A Polarization Compensation Method and System for CV-QKD Continuous Variable Quantum Key Distribution

Abstract

The present invention discloses a polarization compensation method and system for CV-QKD continuous variable quantum key distribution. The method includes: introducing reference light 1 and reference light 2, and estimating the polarization state of the quantum signal light through the polarization change amounts of two reference lights with alternating polarization directions. Specifically, in the vertical polarization direction, the quantum light and reference light 1 are time-division multiplexed according to a preset ratio, and then polarization multiplexed with reference light 2 in the horizontal polarization direction. At the same time, the missing pilot light data is complemented by interpolation method so that there are two adjacent groups of reference light data for estimating the polarization change amount of the quantum signal light. By introducing reference light, the present invention facilitates phase recovery at the receiving end, and at the receiving end, the polarization state of the quantum signal light can be estimated by measuring the polarization change amount of the classical reference light. At the same time, the classical reference light and the quantum signal light can reduce the intensity of their interaction and reduce the excess noise of the system through forms such as polarization multiplexing, time-division multiplexing, and frequency-division multiplexing.

Description

Technical Field

[0001] The present invention belongs to the technical field of quantum secure communication, and particularly relates to a polarization compensation method and system for continuous variable quantum key distribution (CV-QKD). Background Art

[0002] In recent years, network security incidents have occurred frequently, directly threatening the stability of the real world. Network security has become an issue that has to be faced. Although traditional encryption means and their evolved technologies can further strengthen the network security defense line, due to the development of technologies such as quantum computing, it is difficult to ensure absolute communication security. With the development of quantum physics and quantum information theory, quantum cryptography based on the principles of quantum mechanics has been proven to have unconditional security in the sense of information theory. Among them, the most representative technology is to achieve secure online key sharing between communication parties through quantum technology, that is, quantum key distribution (QKD). QKD mainly includes two major technical approaches: discrete variable and continuous variable. Continuous Variable Quantum Key Distribution (CV-QKD) uses the quadrature components of quantum optical fields as information carriers, and has the advantages of high secure bit rate within medium and short transmission distances and being compatible with most devices of traditional optical communication. It is an important development direction of quantum key distribution technology.

[0003] In a CV-QKD system based on fiber optic link transmission, the quantum signal light is inevitably affected by various effects, resulting in an increase in the system excess noise, thereby affecting the secure bit rate of the system. It generally includes polarization random perturbation, laser linewidth and wavelength drift, link dispersion and nonlinear scattering, etc. At the quantum signal receiving end, the CV-QKD system often adopts coherent detection technology. The polarization random perturbation in the optical fiber makes the polarization state of the quantum signal emitted from the Alice side unable to maintain alignment with the polarization main axis of the Bob side, resulting in unstable coherent detection, and further leading to a decrease in the detection efficiency of the quantum state. In addition, when separating the polarization multiplexed pulses at the Bob side, due to the limited polarization extinction ratio of the polarization beam splitter (PBS), a part of the photons will remain in the reference path and leak into the signal path. This leads to an increase in the system excess noise, and further affects the secure bit rate of the system.

[0004] Based on the above analysis, the polarization compensation problem in the optical fiber is one of the core problems restricting the secure bit rate of the system. Therefore, polarization compensation is a crucial step to obtain a high secure bit rate, significantly affecting the overall security and key generation rate of the system.

[0005] The CV-QKD system includes the generation, transmission, detection, and data post-processing of quantum information, and its overall block diagram is as Figure 1 shown. The main steps are as follows:

[0006] 1) The transmitting end (Alice) first prepares a quantum state. The light generated by a continuous light source serves as a carrier, and then the signal to be modulated is loaded onto the carrier.

[0007] 2) The quantum signal light and the classical reference light use time-division / frequency-division / polarization multiplexing technology to increase the isolation degree, reduce the crosstalk from the classical reference light to the quantum signal light, and at the same time improve the multiplexing rate of the optical fiber channel. Then, it is transmitted through the optical fiber quantum channel.

[0008] 3) Subsequently, the receiving end (Bob) first divides the signal into two paths through a polarization beam splitter (PBS), and then converts the optical signal into an electrical signal through coherent detection technology to initially obtain the detection result.

[0009] 4) Next, Bob uses digital signal processing (DSP) technology on the signal in the digital domain to achieve polarization compensation and phase compensation of the quantum signal, and obtains the original key signal.

[0010] 5) Finally, post-processing of the original key signal is performed, including basis comparison (optional), parameter estimation, data negotiation, private key amplification, etc., to remove the part of the information obtained by the eavesdropper, so that the key reaches information-theoretic security.

[0011] In current CV-QKD experiments, the polarization compensation scheme is mainly divided into two types. One is the active compensation scheme, which uses a manual polarization controller (MPC) to control the change of the polarization state. However, this device has a certain insertion loss, which will directly reduce the detection efficiency of the quantum signal at the receiving end. At the same time, this device cannot track the polarization jitter caused by environmental impacts in real time, thus introducing excessive noise. And the commercial dynamic polarization controller (DPC) requires a high-power feedback optical signal, which will introduce a greater insertion loss and has a weak tracking ability for polarization random perturbations. The other is the passive compensation scheme, which uses a digital signal processing algorithm to estimate the polarization change of the quantum signal and perform polarization compensation in the digital domain. Although the active compensation scheme is a commonly used polarization compensation scheme in laboratories, it requires additional optoelectronic devices to complete the polarization detection and compensation of the optical field, with high system complexity, large volume, and high cost. The passive compensation scheme does not require additional optoelectronic devices, has controllable costs, is easier to integrate, and is the preferred scheme for CV-QKD productization. Previous electrical domain polarization control schemes all have disadvantages to varying degrees:

[0012] 1) Time-division multiplexing scheme: As Figure 4 shown, only using the time-division multiplexing scheme has the disadvantage that the isolation degree between the classical light and the quantum light is poor, resulting in a large crosstalk from the classical reference light to the quantum signal light.

[0013] 2) Time-division + single-polarization multiplexing scheme: AsFigure 5 As shown in Figure 5 , in the classical light and quantum light polarization direction separation scheme adopted in the past, the advantage is that the isolation degree between the classical reference light and the quantum signal light is maximized, greatly reducing crosstalk. However, the obvious disadvantage is that after passing through the optical fiber channel, the quantum light and the classical light are very likely to no longer be perpendicular, losing the accuracy of polarization compensation, resulting in residual error after polarization compensation, and the estimated accuracy is difficult to meet the requirements of high-precision polarization compensation, ultimately limiting the actual security bit rate of the system.

[0014] 3) Frequency division + polarization multiplexing scheme: In the past, the scheme of using frequency division multiplexing of classical light and quantum light has relatively high system complexity and is not conducive to practical application.

[0015] In summary, according to the existing technology, it is impossible to effectively control the excess noise of the system. At the same time, inaccurate polarization estimation will limit the accuracy of digital domain polarization compensation, resulting in residual error after polarization compensation, and the estimated accuracy is difficult to meet the requirements of high-precision polarization compensation, ultimately limiting the actual security bit rate of the system. Summary of the Invention

[0016] The purpose of the present invention is to disclose a polarization compensation method and system for CV-QKD continuous variable quantum key distribution to overcome the problems of the existing technology. In the local local oscillator CV-QKD system of the present invention, by introducing reference light, on the one hand, it is convenient for phase recovery at the receiving end, and on the other hand, the polarization state of the quantum signal light can be estimated by measuring the polarization change amount of the classical reference light at the receiving end; at the same time, the classical reference light and the quantum signal light can reduce the intensity of their interaction and reduce the excess noise of the system through forms such as polarization multiplexing, time division multiplexing, and frequency division multiplexing.

[0017] On the one hand, the purpose of the present invention is achieved through the following technical solutions:

[0018] A polarization compensation method for CV-QKD continuous variable quantum key distribution, characterized in that the continuous variable quantum key distribution polarization compensation method includes: introducing reference light 1 and reference light 2, and estimating the polarization state of the quantum signal light through the polarization change amounts of two reference lights that alternately appear in two polarization directions;

[0019] Specifically, in the vertical polarization direction, the quantum light and reference light 1 are time division multiplexed according to a preset ratio, and then polarization multiplexed with reference light 2 in the horizontal polarization direction. At the same time, the missing pilot light data is complemented by interpolation method so that there are two adjacent groups of reference light data for estimating the polarization change amount of the quantum signal light.

[0020] According to a preferred embodiment, the process of polarization control of the reference light and the quantum signal light includes the following steps:

[0021] A. At the transmitting end, the repetition frequency of the signal light pulse is frep , the frequencies of the two reference optical pulses are f pilot , time-shift reference light 1 by 1 / 2f relative to the quantum signal light rep , perform time-division multiplexing with the quantum signal light, and adjust the polarization direction to vertical through polarization controller 1;

[0022] B. At the sending end, time-shift reference light 2 by -1 / 2f relative to the quantum signal light rep , adjust the polarization direction to horizontal through polarization controller 2, then combine the light signals with vertical polarization direction in A for polarization multiplexing, and transmit through the fiber optic quantum channel;

[0023] C. At the receiving end, initially orthogonally receive the two signal lights through a polarization beam splitter, then perform coherent detection to obtain two electrical signals, and finally complete time-division demultiplexing and polarization demultiplexing in the digital domain;

[0024] D. After converting the optical signal to the digital domain, perform polarization compensation through digital signal processing methods.

[0025] According to a preferred embodiment, in step D, the digital signal processing methods include: CMA constant modulus algorithm, Stokes algorithm, Kalman filtering algorithm.

[0026] According to a preferred embodiment, the polarization compensation in step D includes: first, complete the reference signals of two polarization directions at adjacent positions of the quantum signal through interpolation method, then estimate the polarization state of the intermediate quantum signal through the polarization change amount of the reference signals of two adjacent polarization directions, calculate the corresponding Jones matrix, and inversely solve to obtain the original information at the sending end.

[0027] According to a preferred embodiment, the interpolation method includes: Lagrange interpolation, Hermite interpolation, Newton interpolation, piecewise interpolation, cubic spline interpolation, multi-dimensional interpolation.

[0028] On the other hand, the present invention also discloses:

[0029] A CV-QKD system, the CV-QKD system operates based on the foregoing CV-QKD continuous variable quantum key distribution polarization compensation method; the CV-QKD system includes: a sending end and a receiving end, and the sending end is connected through a transmission optical fiber; the sending end is used to realize the preparation and modulation of the quantum signal light, and the receiving end is used to realize the reception and detection of the quantum signal light.

[0030] According to a preferred embodiment, the sending end includes a continuous light source, beam splitter 1, beam splitter 2, combiner, polarization controller 1, polarization controller 2, and polarization combiner;

[0031] The beam splitter 1 splits the optical signal input by the continuous light source to generate a reference light 2 and the input optical signal of the beam splitter 2. The beam splitter 2 splits the received optical signal to generate a quantum signal light and a reference light 1.

[0032] The light beam of the quantum signal light after passing through the optical attenuator 1 and the light beam of the reference light 1 after passing through the optical attenuator 2 are respectively input into a combiner for beam combining processing, and after the beam combining processing, they are input into a polarization controller 1 for polarization direction adjustment.

[0033] The reference light 2 is input into a polarization controller 2 for polarization direction adjustment after passing through the optical attenuator 3.

[0034] The light beams with their polarization directions adjusted by the polarization controller 1 and the polarization controller 2 are polarization multiplexed by a polarization beam combiner, and then transmitted to the receiving end through an optical fiber quantum channel.

[0035] The CV-QKD system operates under low signal-to-noise ratio conditions and needs to control the excess noise at a low level. However, the crosstalk of the strong classical reference light on the quantum signal light has a great impact, which in turn leads to a high excess noise in the system and affects the system's secure bit rate. By adopting time-division multiplexing and pilot light dual-polarization multiplexing technologies, on the one hand, the isolation degree between the classical reference light and the quantum signal light can be greatly improved, reducing the photon leakage of the classical reference light to the quantum signal light, that is, crosstalk. Thus, the excess noise of the system can be kept at a low level. On the other hand, through the alternating multiplexing of the reference lights in two polarization directions and complementing the missing pilot light data by interpolation method, there are two adjacent sets of reference light data to estimate the polarization change amount of the quantum signal light, which will greatly improve the accuracy of polarization estimation and effectively improve the core index of the system - the secure bit rate. The proposed scheme of this method can achieve high-precision polarization estimation in two polarization directions by adding an additional reference light. Compared with the previous patent schemes, the scheme proposed in this patent can achieve smaller excess noise and higher secure bit rate, is suitable for realizing efficient polarization compensation, and has a wider application scenario.

[0036] In order to improve the accuracy of polarization estimation of the signal light, the interpolation method is adopted to calculate the virtual pilot pulses Pilot1’ and Pilot2’ at the missing positions at the Bob side, so that the polarization states of the adjacent signal lights can be well estimated. The significant advantage of the present invention is that when calculating the pilot pulses at the missing positions by the interpolation method, as much experimental data as possible is used, and then the polarization states of the intermediate signal lights are estimated by two adjacent sets of pilot light data with perpendicular polarization directions. Therefore, compared with the previous schemes, the accuracy will be higher.

[0037] The overall strategy of the present invention is to perform time-division multiplexing of the signal light and the reference light 1 in a certain ratio (such as 2:1) in the vertical polarization direction; at the same time, in the horizontal polarization direction, the reference light 2 with a pulse ratio of 1:1 to the reference light 1 is used to perform reverse time shift at the same time interval, and then polarization multiplexing is performed with the mixed light pulse in the vertical polarization direction. Signal detection and polarization demultiplexing are performed at the Bob end, specifically including transforming the data after coherent detection into the digital domain through an analog-to-digital converter ADC, and estimating the change amount of the polarization states of the reference light and the signal light through digital signal processing technologies such as the CMA constant modulus algorithm, the Stokes algorithm, and the Kalman filtering technology, so as to achieve high-precision polarization compensation in the digital domain, thereby improving the security bit rate of the system.

[0038] The additional reference light in the horizontal polarization direction in the present invention has two functions during the entire polarization demultiplexing stage: one is to provide data support for the interpolation method based on the coherent detection result and the polarization change amount of the reference light in the vertical polarization direction, so as to achieve the purpose of accurately estimating the polarization state of the quantum signal light using two adjacent groups of polarization-multiplexed reference lights; the other is to facilitate verifying the different effects of the optical fiber channel on different polarization directions, further studying its influence mechanism, thereby improving the accuracy of polarization compensation in CV-QKD and achieving a higher security bit rate.

[0039] The main solution of the present invention and its various further alternative solutions can be freely combined to form multiple solutions, all of which are the solutions that can be adopted and claimed by the present invention. Those skilled in the art can understand that there are various combinations according to the prior art and common general knowledge after understanding the solution of the present invention, all of which are the technical solutions to be protected by the present invention, and will not be enumerated here.

[0040] Advantages of the present invention:

[0041] The present invention proposes to design dual-polarization pilot-assisted polarization compensation based on digital signal processing technology in a local local oscillator CV-QKD system, which can solve the problems of inter-mode crosstalk and polarization compensation accuracy faced by the polarization-multiplexed local local oscillator CV-QKD system. By performing time-division / polarization multiplexing of the signal light and two alternately appearing pilot lights, while improving the channel utilization rate, it will also effectively reduce the excess noise of the system.

[0042] At the same time, the missing pilot light data can be completed by the interpolation method, so that there are two adjacent groups of reference light data used to estimate the polarization change amount of the quantum signal light, which will greatly improve the accuracy of polarization estimation, and then improve the security bit rate of the CV-QKD system.

[0043] In addition, it can also provide a reference for studying the influence of the optical fiber channel on different polarization directions, and study the difference in the sensitivity of the two polarization directions to polarization perturbation in the actual optical fiber link. Brief description of the drawings

[0044] Figure 1 It is the overall block diagram of polarization multiplexing in the existing CV-QKD system;

[0045] Figure 2 It is the block diagram of the transmitter structure of the CV-QKD system of the present invention;

[0046] Figure 3 It is the block diagram of the receiver structure of the CV-QKD system of the present invention;

[0047] Figure 4 It is the time domain and polarization state of quantum and pilot signals in time division multiplexing;

[0048] Figure 5 It is the time domain and polarization state of quantum and pilot signals in the time division + single polarization multiplexing scheme;

[0049] Figure 6 It is the time domain and polarization state of quantum and pilot signals in the time division + double polarization multiplexing proposed by the present invention;

[0050] Figure 7 It is the schematic diagram of pilot-assisted polarization multiplexing - interpolation method. Detailed implementation manners

[0051] The following uses specific specific examples to illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation manners, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0052] It should be noted that: Similar reference numerals and letters represent similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0053] Embodiment 1:

[0054] This embodiment discloses a CV-QKD system. Referring to Figure 2 , Figure 3 and Figure 6 shown, Figure 2 shows the transmitter of the CV-QKD system, which is also called Alice in this embodiment; Figure 3 shows the receiver of the CV-QKD system, which is also called Bob in this embodiment, Figure 6 is the time domain and polarization state of quantum and pilot signals in the time division + double polarization multiplexing proposed by the present invention.

[0055] The polarization compensation process of the continuous variable quantum key distribution (CV-QKD) system mainly includes the following steps:

[0056] (1) At the transmitter Alice of the CV-QKD system, a 1550 nm continuous light source is modulated by two cascaded amplitude modulators into optical pulses with a pulse width of 4 ns, a repetition frequency f rep of 25 MHz, and a duty cycle of 10%. A beam splitter 1 with a splitting ratio of 50:50 is used to split the laser pulse train into two optical pulses in the upper and lower branches.

[0057] (2) The upper branch passes through a beam splitter 2 according to a splitting ratio of 10:90, and is divided into a weak signal light signal and a strong reference light 1. Among them, the quantum signal light completes Gaussian modulation through an amplitude modulator AM and a phase modulator PM, and the reference light 1 undergoes a delay of 1 / 2f rep and then is time-division multiplexed with the quantum light. The lower branch forms a strong reference light field 2, undergoes a delay of -1 / 2f rep and then is polarization multiplexed with the upper branch for transmission.

[0058] (3) At the receiver, heterodyne detection is used to obtain output electrical signal 1 and output electrical signal 2, which are converted to the digital domain for polarization demultiplexing. Among them, electrical signals 1 and 2 have not undergone time-division and polarization demultiplexing, and the next step will be to implement demultiplexing in the digital domain.

[0059] (4) Through DSP, time-division demultiplexing is performed to obtain the quantum signal light and reference light 1. By using the Lagrangian interpolation method with reference light 1 and reference light 2, the polarization information of the virtual reference light at the missing position in the other polarization direction is calculated. As Figure 7 shown, the polarization change of the reference light in the two polarization directions on both sides of each quantum light is obtained.

[0060] (5) According to the polarization change of the reference light in the two polarization directions on both sides of the quantum signal light pulse, the polarization state of the intermediate quantum light is estimated, so as to achieve high-precision polarization compensation for CV-QKD.

[0061] Utilizing the characteristics of fast hardware data processing speed and good real-time performance of FPGA, the polarization control algorithm is quickly run to search for the target polarization state, realizing high-speed polarization locking in the case of pulsed light. The balanced heterodyne detector at Bob's end is used to measure the quadrature components of the optical field. The classical channel authenticated between Alice and Bob is used to evaluate the system parameters and perform data post-processing.

[0062] Furthermore, in the present invention, to save channel resources, a pilot light alternating polarization multiplexing scheme is adopted. Meanwhile, to improve the accuracy of polarization estimation of the signal light, the Lagrange interpolation method can be used to calculate the missing pilot pulses Pilot1' and Pilot2' at the Bob side. After the missing pilot pulses are estimated, the polarization states of the adjacent signal lights can be well estimated. The significant advantage of this scheme is that two adjacent sets of pilot lights with perpendicular polarization directions are used to estimate one signal light, and the accuracy is much greater than the method of directly using the adjacent pilot lights to estimate the polarization state of the signal light in the previous schemes.

[0063] Estimate Pilot1' and Pilot2' using the Lagrange interpolation method:

[0064] Given n interpolation nodes x1, x2, …, x n and the corresponding function values y1, y, …, y n , using the nth-degree Lagrange interpolation polynomial formula where, the function value of any x at the missing part can be calculated as y(x) = L n (x). Using the Lagrange interpolation method can make the most of the measured pilot light data, relatively accurately estimate the virtual Pilot1' and Pilot2', and thus more accurately estimate the polarization state of the signal light.

[0065] When using the pilot light polarization multiplexing method in the present invention and the signal lights are symmetrically distributed on both sides of the reference light, set the distance between the quantum light and the reference light with the same polarization direction to 1 / 2f rep , and its distance from the reference light with the horizontal polarization direction is -1 / 2f rep . The time slot between two adjacent signal pulses is 1 / f rep , satisfying that the ratio of the signal light pulse to the reference light pulse is 1:1 (in the vertical polarization direction, the ratio of the signal light pulse to the reference light pulse is 2:1).

[0066] Quickly calculate the virtual reference light polarization information at the missing part through the Lagrange interpolation method. Then, the polarization state of the intermediate quantum signal light can be accurately estimated by the polarization change amounts of two sets of reference lights with perpendicular polarization directions on both sides of any signal light pulse. Measure the overall extinction ratio h and calculate the security bit rate k. Compared with the previous schemes, this scheme has better polarization compensation performance and can meet the high-precision polarization compensation requirements of CV-QKD.

[0067] It can be seen that the technical solution provided by the present invention can greatly improve the problem of excessive noise caused by the random polarization perturbation of the optical fiber channel.

[0068] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A polarization compensation method for CV-QKD continuous variable quantum key distribution, characterized in that The continuous variable quantum key distribution polarization compensation method includes: introducing reference light 1 and reference light 2, and estimating the polarization state of the quantum signal light through the polarization change amounts of two reference lights with alternating polarization directions; Specifically, the quantum light and reference light 1 are time-division multiplexed in the vertical polarization direction according to a preset ratio, and then polarization multiplexed with reference light 2 in the horizontal polarization direction. Meanwhile, the missing pilot light data is complemented by interpolation so that there are two adjacent sets of reference light data for estimating the polarization change amount of the quantum signal light; The process of polarization control of the reference light and the quantum signal light includes the following steps: A. At the transmitting end, the repetition frequency of the signal optical pulse is , and the frequencies of the two reference optical pulses are . The reference optical pulse 1 is time-shifted relative to the quantum signal optical pulse by , and is time-division multiplexed with the quantum signal optical pulse. The polarization direction is adjusted to be vertical by the polarization controller 1; B. At the transmitting end, the reference light 2 is time-shifted relative to the quantum signal light , the polarization direction is adjusted to horizontal by the polarization controller 2, and then combined with the optical signal with a vertical polarization direction in A for polarization multiplexing, and transmitted through the fiber optic quantum channel; C. At the receiving end, the two signal lights are orthogonally received by a polarization beam splitter, and then coherent detection is performed to obtain two electrical signals. Finally, time-division demultiplexing and polarization demultiplexing are completed in the digital domain; D. After the optical signal is converted to the digital domain, polarization compensation is performed by a digital signal processing method; The polarization compensation in step D includes: First, the reference signals in two polarization directions at adjacent positions of the quantum signal are complemented by interpolation, and then the polarization state of the intermediate quantum signal is estimated through the polarization change amounts of the reference signals in two adjacent polarization directions, the corresponding Jones matrix is calculated, and the original information at the sending end is obtained by inverse solution.

2. The polarization compensation method for CV-QKD continuous variable quantum key distribution according to claim 1, wherein In step D, the digital signal processing method is one of the following methods: CMA constant modulus algorithm, Stokes algorithm, Kalman filtering algorithm.

3. The polarization compensation method for CV-QKD continuous variable quantum key distribution according to claim 1, characterized in that The interpolation method is one of the following methods: Lagrange interpolation, Hermite interpolation, Newton interpolation, piecewise interpolation, cubic spline interpolation, multi-dimensional interpolation.

4. A CV-QKD system, characterized in that, The CV-QKD system operates based on the continuous variable quantum key distribution polarization compensation method according to any one of claims 1 to 3; The CV-QKD system includes: a sending end and a receiving end, and the sending end and the receiving end are connected by a transmission optical fiber; The sending end is used to realize the preparation and modulation of the quantum signal light, and the receiving end is used to realize the reception and detection of the quantum signal light.

5. The CV-QKD system according to claim 4, wherein, The sending end includes a continuous light source, a beam splitter 1, a beam splitter 2, a combiner, a polarization controller 1, a polarization controller 2, and a polarization combiner; The beam splitter 1 splits the optical signal input by the continuous light source to generate reference light 2 and the input optical signal of the beam splitter 2, and the beam splitter 2 splits the received optical signal to generate quantum signal light and reference light 1; The beam of the quantum signal light after passing through the optical attenuator 1 and the beam of the reference light 1 after passing through the optical attenuator 2 are respectively input to the combiner for combining processing, and after the combining processing, they are input to the polarization controller 1 for polarization direction adjustment; The reference light 2 is input to the polarization controller 2 for polarization direction adjustment after passing through the optical attenuator 3; The optical beams with polarization directions adjusted by the polarization controller 1 and the polarization controller 2 are polarization multiplexed by the polarization combiner, and then transmitted to the receiving end through the fiber optic quantum channel.

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