CN111769881B - Method and system for improving phase compensation precision and communication efficiency of CVQKD system - Google Patents

Method and system for improving phase compensation precision and communication efficiency of CVQKD system Download PDF

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CN111769881B
CN111769881B CN202010540653.4A CN202010540653A CN111769881B CN 111769881 B CN111769881 B CN 111769881B CN 202010540653 A CN202010540653 A CN 202010540653A CN 111769881 B CN111769881 B CN 111769881B
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amplitude
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CN111769881A (en
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刘金璐
徐兵杰
樊矾
张涛
杨杰
王恒
黄伟
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CETC 30 Research Institute
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/50—Transmitters
    • H04B10/516—Details of coding or modulation
    • H04B10/54—Intensity modulation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/50—Transmitters
    • H04B10/516—Details of coding or modulation
    • H04B10/548—Phase or frequency modulation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/70—Photonic quantum communication
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
    • H04L9/08—Key distribution or management, e.g. generation, sharing or updating, of cryptographic keys or passwords
    • H04L9/0816—Key establishment, i.e. cryptographic processes or cryptographic protocols whereby a shared secret becomes available to two or more parties, for subsequent use
    • H04L9/0852—Quantum cryptography

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Abstract

The invention relates to the technical field of communication, and discloses a method and a system for improving the phase compensation precision and the communication efficiency of a CVQKD system. Meanwhile, the length of the check sequence is shortened, the proportion of the check sequence in the whole communication process is reduced, the covered period is reduced from the original 2 pi to pi, and the phase drift value is quickly calculated through an extremum search algorithm, so that the calculation time of the phase drift value is shortened. The invention can reduce the system over-noise caused by phase drift, reduce the resource occupation and effectively improve the system security code rate.

Description

Method and system for improving phase compensation precision and communication efficiency of CVQKD system
Technical Field
The invention relates to the technical field of communication, in particular to a method and a system for improving the phase compensation precision and the communication efficiency of a CVQKD system.
Background
Quantum key distribution is one of the closest practical research directions in quantum information science, and enables both legitimate parties to realize unconditionally secure remote communication. The Continuous Variable Quantum Key Distribution (CVQKD) system has a great development prospect due to the advantages of mature devices, low cost, high speed, compatibility with a classical optical communication system and the like.
The sending end of the CVQKD system based on the Gaussian modulation coherent state protocol generally adopts a coherent state as a light source, then controls the coherent state to generate pulsed light and divides the pulsed light into two beams with different intensities, one beam with stronger intensity is used as local oscillation light, and the other beam with weaker intensity is used as signal light. The orthogonal components of the signal light are subjected to Gaussian modulation with the mean value of zero by adopting an amplitude modulator and a phase modulator, the intensity of the signal light is attenuated to ten-photon magnitude by an attenuator, polarization and time division multiplexing are realized by adopting an unequal arm light path structure and local oscillator light combining beams, and then the signal light enters an optical fiber channel for transmission. After the local oscillation light reaches a receiving end, polarization and time division demultiplexing are firstly completed, then an electro-optical modulator is adopted to carry out 0 or pi/2 random phase loading on the local oscillation light (namely, base selection is completed), quantum state measurement is completed through a balance detector, the quantum state measurement is converted into an electric signal, and the raw data is obtained by collection equipment, processed and analyzed so as to obtain a final security key.
As can be seen from the above, the data acquired by the key distribution system is strongly correlated with the interference result of the local oscillator light and the signal light. The length of the two arms of the unequal arm M-Z interferometer is susceptible to change due to the influence of external environments such as temperature, so that the phase difference of the two arms cannot be kept stable for a long time, and the unstable phase difference caused by the change is called phase drift. Therefore, real-time compensation for phase drift is needed in the system to reduce the impact on the system security code rate. The existing common compensation scheme is to add a check sequence with the intensity equal to the maximum intensity of signal light by adopting a time division multiplexing method in the signal light, and the phase change covers a whole period of 2 pi. And extracting a check sequence from the signal acquired by the balance detector, calculating a phase drift value, and controlling the phase compensation according to the phase drift value. However, since the strength of the check sequence is very weak, noise is inevitably introduced after transmission through the optical fiber channel, resulting in low phase compensation accuracy; the phase traversal range of the check sequence is large, the occupation ratio of the check sequence in unit time is too large, and the time consumption is long when the drift value is calculated, so that the system communication efficiency is low.
The verify pulse sequence for phase compensation in the CVQKD system is designed mainly from a method of actively controlling its amplitude and phase. In the amplitude control, an amplitude modulator for gaussian-modulating the signal light is used, and the amplitude of the check sequence is made larger than the maximum amplitude of the signal light. The method is a simple and easy implementation scheme with low cost, but the scheme can reduce the amplitude modulation range of the signal sequence, reduce the modulation precision and the modulation extinction ratio, thereby increasing the modulation noise and reducing the safe code rate.
Disclosure of Invention
In order to solve the problems, the invention provides a method and a system for improving the phase compensation precision and the communication efficiency of a CVQKD system, which can reduce the system noise caused by phase drift, reduce the resource occupation and effectively improve the system security code rate by independently controlling the amplitudes of a check sequence and an effective sequence into which signal light is divided, shortening the occupation ratio of the check sequence in unit time and optimizing the calculation method of a phase drift value.
The invention discloses a method for improving the phase compensation precision and the communication efficiency of a CVQKD system, which comprises the following steps:
a controller is added in a signal light path in a traditional CVQKD system to independently control the amplitudes of a check sequence and an effective sequence which are divided by signal light, so that the amplitude of the check sequence is larger than the maximum amplitude of the effective sequence, and the phase compensation precision is improved;
the length of the check sequence is shortened, the proportion of the check sequence in the whole communication process is reduced, the covered period is reduced from the original 2 pi to pi, and the phase drift value is quickly calculated through an extremum search algorithm, so that the calculation time of the phase drift value is shortened.
Further, the controller comprises an electrically controlled attenuator, an electro-optic intensity modulator or an acousto-optic modulator.
Further, the repetition frequency of the check sequence operation is consistent with the repetition frequency of the CVQKD system operation.
Further, in the sending end of the CVQKD system:
the optical pulse is divided into two beams with different intensities by a beam splitter, one beam with stronger intensity is used as local oscillation light, one beam with weaker intensity is used as signal light, and the signal light is divided into a check sequence and an effective sequence by adopting a time division method;
and the controller independently controls the intensity or amplitude of the check sequence and the effective sequence, so that the amplitude of the check sequence is larger than the maximum amplitude of the effective sequence, and the number of covered periods of phase modulation in the check sequence is 1 pi.
Further, an intensity or amplitude modulator and a phase modulator are adopted to carry out Gaussian modulation with the mean value of zero on the orthogonal components of the effective sequence; the polarization and time division multiplexing of the signal light and the local oscillator light are realized by combining the light beams through an unequal arm light path structure, and finally the light beams enter an optical fiber channel for transmission.
Further, the check sequence and the effective sequence when the controller performs independent control are before, after or in the gaussian modulation.
Further, in the receiving end of the CVQKD system:
after signal light and local oscillator light reach a receiving end, firstly, an unequal arm interference structure is adopted to finish polarization and time division demultiplexing, after a phase modulator is adopted to randomly load a phase of 0 or pi/2 on a local oscillator light branch, quantum state measurement is finished and converted into an electric signal through a balance detector, and then, original data are obtained by a signal acquisition device, wherein the original data comprise verification data for phase compensation and effective key distribution data;
and calculating the check data by adopting an extremum search algorithm to obtain a phase drift value, loading a corresponding compensation phase value on a phase modulator at a receiving end or a transmitting end according to the relationship between the phase modulator and the phase drift value, and processing and analyzing the data after phase compensation so as to obtain a final security key.
Further, the extremum searching algorithm can search for the amplitude maximum P in the entire check sequencemaxAnd a minimum value PminAnd returns the Index of the position of the corresponding extreme pointmaxAnd IndexminI.e. the position of the pulse at which the extreme point is located in the check sequence.
Further, in the phase compensation, the maximum value P of the amplitude is comparedmaxAnd a minimum value PminTaking the extreme point with larger absolute value as P and the position as Index, if P is>0, the phase drift value is-Index x pi/N, N is the checkThe total number of pulses; if P is<0, the phase shift value is Index π/N.
The system of the invention comprises a sending end and a receiving end, wherein:
the sending end comprises a beam splitter, a controller, an intensity or amplitude modulator, a first phase modulator and a polarization beam combiner, wherein the beam splitter is used for splitting optical pulses into local oscillation light and signal light, the controller is used for independently controlling the amplitudes of a check sequence and an effective sequence into which the signal light is split, so that the amplitude of the check sequence is larger than the maximum amplitude of the effective sequence, the intensity or amplitude modulator and the first phase modulator are used for carrying out Gaussian modulation with the mean value of zero on orthogonal components of the effective sequence, and the polarization beam combiner is used for enabling the signal light and the optical synthesis local oscillation beam to realize polarization and time division multiplexing;
the receiving end comprises a polarization beam splitter, a second phase modulator, a balance detector and signal acquisition equipment, wherein the polarization beam splitter is used for completing polarization and time division demultiplexing, the second phase modulator is used for randomly loading a phase of 0 or pi/2 to local oscillation light, the balance detector is used for completing measurement of a quantum state and converting the quantum state into an electric signal, the acquisition equipment acquires original data, and the first phase modulator or the second phase modulator is used for performing phase compensation according to a phase drift value obtained by an extreme value search algorithm.
The invention has the beneficial effects that:
(1) by independently controlling the amplitudes of the check sequence and the effective sequence into which the signal light is divided, shortening the occupation ratio of the check sequence in unit time and optimizing the calculation method of the phase drift value, the over-noise of the system caused by phase drift can be reduced, the resource occupation is reduced, and the safe code rate of the system is effectively improved;
(2) the strength of the check pulse sequence for phase compensation and the valid sequence for key distribution can be independently controlled;
(3) the phase compensation precision and the communication efficiency can be adjusted and adapted according to different transmission distances;
(4) the phase compensation precision is high, the check pulse sequence used for phase compensation occupies a small pulse sequence proportion in unit time length, and the communication efficiency is high.
Drawings
FIG. 1 is a schematic diagram of the system of the present invention;
FIG. 2 is a schematic diagram of the controller controlling the check sequence and the valid sequence separately;
FIG. 3 is a schematic diagram of an output optical pulse when the phase is not shifted;
fig. 4 is a schematic diagram of four output light pulses during phase drift.
Detailed Description
In order to more clearly understand the technical features, objects, and effects of the present invention, specific embodiments of the present invention will now be described. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the present invention without making any creative effort, shall fall within the protection scope of the present invention.
The embodiment provides a method and a system for improving the phase compensation precision and the communication efficiency of a CVQKD system, wherein the method comprises the following steps:
a controller is added in a signal light path in a traditional CVQKD system to independently control the amplitudes of a check sequence and an effective sequence which are divided by signal light, so that the amplitude of the check sequence is larger than the maximum amplitude of the effective sequence, and the phase compensation precision is improved;
the length of the check sequence is shortened, the proportion of the check sequence in the whole communication process is reduced, the covered period is reduced from the original 2 pi to pi, and the phase drift value is quickly calculated through an extremum search algorithm, so that the calculation time of the phase drift value is shortened.
As shown in fig. 1, a CVQKD system of this embodiment includes a sending end and a receiving end, where:
the sending end comprises a beam splitter, a controller, an intensity or amplitude modulator, a first phase modulator and a polarization beam combiner, wherein the beam splitter is used for splitting optical pulses into local oscillation light and signal light, the controller is used for independently controlling the amplitude of a check sequence and an effective sequence into which the signal light is split, and the amplitude of the check sequence is larger than the maximum amplitude of the effective sequence, as shown in fig. 2, the larger the amplitude of the check sequence is, the smaller the acquired noise is, and the higher the phase compensation precision can be calculated. The intensity or amplitude modulator and the first phase modulator are used for carrying out Gaussian modulation with the mean value of zero on orthogonal components of the effective sequence, and the polarization beam combiner is used for combining the signal light and the local oscillator beam to realize polarization and time division multiplexing.
The receiving end comprises a polarization beam splitter, a second phase modulator, a balance detector and signal acquisition equipment, wherein the polarization beam splitter is used for completing polarization and time division demultiplexing, the second phase modulator is used for randomly loading a phase of 0 or pi/2 to local oscillation light, the balance detector is used for completing measurement of a quantum state and converting the quantum state into an electric signal, the acquisition equipment acquires original data, and the first phase modulator or the second phase modulator is used for performing phase compensation according to a phase drift value obtained by an extreme value search algorithm.
In a preferred embodiment of the invention, the controller may employ an electrically controlled attenuator, an electro-optic intensity modulator, or an acousto-optic modulator.
In a preferred embodiment of the invention, the check sequence operates at a repetition rate that coincides with the repetition rate at which the system operates.
In a preferred embodiment of the invention, in the transmitting end:
the optical pulse is divided into two beams with different intensities by a beam splitter, one beam with stronger intensity is used as local oscillation light, one beam with weaker intensity is used as signal light, and the signal light is divided into a check sequence and an effective sequence by adopting a time division method. The controller controls the intensity or amplitude of the check sequence and the effective sequence independently, so that the amplitude of the check sequence is larger than the maximum amplitude of the effective sequence, and the number of covered periods of phase modulation in the check sequence is 1 pi.
In a preferred embodiment of the invention, an intensity or amplitude modulator and a phase modulator are used to perform gaussian modulation with zero mean on the quadrature components of the active sequence; the polarization and time division multiplexing of the signal light and the local oscillator light are realized by combining the light beams through an unequal arm light path structure, and finally the light beams enter an optical fiber channel for transmission.
In a preferred embodiment of the invention, the check sequence and the valid sequence when independently controlled by the controller are before, after or in the gaussian modulation.
In a preferred embodiment of the invention, in the receiving end:
after signal light and local oscillator light reach a receiving end, firstly, polarization and time division demultiplexing are completed by adopting an unequal arm interference structure, after a local oscillator light branch is loaded with a phase of 0 or pi/2 randomly by adopting a phase modulator, quantum state measurement is completed and converted into an electric signal by a balance detector, and then, original data is obtained by a signal acquisition device, wherein the original data comprises check data for phase compensation and effective key distribution data.
And calculating the check data by adopting an extremum search algorithm to obtain a phase drift value, loading a corresponding compensation phase value on a phase modulator at a receiving end or a transmitting end according to the relationship between the phase modulator and the phase drift value, and processing and analyzing the data after phase compensation so as to obtain a final security key.
In a preferred embodiment of the invention, the extremum searching algorithm is capable of searching for amplitude maxima P in the entire check sequencemaxAnd a minimum value PminAnd returns the Index of the position of the corresponding extreme pointmaxAnd IndexminI.e. the position of the pulse at which the extreme point is located in the check sequence.
In a preferred embodiment of the invention, the amplitude maximum P is compared in the phase compensationmaxAnd a minimum value PminTaking the extreme point with larger absolute value as P and the position as Index, if P is>0, the phase drift value is-Index x pi/N, and N is the total number of the check pulses; if P is<0, the phase shift value is Index π/N.
In a preferred embodiment of the present invention, after the strength of the check sequence is increased, the requirement of the system on the length of the check sequence is reduced, i.e. after the signal-to-noise ratio is increased, the check sequence does not need to be subjected to phase modulation in the range of 2 pi to calculate the phase drift value. The phase modulation range of the check sequence is reduced to pi as described in the present invention, and the results of phase shift when the phase modulation range is pi for 4 are shown in fig. 3 and 4. And meanwhile, matching with the phase drift result to carry out extremum search, and calculating a P point (P1-P4) with the maximum absolute value and a position Index (Index1-Index4) where the P point and the position Index are located, wherein Index < N and N are the number of pulses in the check sequence, thereby calculating the phase drift amount. The amounts of phase drift in FIG. 4 are-Index 1 π/N, -Index2 π/N, Index3 π/N + π, Index4 π/N + π, respectively. Therefore, the invention can effectively improve the phase compensation precision and the communication efficiency.
The foregoing is illustrative of the preferred embodiments of this invention, and it is to be understood that the invention is not limited to the precise form disclosed herein and that various other combinations, modifications, and environments may be resorted to, falling within the scope of the concept as disclosed herein, either as described above or as apparent to those skilled in the relevant art. And that modifications and variations may be effected by those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (10)

1. A method for improving the phase compensation precision and the communication efficiency of a CVQKD system is characterized by comprising the following steps:
a controller is added in a signal light path in a traditional CVQKD system to independently control the amplitudes of a check sequence and an effective sequence which are divided by signal light, so that the amplitude of the check sequence is larger than the maximum amplitude of the effective sequence, and the phase compensation precision is improved;
shortening the length of the check sequence, reducing the proportion of the check sequence in the whole communication process, reducing the covered period from the original 2 pi to pi, and quickly calculating the phase drift value through an extremum search algorithm so as to shorten the calculation time of the phase drift value;
the traditional CVQKD system comprises a sending end and a receiving end, wherein the sending end adopts a coherent state as a light source, then controls the light source to generate pulsed light and divides the pulsed light into two beams with different intensities, one beam with stronger intensity is used as local oscillator light, and the other beam with weaker intensity is used as signal light; performing Gaussian modulation with the mean value of zero on orthogonal components of signal light by adopting an amplitude modulator and a phase modulator, attenuating the intensity of the signal light to ten-photon magnitude by using an attenuator, realizing polarization and time division multiplexing by adopting an unequal arm light path structure and local oscillator beam combination, and then transmitting the signal light in an optical fiber channel; after the local oscillation light reaches a receiving end, polarization and time division demultiplexing are firstly completed, then an electro-optical modulator is adopted to carry out 0 or pi/2 random phase loading on the local oscillation light, quantum state measurement is completed through a balance detector and converted into an electric signal, and acquisition equipment acquires original data, processes and analyzes the data so as to acquire a final security key.
2. A method of improving the accuracy of phase compensation and the efficiency of communication for a CVQKD system according to claim 1, wherein said controller includes an electronically controlled attenuator, an electro-optic intensity modulator, or an acousto-optic modulator.
3. The method of claim 1, wherein the check sequence operates at a repetition rate that is consistent with a repetition rate at which the CVQKD system operates.
4. The method of claim 1, wherein at the transmitting end of the CVQKD system:
the optical pulse is divided into two beams with different intensities by a beam splitter, one beam with stronger intensity is used as local oscillation light, one beam with weaker intensity is used as signal light, and the signal light is divided into a check sequence and an effective sequence by adopting a time division method;
and the controller independently controls the intensity or amplitude of the check sequence and the effective sequence, so that the amplitude of the check sequence is larger than the maximum amplitude of the effective sequence, and the number of covered periods of phase modulation in the check sequence is 1 pi.
5. A method for improving the accuracy of phase compensation and the efficiency of communication in CVQKD systems according to claim 4, characterized in that an intensity or amplitude modulator and a phase modulator are used to implement Gaussian modulation with zero mean value for the quadrature components of the effective sequence; the polarization and time division multiplexing of the signal light and the local oscillator light are realized by combining the light beams through an unequal arm light path structure, and finally the light beams enter an optical fiber channel for transmission.
6. A method for improving the accuracy and communication efficiency of phase compensation in a CVQKD system according to claim 5, wherein the check sequence and the valid sequence when independently controlled by said controller are located before, after or within the Gaussian modulation.
7. The method of claim 6, wherein in a receiving end of the CVQKD system:
after signal light and local oscillator light reach a receiving end, firstly, an unequal arm interference structure is adopted to finish polarization and time division demultiplexing, after a phase modulator is adopted to randomly load a phase of 0 or pi/2 on a local oscillator light branch, quantum state measurement is finished and converted into an electric signal through a balance detector, and then, original data are obtained by a signal acquisition device, wherein the original data comprise verification data for phase compensation and effective key distribution data;
and calculating the check data by adopting an extremum search algorithm to obtain a phase drift value, loading a corresponding compensation phase value on a phase modulator at a receiving end or a transmitting end according to the relationship between the phase modulator and the phase drift value, and processing and analyzing the data after phase compensation so as to obtain a final security key.
8. The method of claim 7, wherein the extremum searching algorithm is capable of searching for the maximum P of the amplitude in the entire check sequencemaxAnd a minimum value PminAnd returns the Index of the position of the corresponding extreme pointmaxAnd IndexminI.e. the position of the pulse at which the extreme point is located in the check sequence.
9. A method for improving the accuracy and communication efficiency of phase compensation in a CVQKD system as claimed in claim 7, wherein in the phase compensation, the amplitude maximum P is comparedmaxAnd a minimum value PminTaking the extreme point with larger absolute value as P and the position as Index, if P is>0, the phase drift value is-Index x pi/N, and N is the total number of the check pulses; if P is<0, the phase shift value is Index π/N.
10. A system based on any one of claims 1 to 9, wherein the system comprises a transmitting end and a receiving end, and the method for improving the phase compensation accuracy and the communication efficiency of the CVQKD system comprises:
the sending end comprises a beam splitter, a controller, an intensity or amplitude modulator, a first phase modulator and a polarization beam combiner, wherein the beam splitter is used for splitting optical pulses into local oscillation light and signal light, the controller is used for independently controlling the amplitudes of a check sequence and an effective sequence into which the signal light is split, so that the amplitude of the check sequence is larger than the maximum amplitude of the effective sequence, the intensity or amplitude modulator and the first phase modulator are used for carrying out Gaussian modulation with the mean value of zero on orthogonal components of the effective sequence, and the polarization beam combiner is used for enabling the signal light and the optical synthesis local oscillation beam to realize polarization and time division multiplexing;
the receiving end comprises a polarization beam splitter, a second phase modulator, a balance detector and signal acquisition equipment, wherein the polarization beam splitter is used for completing polarization and time division demultiplexing, the second phase modulator is used for randomly loading a phase of 0 or pi/2 to local oscillation light, the balance detector is used for completing measurement of a quantum state and converting the quantum state into an electric signal, the acquisition equipment acquires original data, and the first phase modulator or the second phase modulator is used for performing phase compensation according to a phase drift value obtained by an extreme value search algorithm.
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