Quantum key distribution method, apparatus, and system

Abstract

The present application relates to the technical field of networks, and discloses a quantum key distribution method, apparatus, and system. A first quantum device generates a modulated optical signal, the modulated optical signal carrying 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 comprises 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. The classical information comprises quantum key negotiation information. The first quantum device sends the modulated optical signal to a second quantum device by means of an optical fiber link. Quantum information and classical information are modulated on a same polarization of an optical signal, and thus, the system capacity is high. The quantum information and classical information are respectively modulated on subcarriers in different frequency bands in the optical signal, and thus, respective modulation precision requirements of a classic signal and a quantum signal can be met. The quantum information and classical information are simultaneously transmitted by means of one set of devices, thereby saving hardware cost.

Description

Quantum key distribution method, device and system

[0001] This application claims priority to Chinese patent application number 202311375652.9, filed on October 19, 2023, entitled “Quantum Key Distribution Method, Device and System”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of network technology, and in particular to a quantum key distribution method, device and system. Background Art

[0003] With the development of quantum computing, quantum attacks pose a significant threat to currently used cryptographic systems. Quantum attacks are attack algorithms run on quantum computers and can break many currently used key agreement algorithms, such as RSA (a public key encryption algorithm proposed by Ron Rivest, Adi Shamir, and Leonard Adleman) and the Diffie-Hellman key exchange (DH) algorithm, which are used in conjunction with the Advanced Encryption Standard (AES) and SM4 block ciphers. Quantum computers are expected to be available within the next few decades. If an eavesdropper intercepts and stores data encrypted using current encryption algorithms and transmits it over a network, and then uses a quantum attack to decrypt the encryption algorithm used to store the data, the decrypted plaintext data can be obtained. This poses a significant threat to confidential information that needs to be preserved for a long time. Therefore, designing cryptographic technologies that are resistant to quantum attacks is urgent.

[0004] Quantum key distribution (QKD) is a secure key distribution technology that enables the secure transmission of quantum keys (QKs) between two distant communication endpoints. The security of QKD is guaranteed by the fundamental principles of quantum mechanics. In quantum networks, the transmission of quantum keys is theoretically unconditionally secure.

[0005] In the related art, quantum key distribution (QKD) requires a transmitter (Tx) to transmit quantum light signals to a receiver (Rx) via an optical fiber link to convey quantum information. Furthermore, the transmitter and receiver must exchange classical information used to negotiate the quantum key over a classical network, enabling both to generate the same quantum key. The key to QKD is how to achieve this transmission of quantum and classical information between the transmitter and receiver.

[0006] Summary of the Invention

[0007] The present application provides a quantum key distribution method, device and system.

[0008] In a first aspect, a quantum key distribution method is provided. The method includes: a first quantum device generates a modulated optical signal, the modulated optical signal carrying 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 of the multiple subcarriers. The classical information includes quantum key agreement information. The first quantum device transmits the modulated optical signal to a second quantum device via an optical fiber link. The quantum information and the quantum key agreement information are used by the first and second quantum devices to jointly generate the same quantum key.

[0009] In this application, quantum information and classical information containing 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 and the capacity of the system can be doubled. 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. The demodulation of quantum information is less affected by the signal receiving power of the classical information, thereby achieving a higher signal-to-noise ratio of the classical signal and a higher signal-to-noise ratio of the quantum signal 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.

[0010] Optionally, the quantum key agreement information includes one or more of random sample data, error correction auxiliary information, a confidentiality enhancement parameter, basis comparison information, or a consistency check parameter. The quantum key agreement information is information required to be exchanged between the first quantum device and the second quantum device during data processing during the process of generating the quantum key.

[0011] Optionally, the classic information also includes business communication data.

[0012] In this application, 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, a single optical fiber can simultaneously transmit information used to generate quantum keys and business communication data, maximizing the use of the optical fiber link and improving bandwidth efficiency.

[0013] 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.

[0014] 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 including 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 and the average amplitude of the quantum signal frequency band in the target modulated signal 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.

[0015] In this implementation, by performing signal adjustment processing on an analog modulation signal including a quantum signal frequency band and a 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 is adjusted to meet the set requirements. This allows the power intensity of the quantum light signal in the modulated light signal obtained by modulation based on the target modulation signal to 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 transmitter of quantum key distribution, the first quantum device can use a laser to emit an optical signal and a digital-to-analog converter (DAC) to generate an analog modulation signal. Finally, an electro-optical modulator is used to modulate the analog modulation signal after signal modulation processing onto the optical signal emitted by the laser to obtain the modulated light signal to be transmitted. The number of lasers, DACs, and electro-optical modulators required for the first quantum device to generate the modulated light signal is all one, and the hardware cost is low.

[0016] 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 modulated signal is smaller than a second amplitude threshold, and the second amplitude threshold is smaller than the first amplitude threshold.

[0017] 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 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.

[0018] 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 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.

[0019] This implementation uses a filter to perform signal conditioning on an analog modulated signal. By designing the filter's frequency response function to correlate with the distribution of the quantum and classical signal frequency bands in the analog modulated signal, the filter achieves greater frequency attenuation in the quantum signal band, which functions like a filter's stopband. Furthermore, the filter achieves less frequency attenuation in the classical signal band, which functions like a filter's passband. This ensures that the average amplitude difference between the classical and quantum signal bands in the filtered modulated signal meets the specified requirements.

[0020] Optionally, another implementation method for the first quantum device to perform signal adjustment processing on the analog modulated signal to obtain a target modulated signal includes: the first quantum device performs branch processing on the analog modulated signal based on 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 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 the one or more quantum filtered signals. The first quantum device combines all the classical filtered signals and all the attenuated quantum filtered signals to obtain the target modulated signal.

[0021] This implementation uses shunt filtering to achieve signal adjustment processing of the analog modulated signal. 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.

[0022] 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 based on quantum information, and generates a second analog modulation signal based on classical information. 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 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.

[0023] In this implementation, by attenuating the first analog modulated signal including the quantum signal frequency band, the average amplitude difference between the quantum signal frequency band in the attenuated first analog modulated signal and the classical signal frequency band in the second analog modulated signal can meet the set requirements. As a result, the power intensity of the quantum light signal in the final modulated optical signal can be much weaker than the power intensity of the classical light signal, thereby meeting the transmission performance requirements of both quantum light signals and classical light signals.

[0024] Optionally, an implementation of generating a modulated optical signal by the first quantum device based on the second analog modulated signal and the attenuated first analog modulated signal includes: combining the second analog modulated signal and the attenuated first analog modulated signal by the first quantum device to obtain a combined analog modulated signal; and electro-optically modulating the combined analog modulated signal by the first quantum device to obtain a modulated optical signal.

[0025] In this implementation, the first quantum device, acting as the transmitter for quantum key distribution, can use a laser to emit an optical signal and two DACs to generate two analog modulated signals. One analog modulated signal, containing the quantum signal frequency band, is then attenuated and combined with another analog modulated signal containing the classical signal frequency band. Finally, an electro-optical modulator is used to modulate the combined analog modulated signal onto the optical signal emitted by the laser, resulting in a modulated optical signal to be transmitted. The first quantum device requires only one laser and one electro-optical modulator to generate the modulated optical signal, and only two DACs, resulting in low hardware costs.

[0026] Alternatively, 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 electro-optically modulating the attenuated first analog modulation signal using a first electro-optical modulator to obtain a first optical signal; electro-optically modulating the second analog modulation signal using a second electro-optical modulator to obtain a second optical signal; and combining the first optical signal and the second optical signal to obtain a modulated optical signal.

[0027] In this implementation, the first quantum device, acting as the transmitter for quantum key distribution, can use a laser to emit an optical signal, split the optical signal into two paths using an optical beam splitter, and generate two analog modulated signals using two DACs. The analog modulated signal, which contains the quantum signal frequency band, is then attenuated and modulated onto one optical signal from the laser using an electro-optical modulator. Another electro-optical modulator modulates the other analog modulated signal, which contains the classical signal frequency band, onto another optical signal from the laser. Finally, an optical combiner is used to combine the two modulated optical signals to produce the modulated optical signal to be transmitted. The first quantum device requires only one laser to generate the modulated optical signal, and two DACs and two electro-optical modulators, resulting in low hardware costs.

[0028] Optionally, the first analog modulation signal and the second analog modulation signal are generated by different digital-to-analog converters respectively.

[0029] Optionally, the modulated optical signal comes from the same laser.

[0030] In a second aspect, a quantum key distribution method is provided. The method includes: a second quantum device receives a modulated optical signal transmitted by a first quantum device via an optical fiber link. The modulated optical signal carries both quantum information and classical information. The classical information and 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, and the classical information and quantum information are located within different subcarriers within the multiple subcarriers. The classical information includes quantum key agreement information. The second quantum device obtains the quantum information and classical information based on the modulated optical signal. The quantum information and the quantum key agreement information are used by the first and second quantum devices to jointly generate the same quantum key.

[0031] In this application, quantum information and classical information are modulated onto subcarriers in different frequency bands within the optical signal, performing frequency division multiplexing (FDM) on the optical signal. This allows the receiver to obtain quantum information and classical information separately by demodulating different subcarriers. The demodulation of quantum information is less affected by the received power of the classical information, thereby achieving a high signal-to-noise ratio (SNR) for both the classical signal and the quantum signal at the receiver, while simultaneously meeting the modulation accuracy requirements for both classical and quantum signals. Furthermore, the use of a single device for simultaneous transmission of quantum and classical information saves hardware costs.

[0032] 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 check parameters.

[0033] Optionally, the classic information also includes business communication data.

[0034] Optionally, the business communication data includes encrypted data.

[0035] Optionally, a second quantum device acquires quantum information and classical information based on a modulated optical signal, including: the second quantum device uses a coherent detector 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, the quantum signal frequency band corresponds to a subcarrier in the modulated optical signal that carries quantum information, and the classical signal frequency band corresponds to a subcarrier in the modulated optical signal that carries classical information. The second quantum device performs 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. 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.

[0036] 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.

[0037] Optionally, the second quantum device performs received signal adjustment processing 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 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 less than the frequency attenuation of the second frequency band.

[0038] This implementation uses a filter to perform signal conditioning on an analog signal. By designing the filter's frequency response function to correlate with the distribution of the quantum and classical signal frequency bands in the analog signal, the filter achieves minimal frequency attenuation in the quantum signal band, which functions like the filter's passband. Furthermore, the filter achieves significant frequency attenuation in the classical signal band, which functions like the filter's stopband. This results in similar average amplitudes in the classical and quantum signal bands of the filtered target signal.

[0039] Optionally, another implementation of the second quantum device performing received signal adjustment processing on the analog signal to obtain the target signal includes:

[0040] The second quantum device splits the analog signal based on the distribution of quantum signal frequency bands and classical signal frequency bands in the analog signal, obtaining multiple branch signals. The second quantum device uses multiple filters to filter the multiple branch signals, obtaining 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 second quantum device attenuates the one or more classical filtered signals. The second quantum device then combines all quantum filtered signals and all attenuated classical filtered signals to obtain a target signal.

[0041] This implementation uses 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.

[0042] Alternatively, another implementation method for obtaining quantum information and classical information based on a modulated optical signal by a second quantum device includes: the second quantum device uses a coherent detector to convert a 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 overlap, the quantum signal frequency band corresponds to a subcarrier in the modulated optical signal that carries quantum information, and the classical signal frequency band corresponds to a subcarrier in the modulated optical signal that carries classical information. The second quantum device uses a 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 a second analog-to-digital converter to sample the quantum signal frequency band of the analog signal to obtain quantum information.

[0043] 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 their respective sampling accuracy requirements.

[0044] In a third aspect, a quantum key distribution device is provided. The device includes multiple functional modules that interact with each other to implement the method described in the first aspect and its respective embodiments. The multiple functional modules can be implemented using 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.

[0045] In a fourth aspect, a quantum key distribution device is provided. The device includes multiple functional modules that interact with each other to implement the method of the second aspect and its respective 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.

[0046] In a fifth aspect, a quantum key distribution system is provided, comprising: 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 being used to implement the method of the first aspect and its respective embodiments, and the second quantum device being used to implement the method of the second aspect and its respective embodiments.

[0047] In a sixth aspect, a quantum device is provided, comprising: a processor and a memory. The memory is configured to store a computer program, wherein the computer program includes program instructions. The processor is configured to invoke the computer program to implement the method of the first aspect and its respective embodiments, or the method of the second aspect and its respective embodiments.

[0048] 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.

[0049] 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.

[0050] 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

[0051] FIG1 is a schematic diagram of an implementation process of quantum key distribution provided in an embodiment of the present application;

[0052] FIG2 is a schematic diagram of a quantum key generation system provided by related art;

[0053] FIG3 is a schematic diagram of transmission of classical information and quantum information provided by related art;

[0054] FIG4 is a schematic diagram of modulation of classical information and quantum information provided by related art;

[0055] FIG5 is a schematic diagram of the structure of a quantum key distribution system provided in an embodiment of the present application;

[0056] FIG6 is a schematic diagram of a flow chart of a quantum key distribution method provided in an embodiment of the present application;

[0057] FIG7 is a schematic diagram of an implementation flow of a first quantum device generating a modulated optical signal provided by an embodiment of the present application;

[0058] FIG8 is a schematic diagram of a signal adjustment process for an analog modulated signal provided by an embodiment of the present application;

[0059] FIG9 is a schematic diagram of another embodiment of the present application providing a signal adjustment process for an analog modulation signal;

[0060] FIG10 is a schematic diagram of another method of performing signal adjustment processing on an analog modulated signal provided in an embodiment of the present application;

[0061] FIG11 is a schematic diagram of another embodiment of the present application providing a signal adjustment process for an analog modulated signal;

[0062] FIG12 is a schematic diagram of another embodiment of the present application providing a signal adjustment process for an analog modulated signal;

[0063] FIG13 is a schematic diagram of a process for generating a modulated optical signal according to an embodiment of the present application;

[0064] FIG14 is a schematic diagram of an implementation flow of another first quantum device generating a modulated optical signal provided in an embodiment of the present application;

[0065] FIG15 is a schematic diagram of another process for generating a modulated optical signal according to an embodiment of the present application;

[0066] FIG16 is a schematic diagram of a generation process of another modulated optical signal provided in an embodiment of the present application;

[0067] FIG17 is a schematic structural diagram of a coherent receiver provided in an embodiment of the present application;

[0068] FIG18 is a schematic structural diagram of a single polarization receiver provided in an embodiment of the present application;

[0069] FIG19 is a schematic structural diagram of a coherent detector provided in an embodiment of the present application;

[0070] FIG20 is a schematic diagram of a received signal adjustment process for an analog signal provided by an embodiment of the present application;

[0071] FIG21 is a schematic diagram of another embodiment of the present application providing a received signal adjustment process for an analog signal;

[0072] FIG22 is a schematic diagram of the structure of a quantum key distribution device provided in an embodiment of the present application;

[0073] FIG23 is a schematic diagram of the structure of another quantum key distribution device provided in an embodiment of the present application;

[0074] FIG24 is a schematic diagram of the hardware structure of a quantum device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0075] In order to make the objectives, technical solutions and advantages of this application clearer, the implementation methods of this application will be further described in detail below with reference to the accompanying drawings.

[0076] With the rapid development of information technology, demands for communication security are becoming increasingly stringent. Quantum communication, a technology developed based on quantum mechanics and classical information theory, leverages the fundamental principles of quantum mechanics to ensure communication security. Quantum key distribution (QKD) is the most mature technology in quantum communication. It enables the unconditional and secure distribution of symmetric keys between legitimate senders and receivers, assuming that a partial security key has been shared. Unconditional security means that there are no restrictions on the computing resources of eavesdroppers in the channel.

[0077] There are many different quantum key distribution protocols and systems. The two most popular currently are discrete-variable quantum key distribution (DVQKD) and continuous-variable quantum key distribution (CVQKD). DVQKD requires encoding single-photon signals, and single-photon detectors must operate in cryogenic environments. CVQKD, on the other hand, encodes coherent light and uses low-noise coherent receivers (also called coherent detectors) for detection. It eliminates the need for single-photon sources and detectors, allowing it to significantly reuse the existing communications industry chain. Therefore, CVQKD offers the potential advantages of high integration and low cost.

[0078] CVQKD uses a coherent state as a light source at the transmitter end. A modulator modulates the center position of the coherent state. The modulated quantum light signal is transmitted through an optical fiber and detected at the receiver end using a homodyne or heterodyne detector. The analog electrical signal output by the detector is sampled by an analog-to-digital conversion (ADC) before entering a data processing module, which processes and evaluates the data to ultimately generate a secure quantum key.

[0079] For example, FIG1 is a schematic diagram of an implementation process of quantum key distribution provided by an embodiment of the present application. As shown in FIG1 , the transmitting end first generates a quantum random number as the original coding information, and then encodes the coherent state according to the generated quantum random number (i.e., performs quantum state preparation), and then transmits the encoded coherent state signal (i.e., quantum light signal) to the receiving end through a quantum channel. Accordingly, the receiving end generates a quantum random number as the original key information, and randomly measures the X or P regular component of the coherent state using a homodyne detector or a heterodyne detector according to the generated quantum random number (i.e., performs quantum state measurement). Afterwards, the transmitting end and the receiving end perform data processing and evaluation respectively through a data processing module to generate the same quantum key. Referring to FIG1 , the functions of the data processing module generally include signal processing, parameter estimation, data error correction, and privacy amplification (PA).

[0080] Signal processing usually refers to the digital signal processing of the sampled signal at the receiving end to obtain reasonable normal component measurement results.

[0081] Parameter estimation involves randomly comparing portions of data between the sender and receiver to determine the amount of information an eavesdropper could have accessed and whether the current round of distribution can still generate a secure quantum key. If a secure quantum key cannot be generated, the system typically terminates the process and waits for data accumulation for the next round of distribution. If a secure quantum key can be generated, the subsequent processing continues. This process requires a classical channel to allow the sender and receiver to losslessly synchronize information, specifically randomly sampled data.

[0082] Data error correction involves the synchronization of key data between the sender and receiver through a lossless classical channel, where the sender and receiver share a syndrome or other error-correcting information. The corrected key is referred to as the corrected key. This process also requires a classical channel, allowing the sender and receiver to losslessly synchronize information, specifically the error-correcting information.

[0083] Privacy enhancement involves the sender and receiver performing the same hash operation, compressing their corrected keys, and outputting the final quantum key. This process also requires a classical channel, allowing the sender and receiver to losslessly synchronize information. The key parameters of the hash operation (referred to as the privacy enhancement parameters) are synchronized.

[0084] Optionally, please continue to refer to Figure 1. The function of the data processing module also includes basis comparison. In some protocols, because the receiver randomly measures a certain canonical component of the coherent state, it does not have information about both components at the same time. Therefore, a comparison process is required between signal processing and parameter estimation. That is, the receiver discloses to the transmitter which specific canonical component it measured, and the transmitter only retains the information of this canonical component for generating quantum keys. This process also requires a classical channel so that the sender and receiver can synchronize information losslessly. The information synchronized is the relevant information of the measurement basis used by the receiver (referred to as basis comparison information).

[0085] Optionally, please continue to refer to 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, a key consistency verification process is usually added. This process can be added after the data error correction step, or after the confidentiality enhancement step, or even later, when the application end accesses 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 consistency verification parameters).

[0086] From the data processing module described above, it's clear that during quantum key distribution, the transmitter and receiver frequently communicate over classical channels to losslessly transmit information related to each step of the data processing. The traditional solution is to use another classical communication system to transmit this information. For example, the QKD device's data processing module transmits the to-be-transmitted classical information to a router. The router then transmits the to-be-transmitted classical information via the communication network to the receiver based on the communication routing protocol. The router at the receiving end receives the information, parses it, and then transmits it to the receiver's data processing module. Considering that the transmitter and receiver are connected by an optical fiber link to transmit quantum light signals, this optical fiber link can also be used to carry classical channels. Specifically, the quantum channel and classical channel reside in the same optical fiber, but use different wavelengths, and are wavelength-division multiplexed. This is also a commonly used solution in the industry. For example, Figure 2 is a schematic diagram of a quantum key generation system provided by related art. As shown in Figure 2, the classical communication system and the quantum key distribution system are separate systems. The data processing module of the quantum key distribution system transmits the to-be-transmitted classical information to the classical communication system, which then completes bidirectional communication between the sender and receiver via the classical channel. Classical channels don't necessarily require a direct connection between the sender and receiver; information can also be transmitted through a classical communication network. For classical channels where the sender and receiver are directly connected via optical fiber, consider using a classical communication module with a different wavelength from the quantum optical signal, and using wavelength division multiplexing (WDM) to share the same optical fiber to conserve fiber resources.

[0087] However, considering that traditional solutions require an independent classical communication system and have high implementation costs, 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.

[0088] In the first implementation, as shown in Figure 3, a laser is used at the transmitter, whose output light enters a dual-polarization (DP) modulator. Different arbitrary waveform generators (AWGs) are used to generate the quantum information waveform and the classical information waveform, respectively. The DP modulator then modulates the quantum and classical signals onto different polarization states of the optical signal. A common DP modulator is the DP-IQ modulator, a commonly used device in optical communications. For example, as shown in Figure 3, AWG1 generates the quantum information waveform and then modulates it onto one polarization state of the optical signal, such as X polarization. AWG2 generates the classical information waveform and then modulates it onto another polarization state, such as Y polarization. Thus, the output light of the DP modulator contains both quantum and classical optical signals, both in a polarization-multiplexed state. At the receiving end, a polarization controller is first used to reduce polarization crosstalk caused by fiber channel noise. A polarization demultiplexer is then used to separate the quantum and classical optical signals, each fed into a different polarization detector. For example, the separated quantum optical signal is fed into an X-polarization detector, while the separated classical optical signal is fed into a Y-polarization detector. The polarization demultiplexer can be, for example, a polarization diversity coherent receiver. This enables the co-transmission of classical and quantum information. Compared to traditional solutions, this approach is more integrated and eliminates a laser.

[0089] However, the first implementation essentially combines classical and quantum channels through polarization multiplexing. This requires a polarization controller at the receiver to recover the polarization changes in the channel, resulting in high hardware costs. Furthermore, because classical information occupies one polarization, quantum information can only use the other. This effectively loses half the bandwidth of the quantum channel, compromising its transmission efficiency.

[0090] The second implementation scheme, as shown in Figure 4, is that 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.

[0091] While the second implementation scheme allows for the simultaneous generation of classical and quantum signals on the same polarization, its modulation and demodulation are highly challenging, making practical implementation extremely difficult. In terms of modulation, the significant difference in amplitude between the classical and quantum signals makes simultaneous modulation difficult. In terms of reception, even slight fluctuations in the channel, resulting in variations in the received power of the classical signal, can significantly impact the demodulation of the quantum signal, degrading the signal-to-noise ratio. Consequently, the modulation accuracy requirements for quantum signals are often unsatisfactory.

[0092] 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 amplitude between the classical signal and the quantum signal when simultaneously generating quantum signals and classical signals 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 both classical information and quantum information. 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 both classical information and quantum information. 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, both the X polarization and the Y polarization of the modulated optical signal 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 to say, 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. 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, 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, the optical signal is frequency-division multiplexed, the receiving end can obtain quantum information and classical information respectively by demodulating different subcarriers. The demodulation of quantum information is less affected by the signal receiving power of classical information, thereby achieving a higher signal-to-noise ratio of classical signals and a higher signal-to-noise ratio of quantum signals at the receiving end, while meeting the modulation accuracy requirements of classical and quantum signals. The quantum device involved in this application can be a quantum key distribution device.

[0093] 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. The 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. The confidentiality enhancement parameter refers to the information that the first quantum device and the second quantum device need to synchronize when performing the confidentiality enhancement step. The 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. The consistency verification parameter refers 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 the quantum key distribution process shown in Figure 1, and the embodiments of this application will not be repeated here.

[0094] In this embodiment of the present 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, a single optical fiber can simultaneously transmit information used to generate quantum keys and business communication data, maximizing the use of the optical fiber link and improving bandwidth efficiency.

[0095] Optionally, the service 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.

[0096] The technical solutions provided in the embodiments of the present application are described in detail below.

[0097] Embodiments of the present application can be applied to quantum key distribution systems. For example, Figure 5 is a schematic diagram of the structure of a quantum key distribution system provided by an embodiment of the present application. As shown in Figure 5, 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 by an optical fiber link. Optionally, quantum key distribution system 500 can be a CVQKD system, a CVQKD module, or a coherent system that combines CVQKD with classical communication.

[0098] In the embodiments of this application, a first quantum device is used as the transmitter of a quantum key distribution system, and a second quantum device is used as the receiver of the system. The steps performed by the first and second quantum devices during the quantum key distribution process are detailed in the following method embodiments. For example, Figure 6 is a flow chart of a quantum key distribution method provided in an embodiment of this application. As shown in Figure 6, this method includes but is not limited to steps 601 through 603.

[0099] Step 601: A first quantum device generates a modulated optical signal, 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, and 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 agreement information.

[0100] 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. The quantum key negotiation information can be the classical information required to be transmitted by the data processing module in the quantum key distribution system (such as the CVQKD shown in Figure 1).

[0101] 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 from digital to analog to obtain an analog modulation signal, then the analog modulation signal is subjected to signal adjustment processing, and finally the analog modulation signal after signal adjustment processing is electro-optically modulated 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 range of quantum information, the preset frequency range of classical information, and the digital modulation format used by quantum information and classical information. The embodiment of the present application does not limit the digital modulation format used by quantum information and classical information. There is no overlapping frequency between the preset frequency range of quantum information and the preset frequency range of classical information. In the embodiment of the present application, the frequency range where the quantum information in the generated analog modulation signal is located is called the quantum signal frequency band, and the quantum signal frequency band is obtained based on quantum information modulation. The frequency range where the classical information in the analog modulation signal is located is called the classical signal frequency band, and the classical signal band is obtained based on classical information modulation. 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.

[0102] Optionally, the first quantum device can 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 can 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.

[0103] In the first implementation, the implementation process of the first quantum device generating a modulated optical signal is shown in FIG7 , including but not limited to the following steps A1 to A3.

[0104] Step A1: The first quantum device generates an analog modulation signal according to quantum information and classical information. The analog modulation signal includes a quantum signal frequency band and a classical signal frequency band.

[0105] Optionally, the analog modulated signal includes one or more quantum signal frequency bands and one or more classical signal frequency bands. The quantum signal frequency bands and classical signal frequency bands in the analog modulated signal do not overlap. At least one of the classical signal frequency bands carries quantum key negotiation information. There are various possible distribution locations for the quantum signal frequency bands and classical signal frequency bands in the analog modulated signal. The present application describes the following four possible scenarios as examples.

[0106] In the first possible scenario, 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, where the quantum signal frequency band is 10 megahertz (MHz) to 1 GHz, one classical signal frequency band is 1.1 GHz to 10 GHz, and another classical signal frequency band is 11 GHz to 20 Hz; or, the quantum signal frequency band is 10 MHz to 10 GHz, one classical signal frequency band is 10.1 GHz to 20 GHz, and another classical signal frequency band is 21 GHz to 80 Hz; and so on.

[0107] For example, Figure 8 illustrates a distribution of quantum signal frequency bands and classical signal frequency bands in an analog modulation signal. As shown in Figure 8, the analog modulation signal includes a quantum signal frequency band Q and three classical signal frequency bands C1-C3. Quantum signal frequency band Q is in the low frequency range, while classical signal bands C1-C3 are in the high frequency range.

[0108] In the second possible scenario, 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, where 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.

[0109] For example, Figure 9 shows another distribution of quantum signal frequency bands and classical signal frequency bands in an analog modulation signal. As shown in Figure 9, the analog modulation signal includes a quantum signal frequency band Q and three classical signal frequency bands C1-C3. Quantum signal frequency band Q is in the high frequency band, while classical signal bands C1-C3 are in the low frequency band.

[0110] In a third possible scenario, the analog modulation signal includes multiple classical signal bands, and the quantum signal band lies between these bands. For example, Figure 10 illustrates another distribution of quantum and classical signal bands in the analog modulation signal. As shown in Figure 10, the analog modulation signal includes a quantum signal band Q and three classical signal bands C1-C3. Quantum signal band Q lies between classical signal band C1 and classical signal band C2.

[0111] In the fourth possible scenario, the analog modulation signal includes multiple classical signal frequency bands and multiple quantum signal frequency bands, and the multiple quantum signal frequency bands are alternately distributed with the multiple classical signal frequency bands. For example, Figure 11 shows another distribution method of quantum signal frequency bands and classical signal frequency bands in the analog modulation signal. As shown in Figure 11, 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.

[0112] The horizontal axis of the signals shown in Figures 8 to 11 above is the frequency, and the vertical axis 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 into 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 within the frequency band) of the signal frequency band corresponding to the signal frequency band in the power spectrum density of the analog modulated signal. The amplitude can also refer to the average signal energy within 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 numerically proportional to the square root of the aforementioned numerical expressions. Or when the numerical value is not required precisely and only the size trend is identified, the average amplitude of a signal frequency band in the analog modulated signal can also be simply considered as the mean square of the voltage when the signal in the signal frequency band is converted back to voltage, or the root mean square value of the voltage, or the mean of the absolute value of the voltage. When comparing the amplitudes of two signals, if the difference in average power between the two signals is significant, such as by several orders of magnitude, the signal amplitudes are often converted to decibels (dB). In this case, the difference in dB between the two signal amplitudes directly translates to the multiple of the difference in amplitude between the two signals. This is a common representation method used in the fields of electrical and optical signals.

[0113] 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.

[0114] Optionally, when dB is used as the signal amplitude unit, when a numerical value such as average power or average power density is used to describe the signal amplitude, 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 and the average amplitude of the quantum signal frequency band in the analog modulated signal (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 small, the sampling accuracy of the DAC can be guaranteed, so that both the classical signal and the quantum signal have a high signal-to-noise ratio. If the sampling accuracy of the DAC allows, the average amplitude of the quantum signal frequency band in the analog modulated signal can be reduced.

[0115] Please refer to Figures 8 to 11, which respectively illustrate signal conditioning processing for various analog modulation signals with varying signal frequency band distributions. This signal conditioning processing includes filtering, where the filter frequency response is determined based on the distribution of the quantum signal frequency band and the classical signal frequency band. The average amplitude difference between the classical and quantum signal frequency bands in the target modulation signal is significantly greater than the average amplitude difference between the classical and quantum signal frequency bands in the analog modulation signal.

[0116] In the embodiments of the present application, two electrically modulated signals that originally had similar amplitudes and signal-to-noise ratios but were in different frequency bands are converted into one with a higher amplitude and the other with a lower amplitude by filtering. Specifically, a DAC generates an analog modulated signal containing both a quantum signal band and a classical signal band, and then filters the analog modulated signal so that the average amplitude of the quantum signal band is significantly lower than the average amplitude of the classical signal band. Generally speaking, after filtering, the average amplitudes of the quantum signal band and the classical signal band will differ significantly, with the maximum difference even exceeding 50dB.

[0117] Optionally, one implementation of step A2 is that the first quantum device filters the analog modulated signal using a filter to obtain a target modulated signal. The quantum signal frequency band is within a first frequency band of the filter, the classical signal frequency band is within a second frequency band of the filter, and the frequency attenuation in the first frequency band is greater than the frequency attenuation in the second frequency band.

[0118] This implementation uses a filter to perform signal conditioning on an analog modulated signal. By designing the filter's frequency response function to correlate with the distribution of the quantum signal frequency band and the classical signal frequency band in the analog modulated signal, the filter achieves greater frequency attenuation in the quantum signal frequency band, which functions like a filter's stopband. Furthermore, the filter achieves less frequency attenuation in the classical signal frequency band, which functions like a filter's passband. The frequency attenuation of each band in the filter can be set based on actual needs, as long as the average amplitude difference between the classical and quantum signal frequency bands in the filtered modulated signal meets the specified requirements.

[0119] Alternatively, in addition to directly designing a filter to perform signal adjustment processing on the analog modulated signal, the signal adjustment effect can be achieved by first branching, then filtering and attenuating separately, 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 is greater than the first amplitude threshold. The branch filtering method is more likely to form a flatter frequency response within 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.

[0120] In step A21, the first quantum device performs branching processing on the analog modulated signal according to the distribution areas of the quantum signal frequency band and the classical signal frequency band in the analog modulated signal to obtain multiple branched signals.

[0121] The number of branch signals can 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, referring to Figure 8, 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 also 1 (including the classical signal frequency bands C1-C3). Accordingly, the first quantum device can use a splitter to split the analog modulated signal into two paths, thereby obtaining two branch signals. For another example, referring to Figure 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 split the analog modulated signal into three paths, thereby obtaining three branch signals.

[0122] Optionally, the amplitudes of the multiple branch signals may be the same or different.

[0123] In step A22, the first quantum device uses multiple filters to filter the multiple branch signals 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.

[0124] Optionally, the branch signal, like the original analog modulated signal, contains both a quantum signal frequency band and a classical signal frequency band. A filter is used to filter the branch signal so that the filtered branch signal contains only the quantum signal frequency band or the classical signal frequency band. This allows for the generation of quantum filtered signals and classical filtered signals. For example, for the analog modulated signal shown in FIG8 , filtering one branch signal with a low-pass filter can yield a quantum filtered signal comprising the quantum signal frequency band Q; filtering the other branch signal with a high-pass filter can yield a classical filtered signal comprising the classical signal frequency bands C1-C3.

[0125] In step A23 , the first quantum device performs attenuation processing on the one or more quantum filter signals.

[0126] By performing attenuation processing on the quantum filter signal, the amplitude of the quantum filter signal can be reduced.

[0127] 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.

[0128] 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 case in the above step A1) as an example to introduce the implementation process of the above steps A21 to A24. For example, Figure 12 is a schematic diagram of a signal adjustment process for an analog modulated signal provided in an embodiment of the present application. As shown in Figure 12, the analog modulated 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 modulated 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.

[0129] Assuming the splitter's upstream output is a quantum signal path, Figure 12 shows. This path will pass through a low-pass filter with appropriate attenuation. After low-pass filtering and attenuation, the amplitude of the low-frequency quantum signal band will be somewhat attenuated, while the amplitude of the high-frequency classical signal band will experience even greater attenuation. The added attenuation ensures that the output amplitude of the quantum signal band meets the preset requirements. Furthermore, if the system's final quantum signal output amplitude is set to be significantly lower than the classical signal amplitude, the low-pass filtering of the quantum signal path can be omitted. This is because the amplitude of the classical signal band in this path will be significantly smaller than that of the classical signal path, resulting in virtually no impact between the two after combining.

[0130] Continuing with Figure 12, the splitter's downstream output is a classical signal path, which then passes through a high-pass filter. This high-pass filter almost completely removes the low-frequency quantum signal, while allowing the high-frequency classical signal to pass through at a higher amplitude. If this high-pass filter is an active filter, it may also provide some gain to the classical signal.

[0131] 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 processing) 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).

[0132] Continuing with Figure 12, the signals output by the quantum signal path and the signals output by the classical signal path are combined by a combiner to ultimately produce the target modulated signal. In this target modulated signal, the average amplitude of the quantum signal band in the low-frequency band is significantly lower than the average amplitude of the classical signal band in the high-frequency band.

[0133] Alternatively, when the splitter uses an unbalanced directional coupler, the amplitude ratio of its output branches may not be close to 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 (e.g., 99%) can be selected as the classical signal path, while the output path with a lower splitting ratio (e.g., 1%) can be selected as the quantum signal path. In this case, the quantum signal path only needs to be equipped with a low-pass filter, eliminating the need for an additional attenuator.

[0134] Optionally, the splitter can also 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, and 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 the ordinary splitter in the scheme shown in Figure 12 plus a low-pass filter; if the second output only contains signals in the high-frequency band, it is equivalent to the ordinary splitter in the scheme shown in Figure 12 plus a high-pass filter. In the scheme shown in Figure 12, 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. At this time, 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, corresponding filters can be added to the quantum signal path and the classical signal path, but the requirements for each filter are reduced.

[0135] Optionally, when the quantum signal frequency band in the analog modulated 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 step A1 above), the implementation process of filtering the analog modulated signal can refer to the implementation process shown in Figure 12. 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.

[0136] Optionally, when the analog modulated 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 case in step A1 above), the implementation process of filtering the analog modulated signal can refer to the implementation process shown in Figure 12. 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.

[0137] Optionally, when the analog modulated 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 case in step A1 above), the implementation process of filtering the analog modulated signal can refer to the implementation process shown in Figure 12. 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 are 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 adopted; for the branch of the classical signal frequency band, a bandpass filter is adopted. Finally, the various branches are merged together.

[0138] Step A3: The first quantum device electro-optically modulates the target modulation signal to obtain a modulated optical signal.

[0139] 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. 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.

[0140] In this implementation, signal adjustment processing is performed on an analog modulated signal including a quantum signal frequency band and a 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 modulated signal after adjustment meets the set requirements. In this way, the power intensity of the quantum light signal in the modulated light signal obtained by modulation based on the target modulated signal can be much weaker than the power intensity of the classical light signal, thereby meeting the transmission performance requirements of quantum light signals and classical light signals.

[0141] In the implementation of the first quantum device generating a modulated optical signal shown in Figure 7, the first quantum device, acting as the transmitter for quantum key distribution, can use a laser to emit an optical signal and a DAC to generate an analog modulated signal. Finally, an electro-optical modulator modulates the analog modulated signal, which has undergone signal modulation processing, onto the optical signal emitted by the laser, to obtain the modulated optical signal to be transmitted. The number of lasers, DACs, and electro-optical modulators required to generate the modulated optical signal is the same for the first quantum device, resulting in low hardware costs.

[0142] For example, FIG13 is a schematic diagram of a process for generating a modulated optical signal provided by an embodiment of the present application. As shown in FIG13 , 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 for the quantum information and classical information are shown in FIG8 as an example. Specifically, a digital signal processing algorithm can be used to convert the 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 is converted into an analog modulation signal through a DAC. Then, the analog modulation signal is converted into a target modulation signal through a signal adjustment unit. The implementation process of this process refers to step A2 above. After that, the target modulation signal is usually passed through a power amplifier (not shown) and then applied to the electrical input port of an electro-optical modulator. At this time, the output light of the laser enters the optical input port of the electro-optical modulator. After passing through the electro-optical modulator, the optical signal outputs a modulated optical signal, which carries the information of the target modulation signal. Finally, the modulated optical signal is transmitted through an attenuator via an 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.

[0143] In the second implementation, the implementation process of the first quantum device generating a modulated optical signal is shown in FIG14 , including but not limited to the following steps B1 to B3.

[0144] Step B1: The first quantum device generates a first analog modulation signal based on quantum information, and generates a second analog modulation signal based on 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.

[0145] The quantum signal frequency band in the first analog modulation signal and the classical signal frequency band in the second analog modulation signal do not overlap. The selection of the quantum signal frequency band and the classical signal frequency band can refer to the relevant description in step A1 above. For example, the four possible situations described in step A1 can be selected, which will not be further described in this embodiment of the present application.

[0146] 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 the analog modulation signals, wherein one DAC modulates only the quantum signal, specifically sampling only the frequency range in which the quantum information in the digital modulation signal resides. The analog modulation signal output by this DAC (i.e., the first analog modulation signal) contains only the quantum signal frequency band, with only some DAC sampling noise floor in the classical signal frequency band. The other DAC modulates only the classical signal, specifically sampling only the frequency range in which the classical information in the digital modulation signal resides. The analog modulation signal output by this DAC (i.e., the second analog modulation signal) contains only the classical signal frequency band, with the quantum signal frequency band primarily consisting of the DAC sampling noise floor.

[0147] 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 high signal-to-noise ratio.

[0148] 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.

[0149] By attenuating the first analog modulated signal, the amplitude of the first analog modulated signal can be reduced, that is, the average amplitude of the quantum signal frequency band in the first analog modulated signal can be reduced. Optionally, the third amplitude threshold is the same as the first amplitude threshold in step A2 above, for example, 10 dB.

[0150] 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.

[0151] 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.

[0152] Optionally, the first quantum device can also filter the second analog modulated signal, and then generate a modulated optical signal based on the filtered second analog modulated signal and the attenuated first analog modulated signal. This can further suppress the DAC sampling noise floor at the quantum signal frequency band position in the second analog modulated signal, thereby avoiding affecting the signal quality of the subcarrier corresponding to the quantum signal frequency band in the modulated optical signal. The implementation method for filtering the second analog modulated signal can refer to the filtering method for the analog modulated signal in step A2 above. Specifically, the corresponding filter can be designed based on 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 between multiple classical signal frequency bands, the filter selects a band-stop filter or a multi-stopband filter. Of course, if the DAC sampling noise floor in the second analog modulated signal is extremely low and its impact on the signal quality of the quantum signal frequency band position after combining is negligible, the second analog modulated signal can be omitted from filtering.

[0153] In this implementation, by attenuating the first analog modulated signal including the quantum signal frequency band, the average amplitude difference between the quantum signal frequency band in the attenuated first analog modulated signal and the classical signal frequency band in the second analog modulated signal can meet the set requirements. As a result, the power intensity of the quantum light signal in the final modulated optical signal can be much weaker than the power intensity of the classical light signal, thereby meeting the transmission performance requirements of both quantum light signals and classical light signals.

[0154] Optionally, one implementation of step B3 is that the first quantum device combines the second analog modulated signal and the attenuated first analog modulated signal to obtain a combined analog modulated signal. The first quantum device performs electro-optical modulation based on the combined analog modulated signal to obtain a modulated optical signal. In this implementation, the first quantum device, as the transmitter of quantum key distribution, can use a laser to emit an optical signal, and use two DACs to generate two analog modulated signals respectively, and then attenuate the analog modulated signal containing the quantum signal frequency band, and then combine it with the other analog modulated signal containing the classical signal frequency band. Finally, an electro-optical modulator is used to modulate the combined analog modulated 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 the modulated optical signal is one, and the number of DACs is two, so the hardware cost is low.

[0155] For example, Figure 15 is a schematic diagram of another process for generating a modulated optical signal provided by an embodiment of the present application. As shown in Figure 15 , first, the acquired quantum information and classical information are converted into 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 for the quantum information and classical information are shown in Figure 8 as an example. Specifically, a digital signal processing algorithm can be used to convert the digital signal containing quantum information and classical information into a digital modulation signal. The digital signal processing algorithm typically includes frequency shifting, upsampling, pulse shaping, and pre-compensation. Next, the digital modulation signal passes through DAC1 to form analog modulation signal 1 containing the quantum signal frequency band, and the digital modulation signal passes through DAC2 to form analog modulation signal 2 containing the classical signal frequency band. Then, analog modulation signal 1 passes through the attenuator in the signal adjustment unit and reaches the combiner; analog modulation signal 2 passes through the filter in the signal adjustment unit and reaches the combiner. The modulated signal output by the combiner is usually passed through a power amplifier (not shown) and applied to the electrical input port of the electro-optical modulator. At this point, the laser's output light enters the optical input port of the electro-optical modulator. After passing through the modulator, the optical signal outputs a modulated optical signal, which carries the information of the modulated signal output by the combiner. Finally, the modulated optical signal passes through an attenuator and is transmitted through the optical fiber link. The attenuator adjusts the output power of the modulated optical signal to achieve a predetermined optical power level.

[0156] Optionally, another implementation of step B3 is that the first quantum device uses a first electro-optical modulator to electro-optically modulate the attenuated first analog modulated signal to obtain a first optical signal. The first quantum device uses a second electro-optical modulator to electro-optically modulate the second analog modulated 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 transmitter 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 modulated signals respectively, and then after attenuating the analog modulated signal containing the quantum signal frequency band, use an electro-optical modulator to modulate it on one optical signal of the laser, and use another electro-optical modulator to modulate the other analog modulated 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 first quantum device requires only one laser to generate a modulated optical signal, and two DACs and electro-optical modulators, resulting in low hardware costs. The intensities of the two optical signals output by the optical beam splitter can be similar or can differ slightly; for example, the light used to modulate the analog signal containing the quantum signal frequency band can be weaker.

[0157] For example, FIG16 is a schematic diagram of another process for generating a modulated optical signal provided in an embodiment of the present application. As shown in FIG16 , first, the acquired quantum information and classical information are generated into 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 taken as an example as shown in FIG8 . Specifically, a digital signal processing algorithm can 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 point, the laser's output light passes through an optical beam splitter and is split into two paths, each entering the optical input ports of electro-optical modulator 1 and electro-optical modulator 2. One optical signal is modulated by electro-optical modulator 1 and output to the optical combiner. This modulated optical signal carries the information of analog modulated signal 1. The other optical signal is modulated by electro-optical modulator 2 and output to the optical combiner. This modulated optical signal carries the information of analog modulated signal 2. The optical combiner then combines the two modulated optical signals to produce a modulated optical signal. Finally, the modulated optical signal passes through an attenuator and is transmitted through an optical fiber link. The attenuator is used to adjust the output power of the modulated optical signal so that it reaches a predetermined optical power level.

[0158] 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 it through a mixer together with another analog local oscillator (quasi-single-tone sinusoidal local oscillator) and shift it to the corresponding subcarrier frequency band. Both methods can achieve the purpose of generating a subcarrier modulation signal in this application.

[0159] Step 602: The first quantum device sends the modulated optical signal to the second quantum device through an optical fiber link.

[0160] 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.

[0161] Furthermore, 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 performed.

[0162] Step 603: The second quantum device obtains quantum information and classical information based on the modulated optical signal.

[0163] 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 the relevant steps shown in Figure 1, and the embodiments of this application will not be repeated here.

[0164] Optionally, the first implementation of step 603 includes the following steps C1 to C3.

[0165] In step C1, the second quantum device uses a coherent detector to convert the received modulated optical signal into an analog signal, where the analog signal includes a quantum signal frequency band and a classical signal frequency band.

[0166] 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 steps A1 to A3 above, then 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 step A1 above. Alternatively, if the modulated optical signal is generated using steps B1 to B3 above, then 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 step B1 above, 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 step B1 above.

[0167] In the first possible implementation, the coherent detector is a traditional coherent receiver. For example, Figure 17 is a schematic diagram of the structure of a coherent receiver provided in an embodiment of the present application. As shown in Figure 17, 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 light signals, the industry often refers to the I component of the quantum light signal as the x-regular component, and the Q component as the p-regular component. The Y-polarized optical signal behaves similarly. After entering the BS, it is split into two, with the two outputs entering BPD3 and BPD4, respectively. BPD3 and BPD4, combined with the delay difference of the local oscillator (LO), measure the I component (x-regular component) and Q component (p-regular component) of the Y-polarized optical signal, respectively. To enable BPD operation, the coherent receiver also requires a local oscillator (LO) to provide LO light. This LO light undergoes two stages of BS beam splitting, splitting it into four beams that enter BPD1 through BPD4. The two beams entering BPD1 and BPD2 have a phase difference of approximately 90 degrees with the corresponding optical signal; the two beams entering BPD3 and BPD4 also have a phase difference of approximately 90 degrees with the corresponding optical signal.

[0168] 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, Figure 18 is a structural diagram of a single polarization receiver provided in an embodiment of the present application. As shown in Figure 17, the single polarization receiver includes a polarization controller (PC), multiple BSs, and two BPDs. Among them, 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 polarization 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.

[0169] In a third possible implementation, the coherent detector can use only one BPD to receive the optical signal. For example, FIG19 is a schematic diagram of the structure of a coherent detector provided in an embodiment of the present application. As shown in FIG19 , 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 measures the I component and Q component of the polarized light signal in combination with the delay difference of the local oscillator light. Similarly, the coherent detector also requires a local oscillator to provide local oscillator light to enter the BPD.

[0170] The output signals of all BPDs in the coherent detector are analog signals converted by the coherent detector.

[0171] In step C2, the second quantum device performs received signal adjustment processing on the analog signal to obtain a target signal.

[0172] 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. Because the quantum light signal in the optical signal received by the receiver is much weaker than the classical light signal, if the analog signal output by the coherent detector is directly sampled using an 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 will be large, affecting system performance. By performing received signal adjustment processing on the analog 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 made roughly similar to the average amplitude of the classical signal frequency band corresponding to the classical light signal. This fully utilizes the sampling accuracy of the ADC, reduces the sampling noise of the quantum signal frequency band corresponding to the quantum light signal, and minimizes system performance loss.

[0173] Optionally, one implementation of step C2 is that the second quantum device filters the analog signal using a filter to obtain a target signal. The quantum signal frequency band is within a first frequency band of the filter, and the classical signal frequency band is within a second frequency band of the filter. The frequency attenuation in the first frequency band is less than the frequency attenuation in the second frequency band.

[0174] This implementation uses a filter to perform signal conditioning on an analog signal. By designing the filter's frequency response function to correlate with the distribution of the quantum and classical signal frequency bands in the analog signal, the filter achieves low frequency attenuation in the quantum signal band, which functions like the filter's passband. Furthermore, the filter achieves high frequency attenuation in the classical signal band, which functions like the filter's stopband. The frequency attenuation of each band in the filter can be adjusted based on actual needs, as long as the average amplitudes of the classical and quantum signal bands in the filtered target signal are similar.

[0175] Alternatively, in addition to directly designing a filter to adjust the analog signal, a method of first branching, then filtering and attenuating the signals separately, and then combining the signals can be used to achieve the signal adjustment effect, 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 is less than a set amplitude threshold. The branch filtering method is more likely to form a flatter frequency response within 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.

[0176] 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.

[0177] The implementation method of this step C21 can refer to the above-mentioned step A21, and will not be repeated here in this embodiment of the present application.

[0178] In step C22, the second quantum device uses multiple filters to filter the multiple branch signals 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.

[0179] The implementation method of this step C22 can refer to the above-mentioned step A22, and will not be repeated here in this embodiment of the present application.

[0180] In step C23 , the second quantum device performs attenuation processing on the one or more classical filtered signals.

[0181] By performing attenuation processing on the classical filtered signal, the amplitude of the classical filtered signal can be reduced.

[0182] In step C24, the second quantum device combines all quantum filtered signals and all classical filtered signals that have undergone attenuation processing to obtain a target signal.

[0183] 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 case in the above step A1) as an example to introduce the implementation process of the above steps C21 to C24. For example, Figure 20 and Figure 21 are schematic diagrams of a received signal adjustment process for an analog signal provided in an embodiment of the present application. As shown in Figure 20 or Figure 21, 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 received signal adjustment unit, it is first divided into two by a splitter. Among them, a duplex frequency division device is used as a splitter in Figure 20, and the duplex frequency division device can separate the classical signal frequency band and the quantum signal frequency band in the analog signal. A power divider is used as a splitter in Figure 21, and the amplitudes of the two signals output by the power divider are basically the same.

[0184] Assuming the splitter's upstream output is a quantum signal path, as shown in Figure 20 or Figure 21, this path will pass through a low-pass filter. After low-pass filtering, the high-frequency classical signal band is largely filtered out, while the low-frequency quantum signal band is allowed to pass through at a relatively high amplitude.

[0185] Continuing with Figure 20 or Figure 21, the splitter's downstream output is a classical signal path. In Figure 20, the classical signal path can be passed through a full-band attenuation filter or a high-pass filter with appropriate attenuation. In Figure 21, the classical signal path can be passed through a high-pass filter with appropriate attenuation. The purpose of attenuating the classical signal path is to ensure that the average amplitude of the classical signal frequency band in the signal output by the classical signal path (i.e., the classical filtered signal) is similar 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).

[0186] Continuing with Figure 20 or Figure 21, the signals output by the quantum signal path and the classical signal path are combined by a combiner to produce the target signal, which is then input into the ADC. In this target signal, the average amplitude of the low-frequency quantum signal is similar to the average amplitude of the high-frequency classical signal.

[0187] 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.

[0188] In this implementation mode, the receiving end only needs one ADC to complete the sampling of the analog signal, and the hardware cost is low.

[0189] Optionally, the second implementation of step 603 includes the following steps D1 to D3.

[0190] In step D1, the second quantum device uses a coherent detector to convert the received modulated optical signal into an analog signal, where the analog signal includes a quantum signal frequency band and a classical signal frequency band.

[0191] 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.

[0192] The implementation method of this step D1 can refer to the above-mentioned step C1, and will not be repeated here in this embodiment of the present application.

[0193] 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.

[0194] 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.

[0195] Because quantum signal frequency bands are typically narrow, they place high demands on ADC sampling accuracy and are therefore suitable for ADCs with low sampling rates but high bit widths (resolution). In contrast, classical signal frequency bands are typically wide, placing less demanding demands on ADC sampling accuracy and are therefore suitable for ADCs with high sampling rates but low bit widths. In this embodiment, two ADCs can be used to sample the classical and quantum signal bands of the analog signal, respectively, to meet the respective sampling accuracy requirements.

[0196] 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 is performed on the optical signal, the receiving end can obtain quantum information and classical information respectively by demodulating different subcarriers. The demodulation of quantum information is less affected by the signal receiving power of the classical information, thereby achieving a higher signal-to-noise ratio of the classical signal and a higher signal-to-noise ratio of the quantum signal 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.

[0197] 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 circumstances. Any technician familiar with the technical field can easily think of a method of change within the technical scope disclosed in this application, and it 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.

[0198] The following describes the virtual device in the embodiment of the present application by way of example.

[0199] For example, Figure 22 is a schematic diagram of the structure 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. As shown in Figure 22, the quantum key distribution device 2200 includes but is not limited to a generation module 2201 and a transmission module 2202.

[0200] Generation module 2201 is used to generate a modulated optical signal, which carries quantum information and classical information. The classical information and 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 quantum information are located in different subcarriers among the multiple subcarriers. The classical information includes quantum key negotiation information.

[0201] 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 quantum key agreement information are used by the first quantum device and the second quantum device to jointly generate the same quantum key.

[0202] 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 check parameters.

[0203] Optionally, the classic information also includes business communication data.

[0204] Optionally, the business communication data includes encrypted data.

[0205] Optionally, generation module 2201 is configured to generate an analog modulation signal based on quantum information and classical information, the analog modulation signal comprising a quantum signal frequency band obtained by modulation based on quantum information and a classical signal frequency band obtained by modulation based on classical information, wherein the quantum signal frequency band and the classical signal frequency band do not overlap. Signal adjustment processing is performed 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. Electro-optical modulation is performed 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.

[0206] 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 modulated signal is smaller than a second amplitude threshold, and the second amplitude threshold is smaller than the first amplitude threshold.

[0207] Optionally, the generation module 2201 is used to: use a filter to filter the analog modulation signal to obtain a target modulation 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.

[0208] Optionally, generation module 2201 is configured to: split the analog modulated signal based on the distribution of quantum signal frequency bands and classical signal frequency bands in the analog modulated signal to obtain multiple branch signals. Each branch signal is filtered using multiple filters to obtain one or more quantum filtered signals and one or more classical filtered signals, where 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. Attenuation is performed on the one or more quantum filtered signals. All classical filtered signals and all attenuated quantum filtered signals are combined to obtain a target modulated signal.

[0209] Optionally, the generation module 2201 is configured to generate a first analog modulation signal based on quantum information and a second analog modulation signal based on 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 overlap between the quantum signal frequency bands and the classical signal frequency bands. 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.

[0210] Optionally, the generating module 2201 is configured to: combine the second analog modulated signal and the attenuated first analog modulated signal to obtain a combined analog modulated signal, and perform electro-optical modulation on the combined analog modulated signal to obtain a modulated optical signal.

[0211] Optionally, the generating module 2201 is configured to: electro-optically modulate the attenuated first analog modulated signal using a first electro-optical modulator to obtain a first optical signal; electro-optically modulate the second analog modulated signal using a second electro-optical modulator to obtain a second optical signal; and combine the first optical signal and the second optical signal to obtain a modulated optical signal.

[0212] Optionally, the first analog modulation signal and the second analog modulation signal are generated by different digital-to-analog converters respectively.

[0213] Optionally, the modulated optical signal comes from the same laser.

[0214] For another example, Figure 23 is a schematic diagram of the structure of another quantum key distribution device 2300 provided in an embodiment of the present application. This quantum key distribution device 2300 is applied to a second quantum device. As shown in Figure 23, this quantum key distribution device 2300 includes but is not limited to a receiving module 2301 and a processing module 2302.

[0215] Receiving module 2301 is used to receive a modulated optical signal sent by a first quantum device through an optical fiber link. The modulated optical signal carries quantum information and classical information. The classical information and 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 quantum information are located in different subcarriers among the multiple subcarriers. The classical information includes quantum key negotiation information.

[0216] The processing module 2302 is configured to obtain quantum information and classical information based on the modulated optical signal, wherein the quantum information and quantum key agreement information are used by the first quantum device and the second quantum device to jointly generate the same quantum key.

[0217] 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 check parameters.

[0218] Optionally, the classic information also includes business communication data.

[0219] Optionally, the business communication data includes encrypted data.

[0220] Optionally, processing module 2302 is configured to convert the received modulated optical signal into an analog signal using a coherent detector. 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 overlap. The quantum signal frequency band corresponds to a subcarrier in the modulated optical signal that carries quantum information, and the classical signal frequency band corresponds to a subcarrier in the modulated optical signal that carries classical information. The analog signal is subjected to received signal adjustment processing to obtain a target 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 signal is less than an amplitude threshold. An analog-to-digital converter is used 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.

[0221] 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.

[0222] Optionally, processing module 2302 is configured to: split the analog signal based on the distribution of quantum signal frequency bands and classical signal frequency bands in the analog signal to obtain multiple branch signals. Filter the multiple branch signals using multiple filters to obtain one or more quantum filtered signals and one or more classical filtered signals, each quantum filtered signal including one or more adjacent quantum signal frequency bands, and each classical filtered signal including one or more adjacent classical signal frequency bands. Attenuate the one or more classical filtered signals. Combine all quantum filtered signals and all attenuated classical filtered signals to obtain a target signal.

[0223] Optionally, processing module 2302 is configured to convert a received modulated optical signal into an analog signal using a coherent detector. 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 overlap. The quantum signal frequency band corresponds to a subcarrier in the modulated optical signal that carries quantum information, and the classical signal frequency band corresponds to a subcarrier in the modulated optical signal that carries classical information. A first analog-to-digital converter is used to sample the classical signal frequency band of the analog signal to obtain classical information. A second analog-to-digital converter is used to sample the quantum signal frequency band of the analog signal to obtain quantum information.

[0224] Regarding the apparatus 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.

[0225] The following is an example of the basic hardware structure involved in the embodiments of the present application.

[0226] For example, Figure 24 is a schematic diagram of the hardware structure of a quantum device 2400 provided in an embodiment of the present application. As shown in Figure 24, quantum device 2400 includes a processor 2401 and a memory 2402, which are connected via a bus 2403. Figure 24 illustrates processor 2401 and memory 2402 as separate entities. Alternatively, processor 2401 and memory 2402 may be integrated. Quantum device 2400 may, for example, be a quantum key distribution device.

[0227] Memory 2402 is used to store computer programs, including operating systems and program code. 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, registers, optical disk storage, optical disc storage, magnetic disk, or other magnetic storage devices.

[0228] Processor 2401 is a general-purpose processor or a dedicated processor. Processor 2401 may be a single-core processor or a multi-core processor. Processor 2401 includes at least one circuit to execute the above-mentioned quantum key distribution method provided in the embodiment of the present application.

[0229] 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.

[0230] Optionally, quantum device 2400 further includes an input / output (I / O) interface 2405, which is connected to processor 2401 and memory 2402 via bus 2403. Processor 2401 can receive input commands or data through I / O interface 2405. I / O interface 2405 is used to connect quantum device 2400 to input devices, such as a keyboard and mouse. Optionally, in some possible scenarios, the network interface 2404 and I / O interface 2405 are collectively referred to as a communication interface.

[0231] Optionally, quantum device 2400 further includes a display 2406, which is connected to processor 2401 and memory 2402 via bus 2403. Display 2406 can be used to display intermediate results and / or final results generated by processor 2401 executing the above method. In one possible implementation, display 2406 is a touch screen display to provide a human-computer interaction interface.

[0232] Bus 2403 is any type of communication bus for interconnecting the internal devices of quantum device 2400, such as a system bus. This embodiment of the present application uses the example of interconnecting the aforementioned devices within quantum device 2400 via bus 2403. Alternatively, the aforementioned devices within quantum device 2400 may be communicatively connected to each other using other connection methods besides bus 2403, such as interconnecting the aforementioned devices within quantum device 2400 via a logical interface within quantum device 2400.

[0233] The above-mentioned devices can be provided on separate chips, or at least partially or entirely on the same chip. Whether to provide each device independently on different chips or to integrate them on one or more chips often depends on the product design requirements. The embodiments of this application do not limit the specific implementation of the above-mentioned devices.

[0234] The quantum device 2400 shown in FIG24 is merely exemplary. During implementation, the quantum device 2400 may also include other components, which are not listed here. The quantum device 2400 shown in FIG24 can implement quantum key distribution by executing all or part of the steps of the method provided in the above embodiment.

[0235] This embodiment of the present application also provides a quantum key distribution system, comprising: 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 configured to execute the steps performed by the first quantum device in the above method embodiment, such as steps 601 and 602. The second quantum device is configured to execute the steps performed by the second quantum device in the above method embodiment, such as step 603.

[0236] An embodiment of the present application further provides a computer-readable storage medium having instructions stored thereon. 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.

[0237] 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 computer program implements the steps performed by the first quantum device or the second quantum device in the above method embodiment.

[0238] Those 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 a program to instruct the relevant hardware, and the program may be stored in a computer-readable storage medium, which may be a read-only memory, a disk, or an optical disk, etc.

[0239] 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.

[0240] In this application, the term "and / or" simply describes an association between related objects, indicating that three possible relationships exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally indicates that the related objects are in an "or" relationship.

[0241] 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 the relevant laws, regulations and standards of relevant countries and regions.

[0242] The above description is merely an optional embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the concepts and principles of the present application shall be included in the scope of protection 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. Modulation signal, 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; 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 agreement information includes one or more of random sampling data, error correction auxiliary information, confidentiality enhancement parameters, basis comparison information or consistency check 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 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 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 agreement information includes one or more of random sampling data, error correction auxiliary information, confidentiality enhancement parameters, basis comparison information or consistency check 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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