 1 (including the quantum signal frequency band Q), and the number of distribution areas of the classical signal frequency band is also 1 (including the classical signal frequency bands C1-C3). Accordingly, the first quantum device can use a splitter to split the analog modulation signal into two paths to obtain two branch signals. For another example, refer to Fig.10 , the number of distribution areas of the quantum signal frequency band in the analog modulated signal is 1 (including the quantum signal frequency band Q), and the number of distribution areas of the classical signal frequency band is 2 (one of the distribution areas includes the classical signal frequency band C1, and the other distribution area includes the classical signal frequency bands C2 and C3). Accordingly, the first quantum device can use a splitter to divide the analog modulated signal into three paths to obtain three branch signals.

[0120] Optionally, the amplitudes of the multiple branch signals may be the same or different.

[0121] In step A22, the first quantum device uses multiple filters to filter the multiple branch signals respectively to obtain one or more quantum filtered signals and one or more classical filtered signals, each quantum filtered signal includes one or more adjacent quantum signal frequency bands, and each classical filtered signal includes one or more adjacent classical signal frequency bands.

[0122] Optionally, the branch signal, like the original analog modulation signal, contains both the quantum signal frequency band and the classical signal frequency band, and the branch signal is filtered by a filter so that the filtered branch signal only contains the quantum signal frequency band or the classical signal frequency band, thus obtaining a quantum filtered signal and a classical filtered signal. Figure 8 The analog modulated signal shown is filtered by a low-pass filter on a branch signal to obtain a quantum filtered signal, which includes the quantum signal frequency band Q; and filtered by a high-pass filter on another branch signal to obtain a classical filtered signal, which includes the classical signal frequency band C1-C3.

[0123] In step A23, the first quantum device performs attenuation processing on the one or more quantum filter signals.

[0124] By performing attenuation processing on the quantum filter signal, the amplitude of the quantum filter signal can be reduced.

[0125] In step A24, the first quantum device combines all classical filtered signals and all quantum filtered signals that have undergone attenuation processing to obtain a target modulated signal.

[0126] The following takes the quantum signal frequency band in the low frequency band and the classical signal frequency band in the high frequency band (corresponding to the first possible situation in the above step A1) as an example to introduce the implementation process of the above steps A21 to A24. Fig.12 Schematic diagram of a signal adjustment process for an analog modulation signal provided by an embodiment of the present application. Fig.12 As shown, the analog modulation signal includes a quantum signal frequency band Q and three classical signal frequency bands C1-C3. The quantum signal frequency band Q is in the low frequency band, and the classical signal frequency bands C1-C3 are in the high frequency band. After the analog modulation signal enters the signal adjustment unit, it is first split into two by a splitter, and the amplitudes of the two output branch signals can be the same or different.

[0127] See also Fig.12 , assuming that the upstream output of the splitter is a quantum signal path, this path will pass through a low-pass filter with appropriate attenuation. After low-pass filtering and attenuation, the amplitude of the quantum signal frequency band in the low frequency band is attenuated to a certain extent, while the amplitude of the classical signal frequency band in the high frequency band experiences greater attenuation. The addition of attenuation is to ensure that the output amplitude of the quantum signal frequency band meets the preset requirements. In addition, if the system itself sets the quantum signal amplitude of the final output to be much lower than the classical signal amplitude, the low-pass filtering of the quantum signal path can also be omitted, because the amplitude of the classical signal frequency band of this path will be much smaller than the amplitude of the classical signal frequency band of the classical signal path, and the two have almost no effect after the combination.

[0128] Please continue to see Fig.12 , the lower output of the splitter is a classical signal path, which will pass through a high-pass filter. After high-pass filtering, the quantum signal band in the low frequency band is almost completely filtered out, and the classical signal band in the high frequency band is passed through with a higher amplitude. If the high-pass filter is an active filter, it may also produce a certain gain on the amplitude of the classical signal band.

[0129] The ultimate goal of low-pass filtering and attenuation of the quantum signal path and high-pass filtering of the classical signal path is to make the average amplitude of the quantum signal frequency band in the signal output by the quantum signal path (i.e., the quantum filtered signal after attenuation) much lower than the average amplitude of the classical signal frequency band in the signal output by the classical signal path (i.e., the classical filtered signal).

[0130] Please continue to see Fig.12 The signal output by the quantum signal path and the signal output by the classical signal path are combined by a combiner to finally obtain a target modulation signal. In the target modulation signal, the average amplitude of the quantum signal frequency band in the low frequency band is significantly lower than the average amplitude of the classical signal frequency band in the high frequency band.

[0131] Optionally, when the splitter uses an unbalanced directional coupler, the amplitude ratio of its output split may not be around 50:50, and may even reach a very different amplitude ratio of 1:99. In this case, the output path with a high splitting ratio (such as 99%) can be selected as the classical signal path, and the output path with a lower splitting ratio (such as 1%) can be selected as the quantum signal path. In this case, the quantum signal path only needs to add a low-pass filter, and no additional attenuator is needed.

[0132] Alternatively, the splitter can be replaced by another device with a splitting function (which can be called a circuit duplexer). For an input signal containing multiple frequency bands, the circuit duplexer can output signals containing different frequency bands. This function is similar to an optical wavelength demultiplexer. The circuit duplexer can be used as a frequency demultiplexer for circuit signals. For example, if the first output of the circuit duplexer only contains signals in the low frequency band, it is equivalent to Fig.12 The ordinary splitter in the scheme shown is added with a low-pass filter; the second output contains only high-frequency signals, which is equivalent to Fig.12 The solution shown is a normal splitter coupled with a high pass filter. Fig.12 In the scheme shown, if a circuit duplexer is used to replace the ordinary splitter in the signal adjustment unit, the low-frequency output path of the circuit duplexer is selected as the quantum signal path. At this time, the quantum signal path does not need to add a low-pass filter, and only needs to add appropriate attenuation; the high-frequency output path of the circuit duplexer is selected as the classical signal path, and the classical signal path does not need to add a high-pass filter. Of course, if the filtering effect of the circuit duplexer is not good enough, the quantum signal path and the classical signal path can also add corresponding filters, but the requirements for each filter are reduced.

[0133] Optionally, when the quantum signal frequency band in the analog modulation signal is in the high frequency band and the classical signal frequency band is in the low frequency band (corresponding to the second possible situation in the above step A1), the implementation process of filtering the analog modulation signal can refer to Fig.12 In the implementation process shown, the internal structure of the signal adjustment unit is the same, the difference is that in this case, a high-pass filter + attenuation is added to the quantum signal path after the splitter, while a low-pass filter is added to the classical signal path.

[0134] Optionally, when the analog modulation signal includes multiple classical signal frequency bands, and the quantum signal frequency band is between multiple classical signal frequency bands (corresponding to the third possible situation in step A1 above), the implementation process of filtering the analog modulation signal can refer to Fig.12 In the implementation process shown, the internal structure of the signal adjustment unit is the same, the difference is that in this case, a bandpass filter + attenuation is added to the quantum signal path after the splitter, while a bandstop filter is added to the classical signal path.

[0135] Optionally, when the analog modulation signal includes multiple classical signal frequency bands and multiple quantum signal frequency bands, and the multiple quantum signal frequency bands and the multiple classical signal frequency bands are alternately distributed (corresponding to the fourth possible situation in step A1 above), the implementation process of filtering the analog modulation signal can refer to Fig.12 In the implementation process shown, the internal structure of the signal adjustment unit is still similar, but considering that the design and manufacture of multi-frequency bandpass filters and band-stop filters is relatively difficult, a multi-branch and then merge method can be selected. Each branch corresponds to one or more adjacent quantum signal frequency bands, or one or more adjacent classical signal frequency bands. For the branch of the quantum signal frequency band, a combination of bandpass filtering + attenuation is used; for the branch of the classical signal frequency band, a bandpass filter is used. Finally, the various branches are merged together.

[0136] Step A3: The first quantum device performs electro-optical modulation on the target modulation signal to obtain a modulated optical signal.

[0137] Wherein, each subcarrier in the modulated optical signal corresponds to a quantum signal frequency band or a classical signal frequency band in the analog modulated signal generated in step A1. A subcarrier can be an optical signal. The target modulated signal, like the analog modulated signal, includes one or more quantum signal frequency bands and one or more classical signal frequency bands. Accordingly, the modulated optical signal obtained by electro-optically modulating the target modulated signal includes one or more quantum optical signals and one or more classical optical signals. Wherein, the power intensity of the quantum optical signal in the modulated optical signal is much weaker than the power intensity of the classical optical signal.

[0138] In this implementation, signal adjustment processing is performed on the analog modulation signal including the quantum signal frequency band and the classical signal frequency band so that the average amplitude difference between the quantum signal frequency band and the classical signal frequency band in the target modulation signal obtained after adjustment meets the set requirements. In this way, the power intensity of the quantum light signal in the modulated light signal obtained based on the modulation of the target modulation signal can be much weaker than the power intensity of the classical light signal, thereby meeting the transmission performance requirements of the quantum light signal and the classical light signal.

[0139] exist Figure 7In the implementation mode of generating a modulated optical signal by the first quantum device shown, the first quantum device, as the transmitting end of quantum key distribution, can use a laser to emit an optical signal, and use a DAC to generate an analog modulated signal, and finally use an electro-optical modulator to modulate the analog modulated signal after signal modulation processing on the optical signal emitted by the laser to obtain a modulated optical signal to be transmitted. The number of lasers, the number of DACs, and the number of electro-optical modulators required for the first quantum device to generate a modulated optical signal are all one, and the hardware cost is low.

[0140] For example, Fig.13 Schematic diagram of a process of generating a modulated optical signal provided in an embodiment of the present application. Fig.13 As shown, first, the acquired quantum information and classical information are used to generate a digital modulation signal according to a preset format, wherein the quantum information and classical information are modulated in different frequency ranges of the digital modulation signal. Here, the modulation frequency bands selected by the quantum information and classical information are as follows: Figure 8 As shown in the figure, for example. Specifically, a digital signal processing algorithm can be used to convert a digital signal containing quantum information and classical information into a digital modulated signal. The digital signal processing algorithm generally includes frequency shifting, upsampling, pulse shaping and pre-compensation. Secondly, the digital modulated signal passes through a DAC to form an analog modulated signal. Then, the analog modulated signal passes through a signal adjustment unit to form a target modulated signal. The implementation flow of this process refers to step A2 above. After that, the target modulated signal is usually added to the electrical input port of the electro-optical modulator after passing through a power amplifier (not shown in the figure). At this time, the output light of the laser enters the optical input port of the electro-optical modulator, and the optical signal outputs a modulated optical signal after passing through the electro-optical modulator. The modulated optical signal carries the information of the target modulated signal. Finally, the modulated optical signal passes through an attenuator and is transmitted through an optical fiber link. Among them, the attenuator is used to adjust the output power of the modulated optical signal so that the modulated optical signal reaches a predetermined optical power level.

[0141] In the second implementation, the implementation process of the first quantum device generating a modulated optical signal is as follows: Fig.14 As shown, including but not limited to the following steps B1 to B3.

[0142] Step B1: The first quantum device generates a first analog modulation signal according to quantum information, and generates a second analog modulation signal according to classical information, wherein the first analog modulation signal includes one or more quantum signal frequency bands, and the second analog modulation signal includes one or more classical signal frequency bands.

[0143] There is no overlap between the quantum signal frequency band in the first analog modulation signal and the classical signal frequency band in the second analog modulation signal. The frequency band selection of the quantum signal frequency band and the classical signal frequency band can refer to the relevant description in the above step A1, for example, it can be the four possible situations described in step A1, and the embodiments of the present application will not be repeated here.

[0144] Optionally, the first analog modulation signal and the second analog modulation signal are generated by different DACs, respectively. In this implementation, two DACs can be selected to generate analog modulation signals, wherein one DAC only modulates the quantum signal, specifically, only samples the frequency interval where the quantum information in the digital modulation signal is located, then the analog modulation signal (i.e., the first analog modulation signal) output by the DAC only contains the quantum signal frequency band, and only some DAC sampling background noise is present at the classical signal frequency band; the other DAC only modulates the classical signal, specifically, only samples the frequency interval where the classical information in the digital modulation signal is located, then the analog modulation signal (i.e., the second analog modulation signal) output by the DAC only contains the classical signal frequency band, and mainly the DAC sampling background noise is present at the quantum signal frequency band.

[0145] In this implementation, since different DACs are used to modulate the quantum signal and the classical signal respectively, the sampling accuracy of the quantum signal and the classical signal can be guaranteed separately, so that both the classical signal and the quantum signal have a higher signal-to-noise ratio.

[0146] Step B2: The first quantum device performs attenuation processing on the first analog modulation signal so that the difference between the average amplitude of the classical signal frequency band in the second analog modulation signal and the average amplitude of the quantum signal frequency band in the attenuated first analog modulation signal is greater than a third amplitude threshold.

[0147] By attenuating the first analog modulation signal, the amplitude of the first analog modulation signal can be reduced, that is, the average amplitude of the quantum signal frequency band in the first analog modulation signal can be reduced. Optionally, the third amplitude threshold is the same as the first amplitude threshold in step A2, for example, 10 dB.

[0148] Step B3: The first quantum device generates a modulated optical signal based on the second analog modulation signal and the attenuated first analog modulation signal.

[0149] Each subcarrier in the modulated optical signal corresponds to a quantum signal frequency band in the first analog modulation signal or a classical signal frequency band in the second analog modulation signal.

[0150] Optionally, the first quantum device may also filter the second analog modulation signal, and then generate a modulated optical signal based on the filtered second analog modulation signal and the attenuated first analog modulation signal. In this way, the DAC sampling background noise corresponding to the quantum signal frequency band position in the second analog modulation signal can be further suppressed to avoid affecting the signal quality of the subcarrier corresponding to the quantum signal frequency band in the modulated optical signal. Among them, the implementation method of filtering the second analog modulation signal can refer to the filtering processing method of the analog modulation signal in the above step A2, and the corresponding filter can be designed according to the number and arrangement of quantum signal frequency bands and classical signal frequency bands. For example, when the quantum signal frequency bands are all in the low frequency band, the filter selects a high-pass filter; when the quantum signal frequency bands are all in the high frequency band, the filter selects a low-pass filter; when one or more quantum signal frequency bands are in the middle of multiple classical signal frequency bands, the filter selects a band-stop filter, or a multi-stopband filter. Of course, if the DAC sampling background noise in the second analog modulation signal is extremely low, the signal quality of the quantum signal frequency band position after the combination can be ignored, then the second analog modulation signal can be filtered.

[0151] In this implementation, by attenuating the first analog modulation signal including the quantum signal frequency band, the average amplitude difference between the quantum signal frequency band in the attenuated first analog modulation signal and the classical signal frequency band in the second analog modulation signal can reach the set requirement, thereby making the power intensity of the quantum light signal in the modulated light signal finally modulated much weaker than the power intensity of the classical light signal, thereby meeting the transmission performance requirements of the quantum light signal and the classical light signal.

[0152] Optionally, one implementation of step B3 is that the first quantum device combines the second analog modulation signal and the first analog modulation signal that has been attenuated to obtain a combined analog modulation signal. The first quantum device performs electro-optical modulation based on the combined analog modulation signal to obtain a modulated optical signal. In this implementation, the first quantum device, as the transmitting end of quantum key distribution, can use a laser to emit an optical signal, and use two DACs to generate two analog modulation signals respectively, and then attenuate one analog modulation signal containing the quantum signal frequency band, and then combine it with another analog modulation signal containing the classical signal frequency band, and finally use an electro-optical modulator to modulate the combined analog modulation signal on the optical signal emitted by the laser to obtain a modulated optical signal to be transmitted. The number of lasers and electro-optical modulators required for the first quantum device to generate a modulated optical signal is one, and the number of DACs is two, so the hardware cost is low.

[0153] For example, Fig.15 FIG. 1 is a schematic diagram of another process of generating a modulated optical signal provided in an embodiment of the present application. Fig.15 As shown, first, the acquired quantum information and classical information are used to generate a digital modulation signal according to a preset format, wherein the quantum information and classical information are modulated in different frequency ranges of the digital modulation signal. Here, the modulation frequency bands selected by the quantum information and classical information are as follows: Figure 8 As shown in the figure, for example. Specifically, a digital signal processing algorithm can be used to convert a digital signal containing quantum information and classical information into a digital modulated signal. The digital signal processing algorithm generally includes frequency shifting, upsampling, pulse shaping and pre-compensation. Secondly, the digital modulated signal passes through DAC1 to form an analog modulated signal 1 containing a quantum signal frequency band, and the digital modulated signal passes through DAC2 to form an analog modulated signal 2 containing a classical signal frequency band. Then, the analog modulated signal 1 passes through the attenuator in the signal adjustment unit and reaches the combiner; the analog modulated signal 2 passes through the filter in the signal adjustment unit and reaches the combiner. After that, the modulated signal output by the combiner is usually added to the electrical input port of the electro-optical modulator after passing through a power amplifier (not shown in the figure). At this time, the output light of the laser enters the optical input port of the electro-optical modulator, and the optical signal outputs a modulated optical signal after passing through the electro-optical modulator. The modulated optical signal carries the information of the modulated signal output by the combiner. Finally, the modulated optical signal passes through the attenuator and is transmitted through the optical fiber link. Among them, the attenuator is used to adjust the output power of the modulated optical signal so that the modulated optical signal reaches a predetermined optical power level.

[0154] Optionally, another implementation of step B3 is that the first quantum device uses a first electro-optic modulator to electro-optically modulate the attenuated first analog modulation signal to obtain a first optical signal. The first quantum device uses a second electro-optic modulator to electro-optically modulate the second analog modulation signal to obtain a second optical signal. The first quantum device combines the first optical signal and the second optical signal to obtain a modulated optical signal. In this implementation, the first quantum device, as the transmitting end of quantum key distribution, can use a laser to emit an optical signal, and use an optical beam splitter to divide the optical signal into two paths, and use two DACs to generate two analog modulation signals respectively, and then attenuate one analog modulation signal containing the quantum signal frequency band, and use an electro-optic modulator to modulate it on one optical signal of the laser, and use another electro-optic modulator to modulate another analog modulation signal containing the classical signal frequency band on another optical signal of the laser, and finally use an optical combiner to combine the two modulated optical signals to obtain a modulated optical signal to be transmitted. The number of lasers required for the first quantum device to generate modulated optical signals is one, and the number of DACs and electro-optic modulators are both two, so the hardware cost is relatively low. Among them, the intensities of the two optical signals output by the optical beam splitter can be similar, or there can be certain differences. For example, the light used to modulate the analog modulation signal containing the quantum signal frequency band can be weaker.

[0155] For example, Fig.16 FIG. 1 is another schematic diagram of a generation process of a modulated optical signal provided in an embodiment of the present application. Fig.16 As shown, first, the acquired quantum information and classical information are used to generate a digital modulation signal according to a preset format, wherein the quantum information and classical information are modulated in different frequency ranges of the digital modulation signal. Here, the modulation frequency bands selected by the quantum information and classical information are as follows: Figure 8 As shown in the figure, for example. Specifically, a digital signal processing algorithm may be used to convert a digital signal containing quantum information and classical information into a digital modulation signal. The digital signal processing algorithm generally includes frequency shifting, upsampling, pulse shaping and pre-compensation. Secondly, the digital modulation signal passes through DAC1 to form an analog modulation signal 1 containing a quantum signal frequency band, and the digital modulation signal passes through DAC2 to form an analog modulation signal 2 containing a classical signal frequency band. Then, the analog modulation signal 1 passes through the attenuator in the signal adjustment unit and is output to the electrical input port of the electro-optical modulator 1; the analog modulation signal 2 passes through the filter in the signal adjustment unit and is output to the electrical input port of the electro-optical modulator 2. At this time, the output light of the laser passes through the optical beam splitter and is divided into two paths that enter the optical input ports of the electro-optical modulator 1 and the electro-optical modulator 2 respectively. One optical signal is modulated by the electro-optical modulator 1 and output to the optical combiner. The modulated optical signal carries the information of the analog modulation signal 1; the other optical signal is modulated by the electro-optical modulator 2 and is output to the optical combiner. The modulated optical signal carries the information of the analog modulation signal 2. After that, the optical combiner combines the two modulated optical signals to obtain a modulated optical signal. Finally, the modulated optical signal passes through the attenuator and is transmitted through the optical fiber link. The attenuator is used to adjust the output power of the modulated optical signal so that the modulated optical signal reaches a predetermined optical power level.

[0156] Optionally, there are two common ways to modulate a signal to a specific subcarrier frequency band. One way is to shift the frequency of the signal in the digital domain, and the frequency shift amount is the characteristic frequency of the corresponding carrier (generally the center frequency), and then convert it into an analog signal of the corresponding subcarrier through a DAC, that is, the carrier of the subcarrier segment is directly modulated and generated by the DAC. This method has high requirements on the bandwidth and sampling rate of the DAC. Another way is to generate a baseband modulation signal directly by the DAC without performing frequency shift processing in the digital domain (or perform a small amount of frequency shift to avoid noise near DC), and then pass through a mixer together with another analog local oscillator (quasi-single-tone sinusoidal local oscillator), and then shift the frequency to the corresponding subcarrier frequency band. Both methods can achieve the purpose of generating a subcarrier modulation signal in this application.

[0157] Step 602: The first quantum device sends the modulated optical signal to the second quantum device through an optical fiber link.

[0158] The quantum information and quantum key negotiation information are used by the first quantum device and the second quantum device to jointly generate the same quantum key.

[0159] Further, after the second quantum device receives the modulated optical signal sent by the first quantum device through the optical fiber link, the following step 603 is continued to be executed.

[0160] Step 603: The second quantum device acquires quantum information and classical information based on the modulated optical signal.

[0161] Furthermore, the second quantum device can perform data processing based on the quantum key negotiation information in the acquired classical information, and generate the same quantum key as the first quantum device based on the acquired quantum information. The implementation of this process can refer to Figure 1 The related steps shown in the embodiment of the present application will not be repeated here.

[0162] Optionally, the first implementation of step 603 includes the following steps C1 to C3.

[0163] In step C1, the second quantum device uses a coherent detector to convert the received modulated light signal into an analog signal, where the analog signal includes a quantum signal frequency band and a classical signal frequency band.

[0164] Among them, there is no overlapping frequency between the quantum signal frequency band and the classical signal frequency band, the quantum signal frequency band corresponds to the subcarrier carrying quantum information in the modulated optical signal, and the classical signal frequency band corresponds to the subcarrier carrying classical information in the modulated optical signal. If the modulated optical signal is generated using the above steps A1 to A3, the frequency distribution of the quantum signal frequency band and the classical signal frequency band in the analog signal here is the same as the frequency distribution of the quantum signal frequency band and the classical signal frequency band in the analog modulated signal in the above step A1. Alternatively, if the modulated optical signal is generated using the above steps B1 to B3, the frequency distribution of the quantum signal frequency band in the analog signal here is the same as the frequency distribution of the quantum signal frequency band in the first analog modulated signal in the above step B1, and the frequency distribution of the classical signal frequency band in the analog signal is the same as the frequency distribution of the classical signal frequency band in the second analog modulated signal in the above step B1.

[0165] In a first possible implementation, the coherent detector is a conventional coherent receiver. For example, Fig.17 is a schematic diagram of the structure of a coherent receiver provided in an embodiment of the present application. Fig.17As shown, the coherent receiver includes a polarization beam splitter (PBS), multiple beam splitters (BS) and four balanced photodetectors (BPD). Among them, the four BPDs are BPD1 to BPD4. After the optical signal to be measured enters the coherent receiver, it is first divided into two by the PBS to obtain an X-polarized light signal and a Y-polarized light signal. Among them, the X-polarized light signal is divided into two after entering the BS, and the two outputs enter BPD1 and BPD2 respectively. BPD1 and BPD2 combine the delay difference of the local oscillator light to measure the I component and Q component of the X-polarized light signal respectively. When measuring quantum optical signals, the industry often refers to the I component of the quantum optical signal as the x-regular component, and the Q component as the p-regular component. The Y polarized optical signal is similar. After entering the BS, it is split into two. The two outputs enter BPD3 and BPD4 respectively. BPD3 and BPD4 combine the delay difference of the local oscillator light to measure the I component (x regular component) and Q component (p regular component) of the Y polarized optical signal respectively. In order to make the BPD work, the coherent receiver also needs a local oscillator (LO) to provide local oscillator light. The local oscillator light is split into four beams after two levels of BS beam splitting and enters BPD1 to BPD4 respectively. Among them, the two beams of light entering BPD1 and BPD2 have a phase difference of about 90 degrees with the optical signal of the corresponding path; the two beams of light entering BPD3 and BPD4 have a phase difference of about 90 degrees with the optical signal of the corresponding path.

[0166] In the second possible implementation, the coherent detector is a single polarization receiver. A single polarization receiver only receives signals on one polarization and is usually used in scenarios where the transmitter only sends single polarization signals. For example, Fig.18 is a schematic diagram of the structure of a single polarization receiver provided in an embodiment of the present application. Fig.17 As shown, the single polarization receiver includes a polarization controller (PC), multiple BSs and two BPDs. The two BPDs are divided into BPD1 and BPD2. After the optical signal to be measured enters the single polarization receiver, it is first rotated to a specific polarization state by the PC, and then split into two by the BS. The two outputs enter BPD1 and BPD2 respectively. BPD1 and BPD2 combine the delay difference of the local oscillator light to measure the I component and Q component of the incoming polarized light signal respectively. Similarly, the single polarization receiver also requires a local oscillator to provide local oscillator light. The local oscillator light is split into two by the BS and enters BPD1 and BPD2 respectively.

[0167] In a third possible implementation, a coherent detector can use only one BPD to receive the optical signal. Fig.19 is a schematic diagram of the structure of a coherent detector provided in an embodiment of the present application. Fig.19 As shown, the coherent detector includes a PC and a BPD. After the optical signal to be measured enters the coherent detector, it is first rotated to a specific polarization state by the PC, and then enters the BPD. The BPD combines the delay difference of the local oscillator light to measure the I component and Q component of the polarized light signal. Similarly, the coherent detector also requires a local oscillator to provide local oscillator light to enter the BPD.

[0168] The output signals of all BPDs in the coherent detector are analog signals converted by the coherent detector.

[0169] In step C2, the second quantum device performs a receiving signal adjustment process on the analog signal to obtain a target signal.

[0170] Among them, the difference between the average amplitude of the classical signal frequency band in the target signal and the average amplitude of the quantum signal frequency band is less than the amplitude threshold. Since the quantum light signal in the optical signal received by the receiving end is much weaker than the classical light signal, if the analog signal output by the coherent detector is directly sampled by the analog-to-digital converter (ADC) without adjustment, the sampling noise of the quantum signal frequency band corresponding to the quantum light signal in the analog signal is large, which affects the system performance. By adjusting the analog signal for receiving the signal, the average amplitude of the quantum signal frequency band corresponding to the quantum light signal in the adjusted analog signal (i.e., the target signal) can be roughly similar to the average amplitude of the classical signal frequency band corresponding to the classical light signal, so that the sampling accuracy of the ADC can be fully utilized, the sampling noise of the quantum signal frequency band corresponding to the quantum light signal can be reduced, and the loss of system performance can be minimized.

[0171] Optionally, one implementation of step C2 is that the second quantum device uses a filter to filter the analog signal to obtain a target signal. The quantum signal frequency band is located in the first frequency band of the filter, and the classical signal frequency band is located in the second frequency band of the filter. The frequency attenuation of the first frequency band is less than the frequency attenuation of the second frequency band.

[0172] This implementation adopts a filter to implement signal adjustment processing of analog signals. By designing the frequency response function of the filter to be related to the distribution of the quantum signal frequency band and the classical signal frequency band in the analog signal, the frequency attenuation of the frequency band formed by the filter in the quantum signal frequency band is small, and the function of this frequency band is similar to the passband of the filter, and the frequency attenuation of the frequency band formed by the filter in the classical signal frequency band is large, and the function of this band is similar to the stopband of the filter. The frequency attenuation of each frequency band in the filter can be set according to actual needs, as long as the average amplitude of the classical signal frequency band and the quantum signal frequency band in the target signal after filtering is similar.

[0173] Optionally, in addition to the above-mentioned method of directly designing a filter to adjust the received signal of the analog signal, the signal adjustment effect can be achieved by first splitting, then filtering and attenuating respectively, and then combining, so that the difference between the average amplitude of the classical signal frequency band and the average amplitude of the quantum signal frequency band in the target signal finally obtained is less than the set amplitude threshold. The split filtering method is more likely to form a flatter frequency response in the passband and stopband, which can reduce the difficulty of digital signal processing. Specifically, another implementation method of the above step C2 includes the following steps C21 to C24.

[0174] In step C21, the second quantum device performs branching processing on the analog signal according to the distribution areas of the quantum signal frequency band and the classical signal frequency band in the analog signal to obtain multiple branched signals.

[0175] The implementation method of this step C21 can refer to the above-mentioned step A21, and the embodiment of the present application will not be repeated here.

[0176] In step C22, the second quantum device uses multiple filters to filter the multiple branch signals respectively to obtain one or more quantum filtered signals and one or more classical filtered signals, each quantum filtered signal includes one or more adjacent quantum signal frequency bands, and each classical filtered signal includes one or more adjacent classical signal frequency bands.

[0177] The implementation method of this step C22 can refer to the above-mentioned step A22, and the embodiment of the present application will not be repeated here.

[0178] In step C23, the second quantum device performs attenuation processing on the one or more classical filtered signals.

[0179] By attenuating the classical filtered signal, the amplitude of the classical filtered signal can be reduced.

[0180] In step C24, the second quantum device combines all quantum filter signals and all classical filter signals that have undergone attenuation processing to obtain a target signal.

[0181] The following takes the quantum signal frequency band in the low frequency band and the classical signal frequency band in the high frequency band (corresponding to the first possible situation in the above step A1) as an example to introduce the implementation process of the above steps C21 to C24. Fig. 20 and Fig.21 They are schematic diagrams of adjusting a received signal of an analog signal provided by an embodiment of the present application. Fig. 20 or Fig.21 As shown, the analog signal includes a quantum signal frequency band Q and three classical signal frequency bands C1-C3. The quantum signal frequency band Q is in the low frequency band, and the classical signal frequency bands C1-C3 are in the high frequency band. After the analog signal enters the receiving signal adjustment unit, it is first split into two by a splitter. Among them, Fig. 20 A duplex frequency division device is used as a splitter, which can separate the classical signal frequency band and the quantum signal frequency band in the analog signal. Fig.21 A power divider is used as a splitter, and the amplitudes of the two signals output by the power divider are basically the same.

[0182] See also Fig. 20 or Fig.21 , assuming that the uplink output of the splitter is a quantum signal path, this path will pass through a low-pass filter. After low-pass filtering, the classical signal band in the high frequency band is basically filtered out, and the quantum signal band in the low frequency band is passed through with a high amplitude.

[0183] Please continue to see Fig. 20 or Fig.21 , the splitter's lower output is the classic signal path. Fig. 20 In the classic case, the signal path can be passed through a full-band attenuation or through a high-pass filter with appropriate attenuation. Fig.21 In the example, the classical signal path can pass through a high-pass filter with appropriate attenuation. The purpose of attenuating the classical signal path is to make the average amplitude of the classical signal frequency band in the signal output by the classical signal path (i.e., the classical filtered signal) close to the average amplitude of the quantum signal frequency band in the signal output by the quantum signal path (i.e., the attenuated quantum filtered signal).

[0184] Please continue to see Fig. 20 or Fig.21 The signal output by the quantum signal path and the signal output by the classical signal path are combined by a combiner to finally obtain the target signal and input it into the ADC. In the target signal, the average amplitude of the quantum signal frequency band in the low frequency band is similar to the average amplitude of the classical signal frequency band in the high frequency band.

[0185] In step C3, the second quantum device uses an analog-to-digital converter to sample the classical signal frequency band and the quantum signal frequency band of the target signal respectively to obtain classical information and quantum information.

[0186] In this implementation mode, only one ADC is needed at the receiving end to complete the sampling of the analog signal, and the hardware cost is relatively low.

[0187] Optionally, a second implementation of step 603 includes steps D1 to D3.

[0188] In step D1, the second quantum device uses a coherent detector to convert the received modulated light signal into an analog signal, where the analog signal includes a quantum signal frequency band and a classical signal frequency band.

[0189] Among them, there is no overlapping frequency between the quantum signal frequency band and the classical signal frequency band. The quantum signal frequency band corresponds to the subcarrier carrying quantum information in the modulated optical signal, and the classical signal frequency band corresponds to the subcarrier carrying classical information in the modulated optical signal.

[0190] The implementation method of this step D1 can refer to the above-mentioned step C1, and the embodiment of the present application will not be repeated here.

[0191] In step D2, the second quantum device uses the first analog-to-digital converter to sample the classical signal frequency band of the analog signal to obtain classical information.

[0192] In step D3, the second quantum device uses a second analog-to-digital converter to sample the quantum signal frequency band of the analog signal to obtain quantum information.

[0193] Since the frequency band of quantum signal is usually narrow, it has high sampling accuracy requirements for ADC, and is suitable for ADC with low sampling rate but high bit width (resolution). However, the frequency band of classical signal is usually wide, and it has low sampling accuracy requirements for ADC, and is suitable for ADC with high sampling rate but low bit width. In the embodiment of the present application, two ADCs can be used to sample the classical signal band and quantum signal band of the analog signal respectively to meet the sampling accuracy requirements of each.

[0194] In the quantum key distribution method provided in the embodiment of the present application, quantum information and classical information are modulated on the same polarization of the optical signal for transmission at the transmitting end. Compared with the scheme of modulating quantum information and classical information on different polarizations of the optical signal for transmission, one polarization degree of freedom is saved, which can double the capacity of the system. Since quantum information and classical information are modulated on subcarriers in different frequency bands in the optical signal in the embodiment of the present application, that is, frequency division multiplexing of the optical signal is performed, the receiving end can obtain quantum information and classical information respectively by demodulating different subcarriers, and the demodulation of quantum information is less affected by the signal receiving power of the classical information, so that a higher signal-to-noise ratio of the classical signal and a higher signal-to-noise ratio of the quantum signal can be achieved at the receiving end, while meeting the modulation accuracy requirements of the classical signal and the quantum signal. In addition, a set of devices is reused to transmit quantum information and classical information at the same time, saving hardware costs.

[0195] The order of the steps of the quantum key distribution method provided in the embodiment of the present application can be adjusted appropriately, and the steps can also be increased or decreased accordingly according to the situation. Any technician familiar with the technical field can easily think of the method of change within the technical scope disclosed in this application, which should be covered within the scope of protection of this application. For example, the first quantum device in the above embodiment can also be used as the receiving end of the quantum key distribution system, and the second quantum device can also be used as the transmitting end of the quantum key distribution system to realize two-way QKD communication and two-way classical communication. That is, a quantum device can be used as both the transmitting end and the receiving end of the quantum key distribution system, and can simultaneously have the ability to execute the above steps 601 to 603.

[0196] The following is an example of a virtual device in an embodiment of the present application.

[0197] For example, Fig. 22 2 is a schematic diagram of a quantum key distribution device 2200 provided in an embodiment of the present application. The quantum key distribution device 2200 is applied to a first quantum device. Fig. 22 As shown, the quantum key distribution device 2200 includes but is not limited to a generating module 2201 and a sending module 2202.

[0198] The generation module 2201 is used to generate a modulated optical signal, which carries quantum information and classical information. The classical information and the quantum information are simultaneously modulated on at least one polarization of the modulated optical signal. The modulated optical signal includes multiple subcarriers in different frequency bands. The classical information and the quantum information are located in different subcarriers among the multiple subcarriers. The classical information includes quantum key negotiation information.

[0199] The sending module 2202 is used to send a modulated optical signal to the second quantum device through an optical fiber link, wherein the quantum information and the quantum key negotiation information are used by the first quantum device and the second quantum device to jointly generate the same quantum key.

[0200] Optionally, the quantum key agreement information includes one or more of random sampling data, error correction auxiliary information, confidentiality enhancement parameters, basis comparison information or consistency verification parameters.

[0201] Optionally, the classic information also includes business communication data.

[0202] Optionally, the business communication data includes encrypted data.

[0203] Optionally, the generation module 2201 is used to: generate an analog modulation signal according to quantum information and classical information, the analog modulation signal includes a quantum signal frequency band obtained based on quantum information modulation and a classical signal frequency band obtained based on classical information modulation, and there is no overlapping frequency between the quantum signal frequency band and the classical signal frequency band. Perform signal adjustment processing on the analog modulation signal to obtain a target modulation signal, wherein the difference between the average amplitude of the classical signal frequency band in the target modulation signal and the average amplitude of the quantum signal frequency band is greater than a first amplitude threshold. Perform electro-optical modulation on the target modulation signal to obtain a modulated optical signal, wherein each subcarrier in the modulated optical signal corresponds to a quantum signal frequency band or a classical signal frequency band.

[0204] Optionally, the difference between the average amplitude of the classical signal frequency band and the average amplitude of the quantum signal frequency band in the analog modulation signal is less than a second amplitude threshold, and the second amplitude threshold is less than the first amplitude threshold.

[0205] Optionally, the generation module 2201 is used to: use a filter to filter the analog modulated signal to obtain a target modulated signal, wherein the quantum signal frequency band is located in the first frequency band of the filter, the classical signal frequency band is located in the second frequency band of the filter, and the frequency attenuation of the first frequency band is greater than the frequency attenuation of the second frequency band.

[0206] Optionally, the generating module 2201 is used to: perform branching processing on the analog modulation signal according to the distribution area of ​​the quantum signal frequency band and the classical signal frequency band in the analog modulation signal to obtain multiple branch signals. Use multiple filters to filter the multiple branch signals respectively to obtain one or more quantum filter signals and one or more classical filter signals, each quantum filter signal includes one or more adjacent quantum signal frequency bands, and each classical filter signal includes one or more adjacent classical signal frequency bands. Perform attenuation processing on one or more quantum filter signals. Perform combination processing on all classical filter signals and all quantum filter signals that have been attenuated to obtain a target modulation signal.

[0207] Optionally, the generating module 2201 is used to: generate a first analog modulation signal according to quantum information, and generate a second analog modulation signal according to classical information, wherein the first analog modulation signal includes one or more quantum signal frequency bands, and the second analog modulation signal includes one or more classical signal frequency bands, and there is no overlapping frequency between the quantum signal frequency band and the classical signal frequency band. The first analog modulation signal is attenuated so that the difference between the average amplitude of the classical signal frequency band in the second analog modulation signal and the average amplitude of the quantum signal frequency band in the attenuated first analog modulation signal is greater than a third amplitude threshold. A modulated optical signal is generated based on the second analog modulation signal and the attenuated first analog modulation signal, wherein each subcarrier in the modulated optical signal corresponds to a quantum signal frequency band or a classical signal frequency band.

[0208] Optionally, the generating module 2201 is configured to: combine the second analog modulation signal and the attenuated first analog modulation signal to obtain a combined analog modulation signal, and perform electro-optical modulation on the combined analog modulation signal to obtain a modulated optical signal.

[0209] Optionally, the generating module 2201 is configured to: use a first electro-optical modulator to electro-optically modulate the attenuated first analog modulation signal to obtain a first optical signal; use a second electro-optical modulator to electro-optically modulate the second analog modulation signal to obtain a second optical signal; and combine the first optical signal and the second optical signal to obtain a modulated optical signal.

[0210] Optionally, the first analog modulation signal and the second analog modulation signal are generated by different digital-to-analog converters respectively.

[0211] Optionally, the modulated optical signal comes from the same laser.

[0212] For example, Fig.23 2 is a schematic diagram of the structure of another quantum key distribution device 2300 provided in an embodiment of the present application. The quantum key distribution device 2300 is applied to a second quantum device. Fig.23 As shown, the quantum key distribution device 2300 includes but is not limited to a receiving module 2301 and a processing module 2302.

[0213] The receiving module 2301 is used to receive a modulated optical signal sent by a first quantum device through an optical fiber link, where the modulated optical signal carries quantum information and classical information, where the classical information and the quantum information are simultaneously modulated on at least one polarization of the modulated optical signal, where the modulated optical signal includes multiple subcarriers in different frequency bands, where the classical information and the quantum information are located in different subcarriers among the multiple subcarriers, and where the classical information includes quantum key negotiation information.

[0214] The processing module 2302 is used to obtain quantum information and classical information based on the modulated optical signal, wherein the quantum information and quantum key negotiation information are used by the first quantum device and the second quantum device to jointly generate the same quantum key.

[0215] Optionally, the quantum key agreement information includes one or more of random sampling data, error correction auxiliary information, confidentiality enhancement parameters, basis comparison information or consistency verification parameters.

[0216] Optionally, the classic information also includes business communication data.

[0217] Optionally, the business communication data includes encrypted data.

[0218] Optionally, the processing module 2302 is used to: use a coherent detector to convert the received modulated optical signal into an analog signal, the analog signal includes a quantum signal frequency band and a classical signal frequency band, there is no overlapping frequency between the quantum signal frequency band and the classical signal frequency band, the quantum signal frequency band corresponds to the subcarrier carrying quantum information in the modulated optical signal, and the classical signal frequency band corresponds to the subcarrier carrying classical information in the modulated optical signal. Perform received signal adjustment processing on the analog signal to obtain a target signal, wherein the difference between the average amplitude of the classical signal frequency band in the target signal and the average amplitude of the quantum signal frequency band is less than an amplitude threshold. Use an analog-to-digital converter to sample the classical signal frequency band and the quantum signal frequency band of the target signal respectively to obtain classical information and quantum information.

[0219] Optionally, the processing module 2302 is used to: use a filter to filter the analog signal to obtain a target signal, wherein the quantum signal frequency band is located in a first frequency band of the filter, the classical signal frequency band is located in a second frequency band of the filter, and the frequency attenuation of the first frequency band is less than the frequency attenuation of the second frequency band.

[0220] Optionally, the processing module 2302 is used to: perform branch processing on the analog signal according to the distribution area of ​​the quantum signal frequency band and the classical signal frequency band in the analog signal to obtain multiple branch signals. Use multiple filters to filter the multiple branch signals respectively to obtain one or more quantum filtered signals and one or more classical filtered signals, each quantum filtered signal includes one or more adjacent quantum signal frequency bands, and each classical filtered signal includes one or more adjacent classical signal frequency bands. Perform attenuation processing on one or more classical filtered signals. Perform combination processing on all quantum filtered signals and all classical filtered signals that have been attenuated to obtain a target signal.

[0221] Optionally, the processing module 2302 is used to: use a coherent detector to convert the received modulated optical signal into an analog signal, the analog signal includes a quantum signal frequency band and a classical signal frequency band, the quantum signal frequency band and the classical signal frequency band do not have overlapping frequencies, the quantum signal frequency band corresponds to the subcarrier carrying quantum information in the modulated optical signal, and the classical signal frequency band corresponds to the subcarrier carrying classical information in the modulated optical signal. Use a first analog-to-digital converter to sample the classical signal frequency band of the analog signal to obtain classical information. Use a second analog-to-digital converter to sample the quantum signal frequency band of the analog signal to obtain quantum information.

[0222] Regarding the device in the above embodiment, the specific manner in which each module performs operations has been described in detail in the embodiment of the method, and will not be elaborated here.

[0223] The following is an illustration of the basic hardware structure involved in the embodiments of the present application.

[0224] For example, Fig.24 2400 is a schematic diagram of the hardware structure of a quantum device 2400 provided in an embodiment of the present application. Fig.24 As shown, the quantum device 2400 includes a processor 2401 and a memory 2402 , and the memory 2401 and the memory 2402 are connected via a bus 2403 . Fig.24 The processor 2401 and the memory 2402 are described as being independent of each other. Optionally, the processor 2401 and the memory 2402 are integrated together. The quantum device 2400 may be, for example, a quantum key distribution device.

[0225] The memory 2402 is used to store computer programs, including operating systems and program codes. The memory 2402 is various types of storage media, such as read-only memory (ROM), random access memory (RAM), electrically erasable programmable read-only memory (EEPROM), compact disc read-only memory (CD-ROM), flash memory, optical storage, register, optical disk storage, optical disk storage, magnetic disk or other magnetic storage devices.

[0226] The processor 2401 is a general-purpose processor or a special-purpose processor. The processor 2401 may be a single-core processor or a multi-core processor. The processor 2401 includes at least one circuit to execute the above-mentioned quantum key distribution method provided in the embodiment of the present application.

[0227] Optionally, the quantum device 2400 further includes a network interface 2404, which is connected to the processor 2401 and the memory 2402 via a bus 2403. The network interface 2404 enables the quantum device 2400 to communicate with other devices.

[0228] Optionally, the quantum device 2400 further includes an input / output (I / O) interface 2405, which is connected to the processor 2401 and the memory 2402 via the bus 2403. The processor 2401 can receive input commands or data, etc. through the I / O interface 2405. The I / O interface 2405 is used for the quantum device 2400 to connect input devices, such as keyboards, mice, etc. Optionally, in some possible scenarios, the above-mentioned network interface 2404 and I / O interface 2405 are collectively referred to as communication interfaces.

[0229] Optionally, the quantum device 2400 further includes a display 2406, which is connected to the processor 2401 and the memory 2402 via the bus 2403. The display 2406 can be used to display the intermediate results and / or final results generated by the processor 2401 executing the above method. In a possible implementation, the display 2406 is a touch display screen to provide a human-computer interaction interface.

[0230] The bus 2403 is any type of communication bus for interconnecting the internal devices of the quantum device 2400. For example, a system bus. The embodiment of the present application takes the interconnection of the above-mentioned devices inside the quantum device 2400 through the bus 2403 as an example. Optionally, the above-mentioned devices inside the quantum device 2400 are connected to each other in a communication manner other than the bus 2403, for example, the above-mentioned devices inside the quantum device 2400 are interconnected through a logical interface inside the quantum device 2400.

[0231] The above devices may be arranged on independent chips, or at least partially or completely on the same chip. Whether to arrange each device independently on different chips or to integrate them on one or more chips often depends on the needs of product design. The embodiments of the present application do not limit the specific implementation form of the above devices.

[0232] Fig.24 The quantum device 2400 shown is merely exemplary. During implementation, the quantum device 2400 may further include other components, which are not listed one by one herein. Fig.24 The quantum device 2400 shown can implement quantum key distribution by executing all or part of the steps of the method provided in the above embodiment.

[0233] The embodiment of the present application also provides a quantum key distribution system, including: a first quantum device and a second quantum device. The first quantum device and the second quantum device are connected via an optical fiber link. The first quantum device is used to execute the steps executed by the first quantum device in the above method embodiment, such as step 601 and step 602. The second quantum device is used to execute the steps executed by the second quantum device in the above method embodiment, such as step 603.

[0234] An embodiment of the present application further provides a computer-readable storage medium, on which instructions are stored. When the instructions are executed by a processor, the steps performed by the first quantum device or the second quantum device in the above method embodiment are implemented.

[0235] An embodiment of the present application further provides a computer program product, including a computer program. When the computer program is executed by a processor, the steps performed by the first quantum device or the second quantum device in the above method embodiment are implemented.

[0236] A person skilled in the art will understand that all or part of the steps to implement the above embodiments may be accomplished by hardware or by instructing related hardware through a program, and the program may be stored in a computer-readable storage medium, and the above-mentioned storage medium may be a read-only memory, a disk or an optical disk, etc.

[0237] In the embodiments of the present application, the terms “first”, “second” and “third” are used for descriptive purposes only and should not be understood as indicating or implying relative importance.

[0238] The term "and / or" in this application is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0239] It should be noted that the information (including but not limited to user device information, user personal information, etc.), data (including but not limited to data used for analysis, stored data, displayed data, etc.) and signals involved in this application are all authorized by the user or fully authorized by all parties, and the collection, use and processing of relevant data must comply with relevant laws, regulations and standards of relevant countries and regions.

[0240] The above description is only an optional embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the concept and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A quantum key distribution method, characterized in that: The method comprises: A first quantum device generates a modulated optical signal, the modulated optical signal carries quantum information and classical information, the classical information and the quantum information are simultaneously modulated on at least one polarization of the modulated optical signal, the modulated optical signal includes a plurality of subcarriers in different frequency bands, the classical information and the quantum information are located in different subcarriers of the plurality of subcarriers, and the classical information includes quantum key negotiation information; The first quantum device sends the modulated optical signal to the second quantum device through an optical fiber link, wherein the quantum information and the quantum key negotiation information are used by the first quantum device and the second quantum device to jointly generate the same quantum key.

2. The method according to claim 1, characterized in that: The quantum key negotiation information includes one or more of random sampling data, error correction auxiliary information, confidentiality enhancement parameters, basis comparison information or consistency verification parameters.

3. The method according to claim 1 or 2, characterized in that: The classical information also includes business communication data.

4. The method according to claim 3, characterized in that The business communication data includes encrypted data.

5. The method according to any one of claims 1 to 4, characterized in that: The first quantum device generates a modulated optical signal, comprising: The first quantum device generates an analog modulation signal according to the quantum information and the classical information, wherein the analog modulation signal includes a quantum signal frequency band obtained by modulation based on the quantum information and a classical signal frequency band obtained by modulation based on the classical information, and there is no overlapping frequency between the quantum signal frequency band and the classical signal frequency band; The first quantum device performs signal adjustment processing on the analog modulation signal to obtain a target modulation signal, wherein a difference between an average amplitude of the classical signal frequency band and an average amplitude of the quantum signal frequency band in the target modulation signal is greater than a first amplitude threshold; The first quantum device performs electro-optical modulation on the target modulation signal to obtain the modulated optical signal, wherein each subcarrier in the modulated optical signal corresponds to one of the quantum signal frequency bands or one of the classical signal frequency bands.

6. The method according to claim 5, characterized in that The difference between the average amplitude of the classical signal frequency band and the average amplitude of the quantum signal frequency band in the analog modulation signal is less than a second amplitude threshold, and the second amplitude threshold is less than the first amplitude threshold.

7. The method according to claim 5 or 6, characterized in that: The first quantum device performs signal adjustment processing on the analog modulation signal to obtain a target modulation signal, including: The first quantum device uses a filter to filter the analog modulation signal to obtain the target modulation signal, wherein the quantum signal frequency band is located in a first frequency band of the filter, the classical signal frequency band is located in a second frequency band of the filter, and the frequency attenuation of the first frequency band is greater than the frequency attenuation of the second frequency band.

8. The method according to claim 5 or 6, characterized in that: The first quantum device performs signal adjustment processing on the analog modulation signal to obtain a target modulation signal, including: The first quantum device performs branching processing on the analog modulation signal according to the distribution area of ​​the quantum signal frequency band and the classical signal frequency band in the analog modulation signal to obtain a plurality of branched signals; The first quantum device uses a plurality of filters to filter the plurality of branch signals respectively to obtain one or more quantum filtered signals and one or more classical filtered signals, each of the quantum filtered signals includes one or more adjacent quantum signal frequency bands, and each of the classical filtered signals includes one or more adjacent classical signal frequency bands; The first quantum device performs attenuation processing on the one or more quantum filter signals; The first quantum device combines all the classical filtered signals and all the quantum filtered signals that have been attenuated to obtain the target modulated signal.

9. The method according to any one of claims 1 to 4, characterized in that: The first quantum device generates a modulated optical signal, comprising: The first quantum device generates a first analog modulation signal according to the quantum information, and generates a second analog modulation signal according to the classical information, wherein the first analog modulation signal includes one or more quantum signal frequency bands, the second analog modulation signal includes one or more classical signal frequency bands, and the quantum signal frequency bands and the classical signal frequency bands do not have overlapping frequencies; The first quantum device performs attenuation processing on the first analog modulation signal so that the difference between the average amplitude of the classical signal frequency band in the second analog modulation signal and the average amplitude of the quantum signal frequency band in the attenuated first analog modulation signal is greater than a third amplitude threshold; The first quantum device generates the modulated optical signal based on the second analog modulation signal and the attenuated first analog modulation signal, wherein each subcarrier in the modulated optical signal corresponds to one of the quantum signal frequency bands or one of the classical signal frequency bands.

10. The method according to claim 9, characterized in that The first quantum device generates the modulated optical signal based on the second analog modulation signal and the attenuated first analog modulation signal, including: The first quantum device combines the second analog modulation signal and the attenuated first analog modulation signal to obtain a combined analog modulation signal; The first quantum device performs electro-optical modulation on the combined analog modulation signal to obtain the modulated optical signal.

11. The method according to claim 9, characterized in that The first quantum device generates the modulated optical signal based on the second analog modulation signal and the attenuated first analog modulation signal, including: The first quantum device uses a first electro-optic modulator to electro-optically modulate the attenuated first analog modulation signal to obtain a first optical signal; The first quantum device uses a second electro-optic modulator to electro-optically modulate the second analog modulation signal to obtain a second optical signal; The first quantum device performs beam combining processing on the first optical signal and the second optical signal to obtain the modulated optical signal.

12. The method according to any one of claims 9 to 11, characterized in that: The first analog modulation signal and the second analog modulation signal are respectively generated by different digital-to-analog converters.

13. The method according to any one of claims 1 to 12, characterized in that: The modulated optical signals come from the same laser.

14. A quantum key distribution method, characterized in that: The method comprises: The second quantum device receives a modulated optical signal sent by the first quantum device through an optical fiber link, wherein the modulated optical signal carries quantum information and classical information, the classical information and the quantum information are simultaneously modulated on at least one polarization of the modulated optical signal, the modulated optical signal includes a plurality of subcarriers in different frequency bands, the classical information and the quantum information are located in different subcarriers among the plurality of subcarriers, and the classical information includes quantum key negotiation information; The second quantum device acquires the quantum information and the classical information based on the modulated optical signal, wherein the quantum information and the quantum key agreement information are used by the first quantum device and the second quantum device to jointly generate the same quantum key.

15. The method according to claim 14, characterized in that The quantum key negotiation information includes one or more of random sampling data, error correction auxiliary information, confidentiality enhancement parameters, basis comparison information or consistency verification parameters.

16. The method according to claim 14 or 15, characterized in that The classical information also includes business communication data.

17. The method according to claim 16, characterized in that The business communication data includes encrypted data.

18. The method according to any one of claims 14 to 17, characterized in that: The second quantum device acquires the quantum information and the classical information based on the modulated optical signal, including: The second quantum device uses a coherent detector to convert the received modulated optical signal into an analog signal, the analog signal includes a quantum signal frequency band and a classical signal frequency band, the quantum signal frequency band and the classical signal frequency band do not have overlapping frequencies, the quantum signal frequency band corresponds to the subcarrier carrying the quantum information in the modulated optical signal, and the classical signal frequency band corresponds to the subcarrier carrying the classical information in the modulated optical signal; The second quantum device performs a received signal adjustment process on the analog signal to obtain a target signal, wherein a difference between an average amplitude of the classical signal frequency band in the target signal and an average amplitude of the quantum signal frequency band is less than an amplitude threshold; The second quantum device uses an analog-to-digital converter to sample the classical signal frequency band and the quantum signal frequency band of the target signal respectively to obtain the classical information and the quantum information.

19. The method according to claim 18, characterized in that The second quantum device performs a received signal adjustment process on the analog signal to obtain a target signal, including: The second quantum device uses a filter to filter the analog signal to obtain the target signal, wherein the quantum signal frequency band is located in a first frequency band of the filter, the classical signal frequency band is located in a second frequency band of the filter, and the frequency attenuation of the first frequency band is less than the frequency attenuation of the second frequency band.

20. The method according to claim 18, characterized in that The second quantum device performs a received signal adjustment process on the analog signal to obtain a target signal, including: The second quantum device performs branching processing on the analog signal according to the distribution area of ​​the quantum signal frequency band and the classical signal frequency band in the analog signal to obtain a plurality of branched signals; The second quantum device uses a plurality of filters to filter the plurality of branch signals respectively to obtain one or more quantum filtered signals and one or more classical filtered signals, each of the quantum filtered signals includes one or more adjacent quantum signal frequency bands, and each of the classical filtered signals includes one or more adjacent classical signal frequency bands; The second quantum device performs attenuation processing on the one or more classical filtered signals; The second quantum device combines all the quantum filter signals and all the classical filter signals that have been attenuated to obtain the target signal.

21. The method according to any one of claims 14 to 17, characterized in that: The second quantum device acquires the quantum information and the classical information based on the modulated optical signal, including: The second quantum device uses a coherent detector to convert the received modulated optical signal into an analog signal, the analog signal includes a quantum signal frequency band and a classical signal frequency band, the quantum signal frequency band and the classical signal frequency band do not have overlapping frequencies, the quantum signal frequency band corresponds to a subcarrier carrying the quantum information in the modulated optical signal, and the classical signal frequency band corresponds to a subcarrier carrying the classical information in the modulated optical signal; The second quantum device uses a first analog-to-digital converter to sample the classical signal frequency band of the analog signal to obtain the classical information; The second quantum device uses a second analog-to-digital converter to sample the quantum signal frequency band of the analog signal to obtain the quantum information.

22. A quantum key distribution device, characterized in that: Applied to a first quantum device, the apparatus comprises: a generating module, configured to generate a modulated optical signal, wherein the modulated optical signal carries quantum information and classical information, wherein the classical information and the quantum information are simultaneously modulated on at least one polarization of the modulated optical signal, wherein the modulated optical signal comprises a plurality of subcarriers in different frequency bands, wherein the classical information and the quantum information are located in different subcarriers among the plurality of subcarriers, and wherein the classical information comprises quantum key negotiation information; A sending module is used to send the modulated optical signal to a second quantum device through an optical fiber link, wherein the quantum information and the quantum key negotiation information are used for the first quantum device and the second quantum device to jointly generate the same quantum key.

23. The device according to claim 22, characterized in that The quantum key negotiation information includes one or more of random sampling data, error correction auxiliary information, confidentiality enhancement parameters, basis comparison information or consistency verification parameters.

24. The device according to claim 22 or 23, characterized in that The classical information also includes business communication data.

25. The device according to claim 24, characterized in that The business communication data includes encrypted data.

26. The device according to any one of claims 22 to 25, characterized in that The generating module is used for: Generate an analog modulation signal according to the quantum information and the classical information, wherein the analog modulation signal includes a quantum signal frequency band obtained by modulation based on the quantum information and a classical signal frequency band obtained by modulation based on the classical information, and there is no overlapping frequency between the quantum signal frequency band and the classical signal frequency band; Performing signal adjustment processing on the analog modulation signal to obtain a target modulation signal, wherein a difference between an average amplitude of the classical signal frequency band and an average amplitude of the quantum signal frequency band in the target modulation signal is greater than a first amplitude threshold; The target modulation signal is electro-optically modulated to obtain the modulated optical signal, wherein each subcarrier in the modulated optical signal corresponds to one of the quantum signal frequency bands or one of the classical signal frequency bands.

27. The device according to claim 26, characterized in that The difference between the average amplitude of the classical signal frequency band and the average amplitude of the quantum signal frequency band in the analog modulation signal is less than a second amplitude threshold, and the second amplitude threshold is less than the first amplitude threshold.

28. The device according to claim 26 or 27, characterized in that The generating module is used for: The analog modulation signal is filtered by a filter to obtain the target modulation signal, wherein the quantum signal frequency band is located in a first frequency band of the filter, the classical signal frequency band is located in a second frequency band of the filter, and the frequency attenuation of the first frequency band is greater than the frequency attenuation of the second frequency band.

29. The device according to claim 26 or 27, characterized in that The generating module is used for: According to the distribution areas of the quantum signal frequency band and the classical signal frequency band in the analog modulation signal, the analog modulation signal is split to obtain a plurality of split signals; Using a plurality of filters to filter the plurality of branch signals respectively to obtain one or more quantum filtered signals and one or more classical filtered signals, each of the quantum filtered signals includes one or more adjacent quantum signal frequency bands, and each of the classical filtered signals includes one or more adjacent classical signal frequency bands; performing attenuation processing on the one or more quantum filter signals; All the classical filtering signals and all the quantum filtering signals that have been attenuated are combined to obtain the target modulation signal.

30. The device according to any one of claims 22 to 25, characterized in that The generating module is used for: Generate a first analog modulation signal according to the quantum information, and generate a second analog modulation signal according to the classical information, wherein the first analog modulation signal includes one or more quantum signal frequency bands, the second analog modulation signal includes one or more classical signal frequency bands, and there is no overlapping frequency between the quantum signal frequency band and the classical signal frequency band; Performing attenuation processing on the first analog modulation signal so that the difference between the average amplitude of the classical signal frequency band in the second analog modulation signal and the average amplitude of the quantum signal frequency band in the attenuated first analog modulation signal is greater than a third amplitude threshold; The modulated optical signal is generated based on the second analog modulation signal and the attenuated first analog modulation signal, wherein each subcarrier in the modulated optical signal corresponds to one of the quantum signal frequency bands or one of the classical signal frequency bands.

31. The device according to claim 30, characterized in that The generating module is used for: Combining the second analog modulation signal and the attenuated first analog modulation signal to obtain a combined analog modulation signal; The combined analog modulation signal is electro-optically modulated to obtain the modulated optical signal.

32. The device according to claim 30, characterized in that The generating module is used for: Using a first electro-optical modulator to electro-optically modulate the attenuated first analog modulation signal to obtain a first optical signal; Using a second electro-optical modulator to electro-optically modulate the second analog modulation signal to obtain a second optical signal; The first optical signal and the second optical signal are combined to obtain the modulated optical signal.

33. The device according to any one of claims 30 to 32, characterized in that The first analog modulation signal and the second analog modulation signal are respectively generated by different digital-to-analog converters.

34. The device according to any one of claims 22 to 33, characterized in that The modulated optical signals come from the same laser.

35. A quantum key distribution device, characterized in that: Applied to a second quantum device, the device comprises: a receiving module, configured to receive a modulated optical signal sent by a first quantum device through an optical fiber link, wherein the modulated optical signal carries quantum information and classical information, wherein the classical information and the quantum information are simultaneously modulated on at least one polarization of the modulated optical signal, wherein the modulated optical signal includes a plurality of subcarriers in different frequency bands, wherein the classical information and the quantum information are located in different subcarriers among the plurality of subcarriers, and wherein the classical information includes quantum key negotiation information; A processing module is used to obtain the quantum information and the classical information based on the modulated optical signal, wherein the quantum information and the quantum key agreement information are used for the first quantum device and the second quantum device to jointly generate the same quantum key.

36. The device according to claim 35, characterized in that The quantum key negotiation information includes one or more of random sampling data, error correction auxiliary information, confidentiality enhancement parameters, basis comparison information or consistency verification parameters.

37. The device according to claim 35 or 36, characterized in that The classical information also includes business communication data.

38. The device according to claim 37, characterized in that The business communication data includes encrypted data.

39. The device according to any one of claims 35 to 38, characterized in that The processing module is used for: A coherent detector is used to convert the received modulated optical signal into an analog signal, wherein the analog signal includes a quantum signal frequency band and a classical signal frequency band, wherein the quantum signal frequency band and the classical signal frequency band do not have overlapping frequencies, wherein the quantum signal frequency band corresponds to a subcarrier in the modulated optical signal that carries the quantum information, and wherein the classical signal frequency band corresponds to a subcarrier in the modulated optical signal that carries the classical information; Performing a received signal adjustment process on the analog signal to obtain a target signal, wherein a difference between an average amplitude of the classical signal frequency band and an average amplitude of the quantum signal frequency band in the target signal is less than an amplitude threshold; The classical signal frequency band and the quantum signal frequency band of the target signal are sampled respectively by using an analog-to-digital converter to obtain the classical information and the quantum information.

40. The device according to claim 39, characterized in that The processing module is used for: The analog signal is filtered by a filter to obtain the target signal, wherein the quantum signal frequency band is located in a first frequency band of the filter, the classical signal frequency band is located in a second frequency band of the filter, and the frequency attenuation of the first frequency band is less than the frequency attenuation of the second frequency band.

41. The device according to claim 39, characterized in that The processing module is used for: According to the distribution areas of the quantum signal frequency band and the classical signal frequency band in the analog signal, the analog signal is split to obtain a plurality of split signals; Using a plurality of filters to filter the plurality of branch signals respectively to obtain one or more quantum filtered signals and one or more classical filtered signals, each of the quantum filtered signals includes one or more adjacent quantum signal frequency bands, and each of the classical filtered signals includes one or more adjacent classical signal frequency bands; performing attenuation processing on the one or more classically filtered signals; All the quantum filter signals and all the attenuated classical filter signals are combined to obtain the target signal.

42. The device according to any one of claims 35 to 38, characterized in that The processing module is used for: A coherent detector is used to convert the received modulated optical signal into an analog signal, wherein the analog signal includes a quantum signal frequency band and a classical signal frequency band, wherein the quantum signal frequency band and the classical signal frequency band do not have overlapping frequencies, wherein the quantum signal frequency band corresponds to a subcarrier in the modulated optical signal that carries the quantum information, and wherein the classical signal frequency band corresponds to a subcarrier in the modulated optical signal that carries the classical information; Using a first analog-to-digital converter to sample the classical signal frequency band of the analog signal to obtain the classical information; A second analog-to-digital converter is used to sample the quantum signal frequency band of the analog signal to obtain the quantum information.

43. A quantum key distribution system, characterized in that: include: A first quantum device and a second quantum device, wherein the first quantum device and the second quantum device are connected via an optical fiber link, the first quantum device is used to perform the method according to any one of claims 1 to 13, and the second quantum device is used to perform the method according to any one of claims 14 to 21.

44. A quantum device, characterized in that include: Processor and memory; The memory is used to store a computer program, wherein the computer program includes program instructions; The processor is used to call the computer program to implement the method according to any one of claims 1 to 21.

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