Signal processing method and device of quantum key distribution system

Abstract

The invention provides a signal processing method and device for a quantum key distribution system, and the method comprises the steps: receiving a first optical signal which comprises an X polarization state and a Y polarization state, and comprises a quantum optical signal and a pilot optical signal; performing photoelectric conversion on the first optical signal to obtain a first digital signal and a second digital signal; obtaining a first pilot frequency digital signal and a second pilot frequency digital signal; obtaining at least one first coefficient according to the first digital signal, the first pilot frequency digital signal and the second pilot frequency digital signal; and performing polarization demultiplexing processing on the second digital signal according to each of the at least one first coefficient to obtain a first quantum digital signal and a second quantum digital signal. According to the method, the coefficient for polarization demultiplexing of the quantum signal is obtained through the pilot signal, so that the quantum signal is demultiplexed by using the coefficient, and the output signal meets the safety requirement of the QKD system.

Description

Technical Field

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

[0002] With the rapid development of information technology, people have higher and higher requirements for the security of communication. Quantum communication is a technology developed on the basis of quantum mechanics and classical information theory. It uses the basic principles of quantum mechanics to ensure the security of communication. In quantum communication technology, quantum secure communication is the most mature technology. It realizes the unconditional secure distribution of symmetric keys on the premise of sharing some security keys.

[0003] Quantum key distribution (QKD) can be divided into two types: discrete-variable quantum key distribution (DV-QKD) and continuous-variable quantum key distribution (CV-QKD). Taking the CV-QKD system as an example, the system uses a coherent state as a light source at the transmitter, and uses a modulator to shift the center position of the coherent state to achieve Gaussian modulation. After the modulated light is transmitted through the optical fiber, the receiver uses a homodyne or heterodyne detector for detection, and finally performs data post-processing.

[0004] However, in actual CV-QKD systems, devices and channels have non-ideal characteristics. For example, the laser does not emit an ideal coherent state, but contains amplitude noise and phase noise. The modulator is limited by its own performance and the excitation voltage signal and cannot achieve perfect Gaussian modulation. Due to the influence of the non-ideal characteristics of the optical fiber, the polarization state of the signal light will change randomly after it is transmitted in the optical fiber, and the signals between the other two polarizations will also leak into each other. Therefore, how to depolarize the signal so that the output signal meets the security requirements of the QKD system is a technical problem that needs to be solved urgently. Summary of the invention

[0005] The present application provides a signal processing method and device for a quantum key distribution system, which first uses a pilot signal at the receiving end to obtain coefficients for polarization demultiplexing of quantum signals, and then uses the coefficients to demultiplex the quantum signals so that the output signal meets the security requirements of the QKD system.

[0006] In a first aspect, a signal processing method for a quantum key distribution system is provided, comprising: receiving a first optical signal, wherein the first optical signal comprises an X polarization state and a Y polarization state, and the first optical signal comprises a quantum optical signal and a pilot optical signal; performing photoelectric conversion on the first optical signal to obtain a first digital signal and a second digital signal, wherein the first digital signal corresponds to the pilot optical signal, and the second digital signal corresponds to the quantum optical signal; obtaining a first pilot digital signal and a second pilot digital signal, the first pilot digital signal corresponding to the X polarization state of the first digital signal, and the second pilot digital signal corresponding to the Y polarization state of the first digital signal; obtaining at least one first coefficient according to the first digital signal, the first pilot digital signal, and the second pilot digital signal; performing polarization demultiplexing processing on the second digital signal according to the at least one first coefficient to obtain a first quantum digital signal and a second quantum digital signal, the first quantum digital signal corresponding to the X polarization state, and the second quantum digital signal corresponding to the Y polarization state.

[0007] Wherein: the first pilot digital signal and the second pilot digital signal are preconfigured; or the first pilot digital signal and the second pilot digital signal are obtained by performing polarization demultiplexing processing on the first digital signal.

[0008] It should be further explained that there are effects such as polarization rotation in the channel, and the X and Y polarization states generated by the transmitter will interfere with each other after passing through the channel. Therefore, the X polarization signal of the second digital signal at the receiving end may have little correlation with the transmitted X polarization state, and the Y polarization signal of the second digital signal may also have little correlation with the transmitted Y polarization state. In order to improve system performance, the receiving end needs to perform polarization demultiplexing on the second digital signal, so that the obtained first quantum digital signal has a greater correlation with the X polarization information of the transmitter, and also makes the second quantum digital signal have a greater correlation with the Y polarization information of the transmitter.

[0009] In a QKD system, the power of a quantum optical signal is usually lower than that of a pilot optical signal, and the corresponding second digital signal power is also lower than that of the first digital signal power, making it difficult to directly process using an equalization algorithm. The first digital signal corresponding to the classical optical signal has relatively higher power and a higher signal-to-noise ratio. Thus, channel variables or device damage parameters can be quickly extracted through the first digital signal. Therefore, the present application provides a signal processing method, which first obtains at least one first coefficient based on a first digital signal corresponding to a pilot optical signal, and performs polarization demultiplexing on a second digital signal corresponding to the quantum optical signal based on the first coefficient, so that the output signal meets the security requirements of the QKD system.

[0010] In combination with the first aspect, in certain implementations of the first aspect, performing polarization demultiplexing processing on the second digital signal according to each first coefficient of at least one first coefficient includes: performing data transformation on the second digital signal according to the first coefficient to obtain a third digital signal; adding digital noise to the third digital signal to obtain a first quantum digital signal and a second quantum digital signal.

[0011] That is, after data conversion, the signal after polarization multiplexing processing is compensated by adding random numbers to the signal, so that the output quantum signal meets the security requirements of the QKD system. In some implementations, digital noise can be added to the second digital signal according to the singular value of the first coefficient, so as to perform more stable and more widely applicable digital signal processing.

[0012] In combination with the first aspect, in some implementations of the first aspect, adding digital noise to the third digital signal includes: extracting a matrix element of the first coefficient, and adding digital noise to the third digital signal according to the matrix element. That is, by directly calculating and solving, data processing is performed on the second digital signal corresponding to the quantum light signal, which can simplify the data transformation process while making the output signal meet the security requirements of the QKD system.

[0013] In combination with the first aspect, in certain implementations of the first aspect, adding digital noise to the third digital signal includes: performing matrix decomposition on the first coefficient to obtain a first unitary matrix, a second unitary matrix and a diagonal matrix; obtaining complex random noise according to the diagonal elements in the diagonal matrix; performing data transformation on the complex random noise according to the first unitary matrix to obtain digital noise; adding digital noise to the third digital signal. As an implementation, the singular values ​​of the first coefficients can be used to perform polarization demultiplexing processing on the second digital signal, thereby performing more stable digital signal processing. That is, by performing matrix decomposition on the first coefficient to perform data transformation on the second digital signal corresponding to the quantum light signal, the second digital signal can be polarization demultiplexed according to the matrix decomposition result, so that the output signal meets the security requirements of the QKD system. In the case of using singular value decomposition, the diagonal elements can specifically refer to singular values.

[0014] In combination with the first aspect, in some implementations of the first aspect, the second digital signal, the first quantum digital signal, and the second quantum digital signal satisfy the following relationship: out =W η S in +N A , where W η is the first coefficient, S in is the second digital signal, W η S in is the third digital signal, S outis the first quantum digital signal and the second quantum digital signal, N A is digital noise. That is, the second digital signal processed according to the first coefficient, the first quantum digital signal and the second quantum digital signal satisfy the above relationship, so that polarization demultiplexing is performed on the second digital signal.

[0015] In combination with the first aspect, in some implementations of the first aspect, the first coefficient is: Where η is greater than 0, is a coefficient matrix, and the coefficients are determined according to the relationship among the first digital signal, the first pilot digital signal and the second pilot digital signal. That is, after obtaining the first coefficient according to the first digital signal, the coefficient matrix can be adjusted by using η.

[0016] In some implementations, η is determined based on the matrix elements in the coefficient matrix.

[0017] In combination with the first aspect, in some implementations of the first aspect, the digital noise satisfies:

[0018]

[0019] in, is the complex noise in the X polarization state, is the complex noise in the Y polarization state, The variance is equal to 1-η 2 (|ω XX | 2 +|ω YX | 2 ), The variance of is equal to 1-η 2 (|ω YY | 2 +|ω XY | 2 ), and The covariance of 2 [(ω XY ) * ω XX +(ω YY ) * ω YX ].

[0020] In some implementations, the digital noise also satisfies: Among them, γ X =1-η 2 (|ω XX | 2 +|ω YX | 2 ), γ Y =1-η 2 (|ωYY | 2 +|ω XY | 2 ), γ XY =-η 2 [(ω XY ) * ω XX +(ω YY ) * ω YX ], and A complex random number.

[0021] Therefore, by directly calculating and solving the diagonal elements of the first coefficient, data processing is performed on the second digital signal corresponding to the quantum light signal, which can simplify the data transformation process while ensuring that the output signal meets the security requirements of the QKD system.

[0022] In combination with the first aspect, in some implementations of the first aspect, the second digital signal, the first quantum digital signal, and the second quantum digital signal further satisfy the following relationship: Among them, R2 is the first unitary matrix, P is the diagonal matrix, R1 is the second unitary matrix, is complex random noise. Therefore, according to the matrix decomposition result, the second digital signal can be subjected to polarization demultiplexing processing so that the output signal meets the security requirements of the QKD system.

[0023] In combination with the first aspect, in some implementations of the first aspect, the complex random noise satisfies: Among them, p X and p Y are the diagonal elements of a diagonal matrix, and is a complex random number. Thus, according to the matrix decomposition result, the added digital noise is determined so that the output signal meets the security requirements of the QKD system.

[0024] In a second aspect, a signal processing device of a quantum key distribution system is provided, including: a receiving module, used to receive a first optical signal, wherein the first optical signal includes an X polarization state and a Y polarization state, and the first optical signal includes a quantum optical signal and a pilot optical signal; a conversion module, used to perform photoelectric conversion on the first optical signal to obtain a first digital signal and a second digital signal, wherein the first digital signal corresponds to the pilot optical signal, and the second digital signal corresponds to the quantum optical signal; a first processing module, used to perform polarization demultiplexing processing on the first digital signal to obtain a first pilot digital signal and a second pilot digital signal, the first pilot digital signal corresponds to the X polarization state of the first digital signal, and the second pilot digital signal corresponds to the Y polarization state of the first digital signal; a second processing module, used to obtain at least one first coefficient according to the first digital signal, the first pilot digital signal, and the second pilot digital signal; a demultiplexing module, used to perform polarization demultiplexing processing on the second digital signal according to the at least one first coefficient to obtain a first quantum digital signal and a second quantum digital signal, the first quantum digital signal corresponds to the X polarization state, and the second quantum digital signal corresponds to the Y polarization state.

[0025] Wherein: the first pilot digital signal and the second pilot digital signal are preconfigured; or the first pilot digital signal and the second pilot digital signal are obtained by performing polarization demultiplexing processing on the first digital signal.

[0026] It should be further explained that there are effects such as polarization rotation in the channel, and the X and Y polarization states generated by the transmitter will interfere with each other after passing through the channel. Therefore, the X polarization signal of the second digital signal at the receiving end may have little correlation with the transmitted X polarization state, and the Y polarization signal of the second digital signal may also have little correlation with the transmitted Y polarization state. In order to improve system performance, the receiving end needs to perform polarization demultiplexing on the second digital signal, so that the obtained first quantum digital signal has a greater correlation with the X polarization information of the transmitter, and also makes the second quantum digital signal have a greater correlation with the Y polarization information of the transmitter.

[0027] In a QKD system, the power of a quantum optical signal is usually lower than that of a pilot optical signal, and the corresponding second digital signal power is also lower than that of the first digital signal power, making it difficult to directly process using an equalization algorithm. The first digital signal corresponding to the classical optical signal has relatively higher power and a higher signal-to-noise ratio. Thus, channel variables or device damage parameters can be quickly extracted through the first digital signal. Therefore, the present application provides a signal processing device that first obtains at least one first coefficient based on a first digital signal corresponding to a pilot optical signal, and performs polarization demultiplexing on a second digital signal corresponding to the quantum optical signal based on the first coefficient, so that the output signal meets the security requirements of the QKD system.

[0028] In combination with the second aspect, in some implementations of the second aspect, the demultiplexing module includes: a data transformation module, which is used to perform data transformation on the second digital signal according to the first coefficient to obtain a third digital signal; a noise adding module, which is used to add digital noise to the third digital signal to obtain a first quantum digital signal and a second quantum digital signal. That is, after the data transformation, the signal after polarization multiplexing processing is compensated by adding random numbers to the signal, so that the output quantum light signal meets the security requirements of the QKD system. In some implementations, the noise adding module adds digital noise to the second digital signal according to the singular value of the first coefficient, so as to perform more stable and more widely applicable digital signal processing.

[0029] In conjunction with the second aspect, in some implementations of the second aspect, adding digital noise to the third digital signal includes: extracting matrix elements of the first coefficient, and adding digital noise to the third digital signal according to the matrix elements. That is, by directly calculating and solving the diagonal elements of the first coefficient, data processing is performed on the second digital signal corresponding to the quantum light signal, which can simplify the data transformation process while making the output signal meet the security requirements of the QKD system.

[0030] In combination with the second aspect, in some implementations of the second aspect, adding digital noise to the third digital signal includes: performing matrix decomposition on the first coefficient to obtain a first unitary matrix, a second unitary matrix and a diagonal matrix; obtaining complex random noise according to the diagonal elements in the diagonal matrix; performing data transformation on the complex random noise according to the first unitary matrix to obtain digital noise; and adding digital noise to the third digital signal. That is, by performing matrix decomposition on the first coefficient to perform data transformation on the second digital signal corresponding to the quantum light signal, the second digital signal can be polarization demultiplexed according to the matrix decomposition result, so that the output signal meets the security requirements of the QKD system. As an implementation method, the singular value of the first coefficient can be used to perform polarization demultiplexing on the second digital signal, so as to perform more stable digital signal processing. In the case of using singular value decomposition, the diagonal element can specifically refer to the singular value.

[0031] In conjunction with the second aspect, in certain implementations of the second aspect, the second digital signal, the first quantum digital signal, and the second quantum digital signal satisfy the following relationship: out =W η S in +N A , where W η is the first coefficient, S in is the second digital signal, W η S in is the third digital signal, S out is the first quantum digital signal and the second quantum digital signal, NA is digital noise. That is, the second digital signal processed according to the first coefficient, the first quantum digital signal and the second quantum digital signal satisfy the above relationship, so that polarization demultiplexing is performed on the second digital signal.

[0032] In conjunction with the second aspect, in some implementations of the second aspect, the first coefficient is: Where η is greater than 0, is a coefficient matrix, and the coefficients are determined according to the relationship among the first digital signal, the first pilot digital signal and the second pilot digital signal. That is, after obtaining the first coefficient according to the first digital signal, the coefficient matrix can be adjusted by using η.

[0033] In some implementations, η is determined based on the matrix elements in the coefficient matrix.

[0034] In conjunction with the second aspect, in some implementations of the second aspect, the digital noise satisfies:

[0035]

[0036] in, is the complex noise in the X polarization state, is the complex noise in the Y polarization state, The variance is equal to 1-η 2 (|ω XX | 2 +|ω YX | 2 ), The variance of is equal to 1-η 2 (|ω YY | 2 +|ω XY | 2 ), and The covariance of 2 [(ω XY ) * ω XX +(ω YY ) * ω YX ].

[0037] In some implementations, the digital noise also satisfies: in, γ XY =-η 2 [(ω XY ) * ω XX +(ω YY ) * ω YX ], and is a complex random number. Thus, by directly calculating and solving the diagonal element of the first coefficient, the second digital signal corresponding to the quantum light signal is processed, which can simplify the data transformation process while making the output signal meet the security requirements of the QKD system.

[0038] In conjunction with the second aspect, in certain implementations of the second aspect, the second digital signal, the first quantum digital signal, and the second quantum digital signal further satisfy the following relationship: Among them, R2 is the first unitary matrix, P is the diagonal matrix, R1 is the second unitary matrix, is complex random noise. Therefore, according to the matrix decomposition result, the second digital signal can be subjected to polarization demultiplexing processing so that the output signal meets the security requirements of the QKD system.

[0039] In conjunction with the second aspect, in some implementations of the second aspect, the complex random noise satisfies: Among them, p X and p Y are the diagonal elements of a diagonal matrix, and is a complex random number. Thus, according to the matrix decomposition result, the added digital noise is determined so that the output signal meets the security requirements of the QKD system.

[0040] In a third aspect, a communication device is provided, comprising at least one processor coupled to at least one memory, the at least one processor being used to execute a computer program or instruction stored in the at least one memory so that the communication device executes the method of the first aspect.

[0041] In a fourth aspect, a chip is provided, which includes a processor, the processor is coupled to a memory, the memory is used to store a computer program, and the processor is used to execute the computer program stored in the memory, so that some or all steps of the method in the above-mentioned first aspect and any possible implementation thereof are executed.

[0042] In a fifth aspect, a computer-readable storage medium is provided, in which a computer program or instruction is stored. When the computer program or instruction is executed by a processor, part or all of the steps of the method in the above-mentioned first aspect and any possible implementation thereof are executed.

[0043] According to a sixth aspect, a computer program product is provided. When the computer program product is run, part or all of the steps of the first aspect and any possible implementation method thereof are executed. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a system flow diagram of CV-QKD provided in an embodiment of the present application.

[0045] Figure 2 It is a schematic diagram of a signal processing method for a quantum key distribution system provided in an embodiment of the present application.

[0046] Figure 3 It is a schematic diagram of another signal processing method for a quantum key distribution system provided in an embodiment of the present application.

[0047] Figure 4 It is a schematic diagram of another signal processing method for a quantum key distribution system provided in an embodiment of the present application.

[0048] Figure 5 It is a schematic diagram of a signal processing device of another quantum key distribution system provided in an embodiment of the present application.

[0049] Figure 6 This is a schematic diagram of a first demultiplexing module provided in an embodiment of the present application.

[0050] Figure 7 It is a schematic diagram of a signal processing device of another quantum key distribution system provided in an embodiment of the present application.

[0051] Figure 8 It is a schematic diagram of a signal processing device of another quantum key distribution system provided in an embodiment of the present application.

[0052] Fig. 9 It is a schematic diagram of a signal processing device of another quantum key distribution system provided in an embodiment of the present application.

[0053] Fig.10 It is a schematic diagram of a communication device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0054] The technical solution in this application will be described below in conjunction with the accompanying drawings.

[0055] With the rapid development of information technology, people have higher and higher requirements for the security of communication. Quantum communication is a technology developed on the basis of quantum mechanics and classical information theory. It uses the basic principles of quantum mechanics to ensure the security of communication. In quantum communication technology, quantum secure communication is the most mature technology. It realizes the unconditional secure distribution of symmetric keys on the premise of sharing some security keys.

[0056] QKD can be divided into two types: DV-QKD and CV-QKD. Among them, DV-QKD needs to encode single-photon signals, and single-photon detectors need to work in a low-temperature environment, while CV-QKD encodes coherent light, does not require single-photon sources and single-photon detectors, and can reuse the existing communication industry chain to a great extent in system architecture. Therefore, CV-QKD has the potential advantages of high integration and low cost.

[0057] Figure 1 It is a schematic diagram of the system flow of a CV-QKD provided in an embodiment of the present application. The signal processing method and device provided in the embodiment of the present application can be applied to a digital CV-QKD system, which can be used to transmit an optical signal including two polarization states. Alternatively, according to actual conditions, the method and device provided in the embodiment of the present application can also be used in other CV-QKD systems, such as a C-VQKD system with single polarization transmission but dual polarization reception, and the present application does not limit this. Figure 1 As shown, the CV-QKD system mainly includes a transmitter, a channel and a receiver.

[0058] (1) Sending end

[0059] The quantum random number generator generates random coded data as the quantum key data of the transmitter. The quantum key data and pilot coded data of the transmitter together constitute the data to be sent by the transmitter. The data to be sent is preprocessed by the digital signal processing (transmitter-digital signal process, Tx-DSP) algorithm of the transmitter to form a digital signal. Among them, Tx-DSP may include upsampling and pulse shaping. The digital-to-analog converter generates a corresponding analog signal according to the digital signal, and then modulates it to the optical signal generated by the light source through the electro-optical modulator to form the optical signal of the transmitter. The specific electro-optical modulation device is determined according to the actual situation. For example, it can be an in-phase quadrature (IQ) modulator, or it can be a cascade form of an intensity modulator and a phase modulator. The optical signal at the transmitter can be considered to include two parts of the signal: a quantum optical signal and a pilot optical signal, wherein the quantum optical signal is determined by the quantum key data, and the pilot optical signal is determined by the pilot coded data.

[0060] Among the optical signals at the transmitting end, the pilot optical signal usually has two major characteristics: first, the optical power of the pilot optical signal is greater than or equal to the quantum optical signal, and the optical energy of the pilot optical signal within one modulation cycle is higher than that of the quantum optical signal; second, the pilot coded data is pre-set, and the receiving end also knows the sequence, which avoids the need for the receiving end's processing algorithm to wait for the transmitting end to transmit the lossless pilot coded data again.

[0061] It should be understood that the above description of the pilot light signal is only for illustrative purposes. In some implementations, the intensity of the pilot signal light may also be less than the intensity of the quantum signal light. In some implementations, the pilot coded data may also be in the form of random coding, not shared with the receiving end in advance, and these coded data may be quickly synchronized to the receiving end by means of another lossless classical channel.

[0062] (2) Channel

[0063] The optical signal at the transmitting end is transmitted through the channel to the receiving end, which can be called the receiving end optical signal. Among them, the channel can specifically refer to an optical fiber signal, a free space channel, an underwater channel, or a combination of multiple channels, and this application does not limit this. Since the channel state changes in real time, the optical signal will undergo changes such as polarization and attenuation during the transmission process, so the optical signal at the receiving end is not the same as the optical signal at the transmitting end. However, since both the pilot optical signal and the quantum optical signal have experienced the same channel, the changes in the pilot optical signal and the quantum optical signal are approximately the same. Therefore, the changes in the quantum optical signal can be inferred based on the changes in the pilot optical signal.

[0064] In addition to the above, in some QKD systems, the pilot light signal and the quantum light signal can also be transmitted separately through different channels, where the two channels have a special correlation. For example, multi-core optical fiber transmission can be used to send the pilot light signal and the quantum light signal into different cores. The channel state changes of the two cores are correlated, and the crosstalk between the signals is also correlated. Therefore, at the receiving end, the change of the quantum light signal can be inferred from the change of the pilot light signal.

[0065] (3) Receiving End

[0066] After the receiving end receives the optical signal, it enters the receiver for detection, and its output electrical signal enters the post-processing system of the receiving end after analog-to-digital conversion. Among them, the receiver can perform dual-polarization diversity detection on the incoming signal light, that is, the signal light is first split into two by a polarization beam splitter, and the two optical signals are detected separately. The detector for detecting the two optical signals can be a homodyne detector, or a heterodyne detector composed of two homodyne detectors, etc., and this application does not limit this.

[0067] Depending on the structure of the receiver, there will be multiple electrical signal outputs of the detection results. After analog-to-digital conversion and sampling, the digital signal at the receiving end is obtained and enters the post-processing system. These digital signals are usually processed by an equalization algorithm first to eliminate the influence of some channel damage or device damage. The algorithm can be specifically a matched filter algorithm, a clock recovery algorithm, a delay compensation algorithm, etc. Some parameters of each signal processing algorithm, such as channel polarization state, sampling frequency deviation, delay, etc., may come from quasi-static parameters calibrated in advance, or they may be dynamic parameters calculated in real time from the detection data. Among them, the quasi-static parameter can be the circuit delay, and the dynamic parameter can be the channel polarization state.

[0068] In the present application, the digital signal sampled by analog-to-digital conversion output by the receiver is referred to as the first digital signal and the second digital signal, wherein the first digital signal corresponds to the pilot light signal and the second digital signal corresponds to the quantum light signal. Alternatively, in some cases, it may also be referred to as sampling data, which is not limited in the present application. The calculation of dynamic parameters is usually obtained through the first digital signal, because the power of the pilot light signal is relatively strong, and the signal-to-noise ratio (SNR) of the first digital signal formed at the receiving end is relatively high, so that the dynamic parameters can be calculated more quickly and accurately. The algorithm for calculating dynamic parameters can be divided into feedforward and feedback types, which are not limited in the present application. Both quasi-static parameters and dynamic parameters will be used for processing quantum signal data.

[0069] The second digital signal will also go through step S110, digital signal algorithm processing (receiver-digital signal process, Rx-DSP). As a processing method, step S110 specifically includes: delay compensation, spectrum matching, clock recovery, down conversion / down sampling, S111 unit quantization, S112 polarization demultiplexing, polarization compensation / phase compensation, etc. The unit quantization may refer to shot noise unit (SNU) normalization. After the series of algorithm processing included in step S110, the receiving end quantum key digital signal can be obtained. It will be used to evaluate the security key generation rate, and will enter the forward error correction (FEC) and confidentiality enhancement steps to obtain the final security key.

[0070] From the above description, we can see that in the actual CV-QKD system, the devices and channels have non-ideal characteristics. For example, the laser does not emit an ideal coherent state, but contains amplitude noise and phase noise. The modulator is limited by its own performance and the excitation voltage signal and cannot achieve perfect Gaussian modulation. Due to the influence of the non-ideal characteristics of the optical fiber, the polarization state of the signal light will randomly change after it is transmitted in the optical fiber, and the signals between the other two polarizations will also leak each other.

[0071] In view of this, the embodiment of the present application provides a signal processing method and device for a quantum key distribution system, focusing on the polarization demultiplexing of step S112, and performing polarization compensation when there is polarization dependent loss (PDL) in the signal, which can also be called a depolarization algorithm. By first using the pilot signal at the receiving end to obtain the coefficient for polarization demultiplexing of the quantum signal, the quantum signal is demultiplexed using the coefficient, so that the output signal meets the security requirements of the QKD system.

[0072] Figure 2 Schematic diagram of a signal processing method for a quantum key distribution system provided in an embodiment of the present application. Figure 2 As shown, the signal processing method mainly includes:

[0073] S210 , receiving a first optical signal, wherein the first optical signal includes an X polarization state and a Y polarization state, and the first optical signal includes a quantum optical signal and a pilot optical signal.

[0074] The specific form of the first optical signal is determined in combination with the specific CV-QKD system. In some cases, the quantum optical signal and the pilot optical signal included in the first optical signal can be sent through the same channel. In some cases, the quantum optical signal and the pilot optical signal included in the first optical signal can be sent through different channels. In some cases, the pilot optical signal can refer to a classical optical signal, wherein the classical optical signal can be sent through a classical channel. In some cases, the pilot optical signal and the quantum optical signal can be in the form of frequency division multiplexing and time division multiplexing. In some cases, the pilot optical signal and the quantum optical signal can be superimposed and modulated on each other.

[0075] S220, performing photoelectric conversion on the first optical signal to obtain a first digital signal and a second digital signal, wherein the first digital signal corresponds to the pilot optical signal, and the second digital signal corresponds to the quantum optical signal.

[0076] The photoelectric conversion of the first optical signal may include detection, division, analog-to-digital conversion, sampling, etc. of the first optical signal. The detector used for the specific detection may be a heterodyne detector or other types of detectors. The digital signal obtained after the photoelectric conversion may also be understood as data.

[0077] After the specific conversion, how to divide the first digital signal and the second digital signal, the correspondence between the first digital signal and the pilot light signal, and the correspondence between the second digital signal and the quantum light signal are determined in combination with the specific actual situation. As an implementation method, after the first light signal is photoelectrically converted, it can be processed by a DSP algorithm first, and then separated by a signal to obtain the first digital signal and the second digital signal. In some implementation methods, after obtaining the second digital signal corresponding to the quantum light signal, the second digital signal needs to be processed by a DSP algorithm again.

[0078] The specific expression of the first digital signal and the second digital signal can be determined according to the detector. For example, in the case of using a heterodyne detector, the second digital signal S in For example, it includes at least 4 data {S XI ,S XQ ,S YI ,S YQ}. Where X and Y refer to the polarization state of the signal light, respectively, and X and Y are orthogonal. I and Q refer to the two regular components (quadrature) representing the light field state. Alternatively, in the QKD system, they can also be represented by x and p. When other detectors are used, the second digital signal S in It can also include 8 data {S XI ,S XQ ,S YI ,S YQ , S XI+iXQ ,S XI-iXQ ,S YI+iXQ ,S YI-iYQ In the actual processing process, the last four signals can be merged back into the first case mentioned above. Therefore, the subsequent processing of the digital signal includes 4 data as an exemplary description.

[0079] The second digital signal obtained by the receiving end is different from the digital signal sent by the transmitting end. The reason for the difference is that, on the one hand, some digital signal processing algorithms are first used to compensate for the damage of some channels and devices during the photoelectric conversion at the receiving end, and on the other hand, some signal processing algorithms have certain redundant degrees of freedom, such as phase.

[0080] S230, obtaining a first pilot digital signal and a second pilot digital signal, wherein the first pilot digital signal corresponds to an X polarization state of the first digital signal, and the second pilot digital signal corresponds to a Y polarization state of the first digital signal.

[0081] In some implementations, the first pilot digital signal and the second pilot digital signal may be preset by the transmitting end and the receiving end, thereby avoiding the need for the receiving end to process the pilot signal again using an algorithm.

[0082] In some implementations, a first pilot digital signal and a second pilot digital signal can be obtained according to the first digital signal through polarization demultiplexing. Polarization demultiplexing of the first digital signal can be performed using an equalization algorithm. The equalization algorithm is implemented by adaptive algorithm processing, or by channel estimation. Among them, the adaptive algorithm can be understood as automatically adjusting the processing method according to the data characteristics of the first digital signal, and obtaining and updating the equalization coefficient by feedback. Channel estimation can be understood as performing parameter estimation according to the first digital signal through a set channel model to obtain an equalization coefficient. Taking the adaptive algorithm as an example, the specific equalization algorithm processing steps may include a multiple input multiple output (MIMO) algorithm and coefficient update.

[0083] S240, obtain at least one first coefficient according to the first digital signal, the first pilot digital signal and the second pilot digital signal.

[0084] Among them, how to obtain at least one first coefficient according to the first digital signal, the first pilot digital signal and the second pilot digital signal is determined according to the actual situation, and the present application does not limit this. In some implementations, at least one first coefficient may include only one coefficient, which can also be understood as a single-tap coefficient. That is, a single coefficient is introduced using a pilot digital signal to perform polarization demultiplexing on the quantum optical signal. In some implementations, the pilot digital signal may also include multiple subcarriers. In this case, at least one first coefficient includes multiple coefficients, which can also be understood as a multi-tap coefficient. That is, multiple coefficients are introduced to perform polarization demultiplexing on the quantum optical signal. In the following method embodiments, taking the case where the first coefficient is a single-tap coefficient as an example, the case where the first coefficient is a multi-tap coefficient can also be implemented with specific reference to the embodiments in the present application.

[0085] When the MIMO algorithm is used, the first coefficient can be obtained by the MIMO coefficient. In some implementations, the MIMO coefficient can be used as the first coefficient. In some implementations, the MIMO coefficient can also be adjusted, such as scaling the MIMO coefficient, to obtain the first coefficient. Taking the single-tap MIMO coefficient TD-MIMO as an example, its expression is:

[0086]

[0087] Among them (E X E Y ) T Represents the first digital signal, (E outX E outY ) Trepresents the first pilot digital signal and the second pilot digital signal, is the MIMO coefficient matrix W M . T refers to the transpose of the matrix.

[0088] Written in matrix form:

[0089] E out =W M E

[0090] Where E is expressed in matrix form, W M is the coefficient matrix, E out is the pilot digital signal vector output by MIMO.

[0091] According to W M The first coefficient W can be obtained η .Right now Wherein n is greater than 0. The specific value of n is determined according to the actual adjustment needs. In some implementations, n can be determined according to the matrix elements of the coefficient matrix.

[0092] S250, performing polarization demultiplexing processing on the second digital signal according to at least one first coefficient to obtain a first quantum digital signal and a second quantum digital signal, wherein the first quantum digital signal corresponds to an X polarization state, and the second quantum digital signal corresponds to a Y polarization state.

[0093] That is, it is necessary to perform additional data transformation on the second digital signal corresponding to the quantum light signal through the first coefficient so that the algorithm can correspond to physical operations with reasonable meanings, such as linear transformation, etc., so as to ensure that the output signal meets the safety requirements.

[0094] How to perform polarization demultiplexing on the second digital signal according to at least one first coefficient is determined according to actual conditions. In some implementations, each first coefficient in at least one first coefficient can be directly used in a calculation method to perform polarization demultiplexing on the second digital signal. In some implementations, each first coefficient in at least one first coefficient can be matrix decomposed, and data transformation is performed on the second digital signal according to the matrix decomposition result to perform polarization demultiplexing on the second digital signal. The matrix decomposition method is determined according to actual conditions. As an implementation method, the singular value (SVD) of the first coefficient can be used to perform polarization demultiplexing on the second digital signal, thereby performing more stable and more widely applicable digital signal processing. The specific implementation method will be described later in conjunction with Figure 3 and Figure 4 Expand the detailed description.

[0095] In addition, in some implementations, step S250 may further include adding digital noise to the second digital signal according to the first coefficient. That is, by adding random numbers to the signal, the signal after polarization multiplexing is transformed so that the output quantum signal meets the security requirements of the QKD system. In some implementations, the diagonal elements of the first coefficient may be specifically extracted to add digital noise to the second digital signal. In the case of using singular value decomposition, the diagonal elements may specifically refer to singular values.

[0096] In the case where the first coefficient is obtained by the MIMO coefficient, the second digital signal, the first quantum digital signal, and the second quantum digital signal satisfy the following relationship:

[0097] S out =W η S in +N A

[0098] Among them, W η is the first coefficient, S in is the second digital signal, S out is the first quantum digital signal and the second quantum digital signal, N A is digital noise.

[0099] The above S out , S in and W η It can be represented by a binary number, or the above S out , S in and W η It can be represented by a quaternion.

[0100] In the case of binary representation, the I and Q components of X polarization and Y polarization are expressed in complex form, that is, or equivalently, in or Multiply by a phase rotation, the complex number of e:

[0101] S in,2 Represented as a vector:

[0102]

[0103] Corresponding to W η It can be represented as a 2×2 complex matrix W η2 :

[0104]

[0105] In the case of quaternions:

[0106]

[0107] Corresponding to W η It can be represented as a 4×4 real matrix W η4

[0108]

[0109] It is not difficult to understand that S in,2 and S in,4 The two representations are equivalent, or we can say that S in,2 and S in,4 can be converted into each other. out,4 (1) = Re[S out,2 (1)],S out,4 (2) = Im[S out,2 (1)],S out,4 (3) = Re[S out,2 (2)],S out,4 (4) = Im[S out,2 (2)].

[0110] Similarly, W2 and W4 can be transformed into each other. For the proposed linear algorithm, there is the following relationship:

[0111]

[0112] Therefore, in the following specific embodiments, unless otherwise specified, binary numbers are used for representation, and the representation method of quaternions is not described in detail.

[0113] In a QKD system, the power of a quantum optical signal is usually lower than that of a pilot optical signal, and the corresponding second digital signal power is also lower than that of the first digital signal power, making it difficult to directly process using an equalization algorithm. The first digital signal corresponding to the classical optical signal has relatively higher power and a higher signal-to-noise ratio. Thus, channel variables or device damage parameters can be quickly extracted through the first digital signal. Therefore, the present application provides a signal processing method, which first obtains at least one first coefficient based on a first digital signal corresponding to a pilot optical signal, and performs polarization demultiplexing on a second digital signal corresponding to the quantum optical signal based on the first coefficient, so that the output signal meets the security requirements of the QKD system.

[0114] The direct calculation method and matrix decomposition method of the present application are described below in conjunction with the case of a single tap, that is, the case where the at least one first coefficient refers to only one first coefficient.

[0115] Figure 3 is a schematic diagram of another signal processing method of a quantum key distribution system provided in an embodiment of the present application, such as Figure 3 As shown, the signal processing method mainly includes:

[0116] S310 , receiving a first optical signal, wherein the first optical signal includes an X polarization state and a Y polarization state, and the first optical signal includes a quantum optical signal and a pilot optical signal.

[0117] S320, performing photoelectric conversion on the first optical signal to obtain a first digital signal and a second digital signal, wherein the first digital signal corresponds to the pilot optical signal, and the second digital signal corresponds to the quantum optical signal.

[0118] S330, obtaining a first pilot digital signal and a second pilot digital signal, wherein the first pilot digital signal corresponds to an X polarization state of the first digital signal, and the second pilot digital signal corresponds to a Y polarization state of the first digital signal.

[0119] In some implementations, the first pilot digital signal and the second pilot digital signal may be preset by the transmitting end and the receiving end, thereby avoiding the need for the receiving end to process the pilot signal again using an algorithm.

[0120] In some implementations, the first pilot digital signal and the second pilot digital signal can be obtained from the first digital signal by polarization demultiplexing. The method for performing polarization demultiplexing on the first digital signal can be an equalized MIMO algorithm, which can be implemented by adaptive algorithm processing or by channel estimation.

[0121] The first digital signal, the first pilot digital signal and the second pilot digital signal have the following relationship:

[0122]

[0123] Among them (E X E Y ) T Represents the first digital signal, (E outX E outY ) T represents the first pilot digital signal and the second pilot digital signal, is the coefficient matrix W M . T refers to the transpose of the matrix.

[0124] When an adaptive algorithm is used to perform balanced MIMO algorithm processing on a classical optical signal, the coefficient of W needs to be updated. The method for updating the coefficient should be determined according to the actual situation. For example, the least mean square algorithm, constant modulus algorithm, etc. can be used.

[0125] S340: Obtain a first coefficient according to the first digital signal, the first pilot digital signal and the second pilot digital signal.

[0126] In getting W M After that, you canM The coefficient is adjusted to obtain the first coefficient to perform polarization demultiplexing on the quantum light signal. That is, the first coefficient is η is greater than 0.

[0127] In some implementations, the coefficient matrix W M That is, it can be directly used as the first coefficient W η , at this time there is W η =W M , that is, the coefficient η of the matrix element used to adjust the MIMO coefficient is 1.

[0128] In some implementations, the coefficient matrix may be scaled to achieve better results when the first coefficient is used to perform polarization demultiplexing on the second digital signal. As a scaling method, W may be extracted. M The diagonal element {p X ,p Y}, and use the maximum value of the diagonal element L = max{p X ,p Y The maximum value of} for W M As the maximum value of the diagonal element is used to scale W M One way to make adjustments:

[0129] First, use W M The matrix elements define the parameters J and K:

[0130] J=|ω XX | 2 +|ω YX | 2 +|ω XY | 2 +|ω YY | 2

[0131] K=|ω XX ω YY -ω YX ω XY | 2

[0132] Then L can be obtained as:

[0133]

[0134] When it is judged that L>1, a parameter 0<η<1 can be selected so that ηL≤1. The selection of η can be carried out according to a predetermined strategy, for example: 1) η=1 / L, so that ηL=1; 2) there is a predetermined parameter T0, T0 is greater than 0, and η=T0 / L is defined. Therefore, η is actually based on the coefficient matrix W M The matrix elements of are determined.

[0135] S350, performing data transformation on the second digital signal according to the first coefficient to obtain a third digital signal, extracting the matrix element of the first coefficient, and adding the digital noise to the third digital signal according to the matrix element to obtain a first quantum digital signal and a second quantum digital signal. Specifically, the second digital signal, the first quantum digital signal, and the second quantum digital signal satisfy the following relationship:

[0136] S out =W η S in +N A

[0137] Among them, W η is the first coefficient, S in is the second digital signal, W η S in is the third digital signal, S out is the first quantum digital signal and the second quantum digital signal, N A is digital noise.

[0138] N A Specifically including the complex noise of X polarization state and the complex noise of the Y polarization state and From complex random numbers and Construction, where are four source random numbers, and their respective variances are In some implementations, when SNU is counted in digital signal processing and data is quantized using SNU as a unit, all data are divided by Corresponding to the four-way data, the SNU is different, and the corresponding variance can be expressed as N A It can be written as:

[0139]

[0140] in, is the complex noise in the X polarization state, is the complex noise in the Y polarization state, Variance Variance and The covariance of

[0141] Among them, the above variance and covariance are defined as follows:

[0142] Assume that E and F are two real variables, and the variance<E,E> and covariance<E,F> They are defined as

[0143]

[0144]

[0145] Assume that E and F are two complex variables, and the variance<E,E> and covariance<E,F> They are

[0146]

[0147]

[0148] The subscript i represents the i-th value of the variable.

[0149] As a N A The construction method:

[0150]

[0151]

[0152] Among them, γ X , γ Y , γ XY According to the first coefficient W η Sure.

[0153]

[0154]

[0155]

[0156] Or it can be expressed as:

[0157]

[0158] As another N A The construction method:

[0159]

[0160]

[0161] in, are three independent complex random numbers.

[0162] In addition, in S in When it is a quaternion, the digital noise N A It can be written as:

[0163]

[0164] The first coefficient W η Recorded as

[0165]

[0166] in, is real noise, j is an integer ranging from 1 to 4, The variance of If k is also an integer from 1 to 4, and k≠j, then and The covariance of

[0167] After the second digital signal is processed as above, the first quantum digital signal and the second quantum digital signal can be output to continue with the subsequent steps of the QKD system process.

[0168] In such Figure 3 In the method shown, data processing is performed on the second digital signal corresponding to the quantum light signal by directly calculating and solving, which can simplify the data transformation process while making the output signal meet the security requirements of the QKD system.

[0169] Figure 4 is a schematic diagram of another signal processing method of a quantum key distribution system provided in an embodiment of the present application, such as Figure 4 As shown, the signal processing method mainly includes:

[0170] S410 , receiving a first optical signal, wherein the first optical signal includes an X polarization state and a Y polarization state, and the first optical signal includes a quantum optical signal and a pilot optical signal.

[0171] S420, performing photoelectric conversion on the first optical signal to obtain a first digital signal and a second digital signal, wherein the first digital signal corresponds to the pilot optical signal, and the second digital signal corresponds to the quantum optical signal.

[0172] S430, obtaining first pilot digital signal and second pilot digital signal data, wherein the first pilot digital signal corresponds to an X polarization state of the first digital signal, and the second pilot digital signal corresponds to a Y polarization state of the first digital signal.

[0173] In some implementations, the first pilot digital signal and the second pilot digital signal may be preset by the transmitting end and the receiving end, thereby avoiding the need for the receiving end to process the pilot signal again using an algorithm.

[0174] In some implementations, the first pilot digital signal and the second pilot digital signal can be obtained from the first digital signal by polarization demultiplexing. The method for performing polarization demultiplexing on the first digital signal can be an equalized MIMO algorithm, which can be implemented by adaptive algorithm processing or by channel estimation.

[0175] The first digital signal, the first pilot digital signal and the second pilot digital signal have the following relationship:

[0176]

[0177] Among them (E X E Y ) T represents the first digital signal, represents the first pilot digital signal and the second pilot digital signal, is the MIMO coefficient matrix W M .

[0178] When an adaptive algorithm is used to perform balanced MIMO algorithm processing on a classical optical signal, the coefficient of W needs to be updated. The method for updating the coefficient should be determined according to the actual situation. For example, the least mean square algorithm, constant modulus algorithm, etc. can be used.

[0179] S440: Obtain a first coefficient according to the first digital signal, the first pilot digital signal and the second pilot digital signal.

[0180] In getting W M After that, you can M The coefficient is adjusted to obtain the first coefficient to perform polarization demultiplexing on the quantum light signal. That is, the first coefficient is η is greater than 0.

[0181] In some implementations, the coefficient matrix W M That is, it can be directly used as the first coefficient W η , at this time there is W η =W M , that is, the coefficient η of the matrix element used to adjust the MIMO coefficient is 1.

[0182] S450, performing data transformation on the second digital signal according to the first coefficient to obtain a third digital signal, performing matrix decomposition on the first coefficient to obtain a first unitary matrix, a second unitary matrix and a diagonal matrix; obtaining complex random noise according to the diagonal elements in the diagonal matrix; performing data transformation on the complex random noise according to the first unitary matrix to obtain digital noise; and adding digital noise to the third digital signal.

[0183] Specifically, the second digital signal, the first quantum digital signal, and the second quantum digital signal also satisfy the following relationship:

[0184] S out =W η S in +N A

[0185] Among them, W η is the first coefficient, S in is the second digital signal, W η S in is the third digital signal, S out are the first quantum signal and the second quantum signal, N A is digital noise.

[0186] In some implementations, step S450 may be specifically divided into the following three parts:

[0187] 1) Matrix decomposition

[0188] For example, the first coefficient W η Perform singular value decomposition, which can be expressed as W η =R2PR1, R2 is the first unitary matrix, P is the diagonal matrix, and R1 is the second unitary matrix. Specifically, the expressions of R1, R2 and P can be:

[0189]

[0190]

[0191] where p X and p Y is a real number, and 0≤p X ,p Y ≤1; a1, b1, is plural; is the phase, which is a real number.

[0192] 2) According to the first coefficient W η Polarization demultiplexing is performed, which includes three steps:

[0193] The first step is to analyze the quantum signal data S in,2 First, perform two matrix multiplications, namely

[0194] S t1 =PR1S in,2

[0195] The second step is to add complex random noise Right now

[0196]

[0197] Specifically including the complex noise of X polarization state and the complex noise of the Y polarization state and From complex random numbers and Construction, where are four source random numbers, and their respective variances are In some implementations, when SNU is counted in digital signal processing and data is quantized using SNU as a unit, all data are divided by Corresponding to the four-way data, the SNU is different, and the corresponding variance can be expressed as

[0198] The expression can be:

[0199]

[0200] Among them, the coefficient γ X and γ Y According to the diagonal element p of the P matrix X and determine, that is

[0201] When p X When ≤1, γ X =1-(p X ) 2 , or p Y When ≤1, γ Y =1-(p Y ) 2 ;

[0202] When p X >1, γ X =(p X ) 2 -1, or p Y >1, γ Y =(p Y ) 2 -1;

[0203] Comprehensive, γ X =|1-(p X ) 2 |, γ Y =|1-(p Y ) 2 |.

[0204] Using the first coefficient W η The matrix elements of represent the diagonal elements of the diagonal matrix, then γ X =|1-(|ω XX | 2 +|ω YX | 2 )|,γY =|1-(|ω YY | 2 +|ω XY | 2 )|.

[0205] The third step is to t2 Perform matrix multiplication again, that is

[0206] S out,2 =R2S t2

[0207] In some implementations, step S450 may be specifically divided into the following two parts:

[0208] 1) Using the first coefficient W η Directly transform the data, that is

[0209] S t =W η S in,2

[0210] 2) According to the first coefficient W η Adding digital noise

[0211] The diagonal matrix P and the second unitary matrix R2 are obtained by matrix decomposition (such as SVD decomposition), and the complex random noise is determined according to the diagonal matrix P Then rotate the first unitary matrix R2 matrix to get the final added noise

[0212] Here Same as the previous definition:

[0213]

[0214] Combining the above two processing methods of step S450, it can be seen that the second digital signal, the first quantum digital signal and the second quantum digital signal satisfy the relationship S out =W η S in +N A On the basis of

[0215] After the second digital signal is processed as above, the first quantum digital signal and the second quantum digital signal can be output to continue with the subsequent steps of the QKD system process.

[0216] In such Figure 4In the method shown, the first coefficient is matrix decomposed to perform data transformation on the second digital signal corresponding to the quantum light signal, so that the second digital signal can be polarization demultiplexed according to the matrix decomposition result, so that the output signal meets the security requirements of the QKD system.

[0217] In some cases, such as Figure 4 In the method shown, the first coefficient can also be converted into a continuous multiplication form to obtain N first unitary matrices, N second unitary matrices and N diagonal matrices, and the second digital signal is subjected to N data transformations and N digital noise additions according to the N first unitary matrices, N second unitary matrices and N diagonal matrices, where N is a positive integer greater than 1. Thus, the second digital signal is subjected to polarization demultiplexing processing using the N decomposition results, so that the output signal further meets the security requirements of the QKD system.

[0218] Its specific expression is:

[0219]

[0220] The value range of n is 1, 2, …, N.

[0221] Among them, the nth data transformation is performed according to W n The output of the nth data transformation is used as the input of the n+1th data transformation. n The N data transformations implemented can be Figure 4 The same is true in the text, so I will not repeat it here.

[0222] Above Figure 3 and Figure 4 The embodiment specifically provides two different methods of data transformation and adding digital noise to perform polarization demultiplexing on quantum signals to meet the security requirements of the QKD system. It should be understood that any implementation method that summarizes or decomposes the above implementation method into one or more steps, transforms the order of the steps in the method, changes the matrix decomposition formula, replaces the expression from binary to multivariate, and other similar solutions should still fall within the scope of the protection of this application.

[0223] In some cases, the second digital signal, the first quantum digital signal, and the second quantum digital signal may also be considered to satisfy the following relationship:

[0224] S out =ηW M S in +R2N A

[0225] Among them, ηW M is the first coefficient, S in is the second digital signal, Sout are the first quantum signal and the second quantum signal, N A is digital noise.

[0226] 1) As the first possibility, η = T0 / L, R2 is the unit matrix. Among them, the digital noise satisfies:

[0227]

[0228] Among them, γ X =1-η 2 (|ω XX | 2 +|ω YX | 2 ), γ Y =1-η 2 (|ω YY | 2 +|ω XY | 2 ), γ XY =-η 2 [(ω XY ) * ω XX +(ω YY ) * ω YX ].

[0229] 2) As the second possibility, η=1, R2 is calculated by ηW M Matrix decomposition is performed to obtain R2, which is the first unitary matrix. Among them, the digital noise satisfies:

[0230]

[0231] Among them, γ X =|1-(|ω Xx | 2 +|ω Yx | 2 )|,γ Y =|1-(|ω YY | 2 +|ω XY | 2 )|.

[0232] In addition, if Figure 3 or Figure 4 The method can also be specifically applied to the case where at least one first coefficient is a multi-tap coefficient, that is, the at least one first coefficient includes multiple first coefficients. The above method can be specifically applied to processing each first coefficient in the specific at least one first coefficient. For ease of understanding, the case of multi-tap coefficients is briefly introduced below.

[0233] MIMO coefficient matrix WM It is a multi-tap form, and its coefficient components can be expanded into a vector form, that is, ω mn =[ω mn (0),ω mn (1),…,ω mn (L-1)], where m and n represent one of X and Y respectively, L is the tap length, and L>1. The first digital signal, the first pilot digital signal, and the second pilot digital signal have the following relationship:

[0234]

[0235]

[0236] Where 0≤u≤L-1, E X (l) and E Y (l) is the lth symbol of the first digital signal vector. The first digital signal vector is composed of multiple consecutive symbols and can be expressed as E X =[E X (0),E X (1),…,E X (L-1)],E Y =[E Y (0),E Y (1),…,E Y (L-1)].

[0237] In getting W M After that, you can M The coefficient is adjusted to obtain the first coefficient to perform polarization demultiplexing on the quantum light signal. The first coefficient is W η =ηW M , η is greater than 0.

[0238] W η The lth tap coefficient of each component is written in matrix form, that is, the lth first coefficient W is obtained η

[0239]

[0240] In some implementations, you can use In some implementations, it is also possible to Perform matrix decomposition, such as singular value decomposition, which can be expressed as is the lth first unitary matrix, P l is the lth diagonal matrix, is the lth second unitary matrix. Specifically, and P l The expression can be:

[0241]

[0242]

[0243] At this time, the second digital signal, the first quantum digital signal and the second quantum digital signal satisfy the following relationship:

[0244]

[0245]

[0246] in and are the lth symbols of the first and second quantum digital signal vectors, respectively. The first and second quantum digital signal vectors are composed of multiple consecutive symbols and can be expressed as and The expression can be:

[0247]

[0248] where γ X (l) = |1-(p X (l)) 2 |, γ Y (l) = |1-(p Y (l)) 2 |, Four source random numbers, each with a variance of In some implementations, when SNU is counted in digital signal processing and data is quantized using SNU as a unit, all data are divided by Corresponding to the four-way data, the SNU is different, and the corresponding variance can be expressed as

[0249] The method embodiment of the embodiment of the present application is described above, and the corresponding device embodiment is introduced below. The method embodiment and the device embodiment correspond to each other, so the parts not described in detail can refer to each other. The device embodiment of the present application can be specifically implemented by an optical receiving module and an algorithm module. The algorithm module can be implemented by a programmable logic gate array (field programmable gate array, FPGA), an application specific integrated circuit (application specific integrated circuit, ASIC) or a central processing unit (central processing unit, CPU). It should be understood that the division of modules in the device is only an exemplary description, and the specific module design should be determined according to the actual situation.

[0250] Figure 5 Schematic diagram of a signal processing device of a quantum key distribution system provided in an embodiment of the present application. Figure 5 As shown, the device comprises:

[0251] The receiving module 510 is configured to receive a first optical signal, wherein the first optical signal includes an X polarization state and a Y polarization state, and the first optical signal includes a quantum optical signal and a pilot optical signal.

[0252] Among them, the specific form of the first optical signal is determined in combination with the specific CV-QKD system. In some cases, the quantum optical signal and the pilot optical signal included in the first optical signal can be sent through the same channel. In some cases, the quantum optical signal and the pilot optical signal included in the first optical signal can be sent through different channels. In some cases, the pilot optical signal can refer to a classical optical signal, wherein the classical optical signal can be sent through a classical channel. In some cases, the pilot optical signal and the quantum optical signal can be in the form of frequency division multiplexing and time division multiplexing. In some cases, the pilot optical signal and the quantum optical signal can be superimposed and modulated on each other. The form of the receiving module should be set accordingly according to the first optical signal.

[0253] The conversion module is used to perform photoelectric conversion on the first optical signal to obtain a first digital signal and a second digital signal, wherein the first digital signal corresponds to the pilot optical signal and the second digital signal corresponds to the quantum optical signal.

[0254] The conversion module can be used for detecting, dividing, analog-to-digital conversion, sampling, etc. of the first optical signal. The detector used for the specific detection can be a heterodyne detector or other types of detectors. The digital signal obtained after the photoelectric conversion can also be understood as data.

[0255] After the specific conversion, how to divide the first digital signal and the second digital signal, the correspondence between the first digital signal and the pilot light signal, and the correspondence between the second digital signal and the quantum light signal need to be determined in combination with the specific actual situation. As an implementation method, the conversion module may include a first DSP module 521 and a separation module 522. After the first light signal is photoelectrically converted, it may be first processed by a DSP algorithm and then separated to obtain the first digital signal and the second digital signal. In some implementation methods, the conversion module also includes a second DSP module 522. That is, the second digital signal needs to be processed by a DSP algorithm again after separation.

[0256] The specific expression of the first digital signal and the second digital signal can be determined according to the detector. For example, in the case of using a heterodyne detector, the second digital signal S in For example, it includes at least 4 data {S XI ,S XQ ,S YI ,S YQ}. Where X and Y refer to the polarization state of the signal light, and X and Y are orthogonal. I and Q refer to the two canonical components representing the light field state. Alternatively, in the QKD system, they can also be represented by x and p. When other detectors are used, the second digital signal S in It can also include 8 data {S XI ,S XQ ,S YI ,S YQ , S XI+iXQ ,S XI-iXQ ,S YI+iXQ ,S YI-iYQ In the actual processing process, the last four signals can be merged back into the first case mentioned above. Therefore, the subsequent processing of the digital signal includes 4 data as an exemplary description.

[0257] The second digital signal obtained by the receiving end is different from the digital signal sent by the transmitting end. The reason for the difference is that, on the one hand, some digital signal processing algorithms are first used to compensate for the damage of some channels and devices during the photoelectric conversion at the receiving end, and on the other hand, some signal processing algorithms have certain redundant degrees of freedom, such as phase.

[0258] The first processing module 530 is configured to obtain a first pilot digital signal and a second pilot digital signal, wherein the first pilot digital signal corresponds to an X polarization state of the first digital signal, and the second pilot digital signal corresponds to a Y polarization state of the first digital signal.

[0259] In some implementations, the first pilot digital signal and the second pilot digital signal may be pre-set by the transmitting end and the receiving end, that is, the first processing module 530 may retrieve the first pilot digital signal and the second pilot digital signal stored in or outside the module to obtain the first pilot digital signal and the second pilot digital signal.

[0260] In some implementations, the first pilot digital signal and the second pilot digital signal can be obtained according to the first digital signal through polarization demultiplexing. The polarization demultiplexing processing of the first digital signal can be performed using an equalization algorithm. The equalization algorithm is implemented by adaptive algorithm processing, or by channel estimation. The adaptive algorithm can be understood as automatically adjusting the processing method according to the data characteristics of the first digital signal, and obtaining and updating the equalization coefficient by feedback. Channel estimation can be understood as performing parameter estimation according to the first digital signal through a set channel model to obtain the equalization coefficient.

[0261] As a way to achieve this, Figure 6 6 is a schematic diagram of a first processing module provided by an embodiment of the present application. Taking the adaptive algorithm as an example, the first demultiplexing module may include a MIMO module 610 and a coefficient updating module 620.

[0262] The second processing module 540 is configured to obtain at least one first coefficient according to the first digital signal, the first pilot digital signal and the second pilot digital signal.

[0263] Among them, how to obtain at least one first coefficient according to the first digital signal, the first pilot digital signal and the second pilot digital signal is determined according to the actual situation, and the present application does not limit this. In some implementations, at least one first coefficient may include only one coefficient, which can also be understood as a single-tap coefficient. That is, a single coefficient is introduced using a pilot digital signal to perform polarization demultiplexing on the quantum optical signal. In some implementations, the pilot digital signal may also include multiple subcarriers. In this case, at least one first coefficient includes multiple coefficients, which can also be understood as a multi-tap coefficient. That is, multiple coefficients are introduced to perform polarization demultiplexing on the quantum optical signal. In the following device embodiments, taking the case where the first coefficient is a single-tap coefficient as an example, the case where the first coefficient is a multi-tap coefficient can also be implemented with specific reference to the embodiments in the present application.

[0264] When the MIMO algorithm is used, the first coefficient can be obtained by the MIMO coefficient. In some implementations, the MIMO coefficient can be used as the first coefficient. In some implementations, the MIMO coefficient can also be adjusted, such as scaling the MIMO coefficient, to obtain the first coefficient. Taking the single-tap MIMO coefficient TD-MIMO as an example, its expression is:

[0265]

[0266] Among them (E X E Y ) T represents the first digital signal, represents the first pilot digital signal and the second pilot digital signal, is the MIMO coefficient matrix W M .

[0267] Written in matrix form:

[0268] E out =W M E

[0269] Where E is expressed in matrix form, W M is the coefficient matrix, E out is the pilot digital signal vector output by MIMO.

[0270] According to W M The first coefficient W can be obtained η .Right now Wherein n is greater than 0. The specific value of n is determined according to the actual adjustment needs. In some implementations, n can be determined according to the matrix elements of the coefficient matrix.

[0271] The demultiplexing module 550 is used to perform polarization demultiplexing processing on the second digital signal according to at least one first coefficient to obtain a first quantum digital signal and a second quantum digital signal, wherein the first quantum digital signal corresponds to an X polarization state and the second quantum digital signal corresponds to a Y polarization state.

[0272] That is, the demultiplexing module includes a data transformation module, which needs to perform additional data transformation on the second digital signal corresponding to the quantum light signal through at least one first coefficient so that the algorithm can correspond to a physical operation with reasonable meaning, such as linear transformation, etc., thereby ensuring that the output signal meets the safety requirements.

[0273] How to perform polarization demultiplexing on the second digital signal according to at least one first coefficient is determined according to actual conditions. In some implementations, each first coefficient in at least one first coefficient can be directly used in a calculation manner to perform polarization demultiplexing on the second digital signal. In some implementations, each first coefficient in at least one first coefficient can be matrix decomposed, and data transformation can be performed on the second digital signal according to the matrix decomposition result to perform polarization demultiplexing on the second digital signal. The matrix decomposition method is determined according to actual conditions. As an implementation method, the singular values ​​of the first coefficients can be used to perform polarization demultiplexing on the second digital signal. The specific implementation method will be described later in conjunction with Figure 7 and Figure 8 Expand the detailed description.

[0274] In addition, in some implementations, the demultiplexing module 550 may further include a noise adding module, which is used to add random noise to the second digital signal according to the first coefficient. That is, by adding random numbers to the signal, the signal after polarization multiplexing processing is compensated so that the output quantum signal meets the security requirements of the QKD system. In some implementations, the noise adding module adds digital noise to the second digital signal according to the singular value of the first coefficient, thereby performing more stable and more widely applicable digital signal processing.

[0275] In the case where the first coefficient is obtained by the MIMO coefficient, the second digital signal, the first quantum digital signal, and the second quantum digital signal satisfy the following relationship:

[0276] S out =W η S in +N A

[0277] Among them, W η is the first coefficient, S in is the second digital signal, S out is the first quantum digital signal and the second quantum digital signal, R2N A is digital noise.

[0278] In a QKD system, the power of a quantum optical signal is usually lower than that of a pilot optical signal, and the corresponding second digital signal power is also lower than that of the first digital signal power, making it difficult to directly process using an equalization algorithm. The first digital signal corresponding to the classical optical signal has relatively higher power and a higher signal-to-noise ratio. Thus, channel variables or device damage parameters can be quickly extracted through the first digital signal. Therefore, the present application provides a signal processing device that first obtains a first coefficient based on a first digital signal corresponding to a pilot optical signal, and performs polarization demultiplexing on a second digital signal corresponding to the quantum optical signal based on the first coefficient, so that the output signal meets the security requirements of the QKD system.

[0279] The following describes the apparatus for implementing the direct calculation method and the matrix decomposition method of the present application in conjunction with the case of a single tap, that is, the case where the at least one first coefficient refers to a case where only the first coefficient is included.

[0280] Figure 7 Schematic diagram of another signal processing device of a quantum key distribution system provided in an embodiment of the present application. Figure 7 As shown, the device comprises:

[0281] The receiving module 710 is configured to receive a first optical signal, wherein the first optical signal includes an X polarization state and a Y polarization state, and the first optical signal includes a quantum optical signal and a pilot optical signal.

[0282] The conversion module includes a first DSP module 721, a separation module 722 and a second DSP module 723. It is used to perform photoelectric conversion on the first optical signal to obtain a first digital signal and a second digital signal, wherein the first digital signal corresponds to the pilot optical signal and the second digital signal corresponds to the quantum optical signal.

[0283] The first processing module 730 is configured to obtain a first pilot digital signal and a second pilot digital signal, wherein the first pilot digital signal corresponds to an X polarization state of the first digital signal, and the second pilot digital signal corresponds to a Y polarization state of the first digital signal.

[0284] The first digital signal, the first pilot digital signal and the second pilot digital signal have the following relationship:

[0285]

[0286] Among them (E X E Y ) t represents the first digital signal, represents the first pilot digital signal and the second pilot digital signal, is the coefficient matrix W M . T refers to the transpose of the matrix.

[0287] When an adaptive algorithm is used to perform balanced MIMO algorithm processing on a classical optical signal, the coefficient of W needs to be updated. The method for updating the coefficient should be determined according to the actual situation. For example, the least mean square algorithm, constant modulus algorithm, etc. can be used.

[0288] The second processing module 740 is configured to obtain a first coefficient according to the first digital signal, the first pilot digital signal and the second pilot digital signal.

[0289] The second processing module 740 obtains W M After that, you can M The coefficient is adjusted to obtain the first coefficient to perform polarization demultiplexing on the quantum light signal. That is, the first coefficient is η is greater than 0.

[0290] In some implementations, the coefficient matrix W M That is, it can be directly used as the first coefficient W η , at this time there is W η =W M , that is, the coefficient η of the matrix element used to adjust the MIMO coefficient is 1.

[0291] In some implementations, the second processing module 740 may further scale the coefficient matrix, so as to obtain a better effect when polarization demultiplexing is performed on the second digital signal using the first coefficient. As a scaling method, W may be extracted. M The diagonal element {p X ,p Y}, and use the maximum value of the diagonal element L = max{p x ,p Y The maximum value of} for W M As the maximum value of the diagonal element is used to scale W M One way to make adjustments:

[0292] First, use W M The matrix elements define the parameters J and K:

[0293] J=|ω XX | 2 +|ω YX | 2 +|ω XY | 2 +|ω YY | 2

[0294] K=|ω XX ω YY -ω YX ω XY | 2

[0295] Then L can be obtained as:

[0296]

[0297] When it is judged that L>1, a parameter 0<η<1 can be selected so that ηL≤1. The selection of η can be carried out according to a predetermined strategy, for example: 1) η=1 / L, so that ηL=1; 2) there is a predetermined parameter T0, T0 is greater than 0, and η=T0 / L is defined. Therefore, η is actually based on the coefficient matrix W M The matrix elements of are determined.

[0298] The demultiplexing module 750 may include a data conversion module 751 and a noise adding module 752. The data conversion module 751 is used to multiply the first coefficient by the first digital signal to obtain a third digital signal. The noise adding module 752 is specifically used to extract the matrix element of the first coefficient and add digital noise to the third digital signal according to the matrix element.

[0299] Specifically, the second digital signal, the first quantum digital signal, and the second quantum digital signal satisfy the following relationship:

[0300] S out =W η S in +N A

[0301] Among them, W η is the first coefficient, S in is the second digital signal, W η S in is the third digital signal, S out is the first quantum digital signal and the second quantum digital signal, N A is digital noise.

[0302] N A Specifically including the complex noise of X polarization state and the complex noise of the Y polarization state and From complex random numbers and Construction, where are four source random numbers, and their respective variances are In some implementations, when SNU is counted in digital signal processing and data is quantized using SNU as a unit, all data are divided by Corresponding to the four-way data, the SNU is different, and the corresponding variance can be expressed as N A It can be written as:

[0303]

[0304] in, is the complex noise in the X polarization state, is the complex noise in the Y polarization state, Variance Variance and The covariance of

[0305] As a N A The construction method:

[0306]

[0307]

[0308] Among them, γ X , γ Y , γ XY According to the first coefficient W ηSure.

[0309]

[0310]

[0311]

[0312] Or it can be expressed as:

[0313]

[0314] As another N A The construction method:

[0315]

[0316]

[0317] in, are three independent complex random numbers.

[0318] After the second digital signal is processed as above, the first quantum digital signal and the second quantum digital signal can be output to continue with the subsequent steps of the QKD system process.

[0319] In such Figure 7 In the device shown, data processing is performed on the second digital signal corresponding to the quantum light signal by direct calculation, which can simplify the data conversion process while making the output signal meet the security requirements of the QKD system.

[0320] Figure 8 Schematic diagram of another signal processing device of a quantum key distribution system provided in an embodiment of the present application. Figure 8 As shown, the device comprises:

[0321] The receiving module 810 is configured to receive a first optical signal, wherein the first optical signal includes an X polarization state and a Y polarization state, and the first optical signal includes a quantum optical signal and a pilot optical signal.

[0322] The conversion module includes a first DSP module 821, a separation module 822 and a second DSP module 823. It is used to perform photoelectric conversion on the first optical signal to obtain a first digital signal and a second digital signal, wherein the first digital signal corresponds to the pilot optical signal and the second digital signal corresponds to the quantum optical signal.

[0323] The first processing module 830 is configured to obtain a first pilot digital signal and a second pilot digital signal, wherein the first pilot digital signal corresponds to an X polarization state of the first digital signal, and the second pilot digital signal corresponds to a Y polarization state of the first digital signal.

[0324] The first digital signal, the first pilot digital signal and the second pilot digital signal have the following relationship:

[0325]

[0326] Among them (E X E Y ) T represents the first digital signal, represents the first pilot digital signal and the second pilot digital signal, is the coefficient matrix W M . T refers to the transpose of the matrix.

[0327] When an adaptive algorithm is used to perform balanced MIMO algorithm processing on a classical optical signal, the coefficient of W needs to be updated. The method for updating the coefficient should be determined according to the actual situation. For example, the least mean square algorithm, constant modulus algorithm, etc. can be used.

[0328] The second processing module 840 is configured to obtain a first coefficient according to the first digital signal, the first pilot digital signal and the second pilot digital signal.

[0329] The second processing module 840 obtains W M After that, you can M The coefficient is adjusted to obtain the first coefficient to perform polarization demultiplexing on the quantum light signal. That is, the first coefficient is η is greater than 0.

[0330] In some implementations, the coefficient matrix W M That is, it can be directly used as the first coefficient W η , at this time there is W η =W M , that is, the coefficient η of the matrix element used to adjust the MIMO coefficient is 1.

[0331] The demultiplexing module 850 is used to perform data transformation on the second digital signal according to the first coefficient to obtain a third digital signal, and perform matrix decomposition on the first coefficient to obtain a first unitary matrix, a second unitary matrix and a diagonal matrix; obtain complex random noise according to the diagonal elements in the diagonal matrix; perform data transformation on the complex random noise according to the first unitary matrix to obtain digital noise; and add digital noise to the third digital signal.

[0332] Specifically, the second digital signal, the first quantum digital signal, and the second quantum digital signal also satisfy the following relationship:

[0333] S out =W η S in +N A

[0334] Among them, W η is the first coefficient, S in is the second digital signal, W η S in is the third digital signal, S out is the first quantum digital signal and the second quantum digital signal, N A is digital noise.

[0335] In some implementations, the demultiplexing module 850 specifically performs:

[0336] 1) Matrix decomposition

[0337] The decomposition module 851 can be used to decompose the first coefficient W η Perform singular value decomposition, which can be expressed as W η =R2PR1, R2 is the first unitary matrix, P is the diagonal matrix, and R1 is the second unitary matrix. Specifically, the expressions of R1, R2 and P can be:

[0338]

[0339]

[0340] where p X and p Y is a real number, and 0≤p X ,p Y ≤1; a1, b1, is plural; is the phase, which is a real number.

[0341] 2) Data transformation and noise addition, which includes three steps:

[0342] The first step is to analyze the quantum signal data S in,2 First, perform two matrix multiplications, namely

[0343] S t1 =PR1S in,2

[0344] The second step is to add complex random noise Right now

[0345]

[0346] Specifically including the complex noise of X polarization state and the complex noise of the Y polarization state and From complex random numbers and Construction, where are four source random numbers, and their respective variances are In some implementations, when SNU is counted in digital signal processing and data is quantized using SNU as a unit, all data are divided by Corresponding to the four-way data, the SNU is different, and the corresponding variance can be expressed as

[0347] The expression can be:

[0348]

[0349] Among them, the coefficient γ X and γ Y According to the diagonal element p of the P matrix X and determine, that is

[0350] When p X ≤1, γ X =1-(p X ) 2 , or p Y ≤1, γ Y =1-(p Y ) 2 ;

[0351] When p X >1, γ X =(p X ) 2 -1, or p Y >1, γ Y =(p Y ) 2 -1;

[0352] Comprehensive, γ X =|1-(p X ) 2 |, γ Y =|1-(p Y ) 2 |.

[0353] Using the first coefficient W η The matrix elements of represent the diagonal elements of the diagonal matrix, then γ X =|1-(|ω XX | 2 +|ω YX | 2 )|,γ Y =|1-(|ω YY | 2 +|ω XY | 2 )|.

[0354] The third step is to t2 Perform matrix multiplication again, that is

[0355] S out,2 =R2S t2

[0356] In some implementations, the demultiplexing module 850 specifically performs:

[0357] 1) Using the first coefficient W η Directly transform the data, that is

[0358] S t =W η S in,2

[0359] 2) Add digital noise

[0360] The decomposition module 851 obtains the diagonal matrix P and the second unitary matrix R2 by matrix decomposition (such as SVD decomposition), and the noise adding module 853 determines the complex random noise according to the diagonal matrix P. Then rotate the first unitary matrix R2 matrix to get the final added noise

[0361] Here Same as the previous definition:

[0362]

[0363] Combining the above two processing methods of step S450, it can be seen that the second digital signal, the first quantum digital signal and the second quantum digital signal satisfy the relationship S out =W η S in +N A On the basis of

[0364] After the second digital signal is processed as above, the first quantum digital signal and the second quantum digital signal can be output to continue with the subsequent steps of the QKD system process.

[0365] In such Figure 8 In the device shown, the first coefficient is matrix decomposed to perform data transformation on the second digital signal corresponding to the quantum light signal, so that the second digital signal can be polarization demultiplexed according to the matrix decomposition result, so that the output signal meets the security requirements of the QKD system.

[0366] Fig. 9 Schematic diagram of another signal processing device of a quantum key distribution system provided in an embodiment of the present application. Fig. 9 As shown, the device comprises:

[0367] Fig. 9 In the embodiment, the receiving module 910, the conversion module, the first processing module 930, the second processing module 940 and Figure 8 The receiving module 810, the conversion module, the first processing module 830, and the second processing module 840 correspond to each other and are not described in detail here.

[0368] In addition to the above modules, Fig. 9 The illustrated apparatus may also include a demultiplexing module 950 .

[0369] The decomposition module is used to perform N matrix decompositions on the first coefficient to obtain N first unitary matrices, N second unitary matrices and N diagonal matrices.

[0370] Its specific expression is:

[0371]

[0372] The value range of n is 1, 2, …, N.

[0373] N transformation modules are used to perform N data transformations and N random noise additions on the second digital signal according to the N first unitary matrices, the N second unitary matrices and the N diagonal matrices.

[0374] The N transform modules may be in cascade form, and the input of the nth transform module among the N transform modules is the output of the nth transform module. The calculation in the nth transform module is determined by the specific W n Sure.

[0375] Corresponding to the use of W n The N data transformations implemented can be Figure 8 The same is true in the text, so I will not repeat it here.

[0376] In such Fig. 9 In the device shown, polarization demultiplexing is performed on the second digital signal using the N-times decomposition results, so that the output signal further meets the security requirements of the QKD system.

[0377] It should be understood that Figures 7 to 9 The device shown can also be specifically applied to the case where at least one first coefficient is a multi-tap coefficient, that is, the at least one first coefficient includes multiple first coefficients. The above device can be specifically applied to process each first coefficient in the specific at least one first coefficient.

[0378] Fig.101 is a schematic diagram of a communication device provided in an embodiment of the present application. Device 1000 includes a bus 1001, a processor 1002, a communication interface 1003 and a memory 1004. The processor 1002, the memory 1004 and the communication interface 1003 communicate with each other through the bus 1001. Among them, the processor 1002 can be a field programmable gate array (FPGA), an application specific integrated circuit (ASIC), a system on chip (SoC), a central processor unit (CPU), a network processor (NP), a digital signal processor (DSP), a microcontroller unit (MCU), a programmable logic device (PLD), other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, or other integrated chips. The memory 1004 stores the executable code included in the pathological image processing system, and the processor 1002 reads the executable code in the memory 1004 to execute such as Figures 3 to 5 The memory 1004 may also include an operating system and other software modules required for running the process. The operating system may be LINUX TM ,UNIX TM ,WINDOWS TM Etc. Optionally, as an implementation, the chip includes a processor and a communication interface, and the processor reads instructions stored in the memory through the communication interface to execute the above method.

[0379] In addition, an embodiment of the present application also provides a chip, which obtains instructions and executes the instructions to implement the above method.

[0380] Optionally, as an implementation manner, the chip may further include a memory, in which instructions are stored, and the processor is used to execute the instructions stored in the memory. When the instructions are executed, the processor is used to execute the above method.

[0381] An embodiment of the present application also provides a computer-readable storage medium, which stores instructions, and the instructions are used in the method in the above method embodiment.

[0382] The embodiment of the present application also provides a computer program product including instructions, wherein the instructions are used to implement the method in the above method embodiment.

[0383] The terms "component", "module", "system", etc. used in this specification are used to represent computer-related entities, hardware, firmware, a combination of hardware and software, software, or software in execution. For example, a component can be, but is not limited to, a process running on a processor, a processor, an object, an executable file, an execution thread, a program and / or a computer. By way of illustration, both applications running on a computing device and a computing device can be components. One or more components may reside in a process and / or an execution thread, and a component may be located on a computer and / or distributed between two or more computers. In addition, these components may be executed from various computer-readable media having various data structures stored thereon. Components may, for example, communicate through local and / or remote processes according to signals having one or more data packets (e.g., data from two components interacting with another component between a local system, a distributed system and / or a network, such as the Internet interacting with other systems through signals).

[0384] Those of ordinary skill in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of this application.

[0385] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0386] In the several embodiments provided in the present application, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0387] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0388] In addition, each functional unit in each embodiment of the present application may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit.

[0389] If the functions are implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present application, or the part that contributes to the prior art or the part of the technical solution, can be embodied in the form of a software product, which is stored in a storage medium and includes several instructions for a computer device (which can be a personal computer, server, or network device, etc.) to perform all or part of the steps of the methods described in each embodiment of the present application. The aforementioned storage medium includes: various media that can store program codes, such as USB flash drives, mobile hard drives, ROM, RAM, magnetic disks, or optical disks.

[0390] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art who is familiar with the present technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A signal processing method for a quantum key distribution system, characterized in that: include: Receiving a first optical signal, wherein the first optical signal includes an X polarization state and a Y polarization state, and the first optical signal includes a quantum optical signal and a pilot optical signal; Performing photoelectric conversion on the first optical signal to obtain a first digital signal and a second digital signal, wherein the first digital signal corresponds to the pilot optical signal and the second digital signal corresponds to the quantum optical signal; Obtaining a first pilot digital signal and a second pilot digital signal, wherein the first pilot digital signal corresponds to an X polarization state of the first digital signal, and the second pilot digital signal corresponds to a Y polarization state of the first digital signal; Obtain at least one first coefficient according to the first digital signal, the first pilot digital signal and the second pilot digital signal; Polarization demultiplexing is performed on the second digital signal according to each first coefficient of the at least one first coefficient to obtain a first quantum digital signal and a second quantum digital signal, wherein the first quantum digital signal corresponds to the X polarization state and the second quantum digital signal corresponds to the Y polarization state.

2. The signal processing method according to claim 1, characterized in that: in: The first pilot digital signal and the second pilot digital signal are preconfigured; or The first pilot digital signal and the second pilot digital signal are obtained by performing polarization demultiplexing processing on the first digital signal.

3. The signal processing method according to claim 1 or 2, characterized in that: Performing polarization demultiplexing processing on the second digital signal according to each first coefficient of the at least one first coefficient includes: Performing data transformation on the second digital signal according to the first coefficient to obtain a third digital signal; Digital noise is added to the third digital signal to obtain the first quantum digital signal and the second quantum digital signal.

4. The signal processing method according to claim 3, characterized in that: Adding digital noise to the third digital signal comprises: A matrix element of the first coefficient is extracted, and the digital noise is added to the third digital signal according to the matrix element.

5. The signal processing method according to claim 3, characterized in that: Adding digital noise to the third digital signal comprises: Performing matrix decomposition on the first coefficients to obtain a first unitary matrix, a second unitary matrix, and a diagonal matrix; Obtaining complex random noise according to the diagonal elements in the diagonal matrix; Performing data transformation on the complex random noise according to the first unitary matrix to obtain the digital noise; The digital noise is added to the third digital signal.

6. The signal processing method according to any one of claims 3 to 5, characterized in that: The second digital signal, the first quantum digital signal and the second quantum digital signal satisfy the following relationship: S out =W η S in +N A Among them, W η is the first coefficient, S in is the second digital signal, W η S in is the third digital signal, S out are the first quantum digital signal and the second quantum digital signal, N A is the digital noise.

7. The signal processing method according to claim 6, characterized in that: The first coefficient is: Among them, η is greater than is a coefficient matrix, and the coefficient matrix is ​​determined according to the relationship between the first digital signal, the first pilot digital signal and the second pilot digital signal.

8. The signal processing method according to claim 7, characterized in that: η is determined based on the matrix elements in the coefficient matrix.

9. The signal processing method according to claim 7 or 8, characterized in that: The digital noise satisfies: in, is the complex noise in the X polarization state, is the complex noise in the Y polarization state, The variance is equal to 1-η 2 (|ω XX | 2 +|ω YX | 2 ), The variance of is equal to 1-η 2 (|ω YY | 2 +|ω XY | 2 ), and The covariance of 2 [(ω XY ) * ω XX +(ω YY ) * ω YX ].

10. The signal processing method according to claim 9, characterized in that: The digital noise also satisfies: where γ X = 1 - η 2 (|ω XX | 2 + |ω YX | 2 ), γ Y = 1 - η 2 (|ω YY | 2 + |ω XY | 2 ), γX Y = -η 2 [(ω XY ) * ω XX + (ω YY ) * ω YX , and are complex random numbers.

11. The signal processing method according to any one of claims 6 to 8, characterized in that: The second digital signal, the first quantum digital signal and the second quantum digital signal also satisfy the following relationship: Among them, R2 is the first unitary matrix, P is the diagonal matrix, R1 is the second unitary matrix, is complex random noise.

12. The signal processing method according to claim 11, characterized in that: The complex random noise satisfies: Among them, p X and p Y are the diagonal elements of the diagonal matrix, and A complex random number.

13. A signal processing device for a quantum key distribution system, characterized in that: include: A receiving module, configured to receive a first optical signal, wherein the first optical signal includes an X polarization state and a Y polarization state, and the first optical signal includes a quantum optical signal and a pilot optical signal; a conversion module, configured to perform photoelectric conversion on the first optical signal to obtain a first digital signal and a second digital signal, wherein the first digital signal corresponds to the pilot optical signal, and the second digital signal corresponds to the quantum optical signal; A first processing module, configured to obtain a first pilot digital signal and a second pilot digital signal, wherein the first pilot digital signal corresponds to an X polarization state of the first digital signal, and the second pilot digital signal corresponds to a Y polarization state of the first digital signal; A second processing module, configured to obtain at least one first coefficient according to the first digital signal, the first pilot digital signal and the second pilot digital signal; The demultiplexing module is used to perform polarization demultiplexing processing on the second digital signal according to the at least one first coefficient to obtain a first quantum digital signal and a second quantum digital signal, wherein the first quantum digital signal corresponds to the X polarization state and the second quantum digital signal corresponds to the Y polarization state.

14. The signal processing device according to claim 13, characterized in that: in: The first pilot digital signal and the second pilot digital signal are preconfigured; or The first pilot digital signal and the second pilot digital signal are obtained by performing polarization demultiplexing processing on the first digital signal.

15. The signal processing device according to claim 13 or 14, characterized in that: The demultiplexing module comprises: a data transformation module, configured to perform data transformation on the second digital signal according to the first coefficient to obtain a third digital signal; A noise adding module is used to add digital noise to the third digital signal to obtain the first quantum digital signal and the second quantum digital signal.

16. The signal processing device according to claim 15, characterized in that: Adding digital noise to the third digital signal comprises: A matrix element of the first coefficient is extracted, and the digital noise is added to the third digital signal according to the matrix element.

17. The signal processing device according to claim 15, characterized in that: Adding digital noise to the third digital signal comprises: Performing matrix decomposition on the first coefficients to obtain a first unitary matrix, a second unitary matrix, and a diagonal matrix; Obtaining complex random noise according to the diagonal elements in the diagonal matrix; Performing data transformation on the complex random noise according to the first unitary matrix to obtain the digital noise; The digital noise is added to the third digital signal.

18. The signal processing device according to any one of claims 15 to 17, characterized in that: The second digital signal, the first quantum digital signal and the second quantum digital signal satisfy the following relationship: S out =W η S in +N A Among them, W η is the first coefficient, S in is the second digital signal, W η S in is the third digital signal, Sout is the first quantum digital signal and the second quantum digital signal, N A is the digital noise.

19. The signal processing device according to claim 18, characterized in that: The first coefficient is: Where η is greater than 0, is a coefficient matrix, and the coefficient matrix is ​​determined according to the relationship between the first digital signal, the first pilot digital signal and the second pilot digital signal.

20. The signal processing device according to claim 19, characterized in that: η is determined based on the matrix elements in the coefficient matrix.

21. The signal processing device according to claim 19 or 20, characterized in that: The digital noise satisfies: in, is the complex noise in the X polarization state, is the complex noise in the Y polarization state, The variance is equal to 1-η 2 (|ω XX | 2 +|ω YX | 2 ), The variance of is equal to 1-η 2 (|ω YY | 2 +|ω XY | 2 ), and The covariance of 2 [(ω XY ) * ω XX +(ω YY ) * ω YX ].

22. The signal processing device according to claim 21, characterized in that: The digital noise also satisfies: in, γ XY =-η 2 [(ω XY )*ω XX +(ω YY )*ω YX ], and A complex random number.

23. The signal processing device according to any one of claims 18 to 20, characterized in that: The second digital signal, the first quantum digital signal and the second quantum digital signal also satisfy the following relationship: Among them, R2 is the first unitary matrix, P is the diagonal matrix, R1 is the second unitary matrix, is complex random noise.

24. The signal processing device according to claim 23, characterized in that: The complex random noise satisfies: Among them, p X and p Y are the diagonal elements of the diagonal matrix, and A complex random number.

25. A communication device, characterized in that: The communication device comprises at least one processor coupled to at least one memory, and the at least one processor is used to execute a computer program or instruction stored in the at least one memory, so that the communication device performs the method according to any one of claims 1 to 12.

26. A chip, characterized in that: The chip comprises a processor, the processor is coupled to a memory, the memory is used to store a computer program, and the processor is used to execute the computer program stored in the memory, so that the chip executes the method according to any one of claims 1 to 12.

27. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a computer program, and when the computer program is executed on a computer, the computer is caused to execute the method according to any one of claims 1 to 12.

28. A computer program product, characterized in that The computer program product comprises a computer program code, and when the computer program code is run on a computer, the method according to any one of claims 1 to 12 is executed.

Images