Single-carrier frequency domain equalization CV-QKD system and method

Abstract

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

Description

Technical Field

[0001] The present 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 Art

[0002] In recent years, the continuous variable quantum key distribution (CV-QKD) technology has been widely studied and applied in the field of quantum secure communication due to its advantages such as high security code rate in metropolitan area / access distance and compatibility with traditional optical communication devices / links. However, with the surge in the rate and bandwidth of traditional data communication services, in order to meet the high-security encryption requirements of "one-time one-key", the key distribution rate of quantum secure communication systems based on CV-QKD needs to be improved urgently.

[0003] At present, improving the system repetition frequency (bandwidth) is one of the most important and direct technical approaches to improve the key distribution rate of the CV-QKD system. However, with the increase in the bandwidth of the CV-QKD system, 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 a high-performance CV-QKD system. Especially in broadband CV-QKD systems based on optical fiber link transmission, high-speed quantum signals will inevitably be affected by a variety of non-ideal effects such as random perturbations of polarization, wavelength offset domain linewidth of lasers, link dispersion and nonlinear scattering, resulting in excessive system noise. For example, when high-speed quantum signals are transmitted over long distances, they introduce large dispersion noise due to the optical fiber dispersion effect, resulting in limited transmission distance and security code rate of broadband CV-QKD systems.

[0004] In the traditional CV-QKD system, the Bob side often uses a pilot signal light with a high signal-to-noise ratio to compensate for the link noise of the CV-QKD system, but there is still a large compensation deviation. Therefore, the traditional single-carrier CV-QKD system needs to insert a certain proportion of training sequences into the quantum signal on the Alice side and design a corresponding time domain equalizer on the Bob side, and use the time domain equalization technology to further realize the accurate compensation of multiple effect noises. However, the single-carrier time domain equalization technology requires too many tap coefficients in the time domain equalization, and too many hardware resources are required for hardware implementation, so its practicality is limited. In recent years, researchers have designed a multi-carrier CV-QKD system solution, that is, using orthogonal frequency division multiplexing (OFDM) technology to divide the high-speed CV-QKD system into multiple low-speed quantum orthogonal subcarriers, which not only significantly reduces the influence of the dispersion effect of the optical fiber link, but also can realize the frequency domain equalization compensation of multiple effect noises of multiple low-speed quantum orthogonal subcarriers on the Bob side through low-complexity hardware. However, the orthogonal frequency division multiplexing quantum state in the multi-carrier CV-QKD system is composed of multiple independent subcarriers, which will form a large peak-to-average ratio (PARR) during its preparation, affecting the preparation accuracy of high-speed quantum states. At the same time, its system performance is very sensitive to carrier synchronization and phase noise.

[0005] To solve the above problems, it is urgent to integrate the technical advantages of single-carrier CV-QKD and multi-carrier CV-QKD, achieve accurate compensation of multi-effect noise of CV-QKD link at minimal cost, effectively improve its transmission distance and security code rate, and promote 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 and disclose 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 high complexity of time domain equalization hardware in single-carrier CV-QKD system and high PARR and sensitivity to carrier synchronization and phase noise in multi-carrier CV-QKD system, significantly improves the security transmission performance of high-speed CV-QKD system and effectively reduces its multi-effect noise compensation cost.

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

[0008] A single-carrier frequency domain equalization CV-QKD system, the single-carrier frequency domain equalization CV-QKD system comprising: 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;

[0009] At Alice's end, Alice's 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 data connected to Alice's post-processing module;

[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 electrically connected to the balanced detector, and the quantum key demodulation module is data connected to the Bob post-processing module.

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

[0012] A single carrier frequency domain equalization CV-QKD method, using the above-mentioned single carrier frequency domain equalization CV-QKD system, the single carrier frequency domain equalization CV-QKD method comprising:

[0013] The optical signal output by the Alice laser enters the IQ modulator for modulation, where the IQ modulator is loaded with the quantum key electrical signal generated by the quantum key generation module. The IQ modulated optical signal is attenuated by the optical attenuator to form the required quantum signal light;

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

[0015] The obtained initial quantum key enters Bob's post-processing module for parameter estimation, and is combined with Alice's post-processing module to perform relevant 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 outputted from Alice's end reaches Bob's end via an optical fiber channel.

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

[0018] Perform Gaussian or discrete modulation on the quantum random bit stream to form a quantum key sequence with Gaussian or discrete modulation distribution;

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

[0020] After framing, each quantum key digital signal is converted into a digital signal with a sampling rate of f through parallel-to-serial conversion and matched filtering. n, a quantum key serial digital signal with a bandwidth of Δf;

[0021] Inserting pilot frequency f into the quantum key serial digital signal p , and then extract the real and imaginary parts of the signal and convert them into quantum key electrical signals I(t) and Q(t) through 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 of a CV-QKD system.

[0023] According to a preferred embodiment, the process of the quantum key demodulation module demodulating 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 subjected to frequency offset estimation and bandpass filtering 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 fast drifting phase noise.

[0025] The quantum digital signal after pilot compensation is subjected to matched filtering and serial-to-parallel conversion processing to obtain a plurality of quantum digital signals, and then each quantum digital signal is deframed to obtain a plurality of unique word sequences and a plurality of quantum signal sequences;

[0026] Each quantum signal sequence is transformed into several quantum frequency domain signals through discrete Fourier transformation, and the frequency domain equalization processing of each quantum frequency domain signal is completed with the help of the clock synchronization and channel estimation information obtained from each unique word sequence 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 inverse discrete Fourier transform, and finally the initial quantum key is obtained by parallel-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 is the channel impulse response, q n is a low-speed quantum key sequence, v n 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 represents the channel frequency domain response, Q l represents the quantum frequency domain signal, V l Represents the additive noise frequency domain information.

[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 is the tap coefficient of the frequency domain equalizer.

[0037] The aforementioned main scheme of the present application and its further options can be freely combined to form multiple schemes, all of which are schemes that can be adopted and claimed for protection in the present application. After understanding the scheme of the present application, those skilled in the art can understand that there are multiple combinations based on the prior art and common knowledge, all of which are technical schemes to be protected by the present application, and they are not exhaustively listed here.

[0038] Beneficial effects of this application:

[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 has the advantage of low fiber dispersion effect, is suitable for long-distance transmission of broadband CV-QKD system, but also can complete system multi-effect noise compensation with extremely low hardware complexity;

[0040] (2) Compared with the existing multi-carrier CV-QKD method and system, the single-carrier frequency domain equalization CV-QKD method and system proposed in this application not only has the high-performance transmission advantage of multi-carrier CV-QKD, but also avoids its high PARR and sensitivity to carrier synchronization and phase noise, which can further improve the transmission performance of high-speed CV-QKD systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a schematic diagram of the single-carrier frequency domain equalization CV-QKD method of the present application. DETAILED DESCRIPTION

[0042] The following describes the embodiments of the present application through specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the contents disclosed in this specification. The present application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.

[0043] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

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

[0045] In addition, the terms "horizontal", "vertical", "overhanging" and the like do not mean that the components are required to be absolutely horizontal or overhanging, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "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 clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0047] In addition, the present application would like to point out that, in the present application, unless the specific structure, connection relationship, positional relationship, power source relationship, etc. are specifically written out, the structure, connection relationship, positional relationship, power source relationship, etc. involved in the present application are all known by those skilled in the art on the basis of the prior art without creative work.

[0048] Example 1

[0049] This embodiment discloses a single-carrier frequency-domain equalized 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, and 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 data connected to the Alice post-processing module.

[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 data connected to the Bob post-processing module.

[0052] Example 2

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

[0054] Step 1: The optical signal output by Alice laser directly enters the IQ modulator for modulation, and then is attenuated by the optical attenuator to form the required quantum signal light.

[0055] Among them, the IQ modulator is loaded with the 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 modulate the 320 Gbps quantum random bit stream to form a quantum key sequence with a Gaussian modulation distribution with a repetition frequency of 10 GHz, where the quantum random bit stream is generally generated by a high-speed quantum random number generator;

[0057] (2) The quantum key sequence with Gaussian modulation distribution of 10 GHz repetition frequency is converted into N = 10 quantum key sequences with 1 GHz repetition frequency q n (n=1,2,…10), then each quantum key sequence q n The UW sequence is framed at a ratio of 1:4, where the UW sequence not only has a cyclic prefix function, but can also be used for clock synchronization and channel estimation of the CV-QKD system;

[0058] (3) After framing, the multi-channel quantum key digital signal is converted into a signal with a sampling rate of f by parallel-to-serial conversion and matched filtering. s=30GSa / s and a quantum key serial digital signal with a bandwidth of Δf=13GHz;

[0059] (4) Insert frequency f into the quantum key serial digital signal p =7GHz sinusoidal pilot signal, then extract the real and imaginary parts of the signal and convert them into quantum key electrical signals I(t) and Q(t) through 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 by 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 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 an ADC, and then subjected to frequency offset estimation and bandpass filtering to extract the quantum digital signal and the pilot digital signal. The pilot compensation of the quantum digital signal is performed using the shared phase information of the pilot digital signal to eliminate the fast drifting phase noise.

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

[0063] (3) The multi-channel quantum signal sequence is transformed into a multi-channel quantum frequency domain signal R through DFT l =H l Q l +V l (l=1,2,3,…10), and use the clock synchronization and channel estimation information obtained from the multi-channel UW sequence to complete the frequency domain equalization processing of the multi-channel quantum frequency domain signal to obtain the multi-channel quantum key frequency domain signal W l R l =W l H l Q l +W l V l , where W l is the tap coefficient of the frequency domain equalizer;

[0064] (4) The obtained multi-channel quantum key frequency domain signal is then transformed into a multi-channel quantum key sequence by IDFT, which can be expressed as

[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 ′ is the residual excess noise. The multi-channel quantum key sequence finally recovered is converted into the initial quantum key through parallel-serial conversion.

[0069] Step 3: The initial quantum key demodulated by Bob enters Bob's post-processing module for parameter estimation, and is combined with Alice's post-processing module to perform data negotiation, key error correction, and private key amplification to finally obtain a secure quantum key output.

[0070] Compared with the existing single-carrier time-domain equalized CV-QKD method and system, the single-carrier frequency-domain equalized CV-QKD method and system proposed in the present application not only has the advantage of low fiber dispersion effect, is 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; compared with the existing multi-carrier CV-QKD method and system, the single-carrier frequency-domain equalized CV-QKD method and system proposed in the present application not only has the high-performance transmission advantage of multi-carrier CV-QKD, but also avoids its high PARR and sensitivity to carrier synchronization and phase noise, which can further improve the transmission performance of high-speed CV-QKD system.

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

Claims

1. A single carrier frequency domain equalization CV-QKD system, characterized in that: The 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, and an Alice post-processing module and a Bob post-processing module; At Alice's end, Alice's 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 data connected to Alice's post-processing module; 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 electrically connected to the balanced detector, and the quantum key demodulation module is data connected to the Bob post-processing module.

2. A single carrier frequency domain equalization CV-QKD method, characterized in that: Using the single carrier frequency domain equalization CV-QKD system as claimed in claim 1, the single carrier frequency domain equalization CV-QKD method comprises: The optical signal output by the Alice laser enters the IQ modulator for modulation, where the IQ modulator is loaded with the quantum key electrical signal generated by the quantum key generation module. The IQ modulated optical signal is attenuated by the optical attenuator to form the required quantum signal light; The quantum signal light output by Alice reaches Bob and is coupled with the local oscillator light output by Bob's laser by an optical coupler into a balanced detector for coherent detection. The detection result is demodulated by a quantum key demodulation module to obtain the initial quantum key. The obtained initial quantum key enters Bob's post-processing module for parameter estimation, and is combined with Alice's post-processing module to perform relevant data negotiation, key error correction and private key amplification, ultimately achieving secure quantum key output.

3. The single carrier frequency domain equalization CV-QKD method according to claim 2, characterized in that: The process of generating a quantum key electrical signal by the quantum key generation module includes: Perform Gaussian or discrete modulation on the quantum random bit stream to form a quantum key sequence with Gaussian or discrete modulation distribution; The quantum key sequence of Gaussian / discrete modulation distribution is converted into several low-speed quantum key sequences through serial-to-parallel conversion, and then each low-speed quantum key sequence is framed with a unique word sequence according to a preset ratio; After framing, each quantum key digital signal is converted into a digital signal with a sampling rate of f through parallel-to-serial conversion and matched filtering. n , a quantum key serial digital signal with a bandwidth of Δf; Inserting pilot frequency f into the quantum key serial digital signal p , and then extract the real and imaginary parts of the signal and convert them into quantum key electrical signals I(t) and Q(t) through a digital-to-analog converter.

4. The single carrier frequency domain equalization CV-QKD method according to claim 3, characterized in that: The unique word sequence has a cyclic prefix function and can be used for clock synchronization and channel estimation of the CV-QKD system.

5. The single carrier frequency domain equalization CV-QKD method according to claim 2, characterized in that: The process of the quantum key demodulation module demodulating 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 subjected to frequency offset estimation and bandpass filtering 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 fast drifting phase noise. The quantum digital signal after pilot compensation is subjected to matched filtering and serial-to-parallel conversion processing to obtain a plurality of quantum digital signals, and then each quantum digital signal is deframed to obtain a plurality of unique word sequences and a plurality of quantum signal sequences; Each quantum signal sequence is transformed into several quantum frequency domain signals through discrete Fourier transformation, and the frequency domain equalization processing of each quantum frequency domain signal is completed with the help of the clock synchronization and channel estimation information obtained from each unique word sequence to obtain each quantum key frequency domain signal; The obtained quantum key frequency domain signals are then transformed into several quantum key sequences by inverse discrete Fourier transform, and finally the initial quantum key is obtained by parallel-serial conversion.

6. The single carrier frequency domain equalization CV-QKD method according to claim 5, characterized in that: The quantum signal sequence is: Where n = 1, 2, 3, ... N, N is the number of low-speed quantum key sequence paths, h n is the channel impulse response, q n is a low-speed quantum key sequence, v n is additive noise.

7. The single carrier frequency domain equalization CV-QKD method according to claim 5, characterized in that: The quantum frequency domain signal is: R l =H l Q l +V l Where 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 the quantum frequency domain signal, V l Represents the additive noise frequency domain information.

8. The single carrier frequency domain equalization CV-QKD method according to claim 7, characterized in that: The quantum key frequency domain signal is: W l R l =W l H l Q l +W l V l Where W l is the tap coefficient of the frequency domain equalizer.

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