Signal processing method and system in continuous variable quantum key distribution

Abstract

The invention provides a signal processing method and system in continuous variable quantum key distribution, and relates to the technical field of communication. The method comprises the following steps: carrying out up-conversion operation on two double-sideband quadrature phase shift keying signals, and respectively converting the two double-sideband quadrature phase shift keying signals into a first center frequency and a second center frequency to form a first quantum signal in an X polarization direction and a first quantum signal in a Y polarization direction; adding a first pilot signal in the X polarization direction to the first quantum signal in the X polarization direction to obtain a first optical signal in the X polarization direction; adding a first pilot signal in the Y polarization direction to the first quantum signal in the Y polarization direction to obtain a first optical signal in the Y polarization direction; combining the first optical signal in the X polarization direction and the first optical signal in the Y polarization direction into a polarization multiplexing signal by using a polarization coupler; and transmitting the polarization multiplexing signal to a receiving end through a quantum channel. According to the embodiment of the invention, the security key rate of continuous variable quantum key distribution can be improved.

Description

Technical Field

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

[0002] Quantum key distribution mainly uses quantum states to transmit keys. According to the different quantum state carriers, it can be divided into two technical routes: Discrete-Variable Quantum Key Distribution (DV-QKD) and Continuous-Variable Quantum Key Distribution (CV-QKD). DV-QKD uses discrete variables in a finite Hilbert space such as the polarization of light to achieve quantum key distribution. It has advantages in long-distance transmission scenarios and has been used in backbone networks and metropolitan area networks. CV-QKD uses the continuous regular component of the coherent light field to achieve quantum key distribution. It has the advantages of high coding rate in short-distance situations and high compatibility with traditional coherent optical transmission systems. It has a very broad application prospect in scenarios such as metropolitan area networks and access networks. However, the security key rate of CV-QKD in related technologies is relatively low, and needs to be studied and improved.

[0003] It should be noted that the information disclosed in the above background technology section is only used to enhance the understanding of the background of the present disclosure, and therefore may include information that does not constitute the prior art known to ordinary technicians in the field. Summary of the invention

[0004] The present invention provides a signal processing method and system in continuous variable quantum key distribution, which at least improves the security key rate of continuous variable quantum key distribution to a certain extent.

[0005] Other features and advantages of the present disclosure will become apparent from the following detailed description, or may be learned in part by the practice of the present disclosure.

[0006] According to one aspect of the present disclosure, a signal processing method in continuous variable quantum key distribution is provided, comprising:

[0007] Performing up-conversion operation on the two double-sideband quadrature phase-shift keying signals to respectively convert the frequencies to a first center frequency and a second center frequency to form a first quantum signal in an X polarization direction and a first quantum signal in a Y polarization direction, wherein the first center frequency and the second center frequency are different;

[0008] Adding a first pilot signal in the X polarization direction to the first quantum signal in the X polarization direction to obtain a first optical signal in the X polarization direction;

[0009] Adding a first pilot signal in the Y polarization direction to the first quantum signal in the Y polarization direction to obtain a first optical signal in the Y polarization direction; wherein the center frequencies of the first pilot signal in the X polarization direction and the first pilot signal in the Y polarization direction are the third center frequency, and the third center frequency is different from both the first center frequency and the second center frequency;

[0010] Using a polarization coupler, the first optical signal in the X polarization direction and the first optical signal in the Y polarization direction are combined into a polarization multiplexed signal;

[0011] The polarization multiplexed signal is sent to the receiving end through the quantum channel.

[0012] In one embodiment of the present disclosure, the first quantum signal in the X polarization direction is a single sideband quadrature phase shift keying signal having a center frequency of the first center frequency and a bandwidth of the first bandwidth; the first quantum signal in the Y polarization direction is a single sideband quadrature phase shift keying signal having a center frequency of the second center frequency and a bandwidth of the first bandwidth; the first pilot signal in the X polarization direction and the first pilot signal in the Y polarization direction are single frequency signals having a center frequency of the third center frequency;

[0013] The difference between the first center frequency and the third center frequency is greater than half of the first bandwidth, and the difference between the second center frequency and the first center frequency is greater than the first bandwidth.

[0014] In one embodiment of the present disclosure, before performing an up-conversion operation on the two double-sideband quadrature phase shift keying signals, the method further includes:

[0015] Using a quantum random number generator to generate a first bit sequence and a second bit sequence, wherein the first bit sequence and the second bit sequence are randomly distributed binary bit sequences;

[0016] Based on a preset mapping rule, mapping the first bit sequence and the second bit sequence into a first orthogonal phase shift keying symbol sequence and a second orthogonal phase shift keying symbol sequence respectively;

[0017] The first quadrature phase shift keying symbol sequence and the second quadrature phase shift keying symbol sequence are up-sampled and pulse-shaped filtered to obtain two double-sideband quadrature phase shift keying signals with a first bandwidth.

[0018] In one embodiment of the present disclosure, a polarization multiplexing signal is sent to a receiving end through a quantum channel, including:

[0019] An optical attenuator is used to attenuate the quantum signal part in the polarization multiplexed signal into a quantum state;

[0020] The polarization multiplexed signal decayed into a quantum state is sent to the receiving end.

[0021] According to another aspect of the present disclosure, a continuous variable quantum key distribution system is provided, comprising:

[0022] At the transmitting end, two double-sideband quadrature phase-shift keying signals are up-converted to the first center frequency and the second center frequency, respectively, to form a first quantum signal in the X polarization direction and a first quantum signal in the Y polarization direction, wherein the first center frequency is different from the second center frequency; a first pilot signal in the X polarization direction is added to the first quantum signal in the X polarization direction to obtain a first optical signal in the X polarization direction; and a first pilot signal in the Y polarization direction is added to the first quantum signal in the Y polarization direction to obtain a first optical signal in the Y polarization direction; wherein the center frequencies of the first pilot signal in the X polarization direction and the first pilot signal in the Y polarization direction are the third center frequency, which is different from the first center frequency and the second center frequency; a polarization coupler is used to combine the first optical signal in the X polarization direction and the first optical signal in the Y polarization direction into a polarization multiplexing signal; and the polarization multiplexing signal is sent to the receiving end through a quantum channel;

[0023] The receiving end receives the polarization multiplexed signal.

[0024] In one embodiment of the present disclosure, the first quantum signal in the X polarization direction is a single sideband quadrature phase shift keying signal having a center frequency of the first center frequency and a bandwidth of the first bandwidth; the first quantum signal in the Y polarization direction is a single sideband quadrature phase shift keying signal having a center frequency of the second center frequency and a bandwidth of the first bandwidth; the first pilot signal in the X polarization direction and the first pilot signal in the Y polarization direction are single frequency signals having a center frequency of the third center frequency;

[0025] The difference between the first center frequency and the third center frequency is greater than half of the first bandwidth, and the difference between the second center frequency and the first center frequency is greater than the first bandwidth.

[0026] In one embodiment of the present disclosure, the transmitting end also applies a quantum random number generator to generate a first bit sequence and a second bit sequence, and the first bit sequence and the second bit sequence are randomly distributed binary bit sequences; based on a preset mapping rule, the first bit sequence and the second bit sequence are mapped to a first orthogonal phase shift keying symbol sequence and a second orthogonal phase shift keying symbol sequence, respectively; the first orthogonal phase shift keying symbol sequence and the second orthogonal phase shift keying symbol sequence are upsampled, and pulse shaping filtering is performed to obtain two double-sideband orthogonal phase shift keying signals with a bandwidth of the first bandwidth.

[0027] In one embodiment of the present disclosure, the receiving end further divides the polarization multiplexing signal into a second optical signal in an X polarization direction and a second optical signal in a Y polarization direction through a polarization beam splitter; performs photoelectric conversion based on the second optical signal in the X polarization direction and a local local oscillator signal to obtain a first electrical signal; performs photoelectric conversion based on the second optical signal in the Y polarization direction and the local local oscillator signal to obtain a second electrical signal; performs analog-to-digital conversion on the first electrical signal and the second electrical signal to obtain a first baseband digital electrical signal and a second baseband digital electrical signal;

[0028] The first baseband digital electrical signal and the second baseband digital electrical signal are used in the key generation process.

[0029] In one embodiment of the present disclosure, the receiving end further performs bandpass filtering on the first baseband digital electrical signal and the second baseband digital electrical signal to obtain a second quantum signal in the X polarization direction and a second quantum signal in the Y polarization direction; performs a down-conversion operation corresponding to the up-conversion operation at the transmitting end on the second quantum signal in the X polarization direction and the second quantum signal in the Y polarization direction, and converts the second quantum signal in the X polarization direction and the second quantum signal in the Y polarization direction into double-sideband quantum signals.

[0030] In one embodiment of the present disclosure, a receiving end performs bandpass filtering on a first baseband digital electrical signal and a second baseband digital electrical signal, and also obtains a second pilot signal in an X polarization direction and a second pilot signal in a Y polarization direction; based on the first pilot signal in the X polarization direction and the first pilot signal in the Y polarization direction, and the second pilot signal in the X polarization direction and the second pilot signal in the Y polarization direction, an error estimate of the pilot signal is calculated; and the second quantum signal in the X polarization direction and the second quantum signal in the Y polarization direction are compensated using the error estimate through a constant modulus algorithm.

[0031] In one embodiment of the present disclosure, the receiving end also uses frequency offset estimation and phase recovery algorithms to recover the phases of the second pilot signal in the X polarization direction, the second pilot signal in the Y polarization direction, the second quantum signal in the X polarization direction, and the second quantum signal in the Y polarization direction.

[0032] In one embodiment of the present disclosure, the receiving end also downsamples the double-sideband quantum signal to a single sampling rate to obtain a third orthogonal phase shift keying symbol sequence and a fourth orthogonal phase shift keying symbol sequence; normalizes the third orthogonal phase shift keying symbol sequence and the fourth orthogonal phase shift keying symbol sequence to a shot noise unit, and estimates the channel parameters; based on the estimated signal parameters, the security key rate is calculated using a theoretical calculation formula for the security key rate; when the security key rate is greater than 0, a post-processing operation is performed to obtain a binary quantum key sequence.

[0033] According to another aspect of the present disclosure, an electronic device is provided, comprising: a memory for storing instructions; and a processor for calling the instructions stored in the memory to implement the above-mentioned signal processing method in continuous variable quantum key distribution.

[0034] According to another aspect of the present disclosure, a computer-readable storage medium is provided, on which computer instructions are stored. When the computer instructions are executed by a processor, the signal processing method in the continuous variable quantum key distribution is implemented.

[0035] According to another aspect of the present disclosure, a computer program product is provided. The computer program product stores instructions, and when the instructions are executed by a computer, the computer implements the above-mentioned signal processing method in continuous variable quantum key distribution.

[0036] According to yet another aspect of the present disclosure, there is provided a chip, comprising at least one processor and an interface;

[0037] An interface for providing program instructions or data to at least one processor;

[0038] At least one processor is used to execute program instructions to implement the above-mentioned signal processing method in continuous variable quantum key distribution.

[0039] In the signal processing method and system for continuous variable quantum key distribution provided by the embodiments of the present disclosure, the quantum signal and the pilot signal at the transmitting end are frequency-division multiplexed, which can reduce interference to the quantum signal; polarization multiplexing is used between the pilot signals, which can accelerate the convergence speed of the digital signal processing algorithm at the receiving end; frequency-division multiplexing and polarization multiplexing are used between quantum signals, which can better eliminate polarization crosstalk between the two.

[0040] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present disclosure and, together with the description, serve to explain the principles of the present disclosure.

[0042] Obviously, the drawings described below are only some embodiments of the present disclosure, and a person skilled in the art can obtain other drawings based on these drawings without any creative work.

[0043] Figure 1 A flow chart of a signal processing method in continuous variable quantum key distribution in an embodiment of the present disclosure is shown;

[0044] Figure 2A schematic diagram of a CV-QKD signal polarization multiplexing technology in an embodiment of the present disclosure is shown;

[0045] Figure 3 Another schematic diagram of a CV-QKD signal polarization multiplexing technology in an embodiment of the present disclosure is shown;

[0046] Figure 4 A schematic diagram of another CV-QKD signal polarization multiplexing technology in an embodiment of the present disclosure is shown;

[0047] Figure 5 A flow chart of generating a double-sideband quadrature phase shift keying signal in an embodiment of the present disclosure is shown;

[0048] Figure 6 A schematic diagram of a continuous variable quantum key distribution system in an embodiment of the present disclosure is shown;

[0049] Figure 7 A digital signal processing flow chart of a transmitting end in an embodiment of the present disclosure is shown;

[0050] Figure 8 A digital signal processing flow chart of a receiving end in an embodiment of the present disclosure is shown;

[0051] Fig. 9 A schematic diagram of the architecture of a continuous variable quantum key distribution system in an embodiment of the present disclosure is shown;

[0052] Fig.10 A structural block diagram of an electronic device in an embodiment of the present disclosure is shown. DETAILED DESCRIPTION

[0053] In order to make the purpose, technical scheme and advantages of the embodiments of the present disclosure clearer, the technical scheme in the embodiments of the present disclosure will be clearly and completely described below in conjunction with the drawings in the embodiments of the present disclosure. Obviously, the described embodiments are only part of the embodiments of the present disclosure, rather than all of the embodiments. The components of the embodiments of the present disclosure generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present disclosure provided in the drawings is not intended to limit the scope of the present disclosure for protection, but merely represents the selected embodiments of the present disclosure. Based on the embodiments of the present disclosure, all other embodiments obtained by those skilled in the art without making creative work belong to the scope of protection of the present disclosure.

[0054] Continuous-Variable Quantum Key Distribution (CV-QKD) has great development potential, but its practical application still faces many practical problems. On the one hand, the current QKD secret key ratio (SKR) is usually only in the Kbps range, which is far behind classical communication. This is mainly because the CV-QKD system usually works in an environment with a very low signal-to-noise ratio and is very sensitive to noise. How to improve the security key ratio is a critical issue. On the other hand, the compatibility of the current CV-QKD system with the traditional coherent optical communication system has not yet reached the expected level, making it difficult to effectively reduce costs. This is mainly because the current system solution is difficult to effectively adapt to traditional coherent optical communication devices and traditional digital signal processing algorithms. A more complete solution needs to be proposed.

[0055] In order to improve the security key rate (coding rate) of CV-QKD, the current mainstream method is to send a classical pilot signal at the transmitting end in addition to the quantum signal used to generate the key. The power of the pilot signal is usually much greater than that of the quantum signal. It is used to assist in recovering the quantum signal and is usually transmitted together with the quantum signal in time division multiplexing, frequency division multiplexing, polarization multiplexing and other ways.

[0056] In addition, similar to classical coherent optical communication, two quantum signals can also be transmitted simultaneously in a polarization multiplexing manner, which can theoretically effectively improve the security key rate. However, the relevant schemes have the following two problems. First, they cannot effectively solve the crosstalk between the two quantum signals of polarization multiplexing and between the pilot signal and the quantum signal of time division multiplexing, which results in the inability to effectively improve the security key rate. Second, these existing schemes usually require the receiving end to adopt a more complex digital signal processing algorithm, which is difficult to be compatible with classical communication systems.

[0057] The present exemplary implementation is described in detail below with reference to the accompanying drawings and embodiments.

[0058] Figure 1 A flow chart of a signal processing method in a continuous variable quantum key distribution in an embodiment of the present disclosure is shown as follows: Figure 1 As shown, the signal processing method in the continuous variable quantum key distribution provided in the embodiment of the present disclosure includes S101-S105.

[0059] In S101, two double-sideband quadrature phase shift keying (QPSK) signals are up-converted to a first center frequency and a second center frequency, respectively, to form a first quantum signal in an X polarization direction and a first quantum signal in a Y polarization direction, wherein the first center frequency and the second center frequency are different.

[0060] In some embodiments, the double-sideband QPSK signal can be up-converted to the first center frequency by multiplying the single-frequency signal output by the mixer and the local oscillator. Similarly, the double-sideband QPSK signal can also be up-converted to the second center frequency.

[0061] The first quantum signal in the X polarization direction and the first quantum signal in the Y polarization direction are both single sideband QPSK signals.

[0062] In S102, a first pilot signal in the X polarization direction is added to the first quantum signal in the X polarization direction to obtain a first optical signal in the X polarization direction.

[0063] In S103, a first pilot signal in the Y polarization direction is added to the first quantum signal in the Y polarization direction to obtain a first optical signal in the Y polarization direction; wherein the center frequencies of the first pilot signal in the X polarization direction and the first pilot signal in the Y polarization direction are the third center frequency, and the third center frequency is different from both the first center frequency and the second center frequency.

[0064] In S104, a polarization coupler is used to combine the first optical signal in the X polarization direction and the first optical signal in the Y polarization direction into a polarization multiplexed signal.

[0065] In S105, the polarization multiplexing signal is sent to the receiving end through the quantum channel.

[0066] Figure 2 A CV-QKD signal polarization multiplexing technology solution is shown. Figure 2 In the scheme shown, the quantum signals are polarized and multiplexed, resulting in large polarization crosstalk; the quantum signals and pilot signals are time-division multiplexed, resulting in large time domain crosstalk, and the security key rate is not significantly improved. Figure 2 In this scheme, the receiving end needs to introduce a highly complex digital signal processing algorithm to recover the quantum signal, which has low compatibility with traditional coherent optical communication systems and is not conducive to reducing costs.

[0067] Figure 3 Shown above Figure 1 The CV-QKD signal polarization multiplexing technical solution corresponding to the embodiment, Figure 3The scheme shown adopts frequency division multiplexing between quantum signals and pilot signals, polarization and frequency division multiplexing between quantum signals, and polarization multiplexing between pilot signals. This can reduce the interference of pilot signals on quantum signals while reducing polarization crosstalk between two quantum signals, thereby improving the system security key rate. It can be understood that the above quantum signals are Figure 1 The first quantum signal in the X polarization direction and the first quantum signal in the Y polarization direction in the embodiment, the pilot signal is Figure 1 The first pilot signal in the X polarization direction and the first pilot signal in the Y polarization direction in the embodiment. In addition, the embodiment of the present disclosure can also adapt to the mature algorithms of the traditional coherent optical communication system without introducing additional complex algorithms, thereby helping to reduce costs.

[0068] In some embodiments, the first quantum signal in the X polarization direction is a single sideband quadrature phase shift keying signal having a center frequency of the first center frequency and a bandwidth of the first bandwidth; the first quantum signal in the Y polarization direction is a single sideband quadrature phase shift keying signal having a center frequency of the second center frequency and a bandwidth of the first bandwidth; the first pilot signal in the X polarization direction and the first pilot signal in the Y polarization direction are single frequency signals having a center frequency of the third center frequency;

[0069] The difference between the first center frequency and the third center frequency is greater than half of the first bandwidth, and the difference between the second center frequency and the first center frequency is greater than the first bandwidth.

[0070] Reference below Figure 4 The quantum signal and pilot signal multiplexing process in the above embodiment is described in detail.

[0071] The multiplexed signal consists of the X-polarization optical signal S x and Y polarization direction optical signal S y Composition, S x and S y It is composed of quantum signal components and pilot signal components, which can be expressed as:

[0072] S x =S qx +S px

[0073] S y =S qy +S py

[0074] Among them, S qx represents the quantum signal in the X polarization direction, S qy represents the quantum signal in the Y polarization direction, S px represents the pilot signal in the X polarization direction, S py Indicates the pilot signal in the Y polarization direction.

[0075] S qx The center frequency is f q1 , bandwidth is B q Single sideband QPSK signal; S qy The center frequency is f q2 , bandwidth is B q The single-sideband QPSK signal, S px and S py All are center frequencies f p single frequency signal.

[0076] In the embodiment of the present disclosure, the quantum signal adopts a single sideband signal to avoid the interference of low-frequency noise. In addition, the relationship between the various frequencies in the present disclosure satisfies:

[0077] f q1 -f p >B q / 2

[0078] f q2 -f q1 >B q

[0079] The above relationship can avoid the crosstalk of the pilot signal on the quantum signal and the crosstalk between two quantum signals.

[0080] In some embodiments, the above Figure 1 In the embodiment, the first quantum signal in the X polarization direction may be the above-mentioned S qx , the first quantum signal in the Y polarization direction can be the above S qy , the first pilot signal in the X polarization direction may be the above S px , the first pilot signal in the Y polarization direction may be the above S py , the first center frequency can be the above f q1 , the second center frequency can be the above f q2 , the third center frequency can be the above f p .

[0081] In some embodiments, before performing up-conversion operation on the two double-sideband quadrature phase-shift keying signals in S101, the method provided by the embodiment of the present disclosure may further include: Figure 5 S501-S503.

[0082] In S501, a quantum random number generator is used to generate a first bit sequence and a second bit sequence, where the first bit sequence and the second bit sequence are randomly distributed binary bit sequences.

[0083] In S502, based on a preset mapping rule, the first bit sequence and the second bit sequence are mapped to a first orthogonal phase shift keying symbol sequence and a second orthogonal phase shift keying symbol sequence respectively.

[0084] As an example, the mapping rule may be to map every 2 bits into a QPSK symbol. For the 4 possible bit combinations (00, 01, 10, 11), they are mapped to four different complex values ​​respectively:

[0085] 00→1+j

[0086] 01→-1+j

[0087] 10→-1-j

[0088] 11→1-j

[0089] In S503, up-sampling is performed on the first QPSK symbol sequence and the second QPSK symbol sequence, and pulse shaping filtering is performed to obtain two double-sideband QPSK signals with a first bandwidth.

[0090] The QPSK symbols are up-sampled so that the system sampling rate is greater than or equal to the Nyquist rate.

[0091] The disclosed embodiments not only ensure the quality of the signal and the bandwidth limitation, but also provide the necessary basis for subsequent modulation, transmission and reception.

[0092] In some embodiments, the above S105 sends the polarization multiplexing signal to the receiving end through the quantum channel, which may be to use an optical attenuator to attenuate the quantum signal part in the polarization multiplexing signal to a quantum state; and send the polarization multiplexing signal attenuated to the quantum state to the receiving end.

[0093] Using an optical attenuator to attenuate the quantum signal part of the polarization multiplexed signal to the single photon level or weak coherent state (i.e., quantum state) can provide information-theoretic security using the quantum no-cloning theorem. Any eavesdropping behavior will introduce detectable interference, which will be detected by both parties in the communication; attenuation to the single photon level reduces the possibility of transmitting multiple photons each time, reducing the potential risk of information leakage.

[0094] In some embodiments, the optical attenuator may be a variable optical attenuator (VOA) or a fixed optical attenuator (FOA) capable of precisely controlling the attenuation amount to ensure that the output signal reaches the desired single photon level or weak coherent state.

[0095] Figure 6A continuous variable quantum key distribution system provided by an embodiment of the present disclosure is shown, including a transmitting end 601 and a receiving end 602. It can be understood that the transmitting end 601 and the receiving end 602 each correspond to separate hardware.

[0096] The transmitting end 601 performs up-conversion operation on two double-sideband quadrature phase-shift keying signals, respectively converting the frequencies to the first center frequency and the second center frequency, to form a first quantum signal in the X polarization direction and a first quantum signal in the Y polarization direction, wherein the first center frequency and the second center frequency are different; the first pilot signal in the X polarization direction is added to the first quantum signal in the X polarization direction to obtain a first optical signal in the X polarization direction; the first pilot signal in the Y polarization direction is added to the first quantum signal in the Y polarization direction to obtain a first optical signal in the Y polarization direction; wherein the center frequencies of the first pilot signal in the X polarization direction and the first pilot signal in the Y polarization direction are the third center frequency, and the third center frequency is different from both the first center frequency and the second center frequency; the first optical signal in the X polarization direction and the first optical signal in the Y polarization direction are combined into a polarization multiplexing signal by using a polarization coupler; and the polarization multiplexing signal is sent to the receiving end 602 through a quantum channel;

[0097] The receiving end 602 receives the polarization multiplexing signal.

[0098] In some embodiments, the first quantum signal in the X polarization direction is a single sideband quadrature phase shift keying signal having a center frequency of the first center frequency and a bandwidth of the first bandwidth; the first quantum signal in the Y polarization direction is a single sideband quadrature phase shift keying signal having a center frequency of the second center frequency and a bandwidth of the first bandwidth; the first pilot signal in the X polarization direction and the first pilot signal in the Y polarization direction are single frequency signals having a center frequency of the third center frequency;

[0099] The difference between the first center frequency and the third center frequency is greater than half of the first bandwidth, and the difference between the second center frequency and the first center frequency is greater than the first bandwidth.

[0100] In some embodiments, the transmitting end 601 also applies a quantum random number generator to generate a first bit sequence and a second bit sequence, where the first bit sequence and the second bit sequence are randomly distributed binary bit sequences; based on a preset mapping rule, the first bit sequence and the second bit sequence are mapped to a first orthogonal phase shift keying symbol sequence and a second orthogonal phase shift keying symbol sequence, respectively; the first orthogonal phase shift keying symbol sequence and the second orthogonal phase shift keying symbol sequence are upsampled, and pulse shaping filtering is performed to obtain two double-sideband orthogonal phase shift keying signals with a bandwidth of the first bandwidth.

[0101] In some embodiments, the receiving end 602 further divides the polarization multiplexed signal into a second optical signal in an X polarization direction and a second optical signal in a Y polarization direction through a polarization beam splitter; performs photoelectric conversion based on the second optical signal in the X polarization direction and a local local oscillator signal to obtain a first electrical signal; performs photoelectric conversion based on the second optical signal in the Y polarization direction and the local local oscillator signal to obtain a second electrical signal; performs analog-to-digital conversion on the first electrical signal and the second electrical signal to obtain a first baseband digital electrical signal and a second baseband digital electrical signal; wherein the first baseband digital electrical signal and the second baseband digital electrical signal are used in the key generation process.

[0102] In some embodiments, the receiving end 602 further performs bandpass filtering on the first baseband digital electrical signal and the second baseband digital electrical signal to obtain a second quantum signal in the X polarization direction and a second quantum signal in the Y polarization direction; performs a down-conversion operation corresponding to the up-conversion operation at the transmitting end on the second quantum signal in the X polarization direction and the second quantum signal in the Y polarization direction, and converts the second quantum signal in the X polarization direction and the second quantum signal in the Y polarization direction into double-sideband quantum signals.

[0103] In some embodiments, the receiving end 602 performs bandpass filtering on the first baseband digital electrical signal and the second baseband digital electrical signal, and obtains a second pilot signal in the X polarization direction and a second pilot signal in the Y polarization direction; based on the first pilot signal in the X polarization direction and the first pilot signal in the Y polarization direction, and the second pilot signal in the X polarization direction and the second pilot signal in the Y polarization direction, an error estimate of the pilot signal is calculated; and the second quantum signal in the X polarization direction and the second quantum signal in the Y polarization direction are compensated using the error estimate through a constant modulus algorithm.

[0104] In some embodiments, the receiving end 602 further uses frequency offset estimation and phase recovery algorithms to recover the phases of the second pilot signal in the X polarization direction, the second pilot signal in the Y polarization direction, the second quantum signal in the X polarization direction, and the second quantum signal in the Y polarization direction.

[0105] In some embodiments, the receiving end also downsamples the double-sideband quantum signal to a single sampling rate to obtain a third orthogonal phase shift keying symbol sequence and a fourth orthogonal phase shift keying symbol sequence; normalizes the third orthogonal phase shift keying symbol sequence and the fourth orthogonal phase shift keying symbol sequence to shot noise units, and estimates channel parameters; based on the estimated signal parameters, the security key rate is calculated using a theoretical calculation formula for the security key rate; when the security key rate is greater than 0, a post-processing operation is performed to obtain a binary quantum key sequence.

[0106] The disclosed embodiments can adapt to the mature algorithms of traditional coherent optical communication systems while implementing the proposed signal multiplexing method, without introducing additional complex algorithms, which helps to reduce QKD costs and promote the development of future integrated communication and secret technology. Compared with existing solutions, it is possible to reduce the interference of pilot signals on quantum signals while reducing the polarization crosstalk between two quantum signals, thereby improving the system security key rate. In addition, the digital signal processing method for the transceiver end of the CV-QKD system proposed in the present invention can adapt to the mature algorithms of traditional coherent optical communication systems while implementing the proposed signal multiplexing method, without introducing additional complex algorithms, which helps to promote QKD cost reduction and the future development of integrated communication and secret.

[0107] The method and system provided in the embodiments of the present disclosure can be applied to QKD devices and networks, which helps to improve the coding rate of the equipment, while improving the compatibility of existing QKD systems with classical optical communication systems, and promoting the cost reduction of QKD equipment in the future and the development of integrated communication and encryption.

[0108] Reference below Figure 7 Description of the present invention discloses a digital signal processing flow at the transmitting end.

[0109] Quantum random number generation: used to generate the original quantum key bit sequence to be sent, which requires true randomness.

[0110] Bit-symbol mapping: mapping a random bit sequence into a symbol sequence in a specific coding manner. In the present invention, mapping methods such as QPSK and QAM can be used.

[0111] Upsampling & pulse shaping filtering: Upsampling makes the system sampling rate greater than or equal to the Nyquist rate, and a pulse shaping filter is performed to convert the above symbol sequence into a double-sideband baseband digital signal.

[0112] Up-conversion: The double-sideband digital signal is frequency-shifted and converted into a single-sideband operation. This is because the noise near the zero frequency is usually large, and the signal needs to be moved to a frequency band with less noise.

[0113] Add pilot signal: Generate a single-frequency signal of a specific frequency as an auxiliary pilot signal.

[0114] The digital signal processing flow at the sending end is as follows:

[0115] 1. Use a quantum random number generator to generate two randomly distributed binary bit sequences, and map the binary bits into two QPSK symbol sequences through a bit-symbol mapping module;

[0116] 2. After upsampling, the system sampling rate is greater than or equal to the Nyquist rate, and a pulse shaping filter is used to convert the two QPSK symbol sequences into two bandwidths B. q Double-sideband QPSK baseband digital signal;

[0117] 3. Up-convert the two double-sideband QPSK signals, one of which is converted to the center frequency f q1 , and the other frequency is converted to the center frequency f q2 , forming two single-sideband QPSK baseband digital signals E qx and E qy ;

[0118] 4. Add the pilot signal E to the two single-sideband QPSK baseband digital signals respectively px and E py , the pilot signal is the center frequency f p The power of the pilot signal is usually more than 10dB greater than that of the quantum signal, expressed as:

[0119]

[0120] Where i is the imaginary unit, f p is the center frequency of the pilot signal, and t is the time variable. Both pilot signals are single-frequency sine waves of the same frequency, with the same amplitude and phase.

[0121] The two baseband digital electrical signals after adding the pilot signal can be expressed as:

[0122] E x =E qx +E px

[0123] E y =E qy +E py

[0124] Reference below Figure 8 Description of the invention The digital signal processing flow at the receiving end in the embodiment of the present invention is disclosed.

[0125] Bandpass filtering & down-conversion: The received baseband digital electrical signal containing noise is bandpass filtered to obtain the noisy pilot signal and quantum signal respectively, and a down-conversion operation corresponding to the up-conversion at the transmitting end is performed to convert the single-sideband quantum signal into a double-sideband quantum signal.

[0126] Equalization & demultiplexing: Mainly used to separate two quantum signals with polarization aliasing and eliminate inter-symbol interference generated during channel transmission.

[0127] Frequency offset estimation & phase recovery: Estimate and compensate for the center frequency difference between the transmitting and receiving light sources, as well as the phase noise caused by the linewidth of the two light sources.

[0128] Resampling: Resample the signal to single sampling rate, consistent with the symbol at the sending end.

[0129] Normalization & parameter estimation: Estimate the system shot noise, normalize the signal to the shot noise unit, and estimate the channel parameters.

[0130] Security key rate calculation: Based on the estimated signal parameters, the security key rate is substituted into the theoretical calculation formula to obtain the value of the security key rate, which is used as the basis for determining the security of the system.

[0131] The digital signal processing flow at the receiving end is as follows:

[0132] 1. Perform analog-to-digital conversion on the demodulated electrical signal to obtain a baseband digital electrical signal E′ containing noise x and E′ y Perform bandpass filtering to obtain the noisy pilot signal E′ px , E′ py And the quantum signal E′ qx , E′ qy , and perform a down-conversion operation corresponding to the up-conversion at the transmitting end, converting the single-sideband quantum signal into a double-sideband quantum signal;

[0133] 2. Enter the channel equalization & polarization demultiplexing module. The channel equalization & polarization demultiplexing module algorithm can adopt the most commonly used constant modulus algorithm in classical coherent optical communication, in which the error estimation value of the pilot signal is used to compensate the quantum signal, thereby eliminating the damage such as polarization rotation generated during the channel transmission process;

[0134] 3. Use the frequency offset estimation and phase recovery algorithm in classical coherent optical communication to recover the phase of the pilot signal and quantum signal;

[0135] 4. Downsample the quantum signal to single sampling rate to obtain a symbol sequence corresponding to the QPSK symbol sequence at the transmitting end;

[0136] 5. Normalize the downsampled symbol sequence to the shot noise unit and estimate the channel parameters;

[0137] 6. Based on the estimated signal parameters, the theoretical calculation formula of the security key rate is used to obtain the value of the security key rate, which is used as the basis for determining the security of the system;

[0138] 7. If the security key rate is greater than 0, post-processing operations are performed to obtain the final binary quantum key sequence to achieve key distribution.

[0139] Fig. 9 A schematic diagram of the hardware structure of a transmitting end and a receiving end in an embodiment of the present disclosure is shown, and the transmitting end and the receiving end are described in detail below.

[0140] Transmitter digital signal processing module: used to generate the original quantum key bits to be sent, and perform specific encoding and modulation on them to form a baseband electrical signal.

[0141] IQ modulator: Mainly used to modulate the baseband electrical signal onto the optical carrier emitted by the laser to achieve electro-optical conversion.

[0142] Adjustable attenuator: used to attenuate the modulated optical signal power to the quantum state, so that the canonical component of the light field has quantum mechanical properties.

[0143] Polarization coupler: A device used to achieve polarization multiplexing.

[0144] Quantum channel: Generally, you can choose optical fiber channel or free space channel.

[0145] Polarization controller: Preliminarily eliminates signal polarization state rotation caused by channel transmission through hardware control;

[0146] Heterodyne detector: used to recover the original baseband electrical signal from the received optical signal;

[0147] Digital signal processing module at the receiving end: performs a series of noise compensation processing on the electrical signal output by the detector, and restores the quantum key bit data generated by the sending end.

[0148] The hardware processing flow of the system transceiver is as follows:

[0149] 1. The digital signal processing module at the transmitting end generates two polarization state optical signals S x and S y The corresponding baseband digital complex electrical signal E x and E y , respectively expressed as:

[0150] E x =E x-real +iE x-imag

[0151] E y =E y-real +iE y-imag

[0152] 2. The digital-to-analog converter converts E x-real 、E x-imag 、E y-real 、E y-imag Four digital electrical signals are converted into analog electrical signals, among which Ex-real 、E x-imag As the electrical driving signal of the first IQ modulator, E y-real 、E y-imag as an electrical drive signal for a second IQ modulator;

[0153] 3. The optical signal emitted by the first continuous laser is split into two paths by the first beam splitter, which are used as input optical carrier signals of the first IQ modulator and the second IQ modulator respectively;

[0154] 4. After two IQ modulators, E x and E y Modulate onto respective optical carrier signals to form two optical signals, which are then coupled through polarization couplers to form two multiplexed signals in two perpendicular polarization states, X and Y.

[0155] 5. The polarization multiplexed signal is attenuated to a quantum state by an adjustable optical attenuator, and then transmitted through a quantum channel;

[0156] 6. The received signal after quantum channel transmission is divided into two optical signals with mutually perpendicular polarization states through a polarization beam splitter, which are denoted as S′. x and S′ y ; At the same time, the second continuous laser is divided into two signals through the second beam splitter, which are used as local oscillator signals of two heterodyne detectors respectively;

[0157] 7. S′ x and S′ y The two local oscillator signals are respectively input into a first heterodyne detector and a second heterodyne detector to realize photoelectric conversion and obtain electrical signals;

[0158] 8. Perform analog-to-digital conversion on the demodulated electrical signal to obtain a baseband digital electrical signal E′ containing noise x and E′ y , respectively expressed as:

[0159] E′ x =E′ x-real +iE′ x-imag

[0160] E′ y =E′ y-real +iE′ y-imag

[0161] 9. E′ x-real , E′ x-imag , E′ y-real , E′ y-imag Input to the digital signal processing link at the receiving end for subsequent noise compensation and key generation.

[0162] In the embodiments of the present disclosure, the terms “first”, “second” and “third” are used for descriptive purposes only and should not be understood as indicating or implying relative importance.

[0163] The term "and / or" in this disclosure is only a description of the association relationship of associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0164] Furthermore, although the steps of the method in the present disclosure are described in a particular order in the drawings, this does not require or imply that the steps must be performed in this particular order or that all the steps shown must be performed to achieve the desired results.

[0165] In some embodiments, certain steps may be omitted, multiple steps may be combined into one step, and / or one step may be decomposed into multiple steps.

[0166] The concepts of “first”, “second”, etc. mentioned in the present disclosure are only used to distinguish different devices, modules or units, and are not used to limit the order or interdependence of the functions performed by these devices, modules or units.

[0167] It should be noted that, although several modules or units of the device for action execution are mentioned in the above detailed description, such division is not mandatory.

[0168] In fact, according to the embodiments of the present disclosure, the features and functions of two or more modules or units described above can be embodied in one module or unit. Conversely, the features and functions of one module or unit described above can be further divided into multiple modules or units to be embodied.

[0169] Some of the blocks shown in the accompanying drawings are functional entities that do not necessarily correspond to physically or logically independent entities. These functional entities can be implemented in software form, or in one or more hardware modules or integrated circuits, or in different networks and / or processor devices and / or microcontroller devices.

[0170] Refer to the following Fig.10 To describe the electronic device provided by the embodiment of the present disclosure. Fig.10 The electronic device 1000 shown is merely an example and should not bring any limitation to the functions and scope of use of the embodiments of the present disclosure.

[0171] Fig.10 FIG. 1 is a schematic diagram showing the architecture of an electronic device 1000 provided by an embodiment of the present disclosure. Fig.10 As shown, the electronic device 1000 includes but is not limited to: at least one processor 1010 and at least one memory 1020 .

[0172] The memory 1020 is used to store instructions.

[0173] In some embodiments, the memory 1020 may include a readable medium in the form of a volatile storage unit, such as a random access memory unit (RAM) 10201 and / or a cache memory unit 10202 , and may further include a read-only memory unit (ROM) 10203 .

[0174] In some embodiments, memory 1020 may also include a program / utility 10204 having a set (at least one) of program modules 10205, such program modules 10205 including but not limited to: an operating system, one or more application programs, other program modules, and program data, each of which or some combination may include an implementation of a network environment.

[0175] In some embodiments, the memory 1020 may store an operating system, which may be a real-time operating system (RTX), LINUX, UNIX, WINDOWS, or OS X.

[0176] In some embodiments, data may also be stored in the memory 1020 .

[0177] As an example, the processor 1010 may read data stored in the memory 1020 , where the data may be stored at the same storage address as the instruction, or the data may be stored at a different storage address than the instruction.

[0178] The processor 1010 is configured to call the instructions stored in the memory 1020 to implement the steps of various exemplary embodiments of the present disclosure described in the above “Exemplary Method” section of this specification. For example, the processor 1010 may execute the steps of the above-mentioned signal processing method embodiment in continuous variable quantum key distribution.

[0179] It should be noted that the processor 1010 may be a general-purpose processor or a special-purpose processor. The processor 1010 may include one or more processing cores, and the processor 1010 executes various functional applications and data processing by running instructions.

[0180] In some embodiments, the processor 1010 may include a central processing unit (CPU) and / or a baseband processor.

[0181] In some embodiments, the processor 1010 may determine an instruction according to the priority identifier and / or function category information carried in each control instruction.

[0182] In the present disclosure, the processor 1010 and the memory 1020 may be provided separately or integrated together.

[0183] As an example, the processor 1010 and the memory 1020 may be integrated on a single board or a system on chip (SOC).

[0184] like Fig.10 As shown, the electronic device 1000 is in the form of a general-purpose computing device. The electronic device 1000 may further include a bus 1030 .

[0185] The bus 1030 may represent one or more of several types of bus structures, including a memory bus or memory controller, a peripheral bus, an accelerated graphics port, a processor, or a local bus using any of a variety of bus architectures.

[0186] The electronic device 1000 may also communicate with one or more external devices 1040 (e.g., keyboards, pointing devices, Bluetooth devices, etc.), one or more devices that enable a user to interact with the electronic device 1000, and / or any device that enables the electronic device 1000 to communicate with one or more other computing devices (e.g., routers, modems, etc.). Such communication may be performed through an input / output (I / O) interface 1050.

[0187] Furthermore, the electronic device 1000 can also communicate with one or more networks (eg, a local area network (LAN), a wide area network (WAN) and / or a public network, such as the Internet) through the network adapter 1060 .

[0188] like Fig.10 As shown, the network adapter 1060 communicates with other modules of the electronic device 1000 via the bus 1030 .

[0189] It should be understood that although not shown in the figures, other hardware and / or software modules may be used in conjunction with the electronic device 1000, including but not limited to: microcode, device drivers, redundant processing units, external disk drive arrays, RAID systems, tape drives, and data backup storage systems.

[0190] It is understood that the structure shown in the embodiment of the present disclosure does not constitute a specific limitation on the electronic device 1000. In other embodiments of the present disclosure, the electronic device 1000 may include Fig.10More or fewer components may be shown, or some components may be combined or separated, or the components may be arranged differently. Fig.10 The components shown may be implemented in hardware, software or a combination of software and hardware.

[0191] The present disclosure also provides a computer-readable storage medium having computer instructions stored thereon. When the computer instructions are executed by a processor, the signal processing method in the continuous variable quantum key distribution described in the above method embodiment is implemented.

[0192] The computer-readable storage medium in the embodiments of the present disclosure is a computer instruction that can be sent, propagated or transmitted for use by or in conjunction with an instruction execution system, apparatus or device.

[0193] As one example, computer readable storage media are non-volatile storage media.

[0194] In some embodiments, more specific examples of computer-readable storage media in the present disclosure may include, but are not limited to: an electrical connection with one or more wires, a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, a USB flash drive, a mobile hard disk, or any suitable combination of the foregoing.

[0195] In the embodiments of the present disclosure, the computer-readable storage medium may include a data signal propagated in a baseband or as a part of a carrier wave, in which computer instructions (readable program codes) are carried.

[0196] Such a propagated data signal may take a variety of forms, including but not limited to electromagnetic signals, optical signals, or any suitable combination of the foregoing.

[0197] In some examples, computing instructions contained on a computer-readable storage medium may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber cable, RF, etc., or any suitable combination of the foregoing.

[0198] The embodiments of the present disclosure also provide a computer program product, which stores instructions. When the instructions are executed by a computer, the computer implements the signal processing method in continuous variable quantum key distribution described in the above method embodiment.

[0199] The above instructions may be program codes. In specific implementation, the program codes may be written in any combination of one or more programming languages.

[0200] The programming language includes object-oriented programming languages, such as Java, C++, etc., and also includes conventional procedural programming languages, such as "C" language or similar programming languages.

[0201] The program code may execute entirely on the user's computing device, partly on the user's computing device, as a stand-alone software package, partly on the user's computing device and partly on a remote computing device or entirely on the remote computing device or server.

[0202] Where a remote computing device is involved, the remote computing device may be connected to the user computing device through any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computing device (e.g., through the Internet using an Internet service provider).

[0203] The embodiment of the present disclosure also provides a chip, including at least one processor and an interface;

[0204] An interface for providing program instructions or data to at least one processor;

[0205] At least one processor is used to execute program instructions to implement the signal processing method in continuous variable quantum key distribution described in the above method embodiment.

[0206] In some embodiments, the chip may further include a memory, which is used to store program instructions and data, and the memory is located inside or outside the processor.

[0207] Those skilled in the art will appreciate that all or part of the steps for implementing the above embodiments may be implemented in the following forms, namely: a complete hardware implementation, a complete software implementation (including firmware, microcode, etc.), or a combination of hardware and software implementations, which may be collectively referred to herein as "circuits", "modules" or "systems".

[0208] Other embodiments of the disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein.

[0209] The present disclosure is intended to cover any variation, use or adaptation of the present disclosure, which follows the general principles of the present disclosure and includes common knowledge or customary technical means in the technical field not disclosed in the present disclosure. The description and examples are to be regarded as exemplary only, and the true scope and spirit of the present disclosure are indicated by the appended claims.

Claims

1. A signal processing method in continuous variable quantum key distribution, characterized in that: include: Performing up-conversion operation on the two double-sideband quadrature phase-shift keying signals to respectively convert the frequencies to a first center frequency and a second center frequency to form a first quantum signal in an X polarization direction and a first quantum signal in a Y polarization direction, wherein the first center frequency and the second center frequency are different; Adding a first pilot signal in the X-polarization direction to the first quantum signal in the X-polarization direction to obtain a first optical signal in the X-polarization direction; Adding a first pilot signal in the Y polarization direction to the first quantum signal in the Y polarization direction to obtain a first optical signal in the Y polarization direction; wherein the center frequencies of the first pilot signal in the X polarization direction and the first pilot signal in the Y polarization direction are a third center frequency, and the third center frequency is different from both the first center frequency and the second center frequency; Using a polarization coupler to combine the first optical signal in the X polarization direction and the first optical signal in the Y polarization direction into a polarization multiplexed signal; The polarization multiplexing signal is sent to a receiving end through a quantum channel.

2. The method according to claim 1, characterized in that: The first quantum signal in the X polarization direction is a single sideband quadrature phase shift keying signal having a center frequency of the first center frequency and a bandwidth of the first bandwidth; the first quantum signal in the Y polarization direction is a single sideband quadrature phase shift keying signal having a center frequency of the second center frequency and a bandwidth of the first bandwidth; the first pilot signal in the X polarization direction and the first pilot signal in the Y polarization direction are single frequency signals having a center frequency of the third center frequency; The difference between the first center frequency and the third center frequency is greater than half of the first bandwidth, and the difference between the second center frequency and the first center frequency is greater than the first bandwidth.

3. The method according to claim 3, characterized in that: Before performing up-conversion operation on the two double-sideband quadrature phase-shift keying signals, the method further comprises: Using a quantum random number generator to generate a first bit sequence and a second bit sequence, wherein the first bit sequence and the second bit sequence are randomly distributed binary bit sequences; Based on a preset mapping rule, mapping the first bit sequence and the second bit sequence to a first orthogonal phase shift keying symbol sequence and a second orthogonal phase shift keying symbol sequence respectively; The first quadrature phase shift keying symbol sequence and the second quadrature phase shift keying symbol sequence are up-sampled and pulse-shaped filtered to obtain two double-sideband quadrature phase shift keying signals with a bandwidth equal to the first bandwidth.

4. The method according to claim 1, characterized in that: The step of sending the polarization multiplexing signal to a receiving end through a quantum channel comprises: Using an optical attenuator to attenuate the quantum signal portion in the polarization multiplexed signal to a quantum state; The polarization multiplexed signal decayed into a quantum state is sent to the receiving end.

5. A continuous variable quantum key distribution system, characterized in that: include: At the transmitting end, two double-sideband quadrature phase-shift keying signals are up-converted to a first center frequency and a second center frequency, respectively, to form a first quantum signal in an X polarization direction and a first quantum signal in a Y polarization direction, wherein the first center frequency and the second center frequency are different; a first pilot signal in an X polarization direction is added to the first quantum signal in the X polarization direction to obtain a first optical signal in the X polarization direction; and a first pilot signal in a Y polarization direction is added to the first quantum signal in the Y polarization direction to obtain a first optical signal in the Y polarization direction; wherein the center frequencies of the first pilot signal in the X polarization direction and the first pilot signal in the Y polarization direction are a third center frequency, and the third center frequency is different from both the first center frequency and the second center frequency; a polarization coupler is used to combine the first optical signal in the X polarization direction and the first optical signal in the Y polarization direction into a polarization multiplexing signal; and the polarization multiplexing signal is sent to the receiving end through a quantum channel; The receiving end receives the polarization multiplexing signal.

6. The system according to claim 5, characterized in that The first quantum signal in the X polarization direction is a single sideband quadrature phase shift keying signal having a center frequency of the first center frequency and a bandwidth of the first bandwidth; the first quantum signal in the Y polarization direction is a single sideband quadrature phase shift keying signal having a center frequency of the second center frequency and a bandwidth of the first bandwidth; the first pilot signal in the X polarization direction and the first pilot signal in the Y polarization direction are single frequency signals having a center frequency of the third center frequency; The difference between the first center frequency and the third center frequency is greater than half of the first bandwidth, and the difference between the second center frequency and the first center frequency is greater than the first bandwidth.

7. The system according to claim 6, characterized in that The transmitting end also applies a quantum random number generator to generate a first bit sequence and a second bit sequence, wherein the first bit sequence and the second bit sequence are randomly distributed binary bit sequences; based on a preset mapping rule, the first bit sequence and the second bit sequence are respectively mapped to a first orthogonal phase shift keying symbol sequence and a second orthogonal phase shift keying symbol sequence; the first orthogonal phase shift keying symbol sequence and the second orthogonal phase shift keying symbol sequence are upsampled, and pulse shaping filtering is performed to obtain two double-sideband orthogonal phase shift keying signals with a bandwidth of the first bandwidth.

8. The system according to claim 7, characterized in that The receiving end further divides the polarization multiplexing signal into a second optical signal in an X polarization direction and a second optical signal in a Y polarization direction through a polarization beam splitter; performs photoelectric conversion based on the second optical signal in the X polarization direction and a local local oscillator signal to obtain a first electrical signal; performs photoelectric conversion based on the second optical signal in the Y polarization direction and a local local oscillator signal to obtain a second electrical signal; performs analog-to-digital conversion on the first electrical signal and the second electrical signal to obtain a first baseband digital electrical signal and a second baseband digital electrical signal; The first baseband digital electrical signal and the second baseband digital electrical signal are used in a key generation process.

9. The system according to claim 8, characterized in that The receiving end further performs bandpass filtering on the first baseband digital electrical signal and the second baseband digital electrical signal to obtain a second quantum signal in an X polarization direction and a second quantum signal in a Y polarization direction; A down-conversion operation corresponding to the up-conversion at the transmitting end is performed on the second quantum signal in the X polarization direction and the second quantum signal in the Y polarization direction, and the second quantum signal in the X polarization direction and the second quantum signal in the Y polarization direction are converted into double-sideband quantum signals.

10. The system according to claim 9, characterized in that The receiving end performs bandpass filtering on the first baseband digital electrical signal and the second baseband digital electrical signal to obtain a second pilot signal in an X polarization direction and a second pilot signal in a Y polarization direction; Based on the first pilot signal in the X polarization direction and the first pilot signal in the Y polarization direction, and the second pilot signal in the X polarization direction and the second pilot signal in the Y polarization direction, an error estimate value of the pilot signal is calculated; and the second quantum signal in the X polarization direction and the second quantum signal in the Y polarization direction are compensated by using the error estimate value through a constant modulus algorithm.

11. The system according to claim 10, characterized in that The receiving end also recovers the phases of the second pilot signal in the X polarization direction, the second pilot signal in the Y polarization direction, the second quantum signal in the X polarization direction, and the second quantum signal in the Y polarization direction by using a frequency offset estimation and a phase recovery algorithm.

12. The system according to claim 11, characterized in that The receiving end also downsamples the double-sideband quantum signal to a single sampling rate to obtain a third orthogonal phase shift keying symbol sequence and a fourth orthogonal phase shift keying symbol sequence; normalizes the third orthogonal phase shift keying symbol sequence and the fourth orthogonal phase shift keying symbol sequence to a shot noise unit, and estimates channel parameters; Based on the estimated signal parameters, the security key rate is calculated using a theoretical calculation formula for the security key rate; when the security key rate is greater than 0, a post-processing operation is performed to obtain a binary quantum key sequence.

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