A single-carrier frequency domain equalization CV-QKD system and method

Abstract

The application discloses a single-carrier frequency domain equalization CV-QKD system and method, and the single-carrier frequency domain equalization CV-QKD system comprises an Alice laser, an IQ modulator, a quantum key generation module, an optical attenuator, an optical fiber channel, a Bob laser, an optical coupler, a balanced detector, a quantum key demodulation module, and an Alice post-processing module and a Bob post-processing module; at the Alice end, the Alice laser, the IQ modulator, the optical attenuator and the optical fiber channel are optically connected, the quantum key generation module is electrically connected with the IQ modulator, and the quantum key generation module is data-connected with the Alice post-processing module; at the Bob end, the Bob laser, the optical coupler and the balanced detector are optically connected with the optical fiber channel, the quantum key demodulation module is electrically connected with the balanced detector, and the quantum key demodulation module is data-connected with the Bob post-processing module. Through the application, the safety transmission performance of a high-speed CV-QKD system is remarkably improved, and the compensation cost of multi-effect noise is effectively reduced.

Description

Technical Field

[0001] This application belongs to the field of quantum secure communication technology, and in particular relates to a single-carrier frequency domain equalization CV-QKD system and method. Background Technology

[0002] In recent years, Continuous Variable Quantum Key Distribution (CV-QKD) technology has been widely researched and applied in the field of quantum secure communication due to its advantages such as high secure code rate at metropolitan / access distances and compatibility with traditional optical communication devices / links. However, with the surge in the speed and bandwidth of traditional data communication services, the key distribution rate of quantum secure communication systems based on CV-QKD urgently needs to be improved to meet the high-security encryption requirement of "one-time pad".

[0003] Currently, increasing the system repetition frequency (bandwidth) is one of the most important and direct technical approaches to improving the key distribution rate of CV-QKD systems. However, with the increase in the bandwidth of CV-QKD systems, high-speed quantum states face problems such as insufficient device performance and excessive multi-effect noise during preparation, transmission, detection, and data processing, making it difficult to achieve high-performance CV-QKD systems. Especially in broadband CV-QKD systems based on fiber optic links, high-speed quantum signals will inevitably be affected by various non-ideal effects such as polarization random perturbations, laser wavelength offset linewidth, link dispersion, and nonlinear scattering, resulting in excessive system noise. For example, high-speed quantum signals introduce significant dispersion noise due to fiber dispersion effects during long-distance transmission, limiting the transmission distance and secure code rate of broadband CV-QKD systems.

[0004] In traditional CV-QKD systems, high signal-to-noise ratio (SNR) pilot signal light is often used at the Bob end to compensate for link noise, but significant compensation deviations still exist. Therefore, traditional single-carrier CV-QKD systems require inserting a certain proportion of training sequences into the quantum signal at the Alice end and designing a corresponding time-domain equalizer at the Bob end to further achieve accurate compensation for various noise effects using time-domain equalization techniques. However, single-carrier time-domain equalization requires too many tap coefficients and excessive hardware resources, limiting its practicality. In recent years, researchers have designed multi-carrier CV-QKD system schemes, utilizing orthogonal frequency division multiplexing (OFDM) technology to divide the high-speed CV-QKD system into multiple low-speed quantum orthogonal subcarriers. This not only significantly reduces the impact of fiber link dispersion effects but also allows for low-complexity hardware-based frequency-domain equalization compensation of multiple low-speed quantum orthogonal subcarriers in the Bob path. However, in a multi-carrier CV-QKD system, the orthogonal frequency division multiplexing quantum state is composed of multiple independent subcarriers superimposed. During its preparation, a large peak-to-average ratio (PARR) will be formed, which will affect the preparation accuracy of the high-speed quantum state. At the same time, its system performance is very sensitive to carrier synchronization and phase noise.

[0005] To address the aforementioned issues, it is imperative to integrate the technological advantages of single-carrier CV-QKD and multi-carrier CV-QKD to achieve accurate compensation for multi-effect noise in CV-QKD links at minimal cost, effectively improving transmission distance and secure bit rate, and promoting the large-scale application of high-performance CV-QKD systems. Summary of the Invention

[0006] The purpose of this application is to overcome the problems of the prior art by disclosing a single-carrier frequency domain equalization CV-QKD system and method, which not only has the significant advantage of low fiber dispersion effect, but also avoids the problems of high hardware complexity of time domain equalization in single-carrier CV-QKD system and high PARR and sensitivity to carrier synchronization and phase noise in multi-carrier CV-QKD system, significantly improving the secure transmission performance of high-speed CV-QKD system and effectively reducing its multi-effect noise compensation cost.

[0007] On the one hand, the objective of this application is achieved through the following technical solution:

[0008] A single-carrier frequency domain equalization CV-QKD system includes: an Alice laser, an IQ modulator, a quantum key generation module, an optical attenuator, an optical fiber channel, a Bob laser, an optical coupler, a balanced detector, a quantum key demodulation module, as well as an Alice post-processing module and a Bob post-processing module.

[0009] At the Alice end, the Alice laser, IQ modulator, optical attenuator and optical fiber channel are connected by optical fiber, the quantum key generation module is electrically connected to the IQ modulator, and the quantum key generation module is connected to the Alice post-processing module by data.

[0010] At the Bob end, the Bob laser, optical coupler, balanced detector and optical fiber channel are connected by optical fiber, the quantum key demodulation module is connected by electrical connection with the balanced detector, and the quantum key demodulation module is connected by data connection with the Bob post-processing module.

[0011] On the other hand, this application also discloses:

[0012] A single-carrier frequency domain equalization CV-QKD method, employing the aforementioned single-carrier frequency domain equalization CV-QKD system, the single-carrier frequency domain equalization CV-QKD method comprising:

[0013] The optical signal output from the Alice laser is modulated by an IQ modulator, which is loaded with a quantum key electrical signal generated by a quantum key generation module. The IQ modulated optical signal is attenuated by an optical attenuator to form the desired quantum signal light.

[0014] The quantum signal light output from Alice reaches Bob and is coupled with the local oscillator light output from Bob laser through an optical coupler into a balanced detector for coherent detection. The detection result is demodulated by the quantum key demodulation module to obtain the initial quantum key.

[0015] The obtained initial quantum key enters the Bob post-processing module for parameter estimation, and together with the Alice post-processing module, performs related data negotiation, key error correction, and private key amplification, ultimately achieving secure quantum key output.

[0016] According to a preferred embodiment, the quantum signal light output from Alice reaches Bob via an optical fiber channel.

[0017] According to a preferred embodiment, the process by which the quantum key generation module generates a quantum key electrical signal includes:

[0018] The quantum random bit stream is Gaussian or discretely modulated to form a quantum key sequence with a Gaussian or discretely modulated distribution;

[0019] The Gaussian / discrete modulation distributed quantum key sequence is converted into several low-speed quantum key sequences through serial-to-parallel conversion. Then, each low-speed quantum key sequence is framed with a unique word sequence according to a preset ratio.

[0020] After framing, the individual quantum key digital signals undergo parallel-to-serial conversion and matched filtering to form a signal with a sampling rate of f. nA quantum key serial digital signal with a bandwidth of Δf;

[0021] Inserting pilot frequency f into the quantum key serial digital signal p Then, the real and imaginary parts of the signal are extracted and converted into quantum key electrical signals I(t) and Q(t) by a digital-to-analog converter.

[0022] According to a preferred embodiment, the unique word sequence has a cyclic prefix function and can be used for clock synchronization and channel estimation in CV-QKD systems.

[0023] According to a preferred embodiment, the process by which the quantum key demodulation module demodulates the initial quantum key includes:

[0024] The electrical signal output by the balanced detector is converted into a digital signal by an analog-to-digital converter, and then frequency offset estimation and bandpass filtering are performed to extract the quantum digital signal and the pilot digital signal. The shared phase information of the pilot digital signal is used to perform pilot compensation on the quantum digital signal to eliminate the phase noise of rapid drift.

[0025] The pilot-compensated quantum digital signal is subjected to matched filtering and serial-to-parallel conversion to obtain several quantum digital signals. Then, each quantum digital signal is deframed to obtain several unique word sequences and several quantum signal sequences.

[0026] Each quantum signal sequence is transformed into several quantum frequency domain signals through discrete Fourier transform, and the frequency domain equalization of each quantum frequency domain signal is completed by using the clock synchronization and channel estimation information obtained by each unique word sequence, so as to obtain each quantum key frequency domain signal.

[0027] The obtained quantum key frequency domain signals are then transformed into several quantum key sequences by discrete Fourier inverse transform, and finally the initial quantum key is obtained by parallel-to-serial conversion.

[0028] According to a preferred embodiment, the quantum signal sequence is:

[0029]

[0030] Where n = 1, 2, 3, ... N, N is the number of low-speed quantum key sequence paths, h n For the channel impulse response, q n For low-speed quantum key sequences, v n It is additive noise.

[0031] According to a preferred embodiment, the quantum frequency domain signal is:

[0032] R l =H l Q l +V l

[0033] Where l = 1, 2, 3, ... N, N is the number of low-speed quantum key sequence paths, H l Q represents the channel frequency domain response. l V represents a quantum frequency domain signal. l It represents the frequency domain information of additive noise.

[0034] According to a preferred embodiment, the quantum key frequency domain signal is:

[0035] W l R l =W l H l Q l +W l V l

[0036] Among them, W l These are the tap coefficients of the frequency domain equalizer.

[0037] The aforementioned main solution and its various further alternative solutions can be freely combined to form multiple solutions, all of which are solutions that can be adopted and are claimed in this application. Those skilled in the art, after understanding the solution of this application, will realize that there are many combinations based on the prior art and common general knowledge, all of which are technical solutions to be protected in this application, and will not be exhaustively listed here.

[0038] The beneficial effects of this application are:

[0039] (1) Compared with the existing single-carrier time-domain equalization CV-QKD method and system, the single-carrier frequency-domain equalization CV-QKD method and system proposed in this application not only have the advantage of low fiber dispersion effect and are suitable for long-distance transmission of broadband CV-QKD system, but also can complete the system multi-effect noise compensation with extremely low hardware complexity.

[0040] (2) Compared with existing multi-carrier CV-QKD methods and systems, the single-carrier frequency domain equalization CV-QKD method and system proposed in this application not only have the high-performance transmission advantages of multi-carrier CV-QKD, but also avoid its high PARR and sensitivity to carrier synchronization and phase noise, which can further improve the transmission performance of high-speed CV-QKD systems. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the single-carrier frequency domain equalization CV-QKD method of this application. Detailed Implementation

[0042] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. This application can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be noted that, unless otherwise specified, the following embodiments and features in the embodiments can be combined with each other.

[0043] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0044] In the description of this application, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this application is in use. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. In addition, the terms "first," "second," and "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0045] Furthermore, terms such as "horizontal," "vertical," and "sag" do not imply that components must be absolutely horizontal or suspended, but rather that they can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal relative to "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0046] In the description of this application, it should also be noted that, unless otherwise expressly specified and limited, the terms "set up," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0047] Furthermore, it should be noted that unless otherwise specified in this application, the specific structures, connections, positions, power sources, etc. involved are all things that a person skilled in the art can know without creative effort based on the prior art.

[0048] Example 1

[0049] This embodiment discloses a single-carrier frequency domain equalization CV-QKD system, including an Alice laser, an IQ modulator, a quantum key generation module, an optical attenuator, an optical fiber channel, a Bob laser, an optical coupler, a balanced detector, a quantum key demodulation module, as well as an Alice post-processing module and a Bob post-processing module.

[0050] At the Alice end, the Alice laser, IQ modulator, optical attenuator and optical fiber channel are connected by optical fiber, the quantum key generation module is electrically connected to the IQ modulator, and the quantum key generation module is connected to the Alice post-processing module by data.

[0051] At the Bob end, the Bob laser, optical coupler, balanced coherent detector, and optical fiber channel are connected by optical fiber; the quantum key demodulation module is electrically connected to the balanced detector; and the quantum key demodulation module is connected to the Bob post-processing module by data.

[0052] Example 2

[0053] refer to Figure 1 As shown, based on Example 1, this example discloses a single-carrier frequency domain equalization CV-QKD method, including the following steps:

[0054] Step 1: The optical signal output from the Alice laser is directly modulated by the IQ modulator and then attenuated by the optical attenuator to form the desired quantum signal light.

[0055] The IQ modulator is loaded with quantum key electrical signals I(t) and Q(t) generated by the quantum key generation module. The specific process is as follows:

[0056] (1) Gaussian modulation is applied to the 320Gbps quantum random bit stream to form a quantum key sequence with a Gaussian modulation distribution and a repetition frequency of 10GHz. The quantum random bit stream is generally generated by a high-speed quantum random number generator.

[0057] (2) The 10 GHz repetition frequency Gaussian modulated quantum key sequence is converted into an N=10-channel 1 GHz repetition frequency quantum key sequence q through serial-to-parallel conversion. n (n = 1, 2, ... 10), followed by each quantum key sequence q n The UW sequence is framed at a ratio of 1:4, where the UW sequence not only has the function of cyclic prefix, but can also be used for clock synchronization and channel estimation of CV-QKD system;

[0058] (3) The framed multi-channel quantum key digital signals are converted from parallel to serial and matched filtering to form a signal with a sampling rate of f. s=30GSa / s and a quantum key serial digital signal with a bandwidth of Δf = 13GHz;

[0059] (4) Inserting frequency f into the quantum key serial digital signal p A sinusoidal pilot signal of 7 GHz is used, and then the real and imaginary parts of the signal are extracted and converted into quantum key electrical signals I(t) and Q(t) by a DAC.

[0060] Step 2: The quantum signal light generated by Alice reaches Bob's end through the optical fiber channel, and is coupled with the local oscillator light output by Bob's laser through the optical coupler into the balanced detector for coherent detection. The detection result is demodulated by the quantum key demodulation module to obtain the initial quantum key. The specific quantum key demodulation process is as follows:

[0061] (1) The electrical signal output by the balanced detector is converted into a digital signal by the ADC, and then frequency offset estimation and bandpass filtering are performed to extract the quantum digital signal and the pilot digital signal. The shared phase information of the pilot digital signal is used to perform pilot compensation on the quantum digital signal to eliminate the phase noise of rapid drift.

[0062] (2) The pilot-compensated quantum digital signal is subjected to matched filtering and serial-to-parallel conversion to obtain multiple quantum digital signals. The multiple quantum digital signals are then deframed to obtain multiple UW sequences and multiple quantum signal sequences. (n = 1, 2, 3, ... 10), where h n For the channel impulse response, v n It is additive noise;

[0063] (3) The multiple quantum signal sequences are converted into multiple quantum frequency domain signals R by DFT. l =H l Q l +V l (l=1,2,3,…10), and using the clock synchronization and channel estimation information obtained from multiple UW sequences, the frequency domain equalization processing of multiple quantum frequency domain signals is completed to obtain multiple quantum key frequency domain signals W. l R l =W l H l Q l +W l V l , where W l These are the tap coefficients of the frequency domain equalizer;

[0064] (4) The obtained multi-channel quantum key frequency domain signals are then converted into a multi-channel quantum key sequence by IDFT, which can be expressed as follows:

[0065]

[0066] Taking the zero-forcing (ZF) equalization algorithm as an example, the frequency domain tap coefficient W l =1 / H l Formula (1) can be simplified to

[0067]

[0068] Where v n ′ represents residual noise. The recovered multi-channel quantum key sequence is then converted from parallel to serial to obtain the initial quantum key.

[0069] Step 3: The initial quantum key demodulated from the Bob end enters the Bob post-processing module for parameter estimation, and together with the Alice post-processing module, performs data negotiation, key error correction, and private key amplification to finally obtain a secure quantum key output.

[0070] Compared to existing single-carrier time-domain equalization CV-QKD methods and systems, the single-carrier frequency-domain equalization CV-QKD method and system proposed in this application not only have the advantage of low fiber dispersion effect, making them suitable for long-distance transmission in broadband CV-QKD systems, but also can complete system multi-effect noise compensation with extremely low hardware complexity. Compared to existing multi-carrier CV-QKD methods and systems, the single-carrier frequency-domain equalization CV-QKD method and system proposed in this application not only have the high-performance transmission advantage of multi-carrier CV-QKD, but also avoid its high PARR and sensitivity to carrier synchronization and phase noise problems, which can further improve the transmission performance of high-speed CV-QKD systems.

[0071] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A single-carrier frequency domain equalization (CV-QKD) method, characterized in that, A single-carrier frequency domain equalization CV-QKD system is adopted, which includes: an Alice laser, an IQ modulator, a quantum key generation module, an optical attenuator, an optical fiber channel, a Bob laser, an optical coupler, a balanced detector, a quantum key demodulation module, as well as an Alice post-processing module and a Bob post-processing module. At the Alice end, the Alice laser, IQ modulator, optical attenuator and optical fiber channel are connected by optical fiber, the quantum key generation module is electrically connected to the IQ modulator, and the quantum key generation module is connected to the Alice post-processing module by data. At the Bob end, the Bob laser, optical coupler, balanced detector and optical fiber channel are connected by optical fiber, the quantum key demodulation module is connected by electrical connection to the balanced detector, and the quantum key demodulation module is connected by data connection to the Bob post-processing module. The single-carrier frequency domain equalization CV-QKD method includes: The optical signal output from the Alice laser is modulated by an IQ modulator, which is loaded with a quantum key electrical signal generated by a quantum key generation module. The IQ modulated optical signal is attenuated by an optical attenuator to form the desired quantum signal light. The quantum signal light output from Alice reaches Bob and is coupled with the local oscillator light output from Bob laser through an optical coupler into a balanced detector for coherent detection. The detection result is demodulated by the quantum key demodulation module to obtain the initial quantum key. The obtained initial quantum key enters the Bob post-processing module for parameter estimation, and together with the Alice post-processing module, performs related data negotiation, key error correction and private key amplification, ultimately achieving secure quantum key output; The process by which the quantum key demodulation module demodulates the initial quantum key includes: The electrical signal output by the balanced detector is converted into a digital signal by an analog-to-digital converter, and then frequency offset estimation and bandpass filtering are performed to extract the quantum digital signal and the pilot digital signal. The shared phase information of the pilot digital signal is used to perform pilot compensation on the quantum digital signal to eliminate the phase noise of rapid drift. The pilot-compensated quantum digital signal is subjected to matched filtering and serial-to-parallel conversion to obtain several quantum digital signals. Then, each quantum digital signal is deframed to obtain several unique word sequences and several quantum signal sequences. Each quantum signal sequence is transformed into several quantum frequency domain signals through discrete Fourier transform, and the frequency domain equalization of each quantum frequency domain signal is completed by using the clock synchronization and channel estimation information obtained by each unique word sequence, so as to obtain each quantum key frequency domain signal. The obtained quantum key frequency domain signals are then transformed into several quantum key sequences by discrete Fourier inverse transform, and finally the initial quantum key is obtained by parallel-to-serial conversion.

2. The single-carrier frequency domain equalization CV-QKD method as described in claim 1, characterized in that, The process by which the quantum key generation module generates a quantum key electrical signal includes: The quantum random bit stream is Gaussian or discretely modulated to form a quantum key sequence with a Gaussian or discretely modulated distribution; The Gaussian / discrete modulation distributed quantum key sequence is converted into several low-speed quantum key sequences through serial-to-parallel conversion. Then, each low-speed quantum key sequence is framed with a unique word sequence according to a preset ratio. After framing, the individual quantum key digital signals undergo parallel-to-serial conversion and matched filtering to form a signal with a sampling rate of [missing information]. f n Bandwidth is Quantum key serial digital signal; Inserting pilot signals into quantum key serial digital signals f p Then, the real and imaginary parts of the signal are extracted and converted into a quantum key electrical signal via a digital-to-analog converter. I ( t )and Q ( t ).

3. The single-carrier frequency domain equalization CV-QKD method as described in claim 2, characterized in that, The unique word sequence has a cyclic prefix function and can be used for clock synchronization and channel estimation in CV-QKD systems.

4. The single-carrier frequency domain equalization CV-QKD method as described in claim 1, characterized in that, The quantum signal sequence is: r n = h n q n + v n in, n =1, 2, 3, … N N is the number of low-speed quantum key sequence paths. h n For channel impulse response, q n It is a low-speed quantum key sequence. v n It is additive noise.

5. The single-carrier frequency domain equalization CV-QKD method as described in claim 1, characterized in that, The quantum frequency domain signal is: R l = H l Q l + V l in, l =1, 2, 3, … N N is the number of low-speed quantum key sequence paths. H l Represents the channel frequency domain response. Q l Represents quantum frequency domain signals, V l It represents the frequency domain information of additive noise.

6. The single-carrier frequency domain equalization CV-QKD method as described in claim 5, characterized in that, The quantum key frequency domain signal is: W l R l = W l H l Q l + W l V l in W l These are the tap coefficients of the frequency domain equalizer.

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