WO2020140853A1 - 一种基于多芯光纤模分复用的qtth系统及传输方法 - Google Patents

一种基于多芯光纤模分复用的qtth系统及传输方法 Download PDF

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WO2020140853A1
WO2020140853A1 PCT/CN2019/129498 CN2019129498W WO2020140853A1 WO 2020140853 A1 WO2020140853 A1 WO 2020140853A1 CN 2019129498 W CN2019129498 W CN 2019129498W WO 2020140853 A1 WO2020140853 A1 WO 2020140853A1
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mode
signal
classic
mcf
onu
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French (fr)
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郭邦红
张倩琳
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华南师范大学
广东尤科泊得科技发展有限公司
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Priority to KR1020217024120A priority Critical patent/KR102528603B1/ko
Priority to JP2021538491A priority patent/JP7161153B2/ja
Publication of WO2020140853A1 publication Critical patent/WO2020140853A1/zh
Priority to US17/362,964 priority patent/US11309986B2/en

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    • 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
    • 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
    • H04B10/25—Arrangements specific to fibre transmission
    • H04B10/2581—Multimode transmission
    • 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
    • H04B10/40—Transceivers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/50—Transmitters
    • H04B10/516—Details of coding or modulation
    • H04B10/54—Intensity modulation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/02—Wavelength-division multiplex systems
    • H04J14/0227—Operation, administration, maintenance or provisioning [OAMP] of WDM networks, e.g. media access, routing or wavelength allocation
    • H04J14/0241—Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths
    • H04J14/0242—Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths in WDM-PON
    • H04J14/0245—Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths in WDM-PON for downstream transmission, e.g. optical line terminal [OLT] to ONU
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/02—Wavelength-division multiplex systems
    • H04J14/0278—WDM optical network architectures
    • H04J14/0282—WDM tree architectures
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/05—Spatial multiplexing systems
    • H04J14/052—Spatial multiplexing systems using multicore fibre
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/02—Amplitude-modulated carrier systems, e.g. using on-off keying; Single sideband or vestigial sideband modulation
    • 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
    • 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
    • H04L9/0861—Generation of secret information including derivation or calculation of cryptographic keys or passwords
    • H04L9/0869—Generation of secret information including derivation or calculation of cryptographic keys or passwords involving random numbers or seeds

Definitions

  • the invention relates to the field of quantum information, and in particular to a QTTH system and transmission method based on multi-core optical fiber modular division multiplexing.
  • the classic FTTH Fiber To To The Home, fiber to the home
  • end users urgently need to solve the data security, and the absolute security of QC (Quantum Cryptography, Quantum Encryption) obtained theoretical proof has attracted more and more attention.
  • the unconditional protection protocol of QC, QKD Quantum Key Distribution, quantum key distribution
  • QKD Quantum Key Distribution, quantum key distribution
  • the end-to-end quantum communication network application of universally applied QKD systems is far from being realized.
  • the existing FTTH network can be used to integrate QKD and traditional optical communications, thereby minimizing installation and operating costs.
  • WDM Widelength, Division, Multiplexing, Wavelength Division Multiplexing
  • WDM technology using single-mode optical fiber is close to the limit of capacity, and additional equipment is required on the line, which will introduce extra crosstalk and loss and may damage
  • MDM Mode Division Multiplexing, mode division multiplexing
  • SDM Space Division Multiplexing, space division multiplexing
  • MDM was first proposed by S. Berdague and P. Facq. They used spatial filters to select two low-order modes for exciting graded-index multimode fiber for transmission. After 10 meters of transmission, the crosstalk between the two modes was less than- 20dB, which proves the feasibility of analog-division multiplexing in short-distance transmission.
  • the multi-mode fiber used by it has a series of problems such as mode dispersion, inter-mode crosstalk and large loss.
  • the multi-core fiber used in this patent can effectively reduce the mode dispersion, and its hetero-groove structure can further reduce the inter-mode Crosstalk and nonlinear loss.
  • MDM refers to a multiplexing method that uses the mutually orthogonal modes in the optical fiber as an independent channel to transmit information, which is essentially a multi-input and output process of light.
  • MDM can be divided into OAM (Orbital Angular Momentum, orbital angular momentum) based on vortex optical fiber, modular multiplexing of low-mode optical fiber and multi-core optical fiber.
  • OAM Organic Angular Momentum, orbital angular momentum
  • the circular distribution of the OAM mode makes it difficult to interfere between the modes, but the light beam it carries is easily affected by the external environment and can only propagate in special optical fibers such as vortex fibers.
  • Many researchers have proposed the use of low-mode fiber for modular division multiplexing. For example, in 2015, Yuanxiang Chen et al. proposed a new MDM-PON (Passive Optical Network: passive optical network) solution for high-speed/capacity connection Into the network.
  • the low-mode optical fiber can effectively reduce the modal dispersion by only exciting a small number of modes. Its large mode field radius can effectively suppress the nonlinear effect, but it inevitably has strong inter-mode dispersion and mode coupling effects.
  • This patent realizes the fusion of QKD and FTTH through the module division multiplexing technology. Compared with other schemes, on the basis of expanding the transmission capacity and enhancing the safety, the use of heterogeneous grooved auxiliary seven-core fiber further reduces the inter-mode coupling and increases The effective area of the mode field is increased.
  • Existing technology patent (CN208015742U) provides a system for quantum key distribution and PON equipment co-fibre transmission, but co-fibre transmission uses single-mode fiber-based wavelength division multiplexing technology, which is close to the limit of communication capacity .”
  • the invention provides a QTTH (representing the fusion of QKD and FTTH) system and method based on multi-core optical fiber modular division multiplexing to improve communication capacity and security.
  • QTTH representing the fusion of QKD and FTTH
  • the use of heterogeneous groove-assisted seven-core optical fiber for modular division multiplexing can expand communication capacity, and because of its physical isolation structure, weak quantum signals are less interfered by classic signals than other solutions. During simultaneous transmission, better quantum key distribution performance is obtained, and the groove-assisted structure can effectively reduce crosstalk between modes and increase the effective mode field area of light effect.
  • the invention uses QKD technology (DV-QKD) based on the decoy state asymmetric BB84 protocol.
  • the sender Alice randomly sends two sets of single photons under non-orthogonal basis vectors, and the receiver Bob randomly selects the basis vector for measurement.
  • both parties will be secure and Consistent key.
  • the asymmetry is reflected in the unequal probability of being selected between these two sets of non-orthogonal basis vectors.
  • the basis with the selected probability is used for key generation, and the basis with the selected probability is used for security detection. This method can achieve a higher The final key rate.
  • the present invention further introduces a deceptive state that is only used to detect PNS (Photon Number Splitting) attacks, that is, the sender randomly selects different strengths
  • the light source (signal state and decoy state) is sent to the receiver.
  • a QTTH system based on multi-core optical fiber analog division multiplexing including: OLT (Optical Line Terminal), MDM-ODN (Mode Division Multiplexing-Optical Distribution Network, analog division multiplexing-optical distribution network) and ONU end (Optical Network Unit, optical network unit), OLT end, MDM-ODN and ONU end are connected in sequence through optical fiber;
  • OLT Optical Line Terminal
  • MDM-ODN Mode Division Multiplexing-Optical Distribution Network, analog division multiplexing-optical distribution network
  • ONU end Optical Network Unit, optical network unit
  • MDM-ODN includes a mode multiplexer and a mode demultiplexer, and they are connected to each other through MCF (Multi Core Fiber, multi-core fiber).
  • MCF Multi Core Fiber, multi-core fiber.
  • MCF is a hetero-groove-assisted seven-core fiber;
  • the OLT side includes a classic signal transmitter, N DV-QKD (Discrete-Variable-Quantum Key Distribution) units, and N+1 mode converters on the OLT side, and one end of the N+1 mode converters Connect to the classic signal transmitter, and the other end to the MDM-ODN mode multiplexer;
  • N DV-QKD Discrete-Variable-Quantum Key Distribution
  • the ONU includes N DV-QKD receivers, classic signal receivers, N+1 ONU-end mode converters, 2N+1 PDs, and 1 ONU-end OC; N DV-QKD receivers pass PD (light detection) Connected to the mode demultiplexer; N+1 ONU-end mode converters are connected to the demultiplexer, where the N ONU-end mode converters are connected to the classic signal receiver through PD, leaving one ONU-end mode The converter is connected to each classic signal receiver through a PD and an OC (beam splitter) at the ONU end;
  • the N+1 classic signals sent by the classic signal transmitter are converted from the fundamental mode to different and mutually orthogonal modes by the mode converter, and then the N quantum signals sent by the N DV-QKD units enter the mode multiplexer to be converted into Mode suitable for MCF transmission, and sent to the mode demultiplexer through MCF to be decomposed into independent N+1 classic signals and N quantum signals; each decomposed classic signal is converted into the mode of fundamental mode by mode converter, And sent to the classic signal receiver through the connected PD; quantum signals are sent to the DV-QKD receiver through the connected PD.
  • the classic signal transmitter includes a laser diode, a beam splitter, and N intensity modulators, wherein the N OLT-end mode converters are respectively connected to the beam splitter through the intensity modulator, and the remaining OLT-end mode converter and the splitter are connected. Beam directly connected;
  • the N+1 classic signals include a pilot signal and N OOK (On-Off Keying, Binary On-Off Keying) signals.
  • the PD uses an InGaAs avalanche photodiode operating in Geiger mode.
  • quantum signals use 1550nm wavelength channels; classic signals use upstream 1490nm wavelength channels or downstream 1310nm wavelength channels.
  • the mode multiplexer and mode demultiplexer consist of cascaded mode selection couplers.
  • the DV-QKD unit is a DV-QKD unit that generates quantum signals based on the decoy state asymmetric BB84 protocol.
  • the core radius of the MCF is 5 ⁇ m, and the refractive index groove is provided outside the core of the MCF; the thickness of the refractive index groove is 3 ⁇ m, and the core spacing of the MCF is 42 ⁇ m.
  • the refractive index of the core of the MCF is 1.4457; the refractive index difference between the core of the MCF and the cladding of the MCF is 0.003, and the refractive index difference between the refractive index groove and the cladding of the MCF is 0.003.
  • a QTTH transmission method based on multi-core optical fiber analog division multiplexing includes the following steps:
  • System noise test test the system noise when the laser pulse train is emitted from the OLT 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 The preset value, go to steps S2 and S2', if the signal-to-noise ratio is lower than the preset signal-to-noise ratio, a prompt message is generated;
  • Quantum state preparation The DV-QKD unit prepares quantum states according to the decoy state asymmetric BB84 protocol to generate quantum signals;
  • the classic signal transmitter divides the classic signal into N+1 through the beam splitter, one of which is used as the pilot signal, and the other N are modulated into N OOK signals through the intensity modulator; at this time, the classic signal Including pilot signal and N OOK signals;
  • Mode multiplex transmission each signal obtained through S2 and S2’.1 enters the MCF through the mode multiplexer for multiplex transmission, reaches the mode demultiplexer, and is decomposed into multiple signals;
  • each classic signal is converted into a basic mode signal through a mode converter
  • Self homodyne detection perform self homodyne detection on each OOK signal
  • Bit error rate detection The ONU terminal randomly selects a part of the DV-QKD screening code to detect the bit error rate; if the measured bit error rate value is greater than or equal to the theoretical calculation value of the deceptive state, then return to steps S2 and S2', if measured The bit error rate value obtained is less than the theoretical calculation value of decoy state, and a secure communication is established.
  • the preset value of the signal-to-noise ratio is 20 dB, and the theoretical calculation value of the decoy state is 11%.
  • Adopt module division multiplexing technology to realize QTTH technology.
  • the previously proposed multiplexing technology based on single-mode optical fiber WDM/TDM is close to reaching the limit of transmission capacity, and additional equipment is required on the line, which will introduce extra losses and crosstalk. May damage the final safety.
  • the modular division multiplexing of the present invention adopts mutually orthogonal modes for multiplexing, which can improve the transmission capacity and final security of optical communication.
  • Adopt heterogeneous groove-assisted multi-core optical fiber to realize modular division multiplexing.
  • the multi-core optical fiber is isolated based on physical structure, so that strong classic signal and weak quantum signal are transmitted simultaneously with very good signal-to-noise ratio and core isolation , To ensure higher stability and robustness of the system, allowing strictly independent channels to be transmitted through the same fiber.
  • the use of heterogeneous trench-assisted structure can effectively reduce the interference of strong classical signals on weak quantum signals, increase the area of the optical fiber effective field, and reduce crosstalk between different modes.
  • FIG. 1 is a frame diagram of the overall structure of the QTTH system based on the multi-core optical fiber modular division multiplexing of the present invention
  • FIG. 2 is a cross-sectional view of a hetero-slot-assisted seven-core optical fiber of the QTTH system based on multi-core optical fiber modular division multiplexing of the present invention
  • FIG. 3 is a refractive index profile of a hetero-slot-assisted seven-core fiber based on the QTTH system of the multi-core fiber modular division multiplexing of the present invention
  • FIG. 4 is a signal distribution diagram of the QTTH system of the present invention based on multi-core optical fiber analog division multiplexing
  • FIG. 5 is a flowchart of the transmission method of the QTTH system based on multi-core optical fiber analog division multiplexing of the present invention
  • a system based on QTTH of multi-core optical fiber analog division multiplexing includes: an OLT end, an MDM-ODN and an ONU end, and the OLT end, MDM-ODN and the ONU end are sequentially connected through an optical fiber.
  • the MDM-ODN includes a mode multiplexer and a mode demultiplexer.
  • the mode multiplexer and mode demultiplexer are both composed of cascaded mode selection couplers, and are connected to each other through MCF.
  • MCF is a heterogeneous groove assist Type seven-core fiber, which has the advantages of low crosstalk and large mode field area.
  • the cascade mode selection coupler is based on the principle of phase matching. When the fundamental mode and the higher-order mode reach phase matching, evanescent field coupling will occur, which can realize the mode separation function of outputting different modes at different ports, so it can effectively serve as multiple modes.
  • Multiplexer and demultiplexer and it has the advantages of easy manufacturing, high compatibility with optical fiber and low modal crosstalk.
  • the OLT side includes a classic signal transmitter, N DV-QKD units, and N+1 mode converters on the OLT side.
  • One end of the N+1 mode converters is connected to the classic signal transmitter, and the other end is connected to the MDM-ODN Mode multiplexer connection;
  • the ONU includes N DV-QKD receivers, classic signal receivers, N+1 ONU mode converters, 2N+1 PDs, and 1 ONU side OC; N DV-QKD receivers use PD and mode resolution respectively Multiplexer connection; N+1 ONU-end mode converters are connected to the demultiplexer, where the N ONU-end mode converters are connected to the classic signal receiver through PDs respectively, and the remaining ONU-end mode converters pass through a PD Connect with OC of ONU end to each classic signal receiver;
  • the N+1 classic signals sent by the classic signal transmitter are converted from the fundamental mode to different and mutually orthogonal modes by the mode converter, and then the N quantum signals sent by the N DV-QKD units enter the mode multiplexer to be converted into Mode suitable for MCF transmission, and sent to the mode demultiplexer through MCF to be decomposed into independent N+1 classic signals and N quantum signals; each decomposed classic signal is converted into the mode of fundamental mode by mode converter, And sent to the classic signal receiver through the connected PD; quantum signals are sent to the DV-QKD receiver through the connected PD.
  • PD uses InGaAs avalanche photodiodes operating in Geiger mode.
  • the classic signal transmitter includes a laser diode, a beam splitter, and N intensity modulators, wherein the N OLT-side mode converters are respectively connected to the beam splitter through the intensity modulator, and the OLT-side mode converter and the splitter are left
  • the beamers are directly connected, and N+1 classic signals include 1 pilot signal and N OOK signals.
  • a pilot signal is generated by a classic annunciator. Its advantage is that it can use coherent detection at the receiving end to improve spectrum efficiency and network coverage, and reduce the use of narrow-band local oscillator (LO) on the ONU. Related costs, OOK signals can be independently received by automatic detection.
  • LO narrow-band local oscillator
  • the DV-QKD unit generates quantum signals based on the decoy state asymmetric BB84 protocol for key distribution.
  • the protocol uses the MCF spatial dimension instead of polarization as the degree of freedom. Its working principle is to use quantum signals transmitted in any two cores of MCF to generate two unbiased bases.
  • base X is defined as (
  • AB>), and the final key rate R ⁇ I AB -min(I AE , I BE )), where I AB represents Alice (DV-QKD unit on the OLT side) and Bob (DV-QKD receiver on the ONU end) the classic mutual information I XY H(X)-H(X
  • the asymmetry is reflected in the different selection probability of the X and Y bases.
  • the base with a large selected probability is used for key generation, and the base with a small selected probability is used for security detection. This method can achieve a higher final key rate.
  • the deceptive state can effectively resist PNS attacks.
  • Power coupling mode theory is to introduce a system average value in the mode coupling theory, and directly use the power as the coupling parameter, which can effectively analyze the problem of inter-core crosstalk in multi-core optical fibers.
  • the power P i in the i-th core can be expressed as:
  • the summation number represents the sum of the coupling powers of adjacent adjacent cores
  • h ij represents the power coupling coefficient between the core i and the core j. It is assumed here that the power coupling coefficient between the middle core and the surrounding core is equal to h, and the power coupling coefficient between the surrounding cores is also equal to g, then the formula can be specifically expressed as:
  • the power coupling coefficient has a great influence on the crosstalk of multi-core fiber.
  • power coupling mode theory to calculate the crosstalk under different random errors in multi-core fibers, it was found that when the diameter difference between the cores becomes larger, the crosstalk is reduced, which proves that heterogeneous multi-core fibers effectively suppress cross-mode crosstalk .
  • the cross-talk is reduced by about 20-30dB overall, and then increased by increasing the inner diameter of the trench, reducing the outer diameter of the trench, and reducing the refractive index difference between the trench and the cladding.
  • the mode field area further reduces nonlinear damage. This proves that the seven-core optical fiber with the heterogeneous groove structure can make the light waves propagate in the respective cores, greatly reducing the coupling between the cores, so it can be used in analog-division multiplexing.
  • the structure in the upper right corner of the figure is the core, and the outer side of the core is provided with a cladding and groove structure, ⁇ represents the core spacing, ⁇ is set to 42 ⁇ m. Because there is a layer of refractive index groove structure around the core, the electric field far away from the core will be suppressed, so that the overlap integral between the electric fields of adjacent cores will be reduced, thus suppressing the crosstalk to a certain extent.
  • the distance between the center of the core of the MCF and the groove r 2 10 ⁇ m
  • core 1 and core 3 transmit DV-QKD signals
  • core 2 transmits pilots
  • core 4 and core 5 transmit upstream signals
  • 6 and core 7 transmit downstream signals.
  • the quantum signal when the MCF is transmitted, uses a wavelength channel of 1550 nm; the classic signal uses an upstream channel of 1490 nm or a downstream channel of 1310 nm to reduce the influence of Raman scattering noise.
  • System noise test check whether the equipment at the OLT side, MDM-ODN and ONU side can operate normally, and set the initial conditions; when the laser pulse train is emitted from the OLT side, test the system noise to determine whether the signal-to-noise ratio is high At the preset signal-to-noise ratio, if the signal-to-noise ratio is higher than the preset signal-to-noise ratio, proceed to steps S2 and S2'.
  • the classic signal transmitter divides the classic signal into N+1 through the beam splitter, one of which is used as the pilot signal, and the other N are modulated into N OOK signals through the intensity modulator; at this time, the classic signal includes Pilot signal and N OOK signals;
  • each classic signal obtained through step S2' undergoes mode conversion through a mode converter, so that the classic signals in the fundamental mode are converted into different and orthogonal modes through the mode converter, and quantum signals do not require a mode Mode, transmission in the form of basic mode;
  • quantum state preparation DV-QKD unit prepares quantum state according to the decoy state asymmetric BB84 protocol to generate quantum signal, the specific steps include:
  • S2'.1 In each pulse transmission cycle, Alice randomly prepares and sends a signal state or decoy state to Bob, the difference between the two is the average number of photons.
  • the initial state prepared at Alice Through different ports of the Mach-Zehnder interferometer, it is converted into two states with different phases with state with After transmission to the MCF, the MCF uses different spatial dimensions of any two cores (such as core A and core B) to transform the state; After passing through core A, it is transformed into a quantum state After passing through core B, it is transformed into a quantum state Similarly, After different cores are converted into The four states form two mutually unbiased bases, the base X is defined as (
  • S2'.2 Alice uses a classic channel (a separate classic channel is provided between Alice and Bob for communication) to tell Bob which of these states are signal states and which are decoy states;
  • Mode multiplex transmission each signal obtained through S2.1 and S2’.1 enters the MCF through the mode multiplexer for multiplex transmission, reaches the mode demultiplexer, and is decomposed into multiple signals;
  • each classic signal is converted into a fundamental mode signal by a mode converter, and quantum signals do not need to be converted; at this time, both the classic signal and the quantum signal are in fundamental mode and can be transmitted through a single-mode fiber;
  • each signal is detected by a photodetector; here the detector uses InGaAs avalanche photodiode operating in Geiger mode.
  • the working mode of the avalanche diode is divided into linear mode and Geiger mode.
  • the avalanche working in linear mode The diode can only respond to the classic strong light signal but not the quantum weak single photon signal, and the avalanche diode working in Geiger mode can respond to both signals;
  • Bit error rate detection the OLT end randomly selects a part of the screening code to detect the bit error rate; if the measured bit error rate value is greater than or equal to the theoretical calculation value in the deceptive state, then return to steps S2 and S2' to restart a new round
  • the specific steps include:
  • S7.1 Bob randomly selects the measurement base for measurement, and declares the measurement base he used and the quantum states in which cycles he received;
  • S7.2 Alice and Bob end leave the correct part of the base vector comparison as the screening code, and calculate the count rate and bit error rate of the signal state and decoy state respectively, in which only a part of the signal state is extracted for bit error rate estimation;
  • S7.3 Alice and Bob perform bit error rate detection based on the above data to determine whether there is eavesdropping. If there is eavesdropping, the key is discarded and communication is terminated. If there is no eavesdropping, error correction and dense amplification are performed.

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Abstract

一种基于多芯光纤模分复用QTTH的系统，包括：OLT端、MDM-ODN和ONU端，OLT端、MDM-ODN和ONU端通过光纤依次连接；MDM-ODN包括模式复用器和模式解复用器，且相互之间通过MCF连接，MCF为异质沟槽辅助型七芯光纤；OLT端包括经典信号发送器、N个DV-QKD单元和N+1个OLT端的模式转换器，N+1个模式转换器的一端与经典信号发送器连接，另一端与MDM-ODN的模式复用器连接；ONU包括N个DV-QKD接收器、经典信号接收器、N+1个ONU端的模式转换器和2N+1个PD以及1个ONU端的OC；N个DV-QKD接收器分别通过PD与模式解复用器连接；N+1个ONU端的模式转换器与解复用器连接，其中N个ONU端的模式转换器分别通过PD与经典信号接收器连接，剩下一个ONU端的模式转换器经过一个PD和ONU端的OC分别与各个经典信号接收器连接。

Description

一种基于多芯光纤模分复用的QTTH系统及传输方法 技术领域
本发明涉及量子信息领域，尤其涉及一种基于多芯光纤模分复用的QTTH系统及传输方法。
背景技术
经典的FTTH(Fiber To The Home，光纤到户)终端用户亟需解决数据安全性，QC(Quantum Cryptography，量子加密)获得理论证明的绝对安全性受到越来越多的关注。QC、QKD(Quantum Key Distribution，量子密钥分发)的无条件保护协议，可确保两个远程用户方之间的随机比特分布的信息理论安全性。近年来QKD系统，由于设备的兼容性和成本，普遍实用化应用的端到端量子通信网络应用还远未实现。为了降低QKD网络应用的成本，可以利用现有的FTTH网络将QKD和传统光通信集成在一起，以此最大地降低敷设和运营费用。
实现量子和经典融合的常用技术是WDM(Wavelength Division Multiplexing，波分复用)，例如2015年Wei Sun等人提出的基于波分复用的量子密钥分配与千兆位无源光网络的集成实验。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，采用单模光纤的WDM技术已经接近容量的极限，且在线路上都需要额外的设备，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要求。MDM(Mode Division Multiplexing，模分复用)和SDM(Space Division Multiplexing，空分复用)技术有望解决传输容量的问题。
1982年，MDM由S.Berdague和P.Facq首次提出，他们利用空间滤膜选择激发渐变折射率多模光纤的两个低阶模式进行传输，传输10米后两个模式之间的串扰小于-20dB，由此证明模分复用在短距离传输中的可行性。但其采用的多模光纤存在模式色散、模间串扰和较大损耗等一系列问题，而本专利采用的多芯光纤可以有效减小模式色散，其异质沟槽型结构能够进一步降低模间串扰和非线性损耗。MDM是指利用光纤中相互正交的各个模式作为一个独立的信道来传输信息的一种复用方式，本质上是光的多输入输出过程。MDM按技术理念可分为基于涡旋光纤的OAM(Orbital Angular Momentum，轨道角动量)、少模光 纤和多芯光纤的模分复用。
OAM模式的环形分布使得各模式之间具有不易干扰的优势，但其携带的光束易受外界环境的影响，只能在涡旋光纤等特殊光纤中传播。不少学者提出利用少模光纤进行模分复用，例如2015年Yuanxiang Chen等人提出地利用自身非线性检测的新型MDM-PON(Passive Optical Network：无源光纤网络)方案用于高速/容量接入网络。少模光纤通过仅激励少量模式的方法有效降低了模式色散，其较大的模场半径可以有效抑制非线性效应，但其不可避免的存在较强的模间色散和模式耦合效应。
本专利通过模分复用技术实现QKD和FTTH融合，与其他方案将比，在扩大传输容量和增强安全性的基础上，采用异质沟槽型辅助七芯光纤进一步降低了模间耦合，增大了模场有效面积。
“现有技术专利：(CN208015742U)提供了一种量子密钥分发与PON设备共纤传输的系统，但共纤传输使用的是基于单模光纤的波分复用技术，已经接近通信容量的极限。”
“现有技术专利：(CN108028718A)采用模分复用技术提高了FTTH的通信容量，但其没有使用QKD技术，所以在安全性方面有所欠缺。”
发明内容
本发明提供了一种提升通信容量和安全性的基于多芯光纤模分复用的QTTH(表示QKD和FTTH融合)系统及方法。采用异质沟槽辅助型七芯光纤进行模分复用，即能扩大通信容量，又因其物理隔离的结构，使得弱量子信号受到经典信号的干扰较其他方案更小，易在量子和经典同传时获得更好的量子密钥分发性能，且沟槽辅助型结构能够有效减小模间串扰，增大光效有效模场面积。
本发明采用基于诱骗态非对称BB84协议的QKD技术(DV-QKD)。在BB84协议中，发送方Alice随机发送两组非正交基矢下的单光子，接收方Bob随机选择基矢进行测量，理想情况下二者使用相同的基矢时，双方将会得到安全且一致的密钥。非对称性体现在这两组非正交基矢被选择概率不等，被选概率大的基用于密钥生成，被选概率小的基用于安全检测，这种方式可实现更高的最终密钥率。为了解决实际QKD系统由多光子脉冲和信道损耗引入的安全漏洞，本发明进一步引入了仅用来探测PNS(Photon Number Splitting，光子数分个)攻击的诱骗态，即发送方随机选择不同强度的光源(信号态和诱骗态)发送给接收方。为了达到上述技术效果，本发明的技术方案如下：
一种基于多芯光纤模分复用QTTH的系统，包括：OLT端(Optical Line Terminal,光线路终端)、MDM-ODN(Mode Division Multiplexing-Optical Distribution Network，模分复用-光分配网络)和ONU端(Optical Network Unit，光网络单元)，OLT端、MDM-ODN和ONU端通过光纤依次连接；
MDM-ODN包括模式复用器和模式解复用器，且相互之间通过MCF(Multi Core Fiber，多芯光纤)连接，MCF为异质沟槽辅助型七芯光纤；
OLT端包括经典信号发送器、N个DV-QKD(Discrete Variable-Quantum Key Distribution，离散变量-量子密钥分发)单元和N+1个OLT端的模式转换器，N+1个模式转换器的一端与所述经典信号发送器连接，另一端与MDM-ODN的模式复用器连接；
ONU包括N个DV-QKD接收器、经典信号接收器、N+1个ONU端的模式转换器和2N+1个PD以及1个ONU端的OC；N个DV-QKD接收器分别通过PD(光探测器)与模式解复用器连接；N+1个ONU端的模式转换器与解复用器连接，其中N个ONU端的模式转换器分别通过PD与经典信号接收器连接，剩下一个ONU端的模式转换器经过一个PD和ONU端的OC(分束器)分别与各个经典信号接收器连接；
经典信号发送器发送的N+1个经典信号经过模式转化器从基模转换成不同且相互正交的模式后，连同N个DV-QKD单元发送的N个量子信号进入模式复用器转换成适合MCF传输的模式，并通过MCF发送到模式解复用器分解成独立的N+1个经典信号和N个量子信号；分解后的各个经典信号分别通过模式转换器转换成基模的模式，并经过连接的PD发送到经典信号接收器；量子信号通过连接的PD发送到DV-QKD接收器。
优选的，经典信号发送器包括激光二极管、分束器和N个强度调制器，其中N个OLT端的模式转换器分别通过强度调制器与分束器连接，剩下一个OLT端的模式转换器与分束器直接连接；
N+1个经典信号包括1个导频信号和N个OOK(On-Off Keying，二进制启闭键控)信号。
更优选的，PD采用以盖革模式操作的InGaAs雪崩光电二极管。
在MCF进行传输时，量子信号采用1550nm的波长信道；经典信号采用上行1490nm的波长信道或下行1310nm的波长信道。
更优选的，模式复用器和模式解复用器由级联模式选择耦合器组成。
以上的，DV-QKD单元为基于诱骗态非对称BB84协议产生量子信号的DV-QKD单元。
进一步的，MCF的纤芯半径为5μm，MCF的纤芯外侧设置有折射率沟槽；折射率沟槽的厚度为3μm，MCF的芯间距为42μm。
更进一步的，MCF的纤芯折射率为1.4457；MCF的纤芯与MCF的包层之间折射率差为0.003，折射率沟槽与MCF的包层之间的折射率差为0.003。
一种基于多芯光纤模分复用QTTH的传输方法，包括以下步骤：
S1、系统噪声测试：在OLT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，若信噪比高于设定的信噪比预设值，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：DV-QKD单元根据诱骗态非对称BB84协议制备量子态，生成量子信号；
S2’、OOK调制：经典信号发送器把经典信号通过分束器分成N+1个，其中一个作为导频信号，另外N个经过强度调制器被调制成N个OOK信号；此时，经典信号包括导频信号和N个OOK信号；
S2’.1、模式转换：通过步骤S2’得到的各个经典信号经过模式转换器进行模式转换；
S3、模式复用传输：把通过S2和S2’.1得到的各个信号通过模式复用器进入MCF进行复用传输后到达模式解复用器，分解成多路信号；
S4、模式转化：各个经典信号通过模式转换器转换成为基模信号；
S5、自零差检测：对各个OOK信号进行自零差检测；
S6、误码率检测：ONU端随机选取DV-QKD筛选码的一部分检测误码率；若测量得到的误码率值大于等于诱骗态的理论计算值，则返回步骤S2和S2’，若测量得到的误码率值小于诱骗态的理论计算值，建立安全通信。
优选的，信噪比预设值为20dB，诱骗态的理论计算值为11％。
与现有技术相比，本发明技术方案的有益效果是：
1)采用模分复用技术实现QTTH技术，先前提出的基于单模光纤WDM/TDM等复用技术接近到达传输容量的极限，且在线路上都需要额外的设备，会引入格外的损耗和串扰而可能损害最终的安全性。而本发明的模分复用采用相互正交的模式进行复用，能提高光通信的传输容量和最终的安全性。
2)采用异质沟槽辅助型多芯光纤实现模分复用，多芯光纤基于物理结构隔离，使强经典信号和弱量子信号同时传输时有非常好的信噪比和核心之间的隔离，保证了系统更高的 稳定性和鲁棒性，允许通过同一光纤传输严格独立的信道。且采用异质沟槽辅助型结构，可以有效减小强经典信号对弱量子信号的干扰，增大光纤有效场的面积，降低不同模式之间的串扰。
利用自零差检测技术可以有效抑制激光相位噪声，且无需偏振补偿和导频相位校正的多输入输出DSP(数字信号处理)，就可直接检测出独立的OOK信号。
3)利用MCF的两个纤芯生成相互无偏的基，采用诱骗态非对称BB84协议产生量子信号。此方法即能够有效抵御PNS攻击，又提高了密钥生成率、安全性，增加了传输距离。
附图说明
图1是本发明基于多芯光纤模分复用的QTTH系统的整体结构框架图；
图2是本发明基于多芯光纤模分复用的QTTH系统的异质沟槽辅助型七芯光纤横截面图；
图3是本发明基于多芯光纤模分复用的QTTH系统的异质沟槽辅助型七芯光纤折射率分布图；
图4是本发明基于多芯光纤模分复用的QTTH系统的信号分配图；
图5是本发明基于多芯光纤模分复用的QTTH系统的传输方法的流程图；
具体实施方式
下面将结合本发明实施例中的附图，对本发明实施例中的技术方案进行清楚、完整地描述，显然，所描述的实施例仅仅是本发明一部分实施例，而不是全部的实施例。基于本发明中的实施例，本领域普通技术人员在没有付出创造性劳动前提下所获得的所有其他实施例，都属于本发明保护的范围。
实施例1
一种基于多芯光纤模分复用QTTH的系统，如图1所述，包括：OLT端、MDM-ODN和ONU端，OLT端、MDM-ODN和ONU端通过光纤依次连接。
MDM-ODN包括模式复用器和模式解复用器，模式复用器和模式解复用器均由级联模式选择耦合器组成，且相互之间通过MCF连接，MCF为异质沟槽辅助型七芯光纤，其具有低串扰和大模场面积的优势。另外，级联模式选择耦合器基于相位匹配原理，当基模和高阶模达到相位匹配时，将发生倏逝场耦合，可实现在不同端口输出不同模式的模式分离 功能，因此可以有效的充当模式多路复用器和解复用器，且其具有易于制造，与光纤的高兼容性和低模态串扰等优点。
OLT端包括经典信号发送器、N个DV-QKD单元和N+1个OLT端的模式转换器，N+1个模式转换器的一端与所述经典信号发送器连接，另一端与MDM-ODN的模式复用器连接；
ONU包括N个DV-QKD接收器、经典信号接收器、N+1个ONU端的模式转换器和2N+1个PD以及1个ONU端的OC；N个DV-QKD接收器分别通过PD与模式解复用器连接；N+1个ONU端的模式转换器与解复用器连接，其中N个ONU端的模式转换器分别通过PD与经典信号接收器连接，剩下一个ONU端的模式转换器经过一个PD和ONU端的OC分别与各个经典信号接收器连接；
经典信号发送器发送的N+1个经典信号经过模式转化器从基模转换成不同且相互正交的模式后，连同N个DV-QKD单元发送的N个量子信号进入模式复用器转换成适合MCF传输的模式，并通过MCF发送到模式解复用器分解成独立的N+1个经典信号和N个量子信号；分解后的各个经典信号分别通过模式转换器转换成基模的模式，并经过连接的PD发送到经典信号接收器；量子信号通过连接的PD发送到DV-QKD接收器。
其中，PD采用以盖革模式操作的InGaAs雪崩光电二极管。
具体的，经典信号发送器包括激光二极管、分束器和N个强度调制器，其中N个OLT端的模式转换器分别通过强度调制器与分束器连接，剩下一个OLT端的模式转换器与分束器直接连接，N+1个经典信号包括1个导频信号和N个OOK信号。通过经典信号器产生一个导频信号，其优势体现于，在接收端即能使用相干检测以提高频谱效率和网络覆盖范围，又降低了在ONU上使用窄带本地振荡器(LO)等带来的相关成本，OOK信号通过自动检测就可以被独立接收。
具体的，DV-QKD单元为基于诱骗态非对称BB84协议产生量子信号进行密钥分发，该协议利用MCF的空间维度而非偏振作为自由度。其工作原理是利用MCF任意两个纤芯中传输的量子信号，生成两个相互无偏的基，对于芯A和芯B而言，基X定义为(|A>；|B>)，基Y定义为(|A+B>，|A-B>),最终的密钥率R≥I AB-min(I AE，I BE))，其中I AB表示Alice(OLT端的DV-QKD单元)和Bob(ONU端的DV-QKD接收器)之间的经典互信息I XY＝H(X)-H(X|Y),min(I AE，I BE))跟Alice和Eve或者Alice和Eve之间的量子互信息有关。非对称性体现在X基和Y基被选择概率不等，被选概率大的基用于密钥生成，被选概率小 的基用于安全检测，这种方式可实现更高的最终密钥率。而采用诱骗态可以有效抵御PNS攻击。
进一步的，由于多芯光纤不可避免地也存在模间耦合，需运用功率耦合方程来分析多芯光纤的传输特性，看其是否满足模分复用的要求。功率耦合模理论是在模式耦合理论中引入一个系统平均值，直接将功率作为耦合参量，能够有效分析多芯光纤中的芯间串扰问题。当只考虑相邻纤芯的功率耦合时，第i个纤芯中的功率P i可表示为：
Figure PCTCN2019129498-appb-000001
其中求和号表示相邻相邻纤芯耦合功率之和，h ij表示纤芯i和纤芯j之间的功率耦合系数。此处假设中间纤芯与周围纤芯之间的功率耦合系数相等，为h，而周围纤芯之间的功率耦合系数也相等，为g，则公式可具体表述为：
Figure PCTCN2019129498-appb-000002
Figure PCTCN2019129498-appb-000003
Figure PCTCN2019129498-appb-000004
Figure PCTCN2019129498-appb-000005
Figure PCTCN2019129498-appb-000006
Figure PCTCN2019129498-appb-000007
将上述所有公式相加得到：
Figure PCTCN2019129498-appb-000008
Figure PCTCN2019129498-appb-000009
式中
Figure PCTCN2019129498-appb-000010
设中间纤芯在z＝0处功率为P 1(0),根据上述两式得到七芯光纤中中间纤芯和周围纤芯的归一化功率分别为：
Figure PCTCN2019129498-appb-000011
Figure PCTCN2019129498-appb-000012
其中P k(z)(k＝2,3,……，7)为第k个纤芯中的光功率，则在中间纤芯被激励的条件下周围纤芯的串扰为：
Figure PCTCN2019129498-appb-000013
由此可见功率耦合系数对多芯光纤的串扰有很大的影响。利用功率耦合模理论计算多芯光纤中不同随机误差下串扰情况，发现当纤芯之间的直径差异变大时，串扰是降低的，由此证明了异质多芯光纤有效的抑制模间串扰。采用沟槽结构与非沟槽结构相比，串扰又整体降低约20-30dB，进而通过增大沟槽内径、减小沟槽外径、减小沟槽与包层的折射率差来增大模场面积，又进一步减少非线性损伤。由此证明异质沟槽结构的七芯光纤能够使光波在各自纤芯中传播，大大降低了纤芯之间的耦合，因此可被用于模分复用中。
更具体的，如图2所示，对一个沟槽辅助的纤芯来说，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,Λ表示芯间距，Λ设置为42μm。由于纤芯周围存在一层折射率沟槽结构，所以远离纤芯的电场将会被抑制，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。
更具体的，如图3所示，MCF的纤芯外侧设置有折射率沟槽，且MCF的纤芯的折射率n 1＝1.4457，MCF的纤芯与MCF的包层的折射率差Δ1＝0.003，MCF的沟槽与包层的折射率差Δ2＝0.003。另外，MCF的纤芯半径为r 1＝5μm，MCF的纤芯中心与沟槽的距离r 2＝10μm，MCF的沟槽的宽度为r 3＝3μm。经综合分析得，这种参数设置能有效减小模式色散，增大光纤有效模场面积。
更具体的，如图4所示，MCF的异质沟槽辅助型七芯光纤中，芯1和芯3传输DV-QKD信号，芯2传输导频，芯4和芯5传输上行信号，芯6和芯7传输下行信号。
优选的，在MCF进行传输时，量子信号采用1550nm的波长信道；经典信号采用上行1490nm的波长信道或下行1310nm的波长信道，用以减弱拉曼散射噪声的影响。
S1、系统噪声测试：检查OLT端、MDM-ODN和ONU端处的设备是否能正常运转，设定初始条件；在OLT侧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，若信噪比高于设定的信噪比预设值，进入步骤S2和S2'，若信噪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、OOK调制：经典信号发送器把经典信号通过分束器分成N+1个，其中一个作为导 频信号，另外N个经过强度调制器被调制成N个OOK信号；此时，经典信号包括导频信号和N个OOK信号；
S2.1、模式转换：通过步骤S2’得到的各个经典信号经过模式转换器进行模式转换，使处于基模的经典信号经过模式转换器转换成不同且相互正交的模式，而量子信号无需模式模式，以基模形式进行传输；
S2'、量子态制备：DV-QKD单元根据诱骗态非对称BB84协议制备量子态，生成量子信号，具体步骤包括：
S2'.1：在每个脉冲发送周期，Alice随机制备并发送一个信号态或诱骗态给接收方Bob，两者的区别在于平均光子数不同。其中Alice处制备的初始态
Figure PCTCN2019129498-appb-000014
通过马赫-曾德干涉仪的不同端口，转换为两种相位不同的态
Figure PCTCN2019129498-appb-000015
和
Figure PCTCN2019129498-appb-000016
态
Figure PCTCN2019129498-appb-000017
和
Figure PCTCN2019129498-appb-000018
传输到MCF后，MCF利用任意两个纤芯(例如芯A和芯B)的不同空间维度对态进行变换；
Figure PCTCN2019129498-appb-000019
经过芯A后转化为量子态
Figure PCTCN2019129498-appb-000020
经过芯B后转化为量子态
Figure PCTCN2019129498-appb-000021
同理，
Figure PCTCN2019129498-appb-000022
经过不同的纤芯后被分别转化为
Figure PCTCN2019129498-appb-000023
四种态构成两个相互无偏的基，基X被定义为(|A>,|B>),基Y定义为(|A+B>，|A-B>)；
S2'.2：Alice使用经典信道(Alice和Bob之间设有独立的经典信道用以通信)告诉Bob，这些态中哪些是信号态，哪些是诱骗态；
S3、模式复用传输：把通过S2.1和S2’.1得到的各个信号通过模式复用器进入MCF进行复用传输后到达模式解复用器，分解成多路信号；
S4、模式转化：各个经典信号通过模式转换器转换成为基模信号，而量子信号无需转换；此时经典信号和量子信号都为基模模式，可通过单模光纤进行传输；
S5、探测信号：各信号由光电探测器进行探测；此处探测器使用以盖革模式操作的InGaAs雪崩光电二极管，雪崩二极管的工作模式分为线性模式和盖革模式，工作于线性模式的雪崩二极管只能响应经典的强光信号却不能响应量子的弱单光子信号，而工作于盖革模式的雪崩二极管对两种信号都能响应；
S6、自零差检测：所有的信号分别到达接收机，完成信息的传输，导频代替本振对各个OOK信号进行自零差检测，此处无需复杂的DSP；
S7、误码率检测：OLT端随机选取筛选码的一部分检测误码率；若测量得到的误码率值大于等于诱骗态的理论计算值，则返回步骤S2和S2’，重新开始新一轮通信，若测量得到 的误码率值小于诱骗态的理论计算值，建立安全通信；其中，诱骗态的理论计算值为11％，具体步骤包括：
S7.1：Bob随机选择测量基进行测量，并声明自己采用的测量基和接收到了哪些周期中的量子态；
S7.2：Alice和Bob端留下基矢对比正确的部分作为筛选码，分别计算信号态和诱骗态的计数率和误码率，其中信号态只提取一部分进行误码率估计；
S7.3：Alice和Bob端根据上述数据进行误码率检测判断是否存在窃听，存在窃听则抛弃密钥、中止通信，不存在窃听则进行纠错和密性放大等操作。
以上实施例仅用以说明本发明的技术方案，而非对其限制；尽管参照前述实施例对本发明进行了详细的说明，本领域的普通技术人员应当理解：其依然可以对前述实施例所记载的技术方案进行修改，或者对其中部分技术特征进行等同替换；而这些修改或者替换，并不使相应技术方案的本质脱离本发明实施例技术方案的精神和范围。

Claims (10)

  1. 一种基于多芯光纤模分复用QTTH的系统，其特征在于，包括：OLT端、MDM-ODN和ONU端，所述OLT端、MDM-ODN和ONU端通过光纤依次连接；
    所述MDM-ODN包括模式复用器和模式解复用器，且相互之间通过MCF连接，所述MCF为异质沟槽辅助型七芯光纤；
    所述OLT端包括经典信号发送器、N个DV-QKD单元和N+1个OLT端的模式转换器，所述N+1个模式转换器的一端与所述经典信号发送器连接，另一端与MDM-ODN的模式复用器连接；
    所述ONU包括N个DV-QKD接收器、经典信号接收器、N+1个ONU端的模式转换器和2N+1个PD以及1个ONU端的OC；所述N个DV-QKD接收器分别通过PD与模式解复用器连接；所述N+1个ONU端的模式转换器与解复用器连接，其中N个ONU端的模式转换器分别通过PD与经典信号接收器连接，剩下一个ONU端的模式转换器经过一个PD和ONU端的OC分别与各个经典信号接收器连接；
    所述经典信号发送器发送的N+1个经典信号经过模式转化器从基模转换成不同且相互正交的模式后，连同所述N个DV-QKD单元发送的N个量子信号进入所述模式复用器转换成适合所述MCF传输的模式，并通过所述MCF发送到所述模式解复用器分解成独立的N+1个经典信号和N量子信号；所述分解后的各个经典信号分别通过模式转换器转换成基模的模式，并经过连接的PD发送到经典信号接收器；所述量子信号通过连接的PD发送到DV-QKD接收器。
  2. 根据权利要求1所述的一种基于多芯光纤模分复用QTTH的系统，其特征在于：
    所述经典信号发送器包括激光二极管、分束器和N个强度调制器，其中N个OLT端的模式转换器分别通过所述强度调制器与分束器连接，剩下一个OLT端的模式转换器与分束器直接连接；
    所述N+1个经典信号包括1个导频信号和N个OOK信号。
  3. 根据权利要求2所述的一种基于多芯光纤模分复用QTTH的系统，其特征在于：
    所述PD采用以盖革模式操作的InGaAs雪崩光电二极管。
  4. 根据权利要求3所述的一种基于多芯光纤模分复用QTTH的系统，其特征在于：
    在所述MCF进行传输时，所述量子信号采用1550nm的波长信道；所述经典信号采用上行1490nm的波长信道或下行1310nm的波长信道。
  5. 根据权利要求4所述的一种基于多芯光纤模分复用QTTH的系统，其特征在于：
    所述模式复用器和模式解复用器由级联模式选择耦合器组成。
  6. 根据权利要求1至5任一项所述的一种基于多芯光纤模分复用QTTH的系统，其特征在于：
    所述DV-QKD单元为基于诱骗态非对称BB84协议产生量子信号的DV-QKD单元。
  7. 根据权利要求6所述的一种基于多芯光纤模分复用QTTH的系统，其特征在于：
    所述MCF的纤芯半径为5μm；所述MCF的纤芯外侧设置有折射率沟槽，所述折射率沟槽的厚度为3μm；所述MCF的芯间距为42μm。
  8. 根据权利要求7所述的一种基于多芯光纤模分复用QTTH的系统，其特征在于：
    所述MCF的纤芯折射率为1.4457；所述MCF的纤芯与MCF的包层之间折射率差为0.003，所述折射率沟槽与MCF的包层之间的折射率差为0.003。
  9. 一种应用于权利要求1至8任一项所述的一种基于多芯光纤模分复用QTTH的系统的传输方法，其特征在于，包括以下步骤：
    S1、系统噪声测试：在OLT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，若信噪比高于设定的信噪比预设值，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：DV-QKD单元根据诱骗态非对称BB84协议制备量子态生成量子信号；S2’、OOK调制：经典信号发送器把经典信号通过分束器分成N+1个，其中一个作为导频信号，另外N个经过强度调制器被调制成N个OOK信号；此时，经典信号包括导频信号和N个OOK信号；
    S2’.1、模式转换：通过步骤S2’得到的各个经典信号经过模式转换器进行模式转换；
    S3、模式复用传输：把通过S2和S2’.1得到的各个信号通过模式复用器进入MCF进行复用传输后到达模式解复用器，分解成多路信号；
    S4、模式转化：各个经典信号通过模式转换器转换成为基模信号；
    S5、自零差检测：对各个OOK信号进行自零差检测；
    S6、误码率检测：ONU端随机选取DV-QKD筛选码的一部分检测误码率；若测量得到的误码率值大于等于诱骗态的理论计算值，则返回步骤S2和S2’，若测量得到的误码率值小于诱骗态的理论计算值，建立安全通信。
  10. 根据权利要求9所述的一种基于多芯光纤模分复用QTTH的传输方法，其特征在于：
    所述信噪比预设值为20dB，所述诱骗态的理论计算值为11％。
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