CN116192276A - Continuous variable quantum key distribution system and method adapting to rapid polarization disturbance - Google Patents

Continuous variable quantum key distribution system and method adapting to rapid polarization disturbance Download PDF

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CN116192276A
CN116192276A CN202310018118.6A CN202310018118A CN116192276A CN 116192276 A CN116192276 A CN 116192276A CN 202310018118 A CN202310018118 A CN 202310018118A CN 116192276 A CN116192276 A CN 116192276A
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polarization
optical
signal
light
beam splitter
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盘艳
徐兵杰
王恒
邵云
皮峣迪
黄伟
李扬
叶挺
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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
    • H04B10/70—Photonic quantum communication
    • 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
    • H04B10/501—Structural aspects
    • H04B10/503—Laser transmitters
    • 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
    • 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
    • H04B10/60—Receivers
    • H04B10/61—Coherent receivers
    • 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
    • H04B10/60—Receivers
    • H04B10/61—Coherent receivers
    • H04B10/614—Coherent receivers comprising one or more polarization beam splitters, e.g. polarization multiplexed [PolMux] X-PSK coherent receivers, polarization diversity heterodyne coherent receivers
    • 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
    • H04B10/80—Optical aspects relating to the use of optical transmission for specific applications, not provided for in groups H04B10/03 - H04B10/70, e.g. optical power feeding or optical transmission through water
    • H04B10/85—Protection from unauthorised access, e.g. eavesdrop protection
    • 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 provides a continuous variable quantum key distribution system and a method for adapting to rapid polarization disturbance, wherein the system comprises an optical signal transmitting end, a transmission link, a polarization diversity coherent receiving unit, a digital signal processing unit and a data post-processing unit which are connected in sequence; the digital signal processing process of the digital signal processing unit comprises polarization tracking and demultiplexing. The invention adopts orthogonal polarization multiplexing pilot light signals at the transmitting end, adopts polarization diversity coherent detection at the receiving end and combines a fast polarization tracking algorithm to realize polarization tracking and demultiplexing of fast polarization disturbance of a CV-QKD system. The fast polarization tracking algorithm directly calculates the polarization rotation angle caused by polarization disturbance and the phase difference between two orthogonal polarization states through the pilot signal, has the advantages of low calculation complexity, compatibility with other algorithms, parallel processing and the like, and can meet the requirement of a CV-QKD system on real-time tracking of the link fast polarization disturbance.

Description

Continuous variable quantum key distribution system and method adapting to rapid polarization disturbance
Technical Field
The invention relates to the technical field of quantum key distribution, in particular to a continuous variable quantum key distribution system and method adapting to rapid polarization disturbance.
Background
Quantum secret communication is an important technical direction for coping with information security threats due to the fact that the quantum secret communication has information theory security. Among them, quantum key distribution (Quantum Key Distribution, QKD) is one of the most important technological approaches to achieve quantum secret communication. QKD techniques mainly include two major branches, discrete (discrete variable, DV) and continuous (continuous variable, CV) variables. The CV-QKD technology represented by GG02 protocol and No-switch (No Switching) protocol adopts mature optical communication devices and equipment to realize generation, transmission and detection of quantum key signals, so that the generation, transmission and detection of quantum key signals are obviously improved in terms of code rate and compatibility with an optical communication system, and a reliable technical path is provided for realizing high-speed one-time one-secret communication. In the present stage, from the view of the whole structure of the CV-QKD system, the CV-QKD is mainly divided into two modes of a random local oscillator and a local oscillator, and the local oscillator CV-QKD system becomes a main candidate scheme of the high-performance CV-QKD system by the characteristics of higher safety, high speed and the like. Because the local oscillator CV-QKD system adopts independently operated lasers as local oscillator light to carry out coherent detection on quantum signals at the receiving end, the difference between the laser carrier wave at the transmitting end and the local oscillator light at the receiving end in the dimensions of frequency, phase, polarization and the like can influence the precision and efficiency of quantum signal detection. In order to compensate the frequency offset, phase noise and the influence of the optical fiber link on the quantum signal of the laser, a reference light method is often adopted, for example, most systems realize the co-fiber transmission of the reference light and the quantum signal light in a polarization multiplexing mode. Based on the above characteristics, the performance of polarization tracking and demultiplexing is directly related to the stability and effectiveness of the CV-QKD system.
In CV-QKD systems, polarization demultiplexing is largely optical and electrical. The optical method mainly comprises the steps of monitoring the polarization state of an input signal and manually or electrically adjusting a polarization controller to align the polarization main axis of a quantum signal at an input detection end with a receiving device. In 2018, the Shanghai university task group obtains a progressive safety code rate of 3.14Mbps after 25km optical fiber transmission by adopting a local oscillation scheme and manually adjusting a polarization controller. The Chinese electric department 30 adopts a Gaussian modulation coherence state with 100MHz repetition frequency in 2020, and realizes the progressive safe code rate of 7.04Mbps under 25km of optical fiber transmission by automatically adjusting the polarization state through a polarization deviation rectifying instrument. The electrical method is to realize the x and p signal receiving of two orthogonal polarization state signals through a polarization diversity receiver and realize polarization demultiplexing by utilizing a digital signal processing algorithm. The polarization demultiplexing digital signal processing algorithm mainly comprises a Constant Modulus (CMA) algorithm, a kalman filter, a Stokes space-based polarization demultiplexing algorithm and the like. The method of the T.A. Eriksson et al in Sweden adopts a full digital signal processing algorithm for the first time in 2020 to realize multi-effect compensation including phase noise, frequency offset, polarization disturbance (polarization deviation correction is realized by using a CMA algorithm) and the like, builds a CV-QKD experimental system of 194 wavelength multiplexing, and realizes progressive safety code rate of 172.6Mb/s (average single-wavelength safety code rate is about 0.89 Mb/s) under the condition of 25km single-mode fiber transmission. The Shanghai university subject group adopts a Kalman filter in 2019 to realize a 8.4kbps safety code rate under the condition that the simulation deflection speed is 1krad/s and the transmission distance is 20 km. Polarization random disturbance tracking exceeding 3krad/s is achieved through experiments by adopting a polarization demultiplexing algorithm based on Stokes space in 2021 of Chinese electric department 30.
The optical polarization demultiplexing method has various drawbacks. Firstly, an optical deviation rectifying device is added, so that the system cost is high and the system integration is not facilitated. And secondly, the loss of a receiving end is increased, and the safety code rate and the furthest transmission distance of the system are reduced. In addition, when the link polarization state change speed is high, the optical error correcting instrument cannot respond in time, and the system performance can be directly affected. Therefore, the adoption of the electrical polarization demultiplexing method can avoid the defects, and is a development trend of the technology in the field. However, the existing CMA, kalman filter and Stokes space-based polarization demultiplexing and other digital signal processing algorithms have higher algorithm complexity and are difficult to realize real-time dynamic tracking of high-speed polarization random disturbance. Thus, for the problem of fast polarization random disturbance of CV-QKD systems, there is a need to further reduce the complexity of the system or algorithm and to improve the fast polarization tracking capability.
Disclosure of Invention
The invention aims to provide a continuous variable quantum key distribution system and a continuous variable quantum key distribution method which are suitable for rapid polarization disturbance, so as to solve the problem that the performance of the continuous variable quantum key distribution system is reduced under the condition of rapid polarization disturbance.
The invention provides a continuous variable quantum key distribution system and a method for adapting to rapid polarization disturbance, comprising an optical signal transmitting end, a transmission link, a polarization diversity coherent receiving unit, a digital signal processing unit and a data post-processing unit which are connected in sequence; the digital signal processing process of the digital signal processing unit comprises polarization tracking and demultiplexing.
Further, the optical signal transmitting end includes: the device comprises a laser, a fractional device, an optical delay line, an optical attenuator I, a polarization controller I, an electro-optical modulation module, an electric signal generating module, an optical attenuator II and a polarization controller II;
the output end of the laser is connected with the input end of the beam splitter;
the output end I of the beam splitter is connected with the input end I of the polarization beam combiner through the light delay line, the optical attenuator I and the polarization controller in sequence;
the second output end of the beam splitter is connected with the second input end of the polarization beam combiner sequentially through the electro-optical modulation module, the second optical attenuator and the second polarization controller; the electric signal generation module is connected with the electro-optic modulation module;
the output end of the polarization beam combiner is connected with the transmission link.
Further, the polarization diversity coherent receiving unit comprises a polarization beam splitter PSB1, a polarization beam splitter PSB2, an optical mixing unit I, a balance detecting unit I, an optical mixing unit II, a balance detecting unit II, a local oscillator laser and an analog-to-digital conversion unit;
the input end of the polarization beam splitter PSB1 is connected with a transmission link; the output end of the polarization beam splitter PSB1 is connected with the input end I of the first optical mixing unit, and the output end II of the polarization beam splitter PSB1 is connected with the input end II of the second optical mixing unit;
the input end of the polarization beam splitter PSB2 is connected with a local oscillator laser; the output end of the polarization beam splitter PSB2 is connected with the input end II of the first optical mixing unit, and the output end II of the polarization beam splitter PSB2 is connected with the input end I of the second optical mixing unit;
the optical mixing unit is connected with the first input end of the analog-to-digital conversion unit through the balance detection unit;
the second optical mixing unit is connected with the second input end of the analog-to-digital conversion unit through the second balance detection unit;
the output end of the analog-to-digital conversion unit is connected with the digital signal processing unit.
The invention also provides a continuous variable quantum key distribution method adapting to the rapid polarization disturbance, which comprises the following steps:
s10, an optical signal transmitting end outputs a combined optical signal after combining pilot light I, pilot light II and quantum signals;
s20, transmitting the combined optical signal to a polarization diversity coherent receiving unit through a transmission link;
s30, the polarization diversity coherent receiving unit converts the combined light signal into a digital signal;
s40, the digital signal processing unit receives the digital signal and performs digital signal processing including polarization tracking and demultiplexing on the digital signal to recover an original quantum key;
s50, the restored original quantum key is subjected to data post-processing by a data post-processing unit, and a security key is obtained.
Further, step S10 includes the following sub-steps:
s11, the laser emits an optical carrier wave to the beam splitter;
s12, dividing an optical carrier into an upper optical carrier and a lower optical carrier by a beam splitter;
s13, an uplink optical carrier is input into a polarization beam combiner through an optical delay line, an optical attenuator I and a polarization controller I in sequence to form pilot light I; wherein:
the optical delay line adjusts the relative delay of the upper optical carrier and the lower optical carrier;
the optical attenuator I adjusts the relative light intensity of the upper optical carrier and the lower optical carrier;
the polarization controller I adjusts the polarization direction of the uplink optical carrier wave to be aligned with the main axis of the polarization beam combiner;
s14, the downlink optical carrier wave sequentially passes through an electro-optical modulation module, an optical attenuator II and a polarization controller II to be input into a polarization beam combiner to form pilot light II and quantum signal light; wherein:
the electro-optical modulation module modulates the key information sent by the electric signal generation module and the electric signal corresponding to the pilot light to the downlink optical carrier;
the second optical attenuator adjusts the light intensity of the downlink optical carrier wave to meet the light intensity requirement of a quantum signal of a CV-QKD system;
the second polarization controller adjusts the polarization direction of the downlink optical carrier wave to be aligned with the main axis of the polarization beam combiner;
s15, the pilot light I, the pilot light II and the quantum signal light are combined by a polarization beam combiner, and a combined light signal is output.
Further, in the beam combination optical signal, pilot light I and quantum signal light are loaded in the same polarization direction, and pilot light II is loaded in the other orthogonal polarization direction; the first pilot light and the second pilot light form a pilot light structure of orthogonal polarization multiplexing.
Further, step S30 includes the following sub-steps:
s31, the polarization beam splitter PBS1 divides the combined light signal into light signals with two polarization directions; meanwhile, local oscillation light output by the local oscillation laser is input into the polarization beam splitter PBS2 in a mode of forming an included angle of 45 degrees with the main shaft of the polarization beam splitter PBS2 and is uniformly divided into two paths of local oscillation light signals;
s32, the optical signals output by the two polarization beam splitters PBS1 and PBS2 interfere in the first optical mixing unit and the second optical mixing unit respectively and are input into the first balance detection unit and the second balance detection unit respectively for detection;
s33, the electric signals detected by the first balance detection unit and the second balance detection unit enter the analog-to-digital conversion unit to obtain digital signals, and the digital signals are input into the digital signal processing unit.
Further, in step S40, the digital signal processing unit performs digital signal processing on the digital signal, including frequency offset estimation, bandpass filtering, x/p component acquisition, data extraction, polarization tracking and demultiplexing, phase noise estimation and compensation, and signal equalization filtering.
Further, step S40 includes the following sub-steps:
s41, the digital signals are subjected to frequency offset estimation, band-pass filtering and x/p component acquisition, and pilot signals I are respectively extracted
Figure BDA0004041218790000051
And->
Figure BDA0004041218790000052
Pilot signal two->
Figure BDA0004041218790000053
And->
Figure BDA0004041218790000054
Quantum signal +.>
Figure BDA0004041218790000055
And->
Figure BDA0004041218790000056
S42, calculating the polarization rotation parameter alpha (t) and the sum by using the pilot signal two
Figure BDA0004041218790000057
The calculation method is shown in the formulas (1) and (2):
Figure BDA0004041218790000058
/>
Figure BDA0004041218790000061
Figure BDA0004041218790000062
/>
wherein unwrap represents unwind, arctan represents an arctangent function, angle represents a phase angle;
s43, using the polarization rotation parameter alpha (t) and
Figure BDA00040412187900000617
calculating the inverse matrix J of the polarization rotation matrix introduced by the link -1 The expression is shown as a formula (3):
Figure BDA0004041218790000063
s44, inverting matrix J of polarization rotation matrix -1 Jones vector applied to pilot signal one, pilot signal two and quantum signal
Figure BDA0004041218790000064
And +.>
Figure BDA0004041218790000065
Obtaining a signal after fast polarization deviation correction>
Figure BDA0004041218790000066
And->
Figure BDA0004041218790000067
S45, estimating the signal
Figure BDA0004041218790000068
And compensates it to the signal +.>
Figure BDA0004041218790000069
Obtaining compensated signals
Figure BDA00040412187900000610
Estimate signal->
Figure BDA00040412187900000611
And compensates it to the signal +.>
Figure BDA00040412187900000612
Obtaining compensated signals
Figure BDA00040412187900000613
S46, adopting a real-value finite impulse response filtering algorithm to perform signal processing
Figure BDA00040412187900000614
And->
Figure BDA00040412187900000615
Performing signal equalization filtering to obtain an original quantum key E Q (t) the expression of the signal equalization filtering is shown in the formula (4):
Figure BDA00040412187900000616
wherein real represents taking a real part, and imag represents taking an imaginary part; omega ij Representing the tap coefficients of the finite impulse response filter,i and j e {1,2,3,4}.
Further, the tap coefficient of the finite impulse response filter is optimized through a least mean square algorithm of a training sequence.
In summary, due to the adoption of the technical scheme, the beneficial effects of the invention are as follows:
the invention adopts orthogonal multiplexing pilot frequency optical signals to represent the polarization random disturbance of a transmission link on the structure of a continuous variable quantum key distribution (CV-QKD) system, designs a quick polarization tracking algorithm at a receiving end, calculates the polarization disturbance parameters of the transmission link by using the orthogonal multiplexing pilot frequency signals, and realizes quick polarization tracking and demultiplexing oriented to the CV-QKD system. Compared with an optical polarization tracking method, the method adopts a pure digital signal processing algorithm to realize polarization tracking and compensation, has stronger flexibility, reduces the complexity and loss of the system, and has the polarization tracking capability of more than 10 krad/s. Compared with the traditional CMA, kalman filter and Stokes space-based polarization tracking and demultiplexing algorithm, the algorithm provided by the invention has the advantages of low algorithm complexity, simple parallel processing, high polarization tracking speed and the like.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following description will briefly describe the drawings in the embodiments, it being understood that the following drawings only illustrate some embodiments of the present invention and should not be considered as limiting the scope, and that other related drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a schematic diagram of an implementation of a continuous variable quantum key distribution system adapted to rapid polarization perturbation in an embodiment of the present invention.
Fig. 2 is a schematic diagram of an implementation of an optical signal transmitting end according to an embodiment of the present invention.
Fig. 3 is a schematic diagram of optical signal configuration in an optical signal transmitting end according to an embodiment of the present invention.
Fig. 4 is a schematic diagram of an implementation of a polarization diversity coherent receiving unit according to an embodiment of the present invention.
Fig. 5 is a flowchart of an implementation of the digital signal processing unit according to an embodiment of the present invention.
FIG. 6 is a graph showing the result of the over-noise fluctuation measured by the correlation experiment in the embodiment of the present invention.
FIG. 7 is a graph showing the comparison of the over-noise measured by the correlation experiment in the embodiment of the present invention.
Fig. 8 is a diagram showing the result of the security code rate measured by the related experiment in the embodiment of the present invention.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments of the present invention. The components of the embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations.
Thus, the following detailed description of the embodiments of the invention, as presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which have been made by those of ordinary skill in the art without undue burden, are within the scope of the present invention.
Examples
As shown in fig. 1, this embodiment proposes a continuous variable quantum key distribution system adapted to rapid polarization disturbance, which includes an optical signal transmitting end, a transmission link, a polarization diversity coherent receiving unit, a digital signal processing unit and a data post-processing unit that are sequentially connected; the digital signal processing process of the digital signal processing unit comprises polarization tracking and demultiplexing. Wherein:
s10, an optical signal transmitting end outputs a combined optical signal after combining pilot light I, pilot light II and quantum signals;
s20, transmitting the combined optical signals to a polarization diversity coherent receiving unit through a transmission link (optical fiber or free space channel);
s30, the polarization diversity coherent receiving unit converts the combined light signal into a digital signal;
s40, the digital signal processing unit receives the digital signal and performs digital signal processing including polarization tracking and demultiplexing on the digital signal to recover an original quantum key;
s50, the restored original quantum key is subjected to data post-processing by a data post-processing unit, and a security key is obtained.
As shown in fig. 2, the optical signal transmitting terminal includes: the device comprises a laser, a fractional device, an optical delay line, an optical attenuator I, a polarization controller I, an electro-optical modulation module, an electric signal generating module, an optical attenuator II and a polarization controller II; the output end of the laser is connected with the input end of the beam splitter; the output end I of the beam splitter is connected with the input end I of the polarization beam combiner through the light delay line, the optical attenuator I and the polarization controller in sequence; the second output end of the beam splitter is connected with the second input end of the polarization beam combiner sequentially through the electro-optical modulation module, the second optical attenuator and the second polarization controller; the electric signal generation module is connected with the electro-optic modulation module; the output end of the polarization beam combiner is connected with the transmission link. Wherein:
s11, the laser emits an optical carrier wave to the beam splitter;
s12, dividing an optical carrier into an upper optical carrier and a lower optical carrier by a beam splitter;
s13, an uplink optical carrier is input into a polarization beam combiner through an optical delay line, an optical attenuator I and a polarization controller I in sequence to form pilot light I; specifically:
the optical delay line adjusts the relative delay of the upper optical carrier and the lower optical carrier; the optical delay line can be composed of optical fiber delay elements such as a single-mode optical fiber or an adjustable optical delay module;
the optical attenuator I adjusts the relative light intensity of the upper optical carrier and the lower optical carrier; the first optical attenuator can be composed of fixed optical attenuators or adjustable optical attenuators and other elements; the relative light intensity is determined by CV-QKD system requirements;
the polarization controller I adjusts the polarization direction of the uplink optical carrier wave to be aligned with the main axis of the polarization beam combiner; the polarization controller may be composed of a manual polarization controller or an automatic polarization controller.
S14, the downlink optical carrier wave sequentially passes through an electro-optical modulation module, an optical attenuator II and a polarization controller II to be input into a polarization beam combiner to form pilot light II and quantum signal light; specifically:
the electro-optical modulation module modulates the key information sent by the electric signal generation module and the electric signal corresponding to the pilot light to the downlink optical carrier; the electro-optic modulation module can be composed of an optical intensity modulator, a phase modulator, an IQ modulator and other elements; the signal expression sent by the electric signal generating module is Q (t) exp (j 2 f) 2 t)+exp(j2f 1 t). Wherein Q (t) exp (j 2 f) 2 t) is the shifted frequency f 2 Key information of exp (j 2 f) 1 t) is the pilot light-corresponding loaded electrical signal.
The second optical attenuator adjusts the light intensity of the downlink optical carrier wave to meet the light intensity requirement of a quantum signal of a CV-QKD system; the second optical attenuator may be composed of a fixed optical attenuator or a tunable optical attenuator.
The second polarization controller adjusts the polarization direction of the downlink optical carrier wave to be aligned with the main axis of the polarization beam combiner; the polarization controller may be composed of a manual polarization controller or an automatic polarization controller.
S15, the pilot light I, the pilot light II and the quantum signal light are combined by a polarization beam combiner, and a combined light signal is output.
As shown in fig. 3, in the combined optical signal, the first pilot light and the quantum signal light are loaded in the same polarization direction, and the second pilot light is loaded in the other orthogonal polarization direction; the pilot light I and the pilot light II form an orthogonal polarization multiplexing pilot light structure, and can completely represent polarization disturbance information of the quantum signal light in a transmission link.
As shown in fig. 4, the polarization diversity coherent receiving unit includes a polarization beam splitter PSB1, a polarization beam splitter PSB2, an optical mixing unit one, a balance detecting unit one, an optical mixing unit two, a balance detecting unit two, a local oscillator laser and an analog-to-digital conversion unit;
the input end of the polarization beam splitter PSB1 is connected with a transmission link; the output end of the polarization beam splitter PSB1 is connected with the input end I of the first optical mixing unit, and the output end II of the polarization beam splitter PSB1 is connected with the input end II of the second optical mixing unit; the input end of the polarization beam splitter PSB2 is connected with a local oscillator laser; the output end of the polarization beam splitter PSB2 is connected with the input end II of the first optical mixing unit, and the output end II of the polarization beam splitter PSB2 is connected with the input end I of the second optical mixing unit; the optical mixing unit is connected with the first input end of the analog-to-digital conversion unit through the balance detection unit; the second optical mixing unit is connected with the second input end of the analog-to-digital conversion unit through the second balance detection unit; the output end of the analog-to-digital conversion unit is connected with the digital signal processing unit. Wherein:
s31, the polarization beam splitter PBS1 divides the combined light signal into light signals with two polarization directions; meanwhile, local oscillation light output by the local oscillation laser is input into the polarization beam splitter PBS2 in a mode of forming an included angle of 45 degrees with the main shaft of the polarization beam splitter PBS2 and is uniformly divided into two paths of local oscillation light signals;
s32, the optical signals output by the two polarization beam splitters PBS1 and PBS2 interfere in the first optical mixing unit and the second optical mixing unit respectively and are input into the first balance detection unit and the second balance detection unit respectively for detection;
s33, the electric signals detected by the first balance detection unit and the second balance detection unit enter the analog-to-digital conversion unit to obtain digital signals, and the digital signals are input into the digital signal processing unit.
The first optical mixing unit and the second optical mixing unit can be composed of components such as a polarization maintaining coupler or a 90-degree optical mixer, and the coupling of local oscillation light and signal light is realized. The first balance detection unit and the second balance detection unit can be composed of 2 or 4 balance detectors, so that beat frequency of the coupled light signals is realized.
As shown in fig. 5, the digital signal processing unit performs digital signal processing on the digital signal, including frequency offset estimation, bandpass filtering, x/p component acquisition, data extraction, polarization tracking and demultiplexing, phase noise estimation and compensation, and signal equalization filtering. Specifically:
s41, the digital signal is subjected to frequency offset estimation and bandThe first pilot signal is extracted by the filtering and the x/p component acquisition
Figure BDA0004041218790000111
And->
Figure BDA0004041218790000112
Pilot signal two->
Figure BDA0004041218790000113
And->
Figure BDA0004041218790000114
Quantum signal +.>
Figure BDA0004041218790000115
And->
Figure BDA0004041218790000116
S42, calculating the polarization rotation parameter alpha (t) and the sum by using the pilot signal two
Figure BDA0004041218790000117
The calculation method is shown in the formulas (1) and (2):
Figure BDA0004041218790000118
Figure BDA0004041218790000119
wherein, unwrap represents unwrapping, avoiding phase jumps, arctan represents an arctangent function, angle represents a phase angle; it is assumed here that the parametric variations caused by polarization perturbations are a continuous slow-varying process with respect to the quantum signal optical information modulation rate (i.e., quantum signal code rate).
S43, using the polarization rotation parameter alpha (t) and
Figure BDA00040412187900001123
calculating the inverse matrix J of the polarization rotation matrix introduced by the link -1 The expression is shown as a formula (3):
Figure BDA00040412187900001110
s44, inverting matrix J of polarization rotation matrix -1 Jones vector applied to pilot signal one, pilot signal two and quantum signal
Figure BDA00040412187900001111
And +.>
Figure BDA00040412187900001112
Obtaining a signal after fast polarization deviation correction>
Figure BDA00040412187900001113
And->
Figure BDA00040412187900001114
S45, estimating the signal
Figure BDA00040412187900001115
And compensates it to the signal +.>
Figure BDA00040412187900001116
Obtaining compensated signals
Figure BDA00040412187900001117
Estimate signal->
Figure BDA00040412187900001118
And compensates it to the signal +.>
Figure BDA00040412187900001119
Obtaining compensated signals
Figure BDA00040412187900001120
S46, adopting a real-value finite impulse response filtering algorithm to perform signal processing
Figure BDA00040412187900001121
And->
Figure BDA00040412187900001122
Performing signal equalization filtering to obtain an original quantum key E Q (t) the expression of the signal equalization filtering is shown in the formula (4):
Figure BDA0004041218790000121
wherein real represents taking a real part, and imag represents taking an imaginary part; omega ij Tap coefficients i and j e {1,2,3,4} representing the finite impulse response filter. The tap coefficient of the finite impulse response filter can be optimized through a least mean square algorithm of a training sequence, and the like, and can also be realized by other methods.
Finally, the original quantum key E Q And (t) performing data post-processing including the processes of parameter estimation, data quantization negotiation, key error correction, private key amplification and the like by a data post-processing unit after data post-processing to obtain a security key.
FIG. 6 is a graph showing the result of the over-noise fluctuation of the CV-QKD system measured by the related experiment of the present invention. The related experiment adopts a discrete modulation protocol, a transmission link is a 24.49km standard single-mode fiber, the quantum signal code rate is 1GBaud, the frequency difference between the pilot signal I and the quantum signal is 850MHz, and the frequency difference between the pilot signal I and the pilot signal II is 1700MHz. As can be seen from FIG. 6, at scrambling rates of 0.63krad/s, 1.26krad/s, 3.14krad/s, 6.28krad/s, and 12.57krad/s, the over-noise of the CV-QKD system is always maintained in the range of 0.02 to 0.06SNU, where SNU represents the shot noise normalization unit. Therefore, the scheme and the algorithm provided by the invention can keep the stability of the system over noise under the condition of rapid polarization disturbance, and realize stable and reliable quantum key distribution.
FIG. 7 is a graph showing the comparison of the over-noise measured by the correlation test of the present invention. In fig. 7, black circles represent the system noise results calculated at different times when the disturbance rate is 0, gray triangles represent the system noise results calculated at different times when the present invention is used with the disturbance rate of 12.57 rad/s, and black squares represent the system noise results calculated at different times when the present invention is not used with the disturbance rate of 12.57 rad/s. As is clear from fig. 7, the present invention can largely maintain the system performance at a scrambling speed of 12.57 rad/s, so that it is similar to the result under the condition of no polarization scrambling.
Fig. 8 is a graph showing the result of the security code rate measured by the related experiment of the present invention. In fig. 8, the solid line shows the simulated progressive safety code rate of the system under the parameters of 0 disturbance bias speed, 6.15SNU modulation variance, 0.03SNU over noise, 0.15SNU electric noise to shot noise ratio, 0.56 quantum efficiency of the receiving end, 0.95 negotiation efficiency, 20% additional data overhead and the like. The different marks in fig. 8 represent the average progressive safety code rate of the system at different scrambling speeds. As can be seen from fig. 8, under the condition that the scrambling rates are 0.63krad/s, 1.26krad/s, 3.14krad/s, 6.28krad/s and 12.57krad/s, the progressive safety code rate of the system is very similar under the correction condition of sampling the method of the invention, which indicates that the invention has good fast polarization tracking and demultiplexing capability, and can keep the system running stably under the condition of fast change of the polarization state of a transmission link.
The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (10)

1. The continuous variable quantum key distribution system adapting to the rapid polarization disturbance is characterized by comprising an optical signal transmitting end, a transmission link, a polarization diversity coherent receiving unit, a digital signal processing unit and a data post-processing unit which are connected in sequence; the digital signal processing process of the digital signal processing unit comprises polarization tracking and demultiplexing.
2. The continuous variable quantum key distribution system of claim 1, wherein the optical signal transmitting terminal comprises: the device comprises a laser, a fractional device, an optical delay line, an optical attenuator I, a polarization controller I, an electro-optical modulation module, an electric signal generating module, an optical attenuator II and a polarization controller II;
the output end of the laser is connected with the input end of the beam splitter;
the output end I of the beam splitter is connected with the input end I of the polarization beam combiner through the light delay line, the optical attenuator I and the polarization controller in sequence;
the second output end of the beam splitter is connected with the second input end of the polarization beam combiner sequentially through the electro-optical modulation module, the second optical attenuator and the second polarization controller; the electric signal generation module is connected with the electro-optic modulation module;
the output end of the polarization beam combiner is connected with the transmission link.
3. The continuous variable quantum key distribution system for adapting to rapid polarization disturbance according to claim 1, wherein the polarization diversity coherent receiving unit comprises a polarization beam splitter PSB1, a polarization beam splitter PSB2, an optical mixing unit one, a balance detection unit one, an optical mixing unit two, a balance detection unit two, a local oscillator laser and an analog-to-digital conversion unit;
the input end of the polarization beam splitter PSB1 is connected with a transmission link; the output end of the polarization beam splitter PSB1 is connected with the input end I of the first optical mixing unit, and the output end II of the polarization beam splitter PSB1 is connected with the input end II of the second optical mixing unit;
the input end of the polarization beam splitter PSB2 is connected with a local oscillator laser; the output end of the polarization beam splitter PSB2 is connected with the input end II of the first optical mixing unit, and the output end II of the polarization beam splitter PSB2 is connected with the input end I of the second optical mixing unit;
the optical mixing unit is connected with the first input end of the analog-to-digital conversion unit through the balance detection unit;
the second optical mixing unit is connected with the second input end of the analog-to-digital conversion unit through the second balance detection unit;
the output end of the analog-to-digital conversion unit is connected with the digital signal processing unit.
4. A continuous variable quantum key distribution method adapting to rapid polarization disturbance is characterized by comprising the following steps:
s10, an optical signal transmitting end outputs a combined optical signal after combining pilot light I, pilot light II and quantum signals;
s20, transmitting the combined optical signal to a polarization diversity coherent receiving unit through a transmission link;
s30, the polarization diversity coherent receiving unit converts the combined light signal into a digital signal;
s40, the digital signal processing unit receives the digital signal and performs digital signal processing including polarization tracking and demultiplexing on the digital signal to recover an original quantum key;
s50, the restored original quantum key is subjected to data post-processing by a data post-processing unit, and a security key is obtained.
5. The method for continuous variable quantum key distribution adapted to rapid polarization perturbation according to claim 4, wherein step S10 comprises the sub-steps of:
s11, the laser emits an optical carrier wave to the beam splitter;
s12, dividing an optical carrier into an upper optical carrier and a lower optical carrier by a beam splitter;
s13, an uplink optical carrier is input into a polarization beam combiner through an optical delay line, an optical attenuator I and a polarization controller I in sequence to form pilot light I; wherein:
the optical delay line adjusts the relative delay of the upper optical carrier and the lower optical carrier;
the optical attenuator I adjusts the relative light intensity of the upper optical carrier and the lower optical carrier;
the polarization controller I adjusts the polarization direction of the uplink optical carrier wave to be aligned with the main axis of the polarization beam combiner;
s14, the downlink optical carrier wave sequentially passes through an electro-optical modulation module, an optical attenuator II and a polarization controller II to be input into a polarization beam combiner to form pilot light II and quantum signal light; wherein:
the electro-optical modulation module modulates the key information sent by the electric signal generation module and the electric signal corresponding to the pilot light to the downlink optical carrier;
the second optical attenuator adjusts the light intensity of the downlink optical carrier wave to meet the light intensity requirement of a quantum signal of a CV-QKD system;
the second polarization controller adjusts the polarization direction of the downlink optical carrier wave to be aligned with the main axis of the polarization beam combiner;
s15, the pilot light I, the pilot light II and the quantum signal light are combined by a polarization beam combiner, and a combined light signal is output.
6. The method for distributing continuous variable quantum keys adapting to rapid polarization disturbance according to claim 5, wherein in the combined light signal, pilot light I and quantum signal light are loaded in the same polarization direction, and pilot light II is loaded in the other orthogonal polarization direction; the first pilot light and the second pilot light form a pilot light structure of orthogonal polarization multiplexing.
7. The method of continuous variable quantum key distribution adapted to rapid polarization perturbation of claim 6, wherein step S30 comprises the sub-steps of:
s31, the polarization beam splitter PBS1 divides the combined light signal into light signals with two polarization directions; meanwhile, local oscillation light output by the local oscillation laser is input into the polarization beam splitter PBS2 in a mode of forming an included angle of 45 degrees with the main shaft of the polarization beam splitter PBS2 and is uniformly divided into two paths of local oscillation light signals;
s32, the optical signals output by the two polarization beam splitters PBS1 and PBS2 interfere in the first optical mixing unit and the second optical mixing unit respectively and are input into the first balance detection unit and the second balance detection unit respectively for detection;
s33, the electric signals detected by the first balance detection unit and the second balance detection unit enter the analog-to-digital conversion unit to obtain digital signals, and the digital signals are input into the digital signal processing unit.
8. The method of claim 7, wherein in step S40, the digital signal processing unit performs digital signal processing on the digital signal including frequency offset estimation, bandpass filtering, x/p component acquisition, data extraction, polarization tracking and demultiplexing, phase noise estimation and compensation, and signal equalization filtering.
9. The method of continuous variable quantum key distribution adapted to rapid polarization perturbation of claim 8, wherein step S40 comprises the sub-steps of:
s41, the digital signals are subjected to frequency offset estimation, band-pass filtering and x/p component acquisition, and pilot signals I are respectively extracted
Figure FDA0004041218780000041
And->
Figure FDA0004041218780000042
Pilot signal two->
Figure FDA0004041218780000043
And->
Figure FDA0004041218780000044
Quantum signal +.>
Figure FDA0004041218780000045
And->
Figure FDA0004041218780000046
S42, calculating the polarization rotation parameter alpha (t) and the sum by using the pilot signal two
Figure FDA0004041218780000047
The calculation method is shown in the formulas (1) and (2):
Figure FDA0004041218780000048
Figure FDA0004041218780000049
wherein unwrap represents unwind, arctan represents an arctangent function, angle represents a phase angle;
s43, using the polarization rotation parameter alpha (t) and
Figure FDA00040412187800000410
calculating the inverse matrix J of the polarization rotation matrix introduced by the link -1 The expression is shown as a formula (3):
Figure FDA00040412187800000411
s44, inverting matrix J of polarization rotation matrix -1 Jones vector applied to pilot signal one, pilot signal two and quantum signal
Figure FDA00040412187800000412
And +.>
Figure FDA00040412187800000413
Obtaining a signal after fast polarization deviation correction>
Figure FDA00040412187800000414
And->
Figure FDA00040412187800000415
S45, estimating the signal
Figure FDA00040412187800000416
And compensates it to the signal +.>
Figure FDA00040412187800000417
Obtaining compensated signals
Figure FDA00040412187800000418
Estimate signal->
Figure FDA00040412187800000419
And compensates it to the signal +.>
Figure FDA00040412187800000420
Obtaining compensated signals
Figure FDA00040412187800000421
S46, adopting a real-value finite impulse response filtering algorithm to perform signal processing
Figure FDA00040412187800000422
And->
Figure FDA00040412187800000423
Performing signal equalization filtering to obtain an original quantum key E Q (t) the expression of the signal equalization filtering is shown in the formula (4):
Figure FDA00040412187800000424
wherein real represents taking a real part, and imag represents taking an imaginary part; omega ij Tap coefficients i and j e {1,2,3,4} representing the finite impulse response filter.
10. The continuous variable quantum key distribution method for adapting to fast polarization perturbation according to claim 9, wherein the tap coefficients of the finite impulse response filter are optimized by a least mean square algorithm of training sequence.
CN202310018118.6A 2023-01-06 2023-01-06 Continuous variable quantum key distribution system and method adapting to rapid polarization disturbance Pending CN116192276A (en)

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