CN111786732A - High-speed local oscillator continuous variable quantum key distribution system and method - Google Patents

High-speed local oscillator continuous variable quantum key distribution system and method Download PDF

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CN111786732A
CN111786732A CN202010512203.4A CN202010512203A CN111786732A CN 111786732 A CN111786732 A CN 111786732A CN 202010512203 A CN202010512203 A CN 202010512203A CN 111786732 A CN111786732 A CN 111786732A
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CN111786732B (en
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王恒
徐兵杰
皮峣迪
黄伟
李扬
邵云
杨杰
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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
    • H04B10/516—Details of coding or modulation
    • H04B10/548—Phase or frequency modulation
    • H04B10/556—Digital modulation, e.g. differential phase shift keying [DPSK] or frequency shift keying [FSK]
    • H04B10/5563—Digital 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
    • H04B10/60—Receivers
    • H04B10/61—Coherent receivers
    • H04B10/64—Heterodyne, i.e. coherent receivers where, after the opto-electronic conversion, an electrical signal at an intermediate frequency [fIF] is obtained
    • 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

Abstract

The invention relates to the field of quantum secret communication, and discloses a high-speed local oscillator continuous variable quantum key distribution system and a method. The invention can flexibly realize the coherent detection of low noise of quantum signal light and high saturation of classical reference light, has simple system and low cost, greatly improves the repetition frequency and the safe code rate of the CVQKD system, and further promotes the practical process of the high-speed CVQKD system.

Description

High-speed local oscillator continuous variable quantum key distribution system and method
Technical Field
The invention relates to the technical field of quantum secret communication, in particular to a high-speed local oscillator continuous variable quantum key distribution system and a method.
Background
The quantum computing threatens the current mainstream public key cryptography represented by ECC/RSA, and destructively attacks the security of an information system. The Quantum secret communication (QKD) technology based on the Quantum mechanics basic principle fundamentally solves the information security problem in the fields of national defense, finance, government affairs, energy, commerce and the like, has important strategic demands and practical application value, and becomes the strategic competitive focus of developed countries. Among them, Continuous Variable Quantum Key Distribution (CVQKD) is very suitable for short distance metropolitan area networks due to its advantages of high compatibility with coherent optical communication, low cost and high security code rate, and is one of the current directions of domestic and foreign key research, and has attracted extensive attention of researchers. The current CVQKD mainly comprises two technical schemes of a channel-associated local oscillator CVQKD and a local oscillator CVQKD, and the channel-associated local oscillator CVQKD is limited by local oscillator light intensity bottleneck and security loophole, so that the technical scheme of the local oscillator CVQKD is provided to make up the defects of the channel-associated local oscillator CVQKD, and further the secure transmission distance and the key rate of the CVQKD system are improved. However, the local oscillator CVQKD system inevitably needs to transmit a path of classical reference light signal along with the path to accurately compensate for the rapid phase change introduced by two different lasers and channel disturbances, and therefore, multiple multiplexing technologies are needed to realize the common-fiber transmission of the quantum signal light and the classical reference light and to ensure the low noise of the quantum signal light and the high-saturation coherent detection of the classical reference light. Currently, time division multiplexing technology, polarization multiplexing technology and frequency division multiplexing technology are mainly combined for transmitting quantum signal light and classical reference light through a common fiber. The combination of Shanghai transportation university and polarization multiplexing technology successfully realizes the co-fiber transmission of quantum signal light and classical reference light, effectively avoids the crosstalk problem of the classical reference light to the quantum signal light in time domain and polarization dimension, and flexibly realizes the separation and coherent detection of the classical reference light and the quantum signal light (T.Wang, P.Huang, Y.M.Zhou, et al. "Pilot-multiplexed connected-variable quantum key distribution with a local oscillator", Physical Review A,2018,97(1): 012310). However, as the repetition frequency of the CVQKD system is increased, the quantum signal light and the classical reference light are difficult to be accurately separated in time domain space, and the scheme also needs to rely on a base selection module to realize random measurement of two regular components. To increase the repetition frequency of the CVQKD system, germany, hamburger federal defense university proposes to use a high-precision frequency division multiplexing technique to co-fiber transmit Quantum signal light and classical reference light, and to combine a polarization multiplexing technique to effectively separate two optical signals to ensure coherent detection of low noise of the Quantum signal light and high saturation of the classical reference light (f. laudenbach, b. schrenk, c. pacher, et al, "Quantum-assisted acquisition for high-speed coherent-variable-quantity-variable-parameter distribution with longitudinal local oscillator", Quantum,2019,3, 193.). However, this solution requires a high extinction ratio, a complicated polarization multiplexing and demultiplexing device, and a balanced detector with two different detection conditions, resulting in a complicated and expensive system structure.
Disclosure of Invention
The invention provides a high-speed local oscillator continuous variable quantum key distribution system and a method, which can flexibly realize coherent detection of low noise of quantum signal light and high saturation of classical reference light, have simple system and low cost, greatly improve the repetition frequency and the safe code rate of the CVQKD system, and further promote the practical process of the high-speed CVQKD system. The invention discloses a high-speed local oscillator continuous variable quantum key distribution system, which comprises an Alice end and a Bob end, wherein the Alice end is connected with the Bob end through an optical fiber channel, the Alice end comprises a first continuous laser module, an optical beam splitter, a quantum key modulation module, an optical attenuator, an optical frequency shift module and an optical beam combiner, and the Bob end comprises a second continuous laser module, an optical coupler, a balance detection module, an analog-to-digital conversion module, a digital signal processing module and a post-processing module;
the first continuous laser module is connected with the optical beam splitter through an optical fiber, the output end of the optical beam splitter is divided into two paths, the upper path is sequentially provided with the quantum key modulation module and the optical attenuator, the lower path is provided with the optical frequency shift module, and the upper path and the lower path are connected to the optical beam combiner through an optical fiber; the optical combiner is connected with the optical coupler through an optical fiber channel and is in optical fiber coupling with the second continuous laser module to be connected into the balance detection module, the balance detection module is electrically connected with the analog-to-digital conversion module, and data transmission is carried out among the analog-to-digital conversion module, the digital signal processing module and the post-processing module.
Further, the quantum key modulation module comprises a gaussian modulation module or a discrete modulation module containing fixed repetition frequency pulses.
Furthermore, the bandwidth of the balanced detection module can be flexibly adjusted.
The invention discloses a high-speed local oscillator continuous variable quantum key distribution method, which comprises the following steps of:
step 1, the output frequency of the first continuous laser module is f1The continuous light is divided into two paths by the optical beam splitter, and the upper path continuous light is modulated into the continuous light with the repetition frequency f in the quantum key modulation moduleqAnd a bandwidth of 2 Δ fqThe quantum key optical pulse signal is attenuated into quantum signal light containing key information by the optical attenuator, and meanwhile, the down-path continuous light forms a frequency f after passing through the optical frequency shift module1±frOf (2), wherein frIs a frequency shift frequency; finally, quantum signal light and classical reference light are combined by the optical beam combiner and enter an optical fiber channel based on a frequency division multiplexing technology;
step 2, the frequency of the optical signal output by the optical fiber channel and the frequency output by the second continuous laser module is f2The local oscillator light is coupled and input into the balance detection module through the optical coupler to carry out heterodyne coherent detection, and an analog electric signal output by the balance detection module is converted into a time domain digital signal to be processed through the analog-to-digital conversion module;
and 3, processing the time domain digital signal in the digital signal processing module: obtaining non-phase compensated quantum key information X from quantum signal light processing1And P1Obtaining X with reference phase information according to classical reference light processingrAnd PrUsing X to obtain information containing reference phaserAnd PrFor quantum key information X without phase compensation1And P1Performing fast phase compensation processing, and performing slow phase compensation processing by using training sequence in quantum key information to obtain initial quantum key X2And P2；
Step 4, initial quantum key X2And P2And carrying out data coordination and privacy amplification in the post-processing module to obtain final quantum keys X and P.
Further, in step 3, a specific process of processing the time domain digital signal in the digital signal processing module is as follows:
the time domain digital signal is firstly subjected to polarization compensation through a polarization compensation algorithm to ensure that the channel attenuation is an inherent value, and then is subjected to Fourier transform processing to obtain a frequency domain signal and frequency estimation to obtain a frequency value f1-f2；
Aiming at the digital signal processing of quantum signal light, the obtained frequency domain signal is subjected to the center frequency f1-f2A bandwidth of 2 Δ fqThen multiplying the band-pass filtered digital signal containing quantum key information by cos [2 pi (f)1-f2)t]And sin [2 π (f)1-f2)t)]Performing quadrature down-conversion, baseband filtering and data demodulation to obtain quantum key information without phase compensationInformation X1And P1；
Aiming at the digital signal processing of classical reference light, the obtained frequency domain signal is subjected to the center frequency f1-f2±frThen multiplying the narrow-band filtered digital signal containing the reference phase information by cos [2 pi (f)1-f2±fr)t]And sin [2 π (f)1-f2±fr)t]Performing quadrature down-conversion, baseband filtering and data demodulation to obtain X containing reference phase informationrAnd Pr；
Using X for obtaining information containing reference phaserAnd PrFor quantum key information X without phase compensation1And P1Performing fast phase compensation processing, and performing slow phase compensation processing by using training sequence in quantum key information to eliminate phase drift caused by unstable interference and channel disturbance of two different source continuous lights to obtain initial quantum key X2And P2。
Further, the shot noise and the bandwidth Δ f of the balanced detection module are adjustedBHDAnd ensure Δ fBHD>2ΔfqThe method is used for flexibly controlling the responsivity of the classical reference light in coherent detection and ensuring the coherent detection of all key information in a quantum signal light frequency band with the responsivity so as to meet the requirements of low-noise detection of the quantum signal light and high-saturation detection of the classical reference light.
Furthermore, in order to ensure that the quantum signal light and the classical reference light do not interfere with each other in the frequency domain space, the frequency shift frequency f needs to be ensuredr>ΔfqIn the formula,. DELTA.fqIs equal to the repetition frequency f of the modulation signal in the quantum key modulation moduleqAnd (4) correlating.
Furthermore, the quantum key modulation module and the optical frequency shift module are synchronously connected, so that the phase information demodulated by the classical reference light can accurately compensate the quantum signal light.
The invention has the beneficial effects that:
the local oscillation technology is adopted, so that the problems of intensity bottleneck and security loophole of local oscillation light of the channel associated local oscillation CVQKD system are solved, the intensity of the local oscillation light is ensured to meet the limit condition of shot noise detection, and the secure transmission distance and code rate of the CVQKD system are improved;
according to the invention, the quantum signal light and the classical reference light are moved to a high-precision frequency domain space for carrying out common-fiber transmission by adopting a frequency division multiplexing technology, so that the problem of channel crosstalk of the quantum signal light and the classical reference light is effectively avoided, the technical bottleneck of improving the repetition frequency of a local oscillator CVQKD system based on time division multiplexing is broken through, and the safe transmission code rate of the CVQKD system is improved;
according to the invention, the bandwidth of the balanced detection module is adjusted, the responsivity of the classical reference light during coherent detection is flexibly controlled, the low noise of the quantum signal light and the high saturation coherent detection of the classical reference light are realized by combining the intensity adjustment of the local oscillator light, the system cost that a high extinction ratio polarization multiplexing device and two balanced detectors with different detection conditions need to be borrowed in a traditional local oscillator CVQKD system based on frequency division multiplexing is effectively avoided, the cost of the CVQKD system is saved, and the practical process of the high-speed CVQKD system is promoted.
Drawings
FIG. 1 is a schematic diagram of a high-speed local oscillation continuous variable quantum key distribution system according to the present invention;
fig. 2 is a flow chart of digital signal processing of the digital signal processing module according to the present invention.
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.
As shown in fig. 1, this embodiment provides a high-speed local oscillation continuous variable quantum key distribution system, which includes an Alice end and a Bob end, where the Alice end is connected to the Bob end through an optical fiber channel, the Alice end includes a first continuous laser module, an optical splitter, a quantum key modulation module, an optical attenuator, an optical frequency shift module, and an optical combiner, and the Bob end includes a second continuous laser module, an optical coupler, a balance detection module, an analog-to-digital conversion module, a digital signal processing module, and a post-processing module, where:
the first continuous laser module is connected with the optical beam splitter through an optical fiber, the output end of the optical beam splitter is divided into two paths, the upper path is sequentially provided with the quantum key modulation module and the optical attenuator, the lower path is provided with the optical frequency shift module, and the upper path and the lower path are connected to the optical beam splitter through an optical fiber; the optical combiner is connected with the optical coupler through an optical fiber channel and is connected with the second continuous laser module in an optical fiber coupling mode to be connected into the balance detection module, the balance detection module is electrically connected with the analog-to-digital conversion module, and data transmission is carried out among the analog-to-digital conversion module, the digital signal processing module and the post-processing module.
In a preferred embodiment of the invention, the quantum key modulation module comprises a gaussian modulation module or a discrete modulation module containing fixed repetition frequency pulses.
In a preferred embodiment of the invention, the bandwidth of the balanced detection module can be flexibly adjusted.
The principle of the high-speed local oscillator continuous variable quantum key distribution method is as follows:
the continuous optical signal output by the first continuous laser module is:
Figure BDA0002528813070000081
in the formula A1、f1And
Figure BDA0002528813070000082
the amplitude, the frequency and the initial phase of the continuous optical signal output by the first continuous laser module are respectively, the continuous optical signal is divided into two paths by the optical beam splitter, the key information is loaded by the uplink optical signal through the quantum key modulation module, for example, gaussian modulation is used, and the loaded optical signal can be expressed as:
Figure BDA0002528813070000083
wherein R (f)qT) and U (f)qT) are respectively repetition frequencies fqThe optical signal output by the quantum key modulation module is attenuated by the optical attenuator to form Gaussian modulated quantum signal light, AqCorresponding to the amplitude of the quantum optical signal.
After the frequency shift processing of the optical frequency shift module is performed on the downlink continuous optical signal, the formed classical reference optical signal is as follows:
Figure BDA0002528813070000084
in the formula ArAmplitude of classical reference optical signal, frFor frequency shift, two optical signals enter the optical fiber channel through the optical beam combiner for transmission, and are set by fr>ΔfqTo avoid the problem of fiber channel crosstalk between quantum signal light and classical reference light, where Δ fqIs compared with the repetition frequency f of the modulation signal in the quantum key modulation moduleqIt is related.
Quantum signal light and classical reference light are transmitted to an optical coupler at Bob end in an optical fiber channel without crosstalk by utilizing a frequency division multiplexing technology and then enter a balance detection module, and the output frequency of the balance detection module and a second continuous laser module is f2The continuous local oscillator light is subjected to coherent detection, and the formed frequency spectrum sidebands containing quantum key information and classical reference light information are respectively as follows:
Figure BDA0002528813070000091
Figure BDA0002528813070000092
in the formula AloAnd
Figure BDA0002528813070000093
respectively the amplitude and the initial phase of the local oscillator light,
Figure BDA0002528813070000094
is a slowly varying phase between the quantum signal light and the classical reference light,
Figure BDA0002528813070000095
slowly varying phase between output continuous optical signals for a first continuous laser module and a second continuous laser module, ηsigAnd ηrefThe responsivity is detected by the balance of quantum signal light and classical reference light. By adjusting the output power of the second continuous laser module and balancing the bandwidth Δ f of the detection moduleBHDAnd ensure Δ fBHD>2ΔfqThe method and the device can flexibly control the coherent detection responsivity of the shot noise and the classical reference light, and realize the low noise of the quantum signal light and the high saturation detection of the classical reference light.
The analog electrical signal output by the balanced detection module is input into an analog-to-digital conversion module for analog-to-digital conversion, then digital signal processing is performed in a digital signal processing module, the digital signal processing flow is shown in fig. 2, a polarization compensation algorithm is firstly used for polarization compensation of a time domain digital signal to ensure that channel attenuation is an inherent value, then frequency estimation is performed after a frequency domain signal is obtained through Fourier transform processing, and a frequency value f is obtained1-f2。
Aiming at the digital signal processing flow of quantum signal light, the obtained frequency domain signal is processed with the center frequency f1-f2A bandwidth of 2 Δ fqThe band-pass filtering process of (1) multiplying the digital signal containing quantum key information after band-pass filtering by cos [2 π (f)1-f2)t]And sin [2 π (f)1-f2)t)]Performing quadrature down-conversion, baseband filtering and data demodulation to obtain quantum key information X without phase compensation1And P1。
Aiming at the digital signal processing flow of classical reference light, the obtained frequency domain signal is processed with the center frequency of f1-f2±frMultiplying the narrow-band filtered digital signal containing the reference phase information by cos [2 pi (f)1-f2±fr)t]And sin [2 π (f)1-f2±fr)t]Performing quadrature down-conversion, baseband filtering and data demodulation to obtain X containing reference phase informationrAnd Pr。
Using obtained X containing reference phase informationrAnd PrFor quantum key information X without phase compensation1And P1Performing fast phase compensation processing, and performing slow phase compensation processing by using training sequence in quantum key information to obtain initial quantum key X2And P2. Finally, the initial quantum key X is used2And P2And carrying out data coordination and privacy amplification in the post-processing module to obtain final quantum keys X and P.
In a preferred embodiment of the invention, the shot noise is adjusted and the bandwidth Δ f of the detection module is balancedBHDAnd ensure Δ fBHD>2ΔfqThe method is used for flexibly controlling the responsivity of the classical reference light in coherent detection and ensuring the coherent detection of all key information in a quantum signal light frequency band with the responsivity so as to meet the requirements of low-noise detection of the quantum signal light and high-saturation detection of the classical reference light.
In a preferred embodiment of the present invention, in order to ensure that the quantum signal light and the classical reference light do not interfere with each other in the frequency domain space, the following frequency relationship is required to be ensured: f. ofr>ΔfqEnsuring that quantum signal light and classical reference light do not interfere with each other in frequency domain space, wherein delta fqIs compared with the repetition frequency f of the modulation signal in the quantum key modulation moduleqAnd (4) correlating.
In a preferred embodiment of the present invention, the quantum key modulation module and the optical frequency shift module perform a synchronous connection process, so that the phase information demodulated by the classical reference light can accurately compensate the quantum signal light.
In a preferred embodiment of the invention:
firstly, the first continuous laser module at Alice end outputs the center frequency f1The continuous light with 193.0003THz and power of 9dBm is divided into two paths by an optical beam splitter with a splitting ratio of 90:10, 90% of optical signals form classical reference light after being subjected to frequency shift of 200MHz by an optical frequency shift module, 10% of optical signals are subjected to Gaussian signal modulation with repetition frequency of 25MHz by a quantum key modulation module and then are attenuated into quantum signal light by an optical attenuator, wherein the bandwidth of the Gaussian signal with the repetition frequency of 25MHz is about 240MHz (2 Deltaf f)q). Thus, f ofr>Δfq(200MHz>120MHz), which ensures that the quantum signal light and the classical reference light are transmitted without interference in frequency domain in the optical fiber channel with the attenuation of 0.2dB/km and the length of 25 km.
Optical signal output by optical fiber channel and output center frequency f of second continuous laser module2193THz and 10dB of continuous local oscillator light are coupled and input into a balanced detection module through a 50:50 optical coupler, and then the power of the local oscillator light and the bandwidth of the balanced detection module are adjusted to control the responsivity of coherent detection of shot noise and classical reference light, so that low-noise detection of quantum signal light and high-saturation detection of the classical reference light are ensured. The electric signal output by the balance detection module enters a high sampling rate oscilloscope serving as an analog-to-digital conversion module to perform analog-to-digital conversion with the sampling rate of 2Gsa/s and digital signal sampling, and then digital signal processing is performed on the sampled digital signal:
firstly, carrying out polarization compensation on an acquired time domain digital signal, and then carrying out Fourier transform processing and frequency estimation to obtain a frequency value f1-f2(300MHz)。
Aiming at the digital signal processing flow of quantum signal light, the obtained frequency domain signal is processed with the center frequency f1-f2(300MHz) and a bandwidth of about 2 Δ fq(240MHz) and then multiplying the bandpass filtered signal containing the quantum key information by cos [2 π (f)1-f2＝300MHz)t]And sin [2 π (f)1-f2＝300MHz)t]Performing quadrature down-conversion, baseband filtering and signal demodulation to obtain quantum key information X without phase compensation1And P1。
For classical referenceOptical digital signal processing procedure, the obtained frequency domain signal is processed with center frequency f1-f2-frNarrow-band filtering processing of (100MHz) and bandwidth about 1MHz, multiplying the digital signal with reference phase information by cos [2 pi (f)1-f2±fr＝100MHz)t]And sin [2 π (f)1-f2±fr＝100MHz)t]Performing quadrature down-conversion, baseband filtering and signal demodulation to obtain X containing reference phase informationrAnd Pr。
Using obtained X containing reference phase informationrAnd PrFor quantum key information X without phase compensation1And P1Performing fast phase compensation processing, and performing slow phase compensation processing by using training sequence carried in quantum key information to obtain initial quantum key information X2And P2. Then the initial quantum key X2And P2And carrying out data coordination and privacy amplification in the post-processing module to obtain final quantum keys X and P.
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.
In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "inner", "outer", and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings or orientations or positional relationships conventionally placed when the present invention is used, and are only for convenience of description and simplicity of description, but do not indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first," "second," "third," and the like are used solely to distinguish one from another and are not to be construed as indicating or implying relative importance.
In the description of the present invention, it should also be noted that, unless otherwise explicitly specified or limited, the terms "disposed," "mounted," and "connected" are to be construed broadly, e.g., as meaning fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; either a wired or wireless connection.

Claims (8)

1. A high-speed local oscillator continuous variable quantum key distribution system comprises an Alice end and a Bob end, wherein the Alice end is connected with the Bob end through an optical fiber channel;
the first continuous laser module is connected with the optical beam splitter through an optical fiber, the output end of the optical beam splitter is divided into two paths, the upper path is sequentially provided with the quantum key modulation module and the optical attenuator, the lower path is provided with the optical frequency shift module, and the upper path and the lower path are connected to the optical beam combiner through an optical fiber; the optical combiner is connected with the optical coupler through an optical fiber channel and is in optical fiber coupling with the second continuous laser module to be connected into the balance detection module, the balance detection module is electrically connected with the analog-to-digital conversion module, and data transmission is carried out among the analog-to-digital conversion module, the digital signal processing module and the post-processing module.
2. The high-speed local oscillator continuous variable quantum key distribution system according to claim 1, wherein the quantum key modulation module comprises a gaussian modulation module or a discrete modulation module containing fixed repetition frequency pulses.
3. The high-speed local oscillator continuous variable quantum key distribution system according to claim 1, wherein a bandwidth of the balanced detection module is flexibly adjustable.
4. A method for a high-speed local oscillator continuous variable quantum key distribution system according to claim 1, comprising the steps of:
step 1, the output frequency of the first continuous laser module is f1The continuous light is divided into two paths by the optical beam splitter, and the upper path continuous light is modulated into the continuous light with the repetition frequency f in the quantum key modulation moduleqAnd a bandwidth of 2 Δ fqThe quantum key optical pulse signal is attenuated into quantum signal light containing key information by the optical attenuator, and meanwhile, the down-path continuous light forms a frequency f after passing through the optical frequency shift module1±frOf (2), wherein frIs a frequency shift frequency; finally, quantum signal light and classical reference light are combined by the optical beam combiner and enter an optical fiber channel based on a frequency division multiplexing technology;
step 2, the frequency of the optical signal output by the optical fiber channel and the frequency output by the second continuous laser module is f2The local oscillator light is coupled and input into the balance detection module through the optical coupler to carry out heterodyne coherent detection, and an analog electric signal output by the balance detection module is converted into a time domain digital signal to be processed through the analog-to-digital conversion module;
and 3, processing the time domain digital signal in the digital signal processing module: obtaining non-phase compensated quantum key information X from quantum signal light processing1And P1Obtaining X with reference phase information according to classical reference light processingrAnd PrUsing X to obtain information containing reference phaserAnd PrFor quantum key information X without phase compensation1And P1Performing fast phase compensation processing, and performing slow phase compensation processing by using training sequence in quantum key information to obtain initial quantum key X2And P2；
Step 4, beginningInitial quantum key X2And P2And carrying out data coordination and privacy amplification in the post-processing module to obtain final quantum keys X and P.
5. The method according to claim 4, wherein in step 3, the specific process of processing the time domain digital signal in the digital signal processing module is as follows:
the time domain digital signal is firstly subjected to polarization compensation through a polarization compensation algorithm to ensure that the channel attenuation is an inherent value, and then is subjected to Fourier transform processing to obtain a frequency domain signal and frequency estimation to obtain a frequency value f1-f2；
Aiming at the digital signal processing of quantum signal light, the obtained frequency domain signal is subjected to the center frequency f1-f2A bandwidth of 2 Δ fqThen multiplying the band-pass filtered digital signal containing quantum key information by cos [2 pi (f)1-f2)t]And sin [2 π (f)1-f2)t)]Performing quadrature down-conversion, baseband filtering and data demodulation to obtain quantum key information X without phase compensation1And P1；
Aiming at the digital signal processing of classical reference light, the obtained frequency domain signal is subjected to the center frequency f1-f2±frThen multiplying the narrow-band filtered digital signal containing the reference phase information by cos [2 pi (f)1-f2±fr)t]And sin [2 π (f)1-f2±fr)t]Performing quadrature down-conversion, baseband filtering and data demodulation to obtain X containing reference phase informationrAnd Pr；
Using X for obtaining information containing reference phaserAnd PrFor quantum key information X without phase compensation1And P1Performing fast phase compensation processing, and performing slow phase compensation processing by using training sequence in quantum key information to eliminate unstable interference and channel of two different sources of continuous lightPhase drift caused by disturbance to obtain initial quantum key X2And P2。
6. A high-speed local oscillator continuous variable quantum key distribution method as claimed in claim 5, wherein the shot noise and the bandwidth Δ f of the balanced detection module are adjustedBHDAnd ensure Δ fBHD>2ΔfqThe method is used for flexibly controlling the responsivity of the classical reference light in coherent detection and ensuring the coherent detection of all key information in a quantum signal light frequency band with the responsivity so as to meet the requirements of low-noise detection of the quantum signal light and high-saturation detection of the classical reference light.
7. The method as claimed in claim 5, wherein the frequency shift frequency f is ensured to ensure that the quantum signal light and the classical reference light do not interfere with each other in the frequency domain spacer>ΔfqIn the formula,. DELTA.fqIs equal to the repetition frequency f of the modulation signal in the quantum key modulation moduleqAnd (4) correlating.
8. The method according to claim 5, wherein the quantum key modulation module and the optical frequency shift module perform a synchronous connection process, so that phase information demodulated from classical reference light can accurately compensate quantum signal light.
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