WO2021136165A1 - 一种基于mdm-sdm的量子与经典融合通信系统及传输方法 - Google Patents

一种基于mdm-sdm的量子与经典融合通信系统及传输方法 Download PDF

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WO2021136165A1
WO2021136165A1 PCT/CN2020/140114 CN2020140114W WO2021136165A1 WO 2021136165 A1 WO2021136165 A1 WO 2021136165A1 CN 2020140114 W CN2020140114 W CN 2020140114W WO 2021136165 A1 WO2021136165 A1 WO 2021136165A1
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signal
mdm
sdm
quantum
classical
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French (fr)
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郭邦红
张倩琳
胡敏
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广东尤科泊得科技发展有限公司
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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
    • 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
    • H04L9/0858—Details about key distillation or coding, e.g. reconciliation, error correction, privacy amplification, polarisation coding or phase coding
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
    • Y02D30/00—Reducing energy consumption in communication networks
    • Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks

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  • the invention relates to the field of quantum information, in particular to a MDM-SDM-based quantum and classical fusion communication system and transmission method.
  • Quantum secure communication provides the potential of secure key distribution under the guarantee of quantum mechanics, confirms the possibility of unconditional security, and is the fastest-growing, closest-to-practical and large-scale technology in quantum communication.
  • free space and fiber-based QKD (Quantum Key Distribution) experiments have proved the feasibility of quantum secure communication by using different physical principles.
  • the QKD system generally uses dedicated optical fibers and equipment, which has limitations in terms of network scale and practicability.
  • QKD and classic communication systems can be integrated into the existing optical fiber infrastructure to reduce installation and operating costs and improve the scalability of the QKD network.
  • the advantage is that the cores of the MCF are separated based on physical structure, and the quantum signal is less interfered by classical signals, and it is easy to obtain better QKD performance when large-capacity classical signals are simultaneously transmitted.
  • Tobias A. Eriksson et al. studied the feasibility of space division multiplexing with 24.5Gbaud 16QAM (Quadrature Amplitude Modulation) multiplexing CV-QKD signal and WDM in 19-core MCF through experiments. Placing the CV-QKD signal at the wavelength in the guard band of the classical signal band further suppresses crosstalk between signals.
  • the number of fiber cores is limited, which is not conducive to further Increase transmission capacity.
  • the prior art patent CN110247705A provides a quantum access network architecture and method based on multi-core fiber, which can support a large number of quantum users to access, but the seven-core fiber cladding used is limited, which makes it difficult to further increase the communication capacity.
  • the present invention is more Excellently proposed to use FM-MCF special optical fiber to achieve fusion transmission, and use the two-dimensional multiplexing method that combines spatial dimension and mode dimension to solve the bottleneck problem of communication capacity.
  • the prior art patent CN110048776A uses the orthogonality between different modes and proposes a scheme for realizing multiple QKD multiplexing based on a few-mode fiber.
  • the present invention better proposes a quantum and classical fusion transmission scheme, allowing quantum signals and classical signals to share optical fiber infrastructure, saving costs and improving the practicality of QKD Sex.
  • the prior art patent CN109600221A proposes a solution for realizing quantum and classical mode division multiplexing transmission based on a multi-core fiber, which improves the isolation between signals.
  • the adopted DV-QKD protocol has relatively high requirements for light sources and detectors.
  • the present invention further proposes to use the CV-QKD protocol to achieve fusion transmission, which has low cost, strong practicability, and better integration with traditional optical communication networks.
  • the present invention proposes a two-dimensional multiplexing transmission method combining MDM and SDM, that is, multiple cores are placed in a fiber cladding, and each core can transmit multiple modes of FM at the same time.
  • -MCF FewMode-Multi Core Fiber, Few Mode-Multi Core Fiber
  • the invention provides a MDM-SDM-based quantum and classical fusion communication system and transmission method for realizing ultra-large-capacity transmission and improving safety.
  • Choosing an appropriate number of cores and modes can reduce the requirements for signal processing, and it is easy to obtain better quantum key distribution performance in quantum and classical transmission.
  • Its heterogeneous structure makes the crosstalk between the cores insensitive to the degree of bending, and because the cores of heterogeneous cores have a larger effective refractive index difference than the cores of homogenous cores, the crosstalk can be effectively reduced.
  • the trench-assisted structure can effectively reduce the crosstalk between the modes by suppressing the overlap of the electric field distribution of two adjacent cores.
  • the larger mode field area can reduce nonlinear damage while maintaining low dispersion performance.
  • An MDM-SDM-based quantum and classical fusion communication system including an Alice sending end, a Bob receiving end, and an MDM-SDM multiplexing unit.
  • the Alice sending end is connected to the Bob receiving end through the MDM-SDM multiplexing unit;
  • the MDM-SDM multiplexing unit includes an MDM-SDM multiplexer and an MDM-SDM demultiplexer, and the MDM-SDM multiplexer and the MDM-SDM demultiplexer are connected by an FM-MCF special optical fiber.
  • the FM-MCF special fiber is a heterogeneous groove-assisted graded index three-mode seven-core fiber; the refractive index distribution of the core of the FM-MCF special fiber is graded, and three modes can be transmitted in the same fiber core. signal;
  • the Alice transmitting end includes N LD (Laser Diode, semiconductor laser), N BS (Beam Splitter, beam splitter), N AM (Amplitude Modulator, amplitude modulator), N PM (Phase Modulator, phase modulator) Adapter), N PBS (Polarization Beam Splitter, polarization beam splitter), 1 LO (Local Oscillator, local oscillator), N dispersion compensation units, 1 MIMO (Multiple-Input Multiple-Output, multiple-input multiple-output) Delay equalization algorithm) unit, N DSP (Digital Signal Processing, digital signal processing) units, and N signal decision units; the N LDs are connected through BS, AM, PM and PBS in turn, and the N PBSs and MDM -SDM demultiplexer connection, the N decision units are connected to the coherent receiver through the DSP unit, the MIMO unit, and the dispersion compensation unit in turn, the N coherent receivers are connected to the MDM-SDM demultiplexer, the 1
  • the Bob receiving end includes a classic signal transmitter, N CV-QKD receivers, N amplifiers, N 90° optical mixers, N PBSs, and N PCs (Polarization Controller, polarization controller);
  • the classic signal transmitter is connected with the MDM-SDM multiplexer
  • the N CV-QKD receivers are connected with the PC through the amplifier, the 90° optical mixer, and the PBS in turn
  • the N PCs are connected with the MDM-SDM multiplexer connection;
  • the classic signal transmitter sends 2N QPSK (Quadrature Phase Shift Keying, quadrature phase shift keying) signals, which are converted from the fundamental mode to the high-order modes LP 11a and LP 11b through mode conversion, and then enter the MDM-SDM multiplexer and then convert It is converted into a mode suitable for FM-MCF transmission, and sent to the MDM-SDM demultiplexer through FM-MCF, and decomposed into independent 2N classical signals; the decomposed classical signals are respectively subjected to mode conversion from high-order mode to base mode Form, and enter the coherent receiver together with the LO signal for coherent detection, dispersion compensation by the dispersion compensation unit, equalization processing by the MIMO unit, digital signal processing by the DSP unit, and finally signal judgment; the N LDs at the Alice transmitting end Transmit a pulse, divide the pulse into the upper quantum signal and the lower LO signal through a 90/10 BS.
  • 2N QPSK Quadrature Phase Shift Keying, quadrature phase shift
  • the classic signal transmitter includes 2N laser diodes, 2N IQ modulators, 2N AWGs (Arbitrary Waveform Generator, arbitrary waveform generator), and the 2N laser diodes respectively pass the IQ modulator and MDM-SDM complex It is connected with the device, and 2N AWGs are connected with the IQ modulator.
  • the quantum signal adopts a method of sending a local oscillator signal instead of a local local oscillator. More preferably, the quantum signal and the classical signal adopt the method of reverse simultaneous transmission.
  • the quantum signal unit is a unit that generates a CV-QKD signal based on the reverse coordination GG02 protocol.
  • the present invention also provides a MDM-SDM-based quantum and classical fusion communication transmission method, including the following steps:
  • System noise test In the case of Alice transmitting the laser pulse train, test the system noise to determine whether the signal-to-noise ratio is higher than the preset signal-to-noise ratio, if the signal-to-noise ratio is higher than the set signal-to-noise ratio If the signal-to-noise ratio is lower than the set value, proceed to steps S2 and S2', and generate a prompt message if the signal-to-noise ratio is lower than the set signal-to-noise ratio preset value;
  • Quantum state preparation The LD at the transmitting end of Alice emits a pulse with a repetition frequency of 2ns and a wavelength of 1550nm, which is divided into two pulses by a 90/10 asymmetric beam splitter.
  • the pulse beam with stronger light intensity is used as the measuring book for Bob's receiving end Vibration signal, the pulse beam with weaker light intensity is sent to AM unit and PM unit for amplitude and phase modulation, and the modulated signal and local oscillator signal are polarization multiplexed through PBS;
  • each QPSK signal obtained through S2' is converted from the basic mode form to higher-order modes LP 11a and LP 11b through mode conversion;
  • Mode conversion The classic signal output by the MDM-SDM demultiplexer is converted from a high-order mode to a fundamental mode through mode conversion, and then enters the coherent receiver;
  • Quantum signal processing The quantum signal output by the MDM-SDM multiplexer enters the PC unit to correct the polarization offset of the quantum signal and the local oscillator signal.
  • the PBS at the Bob receiving end decomposes the input signal into signal pulses and local oscillator signal pulses.
  • the beam pulse is fed into a 90° optical mixer, the phase and amplitude of the signal are extracted by performing four phase interferences between the signal and the local oscillator, the signal is amplified by an amplifier, and finally it enters the CV-QKD receiver for homodyne detection;
  • the present invention adopts heterogeneous groove assisted graded index type FM-MCF special fiber to realize MDM-SDM multiplexing transmission.
  • FM-MCF is based on physical structure isolation, and the different modes are orthogonal to each other, so that strong classical signals and weak quantum signals have better signal-to-noise ratio and isolation when the spatial channel with weak coupling is transmitted simultaneously, ensuring a higher system
  • the stability and robustness allow the transmission of strictly independent signals through the same FM-MCF fiber.
  • the heterogeneous structure makes the inter-core crosstalk insensitive to the degree of fiber bending, and it has a larger effective refractive index difference than the homogeneous structure, which can reduce the inter-signal crosstalk.
  • FIG. 3 is a refractive index distribution diagram of a heterogeneous trench-assisted graded index type three-mode seven-core optical fiber of the MDM-SDM-based quantum and classical fusion communication system and transmission method of the present invention
  • An MDM-SDM-based quantum and classical fusion communication system including an Alice sending end, Bob receiving end, and an MDM-SDM multiplexing unit.
  • the Alice sending end is connected to the Bob receiving end through the MDM-SDM multiplexing unit;
  • the Alice transmitting end includes N LD, N BS, N AM, N PM, N PBS, 1 LO, N dispersion compensation unit, 1 MIMO unit, N DSP unit and N signal decision Unit;
  • the N LDs are connected to the PBS through BS, AM, PM in turn, the N PBSs are connected to the MDM-SDM demultiplexer, and the N decision units are sequentially connected through the DSP unit, the MIMO unit, and the dispersion compensation unit Connected with a coherent receiver, N coherent receivers are connected with an MDM-SDM demultiplexer, and the 1 LO is connected with N coherent receivers;
  • the classic signal transmitter sends 2N QPSK signals, which are converted from the fundamental mode to the higher-order modes LP 11a and LP 11b through mode conversion, enter the MDM-SDM multiplexer, and are converted into a mode suitable for FM-MCF transmission, and pass the FM-
  • the MCF is sent to the MDM-SDM demultiplexer and decomposed into independent 2N classical signals; the decomposed classical signals are respectively subjected to mode conversion from high-order mode to basic mode, and enters the coherent receiver together with the LO signal for coherent detection ,
  • the dispersion compensation is performed by the dispersion compensation unit, the equalization processing is performed by the MIMO unit, the digital signal processing is performed by the DSP unit, and finally the signal decision is performed; the N LDs at the Alice transmitting end transmit a pulse, and the pulse is divided into 90/10 BS The upper quantum signal and the lower LO signal.
  • the quantum signal adopts the method of sending the local oscillator signal instead of the local local oscillator.
  • the extra noise caused by the local local oscillator due to phase estimation and phase drift may significantly affect the transmission distance and key rate.
  • the structure in the upper right corner of the figure, the core is in the middle, and the outer side of the core is provided with a cladding and trench structure.
  • This structure makes it far away from the fiber.
  • the electric field of the core is suppressed, so that the overlap integral between the electric fields of adjacent cores becomes smaller, which suppresses crosstalk to a certain extent.
  • the reduction in the effective area of the different mode fields between the cores leads to the splicing loss and the optical signal-to-noise ratio between the different modules.
  • the same LP 01 mode field effective area of 110 ⁇ m 2 is used in all cores.
  • the core refractive index of FM-MCF is gradually distributed.
  • cores 1, 3, and 5 are used to transmit signals, because the crosstalk between cores is mainly caused by the crosstalk between adjacent cores.
  • Crosstalk is determined, so the present invention does not allow all cores to transmit signals, but uses an interval distribution method to minimize crosstalk for cores that transmit signals.
  • Each core can transmit three modes, where the fundamental mode LP 01 is used to transmit quantum signals, and the higher-order modes LP 11a and LP 11b are used to transmit classical signals. Because the fundamental mode suffers the least inter-mode crosstalk, it is assigned to the susceptible quantum signal.
  • the coupling mode and coupling power theory are used to calculate the crosstalk between cores, which is a key parameter of FM-MCF to ensure that each core can operate independently.
  • Mode coupling coefficient ⁇ mn and average power coupling coefficient It can be specifically expressed as:
  • ⁇ is the angular frequency of the sinusoidally changing electromagnetic field
  • ⁇ 0 is the dielectric constant of the medium
  • u z is the unit vector pointing outwards
  • E and H represent the electric field and the magnetic field, respectively, obtained by the finite element method.
  • N 2 is the refractive index distribution in the entire coupling region
  • N n is the refractive index distribution of the core n.
  • the middle core with six adjacent cores has the worst crosstalk, which can be specifically expressed as the following formula:
  • N cores is the number of cores closest to each other.
  • the calculated crosstalk is less than -30dB. It can be seen that the heterogeneous groove-assisted graded index FM-MCF special fiber can make each signal propagate in its own core through reasonable core design and signal distribution. Therefore, it is based on FM- MCF special fiber is a feasible solution to realize the two-dimensional multiplexing of quantum signals and classical signals.
  • RCMF Relative Core Multiplicity Factor
  • a eff-m is the effective area of the mode field of the m-th mode
  • Del is the cladding diameter of the FM-MCF
  • a eff-SMF is the effective area of the mode field of the SMF (at 1550 nm, 80 ⁇ m 2 ), the cladding diameter of Del-SMF SMF (125 ⁇ m).
  • the SKR Secret Key Rate
  • I AB represents the mutual information between Alice and Bob, which can be specifically expressed as:
  • V V A +1
  • ⁇ is the modulation efficiency
  • V A is the modulation variance of the Gaussian distribution at the Alice end
  • ⁇ tot is the total additional noise between Alice and Bob
  • ⁇ line is the total channel additional noise
  • T is the channel transmittance
  • ⁇ is the excess noise.
  • ⁇ hom is the total noise of a single regular component of the CV-QKD receiver
  • v el is the additional electrical noise
  • ⁇ is the detector efficiency.
  • ⁇ BE represents the Holevo information between Bob and Eve, which can be specifically expressed as:
  • FM-MCF uses the different spatial dimensions of any two cores (such as cores A and B) to transform the quantum state; after passing through core A, it transforms into a quantum state
  • A> k 1
  • B> k 2
  • Quantum signal processing The quantum signal output by the MDM-SDM multiplexer enters the PC unit to correct the polarization offset of the quantum signal and the local oscillator signal.
  • the PBS at the Bob receiving end decomposes the input signal into signal pulses and local oscillator signal pulses.
  • the beam pulse is fed into a 90° optical mixer, the phase and amplitude of the signal are extracted by performing four phase interferences between the signal and the local oscillator, the signal is amplified by an amplifier, and finally it enters the CV-QKD receiver for homodyne detection.
  • the length of Bob receiving end is The bits of information are given to the sender of Alice to calculate ⁇ X ⁇ 2 , ⁇ Y ⁇ 2 and ⁇ X,Y>, as well as ⁇ a , ⁇ b and ⁇ c ; if Then the parameter estimation test is passed, the security key is generated, and the communication continues; otherwise, the parameter estimation test is not passed, the communication is terminated, and the key that has been generated this round will be discarded.
  • ⁇ a , ⁇ b and ⁇ c are small positive numbers used to balance the robustness of the protocol and the security code rate.
  • ⁇ PE is the maximum probability of parameter estimation failure.

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Abstract

本发明公开了一种基于MDM-SDM的量子与经典融合通信系统，包括Alice发送端、Bob接收端和MDM-SDM复用单元，所述Alice发送端通过MDM-SDM复用单元与Bob接收端连接。本发明采用异质沟槽辅助渐变折射率型FM-MCF特种光纤，实现MDM-SDM二维复用的量子与经典融合传输系统，解决融合网络的容量瓶颈。通过选取合适的纤芯数和模式数，能够降低信号处理的要求，其信号间的模式正交性以及空间隔离性进一步降低了经典信号对量子信号的干扰，易在融合通信时获得更好的量子密钥分发性能。为以后的超大容量融合通信网络建设，提供了一种高安全性、低损耗和低成本的可行方案。

Description

一种基于MDM-SDM的量子与经典融合通信系统及传输方法 技术领域
本发明涉及量子信息领域，尤其涉及一种基于MDM-SDM的量子与经典融合通信系统及传输方法。
背景技术
量子保密通信提供了在量子力学保证情况下安全密钥分发的潜力，证实了无条件安全的可能性，是量子通信中发展最迅速、最接近实用和规模化的技术。在过去30多年里，自由空间和基于光纤的QKD(Quantum Key Distribution，量子密钥分发)实验通过利用不同物理原理都证明了量子保密通信的可行性。但QKD系统一般采用专用的光纤和设备，在网络规模和实用性方面存在限制。为了降低成本并提高光纤传输效率，可在现有的光纤基础设施中集成QKD和经典通信系统，以此降低敷设和运营费用，并提高QKD网络的可扩展性。
1997年，Townsend首次提出针对QKD和经典信号同时传输的方案。使用CWDM(Coarse Wavelength Division Multiplexing，粗波分复用技术)，将1300nm QKD信道与传统的1550nm经典信道进行多路复用，在光纤中实现超过25km的传输。但是考虑到光纤的非线性效应和高速传输光信噪比的要求，基于SMF(Single Mode Fiber，单模光纤)的WDM技术已经接近容量极限，且在链路上需要额外的设备，会引入格外的串扰和损耗而可能损害最终的安全性，亟需采用新的复用技术来提高光传输容量，增加频谱效率，满足日益增长的容量需求。基于FMF(Few Mode Fiber，少模光纤)的MDM(Mode Division Multiplexing，模分复用)共纤同传方案、基于MCF(Multi Core Fiber，多芯光纤)的SDM(Space Division Multiplexing，空分复用)共纤同传方案有望解决上述问题。
2013年，Joel Carpenter等人完成了经典信号和量子信号在一根6个模式FMF中模分复用传输的实验，其中基模传输量子信号，高阶模传输经典信号，经典信道和量子信道的隔离度达35dB。其优势在于利用FMF不同模式的正交性，能有效降低经典信号对量子信号的噪声干扰。但是其在传输过程中不可避免地会出现模式色散，且随着传输模式的增加，传输模式的复用和解复用将变得非常复杂。2016年，J.F.Dynes等人首次在53km的七芯MCF中以空分复用方式实现量子与经典融合传输。其优势在于MCF的各纤芯之间是基于物理结 构隔离的，量子信号受到经典信号的干扰较小，易于在大容量的经典信号同传时获得更好的QKD性能。2019年，Tobias A.Eriksson等人通过实验研究了在19核MCF中CV-QKD信号和WDM复用的24.5Gbaud 16QAM(Quadrature Amplitude Modulation，正交幅度调制)进行空分复用的可行性，其将CV-QKD信号放置在经典信号波段的保护带中的波长处，进一步抑制了信号间串扰，但因其采用的多芯光纤包层空间有限，从而使纤芯的数量受到限制，不利于进一步提升传输容量。
现有技术专利CN110247705A提供了一种基于多芯光纤的量子接入网架构及方法，可支持大量量子用户接入，但其采用的七芯光纤包层有限，难以进一步提高通信容量，本发明更优的提出采用FM-MCF特种光纤实现融合传输，利用空间维度和模式维度相结合的二维复用方式，解决了通信容量瓶颈问题。
现有技术专利CN110048776A利用不同模式之间的正交性，提出了一种基于少模光纤实现多路QKD复用的方案。但其要采用单独的设备实现量子密钥分发，成本较高，本发明更优地提出量子与经典融合传输方案，让量子信号与经典信号共用光纤基础设施，节约了成本，提高了QKD的实用性。
现有技术专利CN109600221A提出了一种基于多芯光纤实现量子与经典模分复用传输的方案，提高了信号间的隔离度。但其采用的DV-QKD协议对光源和探测器的要求比较高，本发明进一步提出使用CV-QKD协议实现融合传输，其成本低、实用性强，与传统光通信网络融合性更好。
发明内容
为了解决上述技术方案的瓶颈，本发明提出了MDM和SDM相结合的二维复用传输方式，即在一个光纤包层内放置多根纤芯，每根纤芯可以同时传输多个模式的FM-MCF(FewMode-Multi Core Fiber，少模-多芯光纤)实现融合传输。
本发明提供了一种实现超大容量传输和提升安全性的基于MDM-SDM的量子与经典融合通信系统及传输方法。采用异质沟槽辅助渐变折射率型FM-MCF特种光纤，实现MDM-SDM二维复用的量子与经典融合传输系统，解决融合网络的容量瓶颈。选取合适的纤芯数和模式数，能够降低信号处理的要求，易在量子和经典传输时获得更好的量子密钥分发性能。其异质结构使得芯间串扰对弯曲程度不敏感并且由于异质纤芯间比同质纤芯间具有更大的有效折射率差，串扰得以有效降低。其沟槽辅助型结构可以通过抑制两个相邻纤芯电 场分布的交叠，能有效减少模间串扰，较大的模场面积在降低非线性损伤的同时又能保持低色散性能。
本发明采用基于RR(Reverse Reconciliation，反向协调)GG02协议的QKD技术(高斯调制相干态CV-QKD)。在GG02协议中，发送方Alice选取服从均值为零的高斯分布的随机序列，并根据其制备相干态发送给Bob。接收方Bob随机选择零差测量的测量基并公布基矢选择，Alice仅保留与Bob所测正则分量相同的数据。Alice和Bob进行数据后处理，最终得到相同的安全密钥。与DV-QKD协议相比，CV-QKD只需普通的相干激光器，平衡零差检测器，成本低、实用性强，且在同等条件下其输出的密钥率远高于DV-QKD技术，且因为其相干检测原理与经典相干通信之间的相似性，使其与传统光通信网络融合性更好。所以本发明更优地选择了CV-QKD技术。为了进一步提高密钥传输距离，本发明进一步引入反向协调纠错协议，即Alice利用Bob发送来的校验信息将手中的数据修正的与Bob的数据相一致。
为了达到上述技术效果，本发明的技术方案如下：
一种基于MDM-SDM的量子与经典融合通信系统，包括Alice发送端、Bob接收端和MDM-SDM复用单元，所述Alice发送端通过MDM-SDM复用单元与Bob接收端连接；
所述MDM-SDM复用单元包括MDM-SDM复用器和MDM-SDM解复用器，所述MDM-SDM复用器和MDM-SDM解复用器通过FM-MCF特种光纤连接，所述FM-MCF特种光纤为异质沟槽辅助渐变折射率型三模七芯光纤；所述FM-MCF特种光纤的纤芯的折射率分布为渐变型，同一根纤芯中可以传输三种模式的信号；
所述Alice发送端包括N个LD(Laser Diode，半导体激光器)、N个BS(Beam Splitter，分束器)、N个AM(Amplitude Modulator，幅度调制器)、N个PM(Phase Modulator，相位调制器)、N个PBS(Polarization Beam Splitter，偏振分束器)、1个LO(Local Oscillator，本地振荡器)、N个色散补偿单元、1个MIMO(Multiple-Input Multiple-Output，多输入多输出延时均衡算法)单元、N个DSP(Digital Signal Processing，数字信号处理)单元和N个信号判决单元；所述N个LD依次通过BS、AM、PM与PBS连接，所述N个PBS与MDM-SDM解复用器连接，所述N个判决单元依次通过DSP单元、MIMO单元、色散补偿单元与相干接收器连接，N个相干接收器与MDM-SDM解复用器连接，所述1个LO与N个相干接收器连接；
所述Bob接收端包括1个经典信号发送器、N个CV-QKD接收器、N个放大器、N个 90°光学混合器、N个PBS和N个PC(Polarization Controller，偏振控制器)；所述经典信号发送器与MDM-SDM复用器连接，所述N个CV-QKD接收器依次通过放大器、90°光学混合器、PBS与PC连接，所述N个PC与MDM-SDM复用器连接；
所述经典信号发送器发送2N个QPSK(Quadrature Phase Shift Keying，正交相移键控)信号，经过模式转换从基模转换成高阶模LP 11a、LP 11b后，进入MDM-SDM复用器后转换成适合FM-MCF传输的模式，并通过FM-MCF发送到MDM-SDM解复用器，分解成独立的2N个经典信号；分解后的各个经典信号分别进行模式转换从高阶模转换成基模的形式，并连同LO信号进入相干接收器进行相干检测，通过色散补偿单元进行色散补偿，通过MIMO单元进行均衡处理，通过DSP单元进行数字信号处理，最后进行信号判决；所述Alice发送端的N个LD发射一个脉冲，通过90/10的BS将脉冲分成上路的量子信号和下路的LO信号，量子信号经AM和PM调制后与LO信号通过PBS耦合到一起，进入MDM-SDM解复用器后，通过FM-MCF进入MDM-SDM复用器，分解成N个独立的量子信号，所述独立的量子信号依次通过PC单元进行偏振校正，通过PBS单元分成上路的量子信号和下路的LO信号，两束信号通过90°光学混合器执行4个90°的相位干涉，从中提取出量子信号的相位和振幅，通过放大器进行信号放大，最后到达CV-QKD接收器。
优选地，所述经典信号发送器包括2N个激光二极管、2N个I-Q调制器、2N个AWG(Arbitrary Waveform Generator，任意波形发生器)，其中2N个激光二极管分别通过I-Q调制器与MDM-SDM复用器连接，2N个AWG与I-Q调制器连接。
优选的，量子信号采用发送本振信号的方式而非本地本振。更优选的，量子信号与经典信号采用反向同传的方式。
优选地，在所述FM-MCF进行传输时，量子信号和经典信号采用非等间隔交错分布的波长，量子信号采用1550nm波段，前N个经典信号采用1530nm波段，后N个经典信号采用1560nm波段。
更优选的，MDM-SDM复用器和解复用器选取全光纤少模多芯光子灯笼复用器。
更优选的，FM-MCF采取DMD管理传输线技术，由两种带正、负DMD的FCM-MCF组成。
以上的，量子信号单元为基于反向协调GG02协议产生CV-QKD信号的单元。
更近一步的，所述FM-MCF特种光纤的纤芯半径r 1＝9.22μm，纤芯中心到沟槽内侧的距离r 2＝14.752μm；纤芯的折射率分布为渐变型，渐变折射率因子α＝2.2，最大纤芯折射 率Δ 1＝0.406％；纤芯外侧设有折射率沟槽，折射率沟槽的厚度W＝2.023μm，沟槽与包层的相对折射率差Δ t＝-0.7％。
更进一步的，所述FM-MCF特种光纤的直径D el＝223μm，外层包层厚度CT＝48.0μm，芯间距Λ＝40.8μm；同一根纤芯中可以传输LP 01、LP 11a、LP 11b三种模式的信号，每种模式的模场有效面积A eff＝110μm 2。
本发明还提供了一种基于MDM-SDM的量子与经典融合通信传输方法，包括以下步骤：
S1、系统噪声测试：在Alice发送端发射激光脉冲串的情况下，测试系统噪声，判断信噪比是否高于设定的信噪比预设值，若信噪比高于设定额信噪比设定值，进入步骤S2和S2’，若信噪比低于设定的信噪比预设值，生成提示信息；
S2、量子态制备：Alice发送端的LD发射一个2ns重复频率、1550nm波长的脉冲，被90/10的不对称分束器分成两束脉冲，光强较强的脉冲束用作Bob接收端的测量本振信号，光强较弱的脉冲束被发送到AM单元和PM单元进行幅度和相位调制，调制后的信号和本振信号通过PBS进行偏振复用；
S2’、QPSK调制：经典信号发送器根据QPSK协议调制经典信息，该协议规定了四种载波相位45°、135°、225°、315°，分别将经典信息编码为比特{11，01，00，00}；载波相位在四个不同的数值之间切换，产生2N路QPSK信号；
S2’.1、模式转换：通过S2’得到的各个QPSK信号经过模式转换从基模形式转换成高阶模LP 11a、LP 11b；
S3、MDM-SDM复用传输：把通过S2得到的各路信号通过MDM-SDM解复用器耦合到一根FM-MCF特种光纤中进行复用传输，之后到达MDM-SDM复用器，分解成N个独立的量子信号输出；把通过S2’.1得到的各路信号通过MDM-SDM复用器耦合到一根FM-MCF特种光纤中进行复用传输，之后到达MDM-SDM解复用器，分解成独立的2N个经典信号输出；
S4、模式转换：MDM-SDM解复用器输出的经典信号通过模式转换从高阶模转换成基模，进入相干接收器；
S5、量子信号处理：MDM-SDM复用器输出的量子信号进入PC单元进行量子信号和本振信号偏振偏移的校正，Bob接收端的PBS将输入信号分解成信号脉冲和本振信号脉冲，两束脉冲馈入90°光学混合器，通过在信号和本振之间执行四个相位干涉来提取信号的相位和振幅，通过放大器进行信号放大，最后进入CV-QKD接收器进行零差检测；
S5’、经典信号处理：本地振荡器产生的本振信号与相干接收器接收到的经典信号进行相干检测；随后进入色散补偿单元进行色散补偿；之后进入MIMO和DSP单元进行均衡处理和信号处理，恢复发送的经典信号；最后完成数据恢复并进行判决；
S6、参数估计测试：Bob接收端发送长度为
Figure PCTCN2020140114-appb-000001
比特的信息给Alice发送端，让它计算‖X‖ 2、‖Y‖ 2和<X,Y>，以及γ a、γ b和γ c；如果
Figure PCTCN2020140114-appb-000002
Figure PCTCN2020140114-appb-000003
那么参数估计测试通过，产生安全密钥，通信继续进行；反之则参数估计测试未过，通信中止，本轮已产生的密钥将会被舍弃。
与现有技术相比，本发明的有益效果：
1)本发明采用MDM-SDM二维复用实现量子与经典融合通信，量子信号和经典信号采用不同且正交的模式，且在基于物理隔离的不同纤芯中传输。先前提出的融合通信的方式一般是波分复用，但基于SMF的波分复用技术已经接近传输容量的极限，不能满足人民日益增长的容量需求。而本发明通过FM-MCF(即在一个光纤包层内放置多根纤芯，每根纤芯可以同时传输多个LP模式)特种光纤实现量子信号和经典信号的MDM-SDM二维复用，大大提升了通信容量，且进一步减小了经典信号对量子信号的影响。
2)本发明采用异质沟槽辅助渐变折射率型FM-MCF特种光纤实现MDM-SDM复用传输。FM-MCF基于物理结构隔离，不同模式之间相互正交，使强经典信号和弱量子信号在具有弱耦合的空间信道同传时具有更好的信噪比和隔离度，保证了系统更高的稳定性和鲁棒性，允许通过同一FM-MCF光纤传输严格独立的信号。异质结构使芯间串扰对光纤弯曲程度不敏感，且其比同质结构具有更大的有效折射率差，能够降低信号间串扰。沟槽结构通过抑制两个相邻纤芯电场分布的交叠来减小串扰。渐变折射率结构能够最小化DMD(Differential Mode Delay，差分模式时延)，降低信号处理的复杂度。采用DMD管理传输线技术，旋转一段FM-MCF将不同的纤芯拼接在一起，实现几乎0ps/km的DMD。
3)本发明量子信号选用高斯调制相干态的CV-QKD实现量子密钥分发。与DV-QKD协议相比，CV-QKD只需普通的相干激光器，平衡零差检测器，成本低、实用性强，且在同等条件下其输出的密钥率远高于DV-QKD技术，又因其相干检测原理与经典相干通信之间的相似性，使其与传统光通信网络融合性更好。
4)本发明采用量子信号和经典信号反向同传的方式，且波长间非等间隔交错。反向同传能够减小后向拉曼散射，进一步降低核间串扰，有利于实现长距离融合通信。且量子信号和经典信号采取非等间隔交错的波长分配方式，减少四波混频，减小两种信号之间的功 率耦合。
5)本发明对信号进行合理的纤芯和模式分配。因为核间串扰主要来源于相邻核芯，本发明通过间隔分配纤芯的方式，使每一根传输信号的纤芯的邻近纤芯都不传输信号。不同模式之间也存在串扰，模间串扰XT 01-01＞XT 01-11＞XT 11-11，所以本发明将量子信号分配到基模LP 01，将经典信号分配给高阶模，使量子信号受到最小的模间串扰。不同模式之间采用较大且相同模场有效面积，进一步减小串扰，相同的模场有效面积能够减少不同模组之间的拼接损耗和光信噪比。
6)本发明选取全光纤少模多芯光子灯笼实现信号的复用和解复用。其采用微结构毛细管模板法制备，相对于相位板、三维光波导和多平面光转换等复用器，该器件具有体积小、与传输光纤高效率耦合和对准等优点。在电信C波段的插入损耗小于0.4dB，满足CV-QKD对插入损耗的要求。且具有良好的可拓展性，可以直接拼接到FM-MCF特种光纤上，从而保证光学集成和高可靠性。
附图说明
图1是本发明基于MDM-SDM的量子与经典融合通信系统及传输方法的原理框架图；
图2是本发明基于MDM-SDM的量子与经典融合通信系统及传输方法的异质沟槽辅助渐变折射率型三模七芯光纤的横截面图；
图3是本发明基于MDM-SDM的量子与经典融合通信系统及传输方法的异质沟槽辅助渐变折射率型三模七芯光纤的折射率分布图；
图4是本发明基于MDM-SDM的量子与经典融合通信系统及传输方法的信号分配图；
图5是本发明基于MDM-SDM的量子与经典融合通信系统及传输方法的流程图。
具体实施方式
为了使本发明的目的、技术方案及优点更加清楚明白，以下结合具体实施例以及附图，对本发明进一步详细说明，但本发明要求的保护范围并不局限于实施例。
实施例1：
如图1所示；
一种基于MDM-SDM的量子与经典融合通信系统，包括Alice发送端、Bob接收端和 MDM-SDM复用单元，所述Alice发送端通过MDM-SDM复用单元与Bob接收端连接；
MDM-SDM复用单元包括MDM-SDM复用器和MDM-SDM解复用器，复用器和解复用器是由微结构毛细管法制备的全光纤少模多芯光子灯笼，且相互通过FM-MCF特种光纤连接，FM-MCF为异质沟槽辅助渐变折射率型三模七芯光纤，其具有低核间串扰、低模式差分延迟和空间效率高等优势。另外，全光纤光子少模多芯光子灯笼能够将输入信号从基本模式选择性地激励成LP 01、LP 11a、LP 11b模式，模式之间相互正交。该复用器是宽带的，横跨整个C波段，具有超低的核间串扰和高模式纯度，且其插入损耗小于0.4dB，满足CV-QKD信号对复用器的要求。
所述Alice发送端包括N个LD、N个BS、N个AM、N个PM、N个PBS、1个LO、N个色散补偿单元、1个MIMO单元、N个DSP单元和N个信号判决单元；所述N个LD依次通过BS、AM、PM与PBS连接，所述N个PBS与MDM-SDM解复用器连接，所述N个判决单元依次通过DSP单元、MIMO单元、色散补偿单元与相干接收器连接，N个相干接收器与MDM-SDM解复用器连接，所述1个LO与N个相干接收器连接；
所述Bob接收端包括1个经典信号发送器、N个CV-QKD接收器、N个放大器、N个90°光学混合器、N个PBS和N个PC；所述经典信号发送器与MDM-SDM复用器连接，所述N个CV-QKD接收器依次通过放大器、90°光学混合器、PBS与PC连接，所述N个PC与MDM-SDM复用器连接；
所述经典信号发送器发送2N个QPSK信号，经过模式转换从基模转换成高阶模LP 11a、LP 11b后，进入MDM-SDM复用器后转换成适合FM-MCF传输的模式，并通过FM-MCF发送到MDM-SDM解复用器，分解成独立的2N个经典信号；分解后的各个经典信号分别进行模式转换从高阶模转换成基模的形式，并连同LO信号进入相干接收器进行相干检测，通过色散补偿单元进行色散补偿，通过MIMO单元进行均衡处理，通过DSP单元进行数字信号处理，最后进行信号判决；所述Alice发送端的N个LD发射一个脉冲，通过90/10的BS将脉冲分成上路的量子信号和下路的LO信号，量子信号经AM和PM调制后与LO信号通过PBS耦合到一起，进入MDM-SDM解复用器后，通过FM-MCF进入MDM-SDM复用器，分解成N个独立的量子信号，所述独立的量子信号依次通过PC单元进行偏振校正，通过PBS单元分成上路的量子信号和下路的LO信号，两束信号通过90°光学混合器执行4个90°的相位干涉，从中提取出量子信号的相位和振幅，通过放大器进行信号放大，最后到达CV-QKD接收器。
其中，量子信号采用发送本振信号的方式而非本地本振。因为本地本振由于相位估计和相位漂移而导致的多余噪声可能会显著影响传输距离以及密钥率。
具体的，经典信号发送器包括2N个激光二极管、2N个I-Q调制器、2N个AWG，其中2N个激光二极管分别通过I-Q调制器与MDM-SDM复用器连接，2N个AWG与I-Q调制器连接；QPSK具有频率利用效率高，抗干扰性强的优势。
具体的，CV-QKD单元采用基于反向协调GG02协议产生连续变量量子信号进行密钥分发。其利用相干态来进行编码，相干态是非正交的，原则上可以实现密钥的安全分发。GG02协议中Alice将真空态沿x和p方向上都进行平移，平移参数为一个复数α＝k(x A+ip A)，得到相干态|α>。其中x A和p A是两个独立同分布的高斯变量，k是比例系数。Bob使用零差探测，随机地选择测量哪一个分量当Bob选择测量x分量时，测量结果就是以tx A为中心的一个高斯分布。当Bob测量x(p)分量时，他的测量结果中不包含Alice所调制的p(x)分量的信息，因此Alice只需要保留Bob所测量分量的调制信息即可。
更具体的，如图2所示，对一个沟槽辅助型的光纤来说，图中右上角的结构，中间是纤芯，纤芯外侧设有包层和沟槽结构，此结构使远离纤芯的电场被抑制，从而会使相邻纤芯的电场间的重叠积分变小，这样在一定程度上抑制了串扰。光纤直径D el＝223μm，以使得光纤制备时的失败率不大于10 -7；外层包层厚度CT＝48.0μm，为了抑制宏弯损耗；芯间距Λ＝40.8μm，具体计算公式可表示为：
Figure PCTCN2020140114-appb-000004
更具体的，渐变折射率因子α＝2.2，最大纤芯折射率Δ 1＝0.406％，为了获得较小的模间串扰和大的模式差分时延，且降低DMD对波长的依赖；FM-MCF的纤芯半径r 1＝9.22μm，纤芯中心到沟槽内侧的距离r 2＝14.752μm，因为沟槽的位置对DMD和DMD的斜率有很大影响，当r 1/r 2＝1.6时，量子信号处的DMD斜率的绝对值最小，接近0ns/km/nm；纤芯外侧设有折射率沟槽,折射率沟槽的厚度W＝2.023μm，沟槽与包层的相对折射率差Δ t＝-0.7％。核芯之间的不同模场有效面积降导致不同模组之间的拼接损耗和光信噪比，为了尽可能减少这种影响，所有核芯中都使用相同的LP 01模场有效面积110μm 2。如图3所示，FM-MCF的纤芯折射率是渐变式分布的。
更具体的，如图4所示，异质沟槽辅助渐变折射率型三模七芯光纤中，芯1、3、5用于传输信号，因为核芯间串扰主要由相邻核芯间的串扰决定，所以本发明没有让所有核芯都传输信号，而是采用间隔分配的方式，使传输信号的核芯受到最小的串扰。每个纤芯可 以传输三种模式，其中基模LP 01用于传输量子信号，高阶模LP 11a和LP 11b用于传输经典信号。因为基模受到的模间串扰最小，所以将其分配给易受影响的量子信号。
为了证明本发明提出方法的可行性，使用耦合模式和耦合功率理论计算核间串扰，其是FM-MCF的关键参数，以保证各个核芯能够独立操作。模式耦合系数κ mn和平均功率耦合系数
Figure PCTCN2020140114-appb-000005
可具体表示为:
Figure PCTCN2020140114-appb-000006
其中，ω是正弦变化电磁场额角频率，ε 0是介质的介电常数，u z是向外指向的单位矢量，E和H分别表示电场和磁场，由有限元法得出。N 2是整个耦合区域中的折射率分布，N n是核芯n的折射率分布。
对于m芯和n芯之间的平均功率耦合系数，
Figure PCTCN2020140114-appb-000007
其中d为相关长度，和
Figure PCTCN2020140114-appb-000008
Figure PCTCN2020140114-appb-000009
Figure PCTCN2020140114-appb-000010
Figure PCTCN2020140114-appb-000011
其中Δβ＝β m-β n，x m和y m为z＝0时m芯的中心坐标。根据平均功率耦合系数，可以进一步导出长度为L km的FM-MCF光纤链路中，相邻两个纤芯m和n之间的核间串扰为：
Figure PCTCN2020140114-appb-000012
另外，具有六个相邻核芯的最中间纤芯具有最差的串扰，可具体表示为以下公式：
XT worst＝XT-10lg(N cores)
此处N cores是最邻近核芯的数量。
计算得出串扰都小于-30dB，可见异质沟槽辅助渐变折射率型FM-MCF特种光纤通过合理的纤芯设计和信号分配，能够使各路信号在各自纤芯中传播，因此基于FM-MCF特种光 纤实现量子信号和经典信号的二维复用是一种可行的方案。
为了评估FM-MCF的空间效率，引入RCMF(Relative Core Multiplicity Factor，相对核芯多重因子)，其具体的计算公式如下所示：
RCMF FM-MCF＝CMF FM-MCF/CMF SMF
Figure PCTCN2020140114-appb-000013
Figure PCTCN2020140114-appb-000014
其中，n是纤芯数，A eff-m是第m个模式的模场有效面积，D el是FM-MCF的包层直径，A eff-SMF是SMF的模场有效面积(在1550nm处为80μm 2),D el-SMFSMF的包层直径(125μm)。本发明采用的三模七芯光纤可达到14.8的RCMF，较之RCMF＝4.7的七芯光纤实现了极高的空间效率。
在集体攻击下，基于反向协调的高斯调制相干态CV-QKD的SKR(Secret Key Rate，密钥率)可以具体表示为：
SKR＝βI AB-χ BE
I AB表示Alice和Bob之间的互信息，可以具体表示为：
Figure PCTCN2020140114-appb-000015
V＝V A+1
ξ tot＝ξ line+ξ hom/T
Figure PCTCN2020140114-appb-000016
Figure PCTCN2020140114-appb-000017
其中，β是调制效率，V A是Alice端高斯分布的调制方差，ξ tot是Alice和Bob之间的总附加噪声，ξ line是总信道附加噪声，T是信道透射率，ε是过量噪声，ξ hom是CV-QKD接收器的单个正则分量的总噪声，v el是附加电噪声，η是探测器效率。
χ BE表示Bob和Eve之间的Holevo信息，可以具体表示为：
Figure PCTCN2020140114-appb-000018
G(x)＝(x+1)log 2(x+1)-xlog 2(x)
Figure PCTCN2020140114-appb-000019
Figure PCTCN2020140114-appb-000020
A＝V 2(1-2T)+2T+T 2(V+ξ line) 2
B＝T 2(1+ξ line) 2
Figure PCTCN2020140114-appb-000021
Figure PCTCN2020140114-appb-000022
其中，λ n是辛特征值。设置光纤损耗系数α＝0.2dB/km，调制效率β＝0.898，探测器效率η＝0.7，电噪声v el＝0.08N 0(N 0是测量的散粒噪声方差)，透射率T＝0.2(包括耦合损耗)，计算出集体攻击下CV-QKD的SKR为138Mbit/s。
基于MDM-SDM的量子与经典融合通信传输方法，包括以下步骤：
S1、系统噪声测试：在Alice发送端发射激光脉冲串的情况下，测试系统噪声，判断信噪比是否高于设定的信噪比预设值，若信噪比高于设定额信噪比设定值，进入步骤S2和S2’，若信噪比低于设定的信噪比预设值，生成提示信息；其中，测试系统的信噪比采用如下公式：SNR＝10lg(P S/P N)，P S为信号功率，P N为噪声功率，信噪比预设值为20dB。
S2、量子态制备：Alice端的CV-QKD单元根据基于反向协调的高斯调制相干态协议制备量子态，生成量子信号，具体步骤包括：
S2.1、Alice将真空态沿x和p方向上都进行平移，平移参数为一个复数α＝k(x A+ip A)，得到相干态|α>。其中x A和p A是两个独立同分布的高斯变量，k是比例系数。
S2.2、相干态|α>经过AM和PM调制，转化为量子态|β>＝ae iθ|α>,其中a为调制幅度，θ为调制相位。
S2.3、量子态|β>进入FM-MCF后，FM-MCF利用任意两个纤芯(例如芯A和B)的不同空间维度对量子态进行变换；经过芯A后转化为量子态|A>＝k 1|β>，经过芯B后转化为量子态|B>＝k 2|β>，其中k 1和k 2是空间维度。
S2’、QPSK调制：经典信号发送器根据QPSK协议调制经典信息，该协议规定了四种载波相位45°、135°、225°、315°，分别将经典信息编码为比特{11，01，00，00}。载波相位在四个不同的数值之间切换，产生2N路QPSK信号；
S2’.1、模式转换：通过S2’得到的各个QPSK信号经过模式转换从基模形式转换成高阶 模LP 11a、LP 11b。
S3、MDM-SDM复用传输：把通过S2得到的各路信号通过MDM-SDM解复用器耦合到一根FM-MCF特种光纤中进行复用传输，之后到达MDM-SDM复用器，分解成N个独立的量子信号输出；把通过S2’.1得到的各路信号通过MDM-SDM复用器耦合到一根FM-MCF特种光纤中进行复用传输，之后到达MDM-SDM解复用器，分解成独立的2N个经典信号输出。
S4、模式转换：MDM-SDM解复用器输出的经典信号通过模式转换从高阶模转换成基模，进入相干接收器。
S5、量子信号处理：MDM-SDM复用器输出的量子信号进入PC单元进行量子信号和本振信号偏振偏移的校正，Bob接收端的PBS将输入信号分解成信号脉冲和本振信号脉冲，两束脉冲馈入90°光学混合器，通过在信号和本振之间执行四个相位干涉来提取信号的相位和振幅，通过放大器进行信号放大，最后进入CV-QKD接收器进行零差检测。
S5’、经典信号处理：本地振荡器产生的本振信号与相干接收器接收到的经典信号进行相干检测；随后进入色散补偿单元进行色散补偿；之后进入MIMO和DSP单元进行均衡处理和信号处理，恢复发送的经典信号；最后完成数据恢复并进行判决。
S6、参数估计测试：Bob接收端发送长度为
Figure PCTCN2020140114-appb-000023
比特的信息给Alice发送端，让它计算‖X‖ 2、‖Y‖ 2和<X,Y>，以及γ a、γ b和γ c；如果
Figure PCTCN2020140114-appb-000024
Figure PCTCN2020140114-appb-000025
那么参数估计测试通过，产生安全密钥，通信继续进行；反之则参数估计测试未过，通信中止，本轮已产生的密钥将会被舍弃。
S6.1、确定协方差矩阵参数的界限
Figure PCTCN2020140114-appb-000026
具体可表示为：
Figure PCTCN2020140114-appb-000027
Figure PCTCN2020140114-appb-000028
Figure PCTCN2020140114-appb-000029
其中δ a、δ b和δ c是小的正数，用于平衡协议的稳健性和安全码率。
S6.2、计算输入‖X‖ 2、‖Y‖ 2、<X,Y>。其中X，Y为全部n个量子态的n个测量结果，可以计算出如下参数：
Figure PCTCN2020140114-appb-000030
Figure PCTCN2020140114-appb-000031
Figure PCTCN2020140114-appb-000032
其中∈ PE为参数估计失败的最大概率。
S6.3、如果满足
Figure PCTCN2020140114-appb-000033
那么测试通过，否则测试失败。
根据上述说明书的揭示和教导，本发明所属领域的技术人员还可以对上述实施方式进行变更和修改。因此，本发明并不局限于上面揭示和描述的具体实施方式，对发明的一些修改和变更也应当落入本发明的权利要求的保护范围内。此外，尽管本发明书中使用了一些特定的术语，但这些术语只是为了方便说明，并不对本发明构成任何限制。

Claims (10)

  1. 一种基于MDM-SDM的量子与经典融合通信系统，其特征在于，包括Alice发送端、Bob接收端和MDM-SDM复用单元，所述Alice发送端通过MDM-SDM复用单元与Bob接收端连接；
    所述MDM-SDM复用单元包括MDM-SDM复用器和MDM-SDM解复用器，所述MDM-SDM复用器和MDM-SDM解复用器通过FM-MCF特种光纤连接；
    所述Alice发送端包括N个LD、N个BS、N个AM、N个PM、N个PBS、1个LO、N个色散补偿单元、1个MIMO单元、N个DSP单元和N个信号判决单元；任意一个LD依次通过BS、AM、PM与PBS连接，所述N个PBS与MDM-SDM解复用器连接，所述N个判决单元依次通过DSP单元、MIMO单元、色散补偿单元与相干接收器连接，N个相干接收器与MDM-SDM解复用器连接，所述1个LO与N个相干接收器连接；
    所述Bob接收端包括1个经典信号发送器、N个CV-QKD接收器、N个放大器、N个90°光学混合器、N个PBS和N个PC；所述经典信号发送器与MDM-SDM复用器连接，所述N个CV-QKD接收器依次通过放大器、90°光学混合器、PBS与PC连接，所述N个PC与MDM-SDM复用器连接；
    所述经典信号发送器发送2N个QPSK信号，经过模式转换从基模转换成高阶模LP 11a、LP 11b后，进入MDM-SDM复用器后转换成适合FM-MCF传输的模式，并通过FM-MCF发送到MDM-SDM解复用器，分解成独立的2N个经典信号；分解后的各个经典信号分别进行模式转换从高阶模转换成基模的形式，并连同LO信号进入相干接收器进行相干检测，通过色散补偿单元进行色散补偿，通过MIMO单元进行均衡处理，通过DSP单元进行数字信号处理，最后进行信号判决；所述Alice发送端的N个LD发射一个脉冲，通过90/10的BS将脉冲分成上路的量子信号和下路的LO信号，量子信号经AM和PM调制后与LO信号通过PBS耦合到一起，进入MDM-SDM解复用器后，通过FM-MCF进入MDM-SDM复用器，分解成N个独立的量子信号，所述独立的量子信号依次通过PC单元进行偏振校正，通过PBS单元分成上路的量子信号和下路的LO信号，两束信号通过90°光学混合器执行4个90°的相位干涉，从中提取出量子信号的相位和振幅，通过放大器进行信号放大，最后到达CV-QKD接收器。
  2. 根据权利要求1所述的一种基于MDM-SDM的量子与经典融合通信系统，其特征在于，所述经典信号发送器包括2N个激光二极管、2N个I-Q调制器和2N个AWG，其中2N个激光二极管分别通过I-Q调制器与MDM-SDM复用器连接，2N个AWG与I-Q调制 器连接。
  3. 根据权利要求1所述的一种基于MDM-SDM的量子与经典融合通信系统，其特征在于，在所述FM-MCF进行传输时，量子信号和经典信号采用非等间隔交错分布的波长，量子信号采用1550nm波段，前N个经典信号采用1530nm波段，后N个经典信号采用1560nm波段。
  4. 根据权利要求1所述的一种基于MDM-SDM的量子与经典融合通信系统，其特征在于，所述FM-MCF特种光纤的纤芯半径r 1＝9.22μm，纤芯中心到沟槽内侧的距离r 2＝14.752μm；纤芯的折射率分布为渐变型，渐变折射率因子α＝2.2，最大纤芯折射率Δ 1＝0.406％；纤芯外侧设有折射率沟槽，折射率沟槽的厚度W＝2.023μm，沟槽与包层的相对折射率差Δ t＝-0.7％。
  5. 根据权利要求1所述的一种基于MDM-SDM的量子与经典融合通信系统，其特征在于，所述量子信号与经典信号采用反向同传的方式。
  6. 根据权利要求1所述的一种基于MDM-SDM的量子与经典融合通信系统，其特征在于，所述MDM-SDM复用器和MDM-SDM解复用器选取全光纤少模多芯光子灯笼复用器。
  7. 根据权利要求1所述的一种基于MDM-SDM的量子与经典融合通信系统，其特征在于，所述量子信号单元为基于反向协调GG02协议产生CV-QKD信号的单元。
  8. 根据权利要求7所述的一种基于MDM-SDM的量子与经典融合通信系统，其特征在于，所述FM-MCF采取DMD管理传输线技术，由两种带正、负DMD的FCM-MCF组成。
  9. 根据权利要求1所述的一种基于MDM-SDM的量子与经典融合通信系统，其特征在于，所述FM-MCF特种光纤的直径D el＝223μm，外层包层厚度CT＝48.0μm，芯间距Λ＝40.8μm；同一根纤芯中可以传输LP 01、LP 11a、LP 11b三种模式的信号，每种模式的模场有效面积A eff＝110μm 2。
  10. 一种基于MDM-SDM的量子与经典融合通信传输方法，其特征在于，包括以下步骤：
    S1、系统噪声测试：在Alice发送端发射激光脉冲串的情况下，测试系统噪声，判断信噪比是否高于设定的信噪比预设值，若信噪比高于设定额信噪比设定值，进入步骤S2和S2’，若信噪比低于设定的信噪比预设值，生成提示信息；
    S2、量子态制备：Alice发送端的LD发射一个脉冲，被90/10的不对称分束器分成两束脉冲，光强较强的脉冲束用作Bob接收端的测量本振信号，光强较弱的脉冲束被发送到AM单元和PM单元进行幅度和相位调制，调制后的信号和本振信号通过PBS进行偏振复用；
    S2’、QPSK调制：经典信号发送器根据QPSK协议调制经典信息，该协议规定了四种载波相位45°、135°、225°、315°，分别将经典信息编码为比特{11，01，00，00}；载波相位在四个不同的数值之间切换，产生2N路QPSK信号；
    S2’.1、模式转换：通过S2’得到的各个QPSK信号经过模式转换从基模形式转换成高阶模LP 11a、LP 11b；
    S3、MDM-SDM复用传输：把通过S2得到的各路信号通过MDM-SDM解复用器耦合到一根FM-MCF特种光纤中进行复用传输，之后到达MDM-SDM复用器，分解成N个独立的量子信号输出；把通过S2’.1得到的各路信号通过MDM-SDM复用器耦合到一根FM-MCF特种光纤中进行复用传输，之后到达MDM-SDM解复用器，分解成独立的2N个经典信号输出；
    S4、模式转换：MDM-SDM解复用器输出的经典信号通过模式转换从高阶模转换成基模，进入相干接收器；
    S5、量子信号处理：MDM-SDM复用器输出的量子信号进入PC单元进行量子信号和本振信号偏振偏移的校正，Bob接收端的PBS将输入信号分解成信号脉冲和本振信号脉冲，两束脉冲馈入90°光学混合器，通过在信号和本振之间执行四个相位干涉来提取信号的相位和振幅，通过放大器进行信号放大，最后进入CV-QKD接收器进行零差检测；
    S5’、经典信号处理：本地振荡器产生的本振信号与相干接收器接收到的经典信号进行相干检测；随后进入色散补偿单元进行色散补偿；之后进入MIMO和DSP单元进行均衡处理和信号处理，恢复发送的经典信号；最后完成数据恢复并进行判决；
    S6、参数估计测试：Bob接收端发送长度为
    Figure PCTCN2020140114-appb-100001
    比特的信息给Alice发送端，让它计算‖X‖ 2、‖Y‖ 2和<X,Y>，以及γ a、γ b和γ c；如果
    Figure PCTCN2020140114-appb-100002
    Figure PCTCN2020140114-appb-100003
    那么参数估计测试通过，产生安全密钥，通信继续进行；反之则参数估计测试未过，通信中止，本轮已产生的密钥将会被舍弃。
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