CN106850073B - User terminal, MDI-QKD system and method and network system in quantum key distribution system - Google Patents

User terminal, MDI-QKD system and method and network system in quantum key distribution system Download PDF

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CN106850073B
CN106850073B CN201710032153.8A CN201710032153A CN106850073B CN 106850073 B CN106850073 B CN 106850073B CN 201710032153 A CN201710032153 A CN 201710032153A CN 106850073 B CN106850073 B CN 106850073B
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pulse
phase
laser
light
light pulse
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CN106850073A (en
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富尧
王真真
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Divine Land Zhejiang Quantum Network Science And Technology Ltd
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Divine Land Zhejiang Quantum Network Science And Technology Ltd
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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
    • H04B10/50—Transmitters
    • H04B10/501—Structural aspects
    • H04B10/503—Laser transmitters
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/50—Transmitters
    • H04B10/508—Pulse generation, e.g. generation of solitons
    • 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
    • H04B10/524—Pulse modulation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/50—Transmitters
    • H04B10/516—Details of coding or modulation
    • H04B10/54—Intensity modulation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/50—Transmitters
    • H04B10/516—Details of coding or modulation
    • H04B10/548—Phase or frequency modulation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/80—Optical aspects relating to the use of optical transmission for specific applications, not provided for in groups H04B10/03 - H04B10/70, e.g. optical power feeding or optical transmission through water
    • 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
    • H04L9/0819—Key transport or distribution, i.e. key establishment techniques where one party creates or otherwise obtains a secret value, and securely transfers it to the other(s)

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Electromagnetism (AREA)
  • Computer Security & Cryptography (AREA)
  • Theoretical Computer Science (AREA)
  • Optics & Photonics (AREA)
  • Optical Communication System (AREA)
  • Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)

Abstract

The present invention provides the user terminals in a kind of quantum key distribution system, it includes modulated light source, and the modulated light source includes that phase prepares laser, optical fiber circulator and pulse generation laser.The present invention also provides MDI-QKD systems, it includes user terminal and public-measurement end, and the user terminal includes the end Alice and the end Bob, and the public-measurement end is the end Charlie, and the end Alice and the end Bob include modulated light source.Invention further provides the cryptographic key distribution methods and networking MDI-QKD system of the above-mentioned MDI-QKD system based on light injection.User terminal of the invention simplifies conventional phase modulation laser and pulse generates the structure of laser, phase feedback system that no setting is required.MDI-QKD system of the invention realizes the integrated morphology of light source and phase-modulator, intensity modulator, relieves phase-modulator, the limitation that intensity modulator applies system high-speed；Modulated light source can directly generate the light pulse with pure phase information, it can be achieved that light pulse phase reference consistency controls between multi-user.

Description

User terminal, MDI-QKD system and method and network in quantum key distribution system System
Technical field
The present invention relates to the communications field, be related to include quantum key distribution system user terminal, in particular to MDI-QKD system Cryptographic key distribution method in system and optical fiber transmission of quantum private communication technology field and quantum secret communication.
Background technique
Lo in 2012 et al. proposes the unrelated quantum-key distribution (measurement-device- of measuring device Independent QKD, MDI-QKD) agreement, light pulses are to untrusted third after Alice and Bob will be encoded in the protocol Square Charlie carries out Bell state measurement, and the attack of any detector side channel can be immunized, substantially increase the reality of QKD system Safety.
MDI-QKD system based on phase code, because the phase-modulation of light pulse transmits strong antijamming capability in a fiber, The available stable detection result of system and higher at code rate, so being very suitable to the secure communication of long range both sides. Mainly being achieved in that for light pulse phase code carries out external modulation, common base using phase-modulator in MDI-QKD system In the phase-modulator of LiNbO3 crystal.In the moment that light pulse reaches, phase-modulator adds a pulse voltage, passes through electricity The refractive index that field changes electrooptical material changes the out of phase of light pulse with this, and the height of pulse voltage determines the phase of modulation Place value.Quantum-key distribution has the light pulse emission of GHz high speed, it is desirable that phase-modulator pulse voltage equally has nanosecond Narrow pulse bandwidth, and phase-modulator itself needs higher half-wave voltage, therefore in the phase-modulation using LiNbO3 crystal When device, system needs to design complicated circuit and carries out drive control.It is driven the crucial device such as analog switch in circuit, delay chip The performance of part limits, and phase-modulator is extremely difficult to i.e. high speed and the ideal Modulated effect of high-voltage value, practical attainable arteries and veins Its waviness phenomena of pulse voltage rushed voltage band width and limit the high-speed applications of system, and generate is to finally have at code rate can not The influence of ignorance.Complicated driving circuit also results in the heaviness of user's end structure, increases the design cost of system.
No matter theory discuss or in actual operation, the MDI-QKD agreement based on phase code usually with inveigle state Thought is used in combination, to resist attack of the listener-in to measurement end and source ends simultaneously.State scheme is inveigled to need use intensity tune Device processed is modulated by force light pulse, the common Mach-Zehnder electrooptic modulator based on LiNbO3 crystal.Intensity modulator The modulation of pulse voltage can only equally be received and need higher half-wave voltage, complicated driving circuit and phase-modulator Driving circuit has the shortcomings that similar.And Mach-Zehnder electrooptic modulator has periodic transfer function, to avoid letter Number distortion, it is necessary to make modulator work in just bias point, i.e., control is strong when taking in the application of quantum key distribution system Spend the bias point of modulator.But due to by time drift, environment temperature, system laser power, that is, optical fiber insertion and coupling loss Equal factors influence, and are actually difficult control bias point and stablize, intensity modulator output signal is caused to deteriorate.Bias point control Further increase the structural burden of user terminal.
In the MDI-QKD system based on phase code, other than said modulator brings problem, system also faces list The problem for two light pulse phase basic vector of the front and back calibration that a user terminal issues.In systems, phase code process generally uses one A non-equilibrium Mach increases Dare interferometer (AMZI) and a light pulse is divided into two, and generates former and later two sub-light pulses, and make Phase-modulation is carried out to one of subpulse with phase-modulator and realizes cataloged procedure.But the arm length difference of AMZI is defeated at its Additional transmission phase difference is caused between former and later two subpulses out, and interferometer arm length difference is vulnerable to environment temperature, stress etc. The influence of factor and change, cause the drift that phase difference is transmitted between two subpulses.The presence of transmission phase difference destroys two The consistency of subpulse phase reference influences the interference contrast and detection result at public-measurement end.In order to control transmission phase The drift of potential difference is simultaneously stablized in 0 value, needs human intervention environmental factor to be stablized, interferometer is such as sealed in narrow sky Between, interferometer is isolated using internal high thermal conductivity, insulating back-up material；Or it needs by adding active feedback in systems Module is controlled, and phase shifter and its attached feedback system are inserted into such as in an arm of interferometer, anti-by what is become slowly Feedback signal changes phase shifter voltage, poor with the 0 value transmission of phase for guaranteeing stable.Equally, front and back arteries and veins single user end issued The control for rushing phase reference consistency keeps MDI-QKD system structure more complicated, and design cost is higher.
To sum up, following defect exists in the prior art:
1. existing MDI-QKD system light pulse phase code needs phase-modulator, intensity modulation to need intensity modulated Device, the use of two kinds of modulation devices not only limits the high-speed applications of system, and the driving circuit of the two complexity makes user terminal Structure bulky, increased costs are unfavorable for the networking extension of MDI-QKD.
2. the phase reference consistency for the front and back light pulse that existing MDI-QKD system single user end issues needs phase Position feedback system guarantees, it is huge that engineering is designed in networked system.
Above-mentioned two big defect constrains the application of the MDI-QKD system networking based on phase code, more particularly to simultaneously When between guarantee multi-user the problem of light pulse phase reference consistency, the phase feedback system of whole network will be one great Engineering design.
Summary of the invention
The present invention provides the user terminal in a kind of quantum key distribution system, which simplifies conventional phase modulation Laser and pulse generate the structure of laser, and phase feedback system that no setting is required has saved cost.
For this purpose, the invention adopts the following technical scheme:
The user terminal includes modulated light source, and the modulated light source includes:
Phase prepares laser, optical fiber circulator and pulse and generates laser.
The phase prepares laser by generating light pulse after phase premodulated；
The fiber optical circulator first port connects the phase and prepares laser, the second port closed on first port It connects pulse and generates laser, the second port that the light pulse of the phase preparation laser modulation passes through the optical fiber circulator It injects the pulse and generates laser,
Particularly, the light pulse that the phase that the pulse generates that laser is injected prepares laser generation excites and its oneself Body intensity modulated generates light pulse, the modulated light source output phase modulation and the light pulse after intensity modulated.So far, it is modulating Light source internal completes the phase code and intensity modulated of light pulse.
Preferably, the intensity modulated includes time encoding modulation or/and state is inveigled to modulate.
Include the pulse of signal state in the trick state signal, inveigle state pulse and vacuum state pulse, and varying strength is set The duty ratio of light pulse.
Invention further provides a kind of MDI-QKD system based on light injection, which realizes light source and phase-modulation The integrated morphology of device, intensity modulator, simplifies system structure, relieves phase-modulator, intensity modulator to system high-speed The limitation of application；Modulated light source can directly generate the light pulse with pure phase information, be not necessarily to phase feedback system, can be real Light pulse phase reference consistency controls between existing multi-user.
For this purpose, the invention adopts the following technical scheme:
The MDI-QKD system includes user terminal and public-measurement end, and the user terminal includes the end Alice and the end Bob, institute Stating public-measurement end is the end Charlie, and the end Alice and the end Bob include modulated light source, and the modulated light source includes:
Phase prepares laser, and the phase prepares laser by generating light pulse after phase premodulated；
Optical fiber circulator, the fiber optical circulator first port connect the phase and prepare laser, face with first port Close second port connection
Pulse generates laser, and the light pulse of the phase preparation laser modulation passes through the second of the optical fiber circulator Port injects the pulse and generates laser, and the pulse generates the light arteries and veins that the phase that laser is injected prepares laser generation Impulse hair, makes the modulated light pulse of modulated light source output phase；The pulse generates the phase preparation that laser is injected and swashs The light pulse excitation and its self-strength modulation that light device generates, make the modulated light pulse of modulated light source output intensity；The tune The light pulse of light source output processed is by the third port output of the fiber optical circulator closed on second port and via quantum Transmission is to the end Charlie, and the end Charlie is as Bell's state measuring device；The transmission of the optical fiber circulator Direction is first port to second port, second port to third port.
Preferably, the end Charlie is as Bell's state measuring device comprising:
Polarization control unit group, for receiving light pulse and system by the transmission of the quantum channel at the end Alice and the end Bob respectively One and stablize the polarization state of two-way light pulse；
Polarization-maintaining fiber coupler, for receiving the light pulse by polarization control unit output and forming interference；And two lists Photon detector carries out different responses for being formed by result of interference to the light pulse in the polarization-maintaining fiber coupler.
Preferably, the pulse generates the intensity modulated of laser and includes time encoding modulation or/and state is inveigled to modulate
Preferably, the phase prepares laser and pulse generates laser and forms transmission channel by optical fiber circulator.
Preferably, the optical fiber circulator is set there are three port, and the phase prepares laser connection first port, described Pulse generates laser and connects second port, and the third port connects quantum channel.
Preferably, strength retrogression is arranged on the output end that pulse generates laser in the end Alice and the end Bob Device, for the light pulse after coding to be decayed to single photon level.The user terminal keeps two-way light pulse same by synchronization module When reach the end Charlie.
Preferably, the phase prepares laser and pulse generates the light pulse that laser generates and includes signal state, inveigles State and vacuum state, and the duty ratio of varying strength light pulse is set.
Preferably, the end Alice and the end Bob are provided with randomizer, respectively generate one group of random number sequence conduct The random bit value of the two, and respectively generate another group of random sequence for select coding basic vector, wherein 0 represents phase code base Arrow, 1 represents time encoding basic vector.
Preferably, the end Alice and the end Bob make two-way light pulse by synchronization module while reaching the end Charlie.Institute State synchronization module include be arranged in path selection module that the end Alice and the end Bob are arranged after intensity attenuators and with phase system Standby laser generates the time synchronization module that laser is connected simultaneously with pulse, the path selection module and intensity attenuators it Between a wavelength-division recombiner is set, the wavelength-division recombiner is connected by a photodetector with the time synchronization module, described The path selection module at the end Alice is connected with the path selection module at the end Bob；
The end Charlie is separately arranged second on polarization-maintaining fiber coupler all the way to a single-photon detector transmission line Optical fiber circulator, the second optical fiber circulator successively connect with polarization-maintaining fiber coupler, single-photon detector and synchronous radiant respectively It connects, the outbound course of second fiber optical circulator is that synchronous radiant is coupled to polarization-maintaining fiber coupler direction, polarization maintaining optical fibre Device is to single-photon detector direction；The light pulse that the synchronous radiant generates is by the second optical fiber circulator through polarization maintaining optical fibre coupling Clutch is transmitted separately to the path selection module at the end Alice and the end Bob, which is turned to and transmitted by the path selection module Respective time synchronization module is arrived after to other side's path selection module again and realizes synchronization；
The path selection module is directly exported to common end Charlie when exporting the light pulse that modulated light source issues, The light pulse of arrival is transmitted to another path selection module when transmitting the light pulse of synchronous radiant, another Path selection mould The pulse signal is transmitted to photodetector by wavelength division multiplexer again by block, and it is same that photodetector transmits a signal to the time again Module is walked, time synchronization module prepares laser according to signal phase-triggered and pulse generates laser works, and completion, which synchronizes, to be set It sets.
Present invention technical problem also to be solved is to provide the key distributor of the above-mentioned MDI-QKD system based on light injection Method, it the following steps are included:
The phase at the end S101Alice and the end Bob prepares laser by generating light pulse after phase premodulated, and passes through light Fine circulator injected pulse generates laser；
Pulse described in S102 generates the light pulse excitation that the phase that laser is injected prepares laser generation, makes modulation light The modulated light pulse of source output phase；The pulse generates the light pulse that the phase that laser is injected prepares laser generation Excitation and its self-strength modulation, make the modulated light pulse of modulated light source output intensity, so far, the light that modulated light source generates Pulse is exported through optical fiber circulator, and decays to single photon level, the light pulse at the end Alice and the end Bob by intensity attenuators Polarization control unit group by synchronization module through quantum channel simultaneous transmission to the end Charlie；
Polarization state of the polarization control unit group respectively by the light pulse from the end Alice and the end Bob described in S103 is united One and stablize, and uniform transmission forms high contrast into polarization-maintaining fiber coupler and interferes, different result of interference will cause two The different responses of a single-photon detector, to judge whether to produce legal Bell's state；
Legal Bell's state information is sent to Alice and Bob by disclosed classic network by S104 Charlie, Alice and Bob generates final security key according to the processing of MDIQKD protocol contents.
Further, in the step S101, phase prepares laser and carries out phase premodulated process:
Phase prepares laser modulation and triggers electric signal, introduces Δ U's within one duration of the middle position of electric signal Electric signal disturbance, it is Δ φ that the part for causing light pulse front and back unmodulated, which forms phase phase difference, completes phase premodulated, and phase Position prepares the light pulse of laser transmitting, and the part of in-between phase premodulated respective pulses when light injects generate laser Electric signal interval is triggered, the only unmodulated part in its front and back generates laser generation light injection effect to pulse.
Further, in the step S101 and step S102, the end Alice and the end Bob are provided with random number Device, respectively generate one group of random number sequence as both random bit value, and respectively generate another group of random sequence for select volume Code basic vector, wherein 0 represents phase code basic vector, 1 represents time encoding basic vector.
Further, the phase prepares laser during phase premodulated:
When Systematic selection phase code basic vector encoding ratio paricular value, phase code basic vector is X=[0, π], phase basic vector X Include two kinds of phase states | 0 > with | π >, | 0 > phase states encoding ratio paricular value 0, | π > phase states encoding ratio paricular value 1, Δ φ=0 are corresponding | 0 > phase states, Δ φ=π are corresponding | and π > phase states, the triggering electric signal for making phase prepare laser have Δ U1=0 and Δ U2= UπElectric signal disturbance, be respectively formed the light pulse with Δ φ=0 or Δ φ=π phase premodulated information, injected pulse produces Raw laser.
When Systematic selection time encoding basic vector encoding ratio paricular value, the triggering electric signal that phase prepares laser has Δ U1=0 electric signal disturbance, forms the light pulse with Δ φ=0.
Further, the pulse generates laser in intensity modulation process:
When Systematic selection phase code basic vector encoding ratio paricular value, pulse generates laser and normally provides two pulses of front and back Triggering electric signal；
When Systematic selection time encoding basic vector encoding ratio paricular value, pulse generates laser and carries out time encoding modulation, Time encoding basic vector Z, basic vector Z contain the intensity distribution state 0 or 1 that two kinds of pulses generate laser transmitting light pulse pair, modulation Pulse generates the triggering electric signal of laser, and when the coding to bit value 0, closing timing is distributed the triggering of the light pulse of front Electric signal makes its light intensity 0, normally provides the trigger voltage signal of subsequent light pulse, makes its light intensity normal value；Work as comparison When the coding of paricular value 1, closing timing is distributed the triggering electric signal of subsequent light pulse, makes its light intensity 0, normal offer front The trigger voltage signal of light pulse makes its light intensity normal value.
When system carries out inveigling state modulation, phase code basic vector coding and the time of laser effect are generated for pulse The light pulse for encoding basic vector coding, on all luminous timing positions, modulation pulse generates the triggering electric signal of laser, makes It is with different intensity values, to form and inveigle the light pulse of each state respective strengths in state scheme.
Further, synchronization module of the present invention includes that setting is arranged after intensity attenuators at the end Alice and the end Bob Path selection module and prepare laser and pulse with phase and generate the time synchronization module that laser is connected simultaneously, the road One wavelength-division recombiner is set between diameter selecting module and intensity attenuators, and the wavelength-division recombiner passes through a photodetector and institute It states time synchronization module to be connected, the end Alice path selection module is connected with the path selection module at the end Bob；
The second optical fiber is separately arranged in the end Charlie on polarization-maintaining fiber coupler all the way to single-photon detector transmission line Circulator, the second optical fiber circulator are connected with polarization-maintaining fiber coupler, single-photon detector, and connect a synchronous radiant, institute State the second optical fiber circulator transmission direction from synchronous radiant to polarization-maintaining fiber coupler, from polarization-maintaining fiber coupler to single photon Detector；The path selection module is directly exported to common end Charlie when exporting the light pulse that modulated light source issues, In The light pulse of arrival is transmitted to another path selection module when transmitting the pulse of synchronous radiant, another path selection module is again The pulse signal is transmitted to photodetector by wavelength division multiplexer, photodetector transmits a signal to time synchronization mould again Block, time synchronization module prepares laser according to signal phase-triggered and pulse generates laser works.
Further, two single-photon detectors respectively judge the time location of detection, if two detections Device has response, and in the period at the same time, and it is 0 that a single-photon detector, which detects time location, a single photon It is 1 that detector, which detects time location, then it is assumed that is at this time legal Bell's state.
In the step S101 and step S102, phase prepares laser and pulse generates the light pulse packet that laser generates It includes signal state, inveigle state and vacuum state, and the duty ratio of varying strength light pulse is set.
The last technical issues that need to address of the present invention are to provide a kind of networking MDI-QKD system based on light injection, It include modulated light source the system comprises 2 and 2 or more user terminals and a public-measurement end, each user terminal, the tune Light source processed includes:
Phase prepares laser, and the phase prepares laser by generating light pulse after phase premodulated；
Optical fiber circulator, the fiber optical circulator first port connect the phase and prepare laser, face with first port Close second port connection pulse generates laser, and the light pulse of the phase preparation laser modulation passes through the fiber annular The second port of device is injected
Pulse generates laser, and the light pulse that the phase that the pulse generation laser is injected prepares laser generation swashs Hair, makes the modulated light pulse of modulated light source output phase；The pulse generates the phase that laser is injected and prepares laser The light pulse excitation of generation and its self-strength modulation, make the modulated light pulse of modulated light source output intensity, the modulation light Light pulse after the modulation of source output phase and intensity modulated is extremely
Public-measurement end, the public-measurement end is as Bell's state measuring device, and the public-measurement end is in user terminal It is disposed with photoswitch and filter on transmission line, polarization control unit is set after filter, and the photoswitch is for selecting Need to be switched to the user terminal at public-measurement end.
Further, the public-measurement end includes:
Polarization control unit group, for receiving light pulse and unification by the quantum channel transmission of user terminal respectively and stablizing The polarization state of two-way light pulse；
Polarization-maintaining fiber coupler, for receiving the light pulse by polarization control unit output and forming interference；And
Two single-photon detectors, for the light pulse in the polarization-maintaining fiber coupler be formed by result of interference into The different response of row.
Further, the light pulse that the pulse generates laser output decays to single photon level by intensity attenuators It is transmitted to public-measurement end again；The public-measurement end is disposed with photoswitch, filter on the transmission line after quantum channel Polarization control unit is arranged after filter in wave device.
Particularly, the public-measurement end only allows two-way user terminal to access when in use.
Further, the user terminal is additionally provided with synchronization module comprising time synchronization module and path selection module, The time synchronization module prepares laser with phase and pulse generates laser and is connected, and a wavelength-division recombiner is arranged, described Wavelength-division recombiner connects modulated light source all the way, and another way is connect with time synchronization module by a photon detector, connected after compound Path selection module is connect, the path selection module is connect with quantum channel again；
The public-measurement end is separately arranged on polarization-maintaining fiber coupler all the way to a single-photon detector transmission line Two optical fiber circulators, the second optical fiber circulator respectively successively with polarization-maintaining fiber coupler, single-photon detector and synchronous radiant Connection, the outbound course of the second light circulator are to synchronize radiant to polarization-maintaining fiber coupler direction, polarization maintaining optical fibre coupling Clutch is to single-photon detector direction；The light pulse that the synchronous radiant generates is coupled by optical fiber circulator through polarization maintaining optical fibre Device is transmitted separately to the path selection module of user terminal, and light pulse steering is transmitted to communication counterpart by the path selection module Path selection module after arrive respective time synchronization module again and realize and synchronize.
Further, the path selection module of user terminal is connected to a gating module, the gating module connection pair simultaneously The path selection module for the two-way user terminal for needing to be connected to public-measurement end for answering photoswitch to connect.
The present invention finally provides a kind of cryptographic key distribution method of networking MDI-QKD system based on light injection, The quantum key delivering method the following steps are included:
S101 phase prepares laser by generating light pulse after phase premodulated, and passes through optical fiber circulator injected pulse Generate laser；
Pulse described in S102 generates the light pulse excitation that the phase that laser is injected prepares laser generation, makes modulation light The modulated light pulse of source output phase；The pulse generates the light pulse that the phase that laser is injected prepares laser generation Excitation and its self-strength modulation, make the modulated light pulse of modulated light source output intensity, so far, the light arteries and veins that modulated light source generates Punching is exported through optical fiber circulator, and decays to single photon level by intensity attenuators, and the light pulse of user terminal passes through synchronous mould Block is through quantum channel simultaneous transmission to the polarization control unit at public-measurement end；
The polarization state of light pulse from user terminal is carried out unified and stablized by polarization control unit group described in S103 respectively, And uniform transmission forms high contrast interference into polarization-maintaining fiber coupler, different result of interference will cause two single-photon detectings The different responses of device are surveyed, to judge whether to produce legal Bell's state；
Legal Bell's state information is sent to user terminal, user terminal by disclosed classic network by S104 public-measurement end Final security key is generated according to the processing of MDIQKD protocol contents.
Further, it is provided with photoswitch on the user terminal and the transmission line at public-measurement end, to control user terminal Whether public-measurement end is accessed, and the public-measurement end only allows two-way user terminal to access when in use.
Further, the light pulse that the synchronous radiant generates is by the second optical fiber circulator through polarization-maintaining fiber coupler It is transmitted separately to the two-way user terminal for needing to be connected to public-measurement end connected by the correspondence photoswitch that gating module is connected Light pulse steering is transmitted to after the path selection module of other side and arrives again respectively by path selection module, the path selection module Time synchronization module realize synchronize.
Present invention combination modulated light source and when both m- phase encoding schemes the advantages of, omit to phase-modulator and strong The use for spending modulator does not need the phase reference consistency for guaranteeing front and back pulse using phase feedback system, as far as possible yet Simplify point-to-point MDI-QKD system structure and save design cost, while guaranteeing that point-to-point MDI-QKD system has high contrast Modulated signal, finally allow MDI-QKD system practical closer to networked instruments, meanwhile, realize phase-modulation and intensity It is lower to modulate the half-wave voltage needed, is conducive to the high-speed applications of system.Point-to-point MDI-QKD system of the invention is in networking The huge engineering design that this part is related to can be saved in MDI-QKD system, so that system structure has been obtained great simplification, finally Purpose is the networking for pushing MDI-QKD, practical development.
Detailed description of the invention
The part (a) of Fig. 1-(e) is respectively that phase prepares the pulse-triggered electric signal of laser, phase prepares laser hair The light phase evolution process of the long pulse, long pulse penetrated, pulse generate the triggering electric signal of laser, pulse generates laser hair The short pulse penetrated.
The part (a) of Fig. 2-(c) is respectively the triggering that phase prepares the triggering electric signal of laser, pulse generation laser The phase modulated short pulse sequence that electric signal, modulated light source export.
Fig. 3 is the point-to-point MDI-QKD system light path figure injected based on light.
The part (a) of Fig. 4-(c) is respectively the triggering that phase prepares the triggering electric signal of laser, pulse generation laser Electric signal, modulated light source output through when m- phase code after short pulse sequence.
The part (a) of Fig. 5-(c) is respectively the triggering that phase prepares the triggering electric signal of laser, pulse generation laser The short pulse sequence result of electric signal, modulated light source m- phase code and trick state scheme superposition modulated when carrying out.
Fig. 6 is the selection schematic diagram of Bell's state in embodiment one.
Fig. 7 is the Time Synchronizing exemplary diagram of embodiment one.
Fig. 8 is the preferred embodiment of path selection module described in embodiment two, i.e., constructs this mould using three optical fiber circulators Block.
Fig. 9 is the networking MDI-QKD system light path figure injected based on light.
Figure 10 is the synchronization scheme for the networking MDI-QKD system that embodiment three is injected based on light.
Figure 11 is the preferred embodiment of the gating module.
Specific embodiment
Below in conjunction with attached drawing, the present invention is further elaborated.
Embodiment one:
Primary content of the invention is the use to modulated light source.As shown in figure 3, modulated light source by two laser LD1, The optical fiber circulator 1/6 of LD2 and connection two-laser is constituted.Two-laser prepares laser respectively as phase and pulse generates Laser.The light pulse that phase prepares laser output generates laser through 1/6 injected pulse of optical fiber circulator, and pulse, which generates, to swash The light pulse of light device output exports outward through optical fiber circulator.The output of modulated light source is substantially the output that pulse generates laser As a result.
Particularly, when phase prepares laser and pulse generates laser autonomous working, the triggering of two-laser is modulated Electric signal makes the equally spaced uniform pulse sequence of each spontaneous emission of two-laser, and adjusts the period of two kinds of pulse train, makes phase The each long pulse for preparing laser sending generates a pair of of bursts period that laser issues comprising pulse on the period.Two Arbitrary neighborhood pulse in kind pulse train all has random phase relationship.
Specifically, the core concept of modulated light source is light injection, phase is prepared to the length of the presetting Δ φ phase difference of laser Impulses injection pulse generate laser, can excitation pulse generate laser, make pulse generate laser transmitting a pair of of short pulse Phase difference is Δ φ.
The phase modulation process of modulated light source is as shown in Figure 1.
The part (a) of Fig. 1-(e) is respectively that phase prepares the pulse-triggered electric signal of laser, phase prepares laser hair The light phase evolution process of the long pulse, long pulse penetrated, pulse generate the triggering electric signal of laser, pulse generates laser hair The short pulse penetrated.
As shown in part (a) of Fig. 1, phase modulation prepares the pulse-triggered electric signal of laser, in pulse-triggered telecommunications Number one duration of Δ t of middle position in introduce Δ U disturbance, this modulation pulse-triggered electric signal phase-triggered preparation swash Light device emits the long pulse as shown in part (b) of Fig. 1.The disturbance Δ U of triggering electric signal changes phase and prepares laser increasing The concentration of beneficial medium carrier, causes the variation of gain media refractive index, thus changes the frequency of laser output light, for The variation of this position light frequency of the long pulse of generation to the linear effect of its phase evolution as shown in part (c) of Fig. 1, i.e. optical frequency The fractional phase difference Δ φ that difference causes long pulse front and back unmodulated.From part (b) of Fig. 1 as can be seen that triggering electric signal Disturbance equally change the amplitude of this position of long pulse.To avoid the parasitisms such as phase modulation duration pulse frequency, phase, amplitude fluctuations Effect injects the influence of excited short pulse to light, and as shown in part (d) of Fig. 1, phase is prepared laser triggering telecommunications Number disturbance Δ U duration of Δ t alignment pulse generate laser triggering electric signal interval, i.e., closing pulse generate laser To the gain of long pulse herein, make finally the only unmodulated part in long pulse front and back in light injected pulse generation laser Excitation is played, is generated in laser in pulse and inspires two indistinguishable short pulses, and by pure phase difference φ is transmitted between two short pulses.The part (e) institute of phase modulated two short pulse such as Fig. 1 of final modulated light source transmitting Show.In MDI-QKD system, pure two short pulse of front and back of phase is directly generated using modulated light source, is avoided first to phase The use of modulator, next, which does not need to consider further that, carries out two arteries and veins of phase external modulation bring front and back by AMZI and phase-modulator Rush the inconsistent problem of phase reference.Two pulses of front and back will undergo identical path to reach public-measurement end after phase code.
It is in a linear relationship between Δ φ and Δ U, Δ φ can be modulated to arbitrary value by the way that Δ U is arranged.Fig. 2 be modulated light source only The luminous exemplary diagram of two-laser when phase modulation is carried out, the part (a)-(c) of Fig. 2 is respectively the triggering telecommunications that phase prepares laser Number, pulse generate laser triggering electric signal, modulated light source output phase modulated short pulse sequence.U pairs of Δ in Fig. 2 Δ φ=π is answered, and when the triggering electric signal disturbance that phase prepares laser is 0, light injects afterpulse and generates laser transmitting The short pulse that a pair of of phase difference is 0.Still there is two betweens of adjacent short pulses random phase after (c) partially visible phase modulation of Fig. 2 Position.U=0.35 volts of the half-wave voltage Δ of modulated light source, i.e. Uπ=0.35 volt, far smaller than LiNbO3 crystalline phase is modulated Half-wave voltage level (the U of deviceπ4 volts of ≈).It is close that the lower half-wave voltage of modulated light source is advantageously implemented high speed, efficient quantum Key distribution, and its integrated structure for simplifying user terminal to light source and phase-modulator.
As described above, by phase modulation prepare laser triggering electric signal, it can be achieved that modulated light source phase modulation process. And when modulation pulse generates the triggering electric signal of laser, and pulse is made to generate the short pulse of laser output varying strength, just It realizes modulated light source the modulated process of light intensity, light source and the integrated of intensity modulator are equally beneficial for realizing at a high speed, efficiently Quantum key distribution and simplify the structure of user terminal.
Fig. 3 is the point-to-point MDI-QKD system light path figure injected based on light, and there are three nodes altogether in figure: user terminal Alice, user terminal Bob and public-measurement end Charlie.The two-way of Alice and Bob to Charlie optical path knot having the same Structure, system can reach the shellfish of Charlie by the light pulse that synchronization module control Alice and Bob (as shown in Figure 7) is issued simultaneously That state measuring device.
The present invention use based on when m- phase code quantum key distribution scheme.This scheme does not require to guarantee measurement end Relative to the consistency of user terminal basic vector benchmark, the detectable signal of high contrast can be generated, provide it is higher at code rate and Simple system structure.The advantages of this scheme is utilized in the present invention, and the advantage of modulated light source is combined, structural texture is more simple Single MDI-QKD system.
In the present invention, user terminal Alice and Bob uses phase and prepares laser LD1, pulse generation laser LD2 The modulated light source constituted with optical fiber circulator 1/6, for generating light pulse and carrying out the phase code and time encoding of light pulse. The output end bonding strength attenuator ATT of modulated light source, for the light pulse after coding to be decayed to single photon level.2 and 7 are Quantum channel is transferred to Charlie from Alice and Bob for the light pulse after ATT decays.The end Charlie is as Bell's state Measuring device, light pulse enters polarization control unit PC in Charlie, to unify and stablize the polarization state of two-way light pulse, High contrast interference, polarization-maintaining will be formed in polarization-maintaining fiber coupler 3 by the two-way light pulse that polarization control unit PC is adjusted Two output ends of fiber coupler 3 are separately connected single-photon detector 4/5, and different result of interference will cause single-photon detector 4 and 5 different responses.
Selected phase encodes basic vector X=[0, π] (or Y=[pi/2,3 pi/2s], this embodiment selects basic vector X), two kinds of phase states Corresponding relationship between bit value can be set as: | 0 > phase states encoding ratio paricular value 0, | π > phase states encoding ratio paricular value 1.The phase of system Position cataloged procedure is substantially that a pair of of short pulse phase difference value Δ φ of modulated light source selection output is how many processes, Δ φ=0 It is corresponding | 0 > phase states, Δ φ=π are corresponding | π > phase states.According to the corresponding relationship of Δ φ and Δ U, two kinds of phase preparations are set and are swashed The triggering electric signal of light device, makes it be respectively provided with Δ U1=0 and Δ U2=UπDisturbance, this two kinds triggering electric signals respectively correspond Modulated light source output | 0 > phase states and | π > phase states short pulse pair.
Select time encoding basic vector for Z, basic vector Z contains the intensity distribution state of two kinds of short pulses pair.Timing distribution is gone forward The short pulse intensity in face is 0, and subsequent short pulse intensity is constant, this intensity distribution state encoding ratio paricular value 0；The short pulse of front is strong Spend it is constant, subsequent short pulse intensity be 0, this intensity distribution state encoding ratio paricular value 1.The time encoding of system is substantially modulation light Source generates the modulated process of laser triggering electric signal to pulse, and phase prepares laser triggering electric signal disturbance when time encoding It is 0.The triggering electric signal that pulse generates laser is modulated, when the coding to bit value 0, closing timing is distributed the short of upper front The triggering electric signal of pulse makes its light intensity 0, normally provides the trigger voltage signal of subsequent short pulse；When to bit value 1 When coding, closing timing is distributed the triggering electric signal of upper subsequent short pulse, makes its light intensity 0, normal to provide the short arteries and veins of front The trigger voltage signal of punching.
In the present invention, selection may is that Bell's state measurement is set after Bell's state of the MDIQKD scheme of m- phase code when 2 detectors 4/5 in standby respectively judge the time location of detection, if 2 detectors have response, and same A time cycle, and a detection is in time location 0, a detection is in (the time difference of position 0 and position 1 of time location 1 Two shorter pulse times intervals before and after corresponding modulating light source output), then it is assumed that it is at this time legal Bell's state.
Inside Alice and Bob, randomizer (being not drawn into Fig. 3) respectively generates one group of random number sequence as two The random bit value of person, and respectively generate another group of random sequence for select coding basic vector, wherein 0 represents X basic vector, 1 represents Z base Arrow.
As shown in the top sheet of Fig. 4, if Alice generates 0110 random bit string, and Z, X, Z, X basic vector are successively selected Random bit string is encoded.(a) of Fig. 4-(c) partially illustrates the when m- phase code process of Alice modulated light source, (a) of Fig. 4-(c) part be respectively phase prepare laser triggering electric signal, pulse generate laser triggering electric signal, Modulated light source output through when m- phase code after short pulse sequence.As shown in part (a) of Fig. 4, when Alice uses Z base When arrow first bit value 0 of coding, it is 0 that phase, which prepares laser triggering electric signal disturbance,；As shown in part (b) of Fig. 4, long pulse After washing injection off, pulse generates laser according to intensity distribution state Tidal stress electric signal corresponding with bit value 0, makes timing point The forward triggering electric signal as at the position a' is 0 on cloth, in timing distribution rearward be such as triggering electric signal of the b " at position Normal value.Light injects and two are triggered electric signals to the exercising result of pulse generation laser as shown in part (c) of Fig. 4, right Answer forward such as a in timing distribution " short pulse intensity is 0 at position, in timing distribution rearward as short pulse is strong at position by b " Degree is normal value.When Alice is using Z basic vector coding third bit value 1, phase prepares laser triggering electric signal disturbance and is 0, part (b) on the contrary, such as Fig. 4 is modulated when pulse generates the method for laser triggering electric signal and encodes first bit value 0 It is triggered shown in electric signal at the middle position e', f', generates the result of light pulse also in contrast, portion (c) of light pulse result such as Fig. 4 Short pulse in point at e ", f " position is to shown.A pair of of short pulse after Z basic vector coding has random phase with adjacent short pulse Position relationship.
As shown in part (a) and (b) of Fig. 4, when Alice encodes second bit value 1 using X basic vector, to phase system Standby laser tape has disturbance Δ U2Triggering electric signal, to pulse generate laser correspond to it is slightly less than normal at timing position c'd' Triggering electric signal.Then the presetting Δ φ of laser is prepared by phase2The long pulse of phase, injected pulse generate laser after The position c " d " inspires a pair of of short pulse that phase difference is π, as a result as shown in part (c) of Fig. 4.When Alice is compiled using X basic vector When the 4th bit value 0 of code, as shown in part (a) and (b) of Fig. 4, preparing laser tape to phase has disturbance Δ U1Triggering Electric signal generates laser to pulse and corresponds to timing position g'h' upper two slightly less than normal triggering electric signals, as a result such as Fig. 4 The part (c) shown in, timing position g " h " go up pulse generate laser phase difference output Δ φ1=0 a pair of of short pulse.At this In the coding mode of invention, single short pulse intensity is the half of single short pulse intensity under Z basic vector coding under X basic vector coding, This is related with the distribution probability of single photon quantum state, does not explain in detail herein.Part (c) of Fig. 4 is whole to illustrate the modulation of Alice Coding result of the light source to 0110 random bit.
The when m- phase code Principle of Process of Bob modulated light source is identical as Alice, and no longer citing is repeated herein.Alice In Bob, the short pulse sequence of m- phase code is exported from modulated light source when passing through, and reaches intensity along optical fiber onwards transmission The short pulse of arrival is decayed to single photon level by attenuator ATT, intensity attenuators ATT, the short pulse sequence difference after decaying Continue to transmit in quantum channel 2/9 and reaches Charlie.
In the present embodiment, the when m- phase code process of above-mentioned light pulse, which is not bound with, inveigles state thought, in order to make system Listener-in can be resisted simultaneously to attack the loophole of imperfect light source, and often MDI-QKD and trick state thought are used in combination.This When, modulated light source needs to export the light pulse of varying strength: signal state inveigles state and vacuum state, and varying strength light arteries and veins is arranged The duty ratio of time of punching.We are to be arranged identical signal state to two kinds of short pulses under Z basic vector coding and X basic vector coding and lure State is deceived, for furthermore preparing vacuum state pulse and encoding without using any basic vector, to illustrate system time-phase code and inveigle The superposition modulated process of state scheme.If signal state inveigles the burst length ratio of state and vacuum state to be pμ:pv:p0(pμ+pv+p0= 1), the average pulse number of photons of three kinds of states is respectively μ, v, 0 after intensity attenuators ATT decaying.
As previously mentioned, modulation pulse generates the triggering electric signal of laser, pulse is made to generate laser output varying strength Short pulse, to realize modulation of the modulated light source to light intensity.Be arranged Z basic vector encode lower signal state short pulse to, inveigle the short arteries and veins of state The pulse of punching pair generates the corresponding two kinds of value U of laser triggering electric signalμZ、UvZ, make in triggering electric signal UμZTriggering under, arteries and veins The signal state short pulse that punching generates laser transmitting can decay to μ level to through intensity attenuators ATT, in triggering electric signal UvZ's Under triggering, the trick state short pulse that pulse generates laser transmitting can decay to v level to through intensity attenuators ATT；It sets simultaneously X basic vector is set to encode lower signal state, the pulse of state is inveigled to generate the corresponding two kinds of value U of laser triggering electric signalμX、UvX, make touching Electrical signal UμXTriggering under, pulse generate laser transmitting signal state short pulse can equally decline to through intensity attenuators ATT μ level is reduced to, in triggering electric signal UvXTriggering under, pulse generate laser transmitting trick state short pulse to through strength retrogression Device ATT can equally decay to v level；When vacuum state, phase prepares the triggering electric signal that laser has 0 disturbance, and pulse produces Raw laser does not work, and short pulse is 0 to intensity.
Fig. 5 is the cataloged procedure of modulated light source when the modulation of state scheme is inveigled in addition on the basis of fig. 4.In Fig. 5 we New bit value 1 is added, to describe the modulated process of vacuum state.The part (a) of Fig. 5-(c) is respectively that phase prepares laser Triggering electric signal, m- phase code and inveigle state scheme when pulse generates the triggering electric signal of laser, modulated light source carries out The short pulse sequence result of superposition modulated.
As shown in the top sheet of Fig. 5, bit 01101 is successively selected Z, X, Z, X, (not selecting basic vector) basic vector coding and Signal state, signal state inveigle state, inveigle state, the intensity modulated of vacuum state.As shown in part (a) of Fig. 5 when m- phase volume Code and inveigle state scheme superposition modulated in, phase prepare laser modulation by inveigle state scheme do not influenced, with it is aforementioned not Add triggering electric signal identical when inveigling state scheme, and disturbing in vacuum state modulation offer 0.As Fig. 5 (b) part shown in when In the superposition modulated of m- phase code and trick state scheme, when carrying out the modulation of signal state, pulse generates laser in Z basic vector U is respectively provided on the timing position (such as b' point and c', d' two o'clock) of coding and X basic vector encoded luminescentμZAnd UμXTriggering telecommunications Number, triggering electric signal on non-luminous timing position (such as a' point) is still 0；When carrying out inveigling the modulation of state, pulse is produced Raw laser is respectively provided with U on luminous timing position (such as e' point and g', h' two o'clock)vZAnd UvXTriggering electric signal, In It is still 0 that electric signal is triggered on non-luminous timing position (such as f' point)；When carrying out the modulation of vacuum state, pulse generates laser Device two timing positions (such as i', j' point) on triggering electric signal be all 0.(c) of Fig. 5 is partially obtain plus trick state The output optical pulse sequence of modulated light source afterwards.By the attenuation of intensity attenuators ATT, under Z basic vector coding is encoded with X basic vector Signal state inveigles the short pulse of state and vacuum state to being attenuated respectively as μ, v and 0 horizontal.Short pulse sequence after decaying exists Continue to transmit in quantum channel 2/9 and reaches Charlie.
Trick state scheme of the invention is not limited to this, this embodiment is only the tune for illustrating to inveigle pulse strength in state scheme Mode processed, other implementable types are higher at code rate in the way of this, the higher trick state scheme of safety.
In Charlie, Alice and Bob two-way light pulse initially enters polarization control unit PC, and PC adjusts two-way light arteries and veins The polarization state of punching keeps the two polarization state unified, and guarantees that stable light pulse polarizes by internal feedback system (Fig. 3 is not drawn into) State is adjusted.Alice and Bob two-way light pulse by unified polarization state interferes on polarization-maintaining fiber coupler 3, interference knot Fruit inputs single-photon detector 4/5 and carries out probe response.The time location responded to single-photon detector 4/5 is analyzed, with Judge whether to produce legal Bell's state.A week is divided between the two front and back shorter pulse times generated when encoding with modulated light source Time value, and correspondence of meeting twice before and after taking two pairs of short pulses of Alice and Bob sending to occur on polarization-maintaining fiber coupler 3 Single-photon detector 4/5 detect timing position be respectively t0、t1, then as shown in the rear selection of Fig. 6 Bell's state measuring device, such as Fruit single-photon detector 4/5 has response within the same period, and a detector is in time location t0It is upper to respond, Another detector is in time location t1It is upper to respond, then it is assumed that be at this time legal Bell's state.Then, Legal Bell's state information is sent to Alice and Bob by disclosed classic network by Charlie, Alice and Bob according to The Data Post process of MDIQKD protocol contents carries out the operations such as basic vector comparison, error correction and privacy amplification to these Bell's states, Generate final security key.
Embodiment two:
System can be same by the light pulse that synchronization module (being not drawn into Fig. 3) controls Alice and Bob sending in embodiment one When reach Charlie Bell's state measuring device.This gives the examples of this synchronization module, as shown in Figure 7.Because Alice with Bob two paths of signals light synchronize be largely determined by two long ranges separation quantum channel 2 and 7 differentia influence, utilize Quantum channel 2 and quantum signal 7 are main path configuration circular path, make both synchronizable optical and signal light of user terminal Alice The sum of path is Chong Die with this circular path, keeps the sum of both synchronizable optical and signal lights of user terminal Bob path equally annular with this The optical path of path overlap, i.e. Alice and Bob all circular paths thus both can then get rid of path difference caused by synchronization It influences.
Fig. 7 is the Time Synchronizing exemplary diagram of embodiment one.Synchronous radiant LD3 is accessed using optical fiber circulator 14 The synchronizable optical that public-measurement end Charlie, light source LD3 are issued is transmitted to polarization-maintaining fiber coupler 3 through optical fiber circulator 14.In order to Anti- process synchronizable optical here leaks into single-photon detector 5 through optical fiber circulator 14, leaks into monochromatic light through polarization-maintaining fiber coupler 3 Sub- detector 4, between optical fiber circulator 14 and single-photon detector 5, polarization-maintaining fiber coupler 3 and single-photon detector 4 it Between respectively addition can filter out the bandpass filter BPF of synchronizable optical.
The circular path of Alice: the synchronizable optical of synchronous radiant LD3 transmitting is divided after reaching polarization-maintaining fiber coupler 3 For two-way, all the way through polarization control unit PC2 (not working at this time), the laggard access customer end Bob of quantum channel 7.This synchronizable optical according to The secondary port B1 through user terminal Bob path selection module B, the port B2 and user terminal Alice path selection module A the port A2, The public port of the port A3 arrival Alice wavelength division multiplexer 10.An output end through wavelength division multiplexer 10 enters photodetection Device 8, photodetector 8 synchronize photoresponse to this and start the time synchronization module work of Alice, and time synchronization module generates system System clock, the phase for triggering Alice prepares laser LD1 and pulse generates the work of laser LD2, and phase prepares laser The course of work that LD1 and pulse generate laser LD2 is the same as example 1, and is no longer repeated herein.Alice modulated light source generates Light pulse, that is, signal light enter the another output of wavelength division multiplexer 10 after the decaying of intensity attenuators ATT, and by wave The public port of division multiplexer 10 is exported to path selection module A.Enter behind the port A3 of path selection module A and the port A1 Quantum channel 2, and enter Charlie.It is adjusted polarization state at polarization control unit PC1, is then transmit to polarization maintaining optical fibre coupling Clutch 3.
The circular path of Bob optical signal: the another way that the synchronizable optical of LD3 transmitting is separated by polarization-maintaining fiber coupler 3, through inclined Vibration control unit PC1 (not working at this time), the laggard access customer end Alice of quantum channel 2.This synchronizable optical is successively through user terminal The port A1 of Alice path selection module A, the port B2 of the port A2 and user terminal Bob path selection module B, the port B3 reach The public port of Bob wavelength division multiplexer 11.An output end through wavelength division multiplexer 11 enters photodetector 9, photodetection Device 9 synchronizes photoresponse to this and starts the time synchronization module work of Bob, and time synchronization module generation system clock triggers Bob Phase prepare the work that laser LD1 and pulse generate laser LD2, phase prepares laser LD1 and pulse generates laser The course of work of device LD2 is the same as example 1, and is no longer repeated herein.The light pulse that Bob modulated light source generates, that is, signal light warp Enter the another output of wavelength division multiplexer 11 after the decaying of intensity attenuators ATT, and by the common end of wavelength division multiplexer 11 Mouth is exported to path selection module B.The port B3 and the port B1 through path selection module B enter quantum channel 7, and enter Charlie.It is adjusted polarization state at polarization control unit PC2, is then transmit to polarization-maintaining fiber coupler 3.
The synchronizable optical and signal light of Alice and Bob is passed by identical circular path, and the light pulse of the two is in polarization maintaining optical fibre coupling Clutch 3 is met to carry out the measurement of Bell state.Compared with the difference between two long range quantum channels 2 and 7, it can be ignored and synchronize herein Light and signal light the walking path difference inside Alice and Bob cause the time difference to influence.
Fig. 8 is the preferred embodiment of path selection module described in the present embodiment, i.e., constructs this mould using three optical fiber circulators Block.In this preferred embodiment, in three optical fiber circulators 121,122,123 and path selection module B in path selection module A Three optical fiber circulators 131,132,133 all have there are three port P1, P2 and P3, for this six optical fiber circulators, light exists Direction of travel therein is all are as follows: two kinds of P1 → P2, P2 → P3.
The connection type of optical fiber circulator are as follows: in path selection module A, the port P1 of optical fiber circulator 121, fiber optic loop The port P3 of shape device 123 is connect with the port P3 of optical fiber circulator 122, the port P1 respectively, the port P3 of optical fiber circulator 121 with The port P1 of optical fiber circulator 123 is connected, the port P2 of optical fiber circulator 121, optical fiber circulator 123 the port P2 respectively as The port A3, the port A1 of path selection module A, A2 port of the port P2 of optical fiber circulator 122 as path selection module A； In path selection module B, the port P1 of optical fiber circulator 131, optical fiber circulator 133 the port P3 respectively with optical fiber circulator 132 port P3, the connection of the port P1, the port P3 of optical fiber circulator 131 are connected with the port P1 of optical fiber circulator 133, optical fiber The port P2 of circulator 131, optical fiber circulator 133 B3 port, B1 port of the port P2 respectively as path selection module B, B2 port of the port P2 of optical fiber circulator 132 as path selection module B；The port P2 of optical fiber circulator 132 and fiber optic loop The port P2 of shape device 122 is connected.According to P1 → P2 of optical fiber circulator 121-123 and optical fiber circulator 131-133, P2 → P3 Direction of travel, it can realize the circular path of this implementation Alice and the circular path of Bob.
In order to reduce the optical devices insertion loss such as wavelength division multiplexer 10/11, path selection module A/B inner fiber circulator It, can be by the intensity attenuators of Alice and Bob two-way Deng the influence of the single photon level light pulses exported to intensity attenuators ATT ATT is individually positioned on the connecting line between the port P3 of optical fiber circulator 121 and the port P1 of optical fiber circulator 123, fiber optic loop On connecting line between the port P3 of shape device 131 and the port P1 of optical fiber circulator 133, make the monochromatic light of intensity attenuators ATT output Sub- level light pulses pass through less optical device.
Embodiment three:
Fig. 9 is the networking MDI-QKD system light path figure injected based on light.The present embodiment is point-to-point in embodiment one The networking extension carried out in system-based, each user terminal equipment having the same forms and connection type.User terminal and public The structure of measurement end Charlie, coding, inveigles state modulation, detection method etc. and the basic phase of embodiment one at the generation of light pulse Together, the selection of legal Bell state is the same as example 1.The difference is that being added before Charlie polarization control unit PC Photoswitch 15 and filter BPF (16/17), the switching of photoswitch 15 make two users end needed by access measurement end Charlie, Two-way filter BFP (16/17) is used to filter out the stray light in two accessing user's light pulses in Charlie.
Example IV:
Figure 10 is the synchronization scheme for the networking MDI-QKD system that embodiment three is injected based on light, synchronizes thought and reality The synchronization thought applied in example two is identical, using the quantum channel between two communication users and public-measurement end Charlie as predominating path Circular path is constructed, keeps the sum of the synchronizable optical of two communication users and the walked optical path of signal light Chong Die with this circular path, makes two to lead to The optical path of credit household all circular paths thus, get rid of two communication user path difference influences caused by synchronization with this.
The composition of user terminal is as follows in the synchronization scheme of this networked system: for the convenience of description, we are by embodiment three The modulated light source (LD1, circulator 1 and LD2) of middle user terminal Alice, intensity attenuators ATT, wavelength division multiplexer 10, photodetection Device 8 and the time synchronization module being attached thereto are set as sending module, and each user terminal composition of the present embodiment removes this sending module The path selection module being also attached thereto outside.
Because of path selection module A and path selection module B in embodiment two actually symmetrical structure, this implementation Path selection module in example can be optionally first, and select corresponding connection type, i.e. the No.1 port of path selection module (such as A1/B1 in embodiment two) the corresponding quantum channel of connection user terminal, No. three port (such as embodiments two of path selection module In A3/B3) connection user terminal sending module in wavelength division multiplexer public port.In the entire user side of the present embodiment, One gating module is set to access No. two ports of all user terminal path selection modules (A2/B2 in such as embodiment two), Function is to make the circular path between two user terminals can according to No. two ports for needing to be connected to two user terminal path selection modules Loop effect occurs to be connected to, while cutting off the connection of other users end path selection module Two-port netwerk, it is described as needed Two user terminals of connection are two users end that photoswitch 15 cuts public-measurement end Charlie in example IV.
Figure 11 is the preferred embodiment of above-mentioned gating module, as a n*2 photoswitch.1~n input terminal of n*2 photoswitch Mouth is sequentially connected No. two ports (port A2/B2 in such as embodiment two) of 1~n user terminal path selection module, n*2 photoswitch Output port P1, P2 be connected with each other.When having an effect, n*2 photoswitch is controlled by system makes its certain two input port difference It is connected to two output port P1, P2, because P1, P2 are connected with each other, two input ports opened with n*2 photoswitch connect respectively Circular path is connected between two users end connect, can realize the synchronization scheme such as two communication user ends in embodiment two, institute Stating certain two input port being connected to respectively with two output port P1, P2 is the incision of photoswitch 15 public-measurement in example IV Hold the corresponding ports at two users end of Charlie.
Although the embodiments of the present invention has been shown and described above, it is to be understood that above-described embodiment is example Property, it is not considered as limiting the invention, those skilled in the art are not departing from the principle of the present invention and objective In the case where can make changes, modifications, alterations, and variations to the above described embodiments within the scope of the invention.It is all of the invention Within spirit and principle, any modification, equivalent replacement, improvement and so on be should all be included in the protection scope of the present invention.

Claims (16)

1. a kind of MDI-QKD system based on light injection, it includes user terminal and public-measurement end, and the user terminal includes The end Alice and the end Bob, the public-measurement end are the end Charlie, which is characterized in that the end Alice and the end Bob include Modulated light source, the modulated light source include:
Phase prepares laser, and the phase prepares laser by generating light pulse after phase premodulated；
Optical fiber circulator, the optical fiber circulator first port connect the phase and prepare laser, close on first port Second port connects pulse and generates laser；
Pulse generates laser, the second port that the light pulse of the phase preparation laser modulation passes through the optical fiber circulator It injects the pulse and generates laser, the light pulse that the phase that the pulse generation laser is injected prepares laser generation swashs Hair, makes the modulated light pulse of modulated light source output phase；The pulse generates the phase that laser is injected and prepares laser The light pulse excitation of generation and its self-strength modulation, make the modulated light pulse of modulated light source output intensity；Modulated light source is defeated Light pulse out is exported by the third port of the optical fiber circulator closed on second port and is transmitted via quantum channel To the end Charlie, the end Charlie is as Bell's state measuring device；The transmission direction of the optical fiber circulator is the Single port is to second port, second port to third port；
An intensity attenuators are arranged in the user terminal between optical fiber circulator third port and quantum channel, and light pulse is decayed To single photon level；The user terminal makes two-way light pulse by synchronization module while reaching the end Charlie；The synchronization module Including the path selection module after intensity attenuators is arranged in and prepares laser with phase and pulse generates the same phase of laser Time synchronization module even, is arranged a wavelength-division recombiner between the path selection module and intensity attenuators, the wavelength-division is multiple Clutch is connected by a photodetector with the time synchronization module, path selection module and the end Bob at the end Alice Path selection module is connected；
The second optical fiber is separately arranged on polarization-maintaining fiber coupler all the way to a single-photon detector transmission line in the end Charlie Circulator, the second optical fiber circulator are successively connected with polarization-maintaining fiber coupler, single-photon detector and synchronous radiant respectively, institute Stating the outbound course of the second optical fiber circulator is synchronous radiant to polarization-maintaining fiber coupler direction, polarization-maintaining fiber coupler to list Photon detector direction；The light pulse that the synchronous radiant generates is by the second optical fiber circulator through polarization-maintaining fiber coupler point Supplementary biography transports to the path selection module at the end Alice and the end Bob, and light pulse steering is transmitted to other side by the path selection module Respective time synchronization module is arrived after path selection module again and realizes synchronization.
2. a kind of MDI-QKD system based on light injection according to claim 1, which is characterized in that the end Charlie Include:
Polarization control unit group, for receive respectively by the quantum channel at the end Alice and the end Bob transmission light pulse and uniformly and Stablize the polarization state of two-way light pulse；
Polarization-maintaining fiber coupler, for receiving the light pulse by polarization control unit output and forming interference；And
Two single-photon detectors carry out not for being formed by result of interference to the light pulse in the polarization-maintaining fiber coupler Same response.
3. a kind of MDI-QKD system based on light injection according to claim 1, which is characterized in that the pulse generates The intensity modulated of laser includes time encoding modulation or/and state is inveigled to modulate.
4. a kind of MDI-QKD system based on light injection according to claim 3, which is characterized in that the Path selection Module is directly exported to common end Charlie when exporting the light pulse that modulated light source issues, in the light for transmitting synchronous radiant The light pulse of arrival is transmitted to another path selection module when pulse, the light pulse that another path selection module will receive again It is transmitted to photodetector by wavelength division multiplexer, photodetector transmits a signal to time synchronization module, time synchronization again Module prepares laser according to signal phase-triggered and pulse generates laser works, completes synchronous setting.
5. a kind of cryptographic key distribution method of the MDI-QKD system based on light injection, the system comprises user terminal and public-measurements End, the user terminal include the end Alice and the end Bob, and the public-measurement end is the end Charlie, which is characterized in that it include with Lower step:
The phase at the end S101 Alice and the end Bob prepares laser by generating light pulse after phase premodulated, and passes through optical fiber Circulator injected pulse generates laser；
Pulse described in S102 generates the light pulse excitation that the phase that laser is injected prepares laser generation, keeps modulated light source defeated Light pulse after phase-modulation out；The pulse generates the light pulse excitation that the phase that laser is injected prepares laser generation And its self-strength modulation, make the modulated light pulse of modulated light source output intensity；So far, the light pulse warp that modulated light source generates Optical fiber circulator output, and single photon level is decayed to by intensity attenuators, the light pulse at the end Alice and the end Bob passes through same Walk polarization control unit group of the module through quantum channel simultaneous transmission to the end Charlie；
Polarization control unit group described in S103 respectively by the polarization state of the light pulse from the end Alice and the end Bob carry out it is unified and Stablize, and uniform transmission forms high contrast interference into polarization-maintaining fiber coupler, different result of interference will cause two lists The different responses of photon detector, to judge whether to produce legal Bell's state；
Legal Bell's state information is sent to Alice and Bob by disclosed classic network by S104 Charlie, Alice and Bob generates final security key according to the processing of MDI-QKD protocol contents；
In the step S101, phase prepares laser and carries out phase premodulated process:
Tidal stress electric signal introduces electric signal disturbance within one duration of the middle position of electric signal, phase is caused to prepare It is Δ φ that unmodulated part, which forms phase difference, before and after the light pulse of laser transmitting, completes phase premodulated, and phase system The light pulse of standby laser transmitting, the part of in-between phase premodulated respective pulses when light injects generate the triggering of laser Electric signal interval, the only unmodulated part in its front and back generate laser to pulse and light injection effect occur；
The phase prepares laser during phase premodulated:
When Systematic selection phase code basic vector encoding ratio paricular value, phase code basic vector is X=[0, π], and phase basic vector X includes Two kinds of phase states | 0 > with | π >, | 0 > phase states are used for encoding ratio paricular value 0, | π > phase states are used for encoding ratio paricular value 1, Δ φ=0 It is corresponding | 0 > phase states, Δ φ=π are corresponding | and π > phase states, the triggering electric signal for making phase prepare laser have Δ U1=0 or ΔU2=UπElectric signal disturbance, be respectively formed the light pulse with Δ φ=0 or Δ φ=π phase premodulated information；
When Systematic selection time encoding basic vector encoding ratio paricular value, the triggering electric signal that phase prepares laser has Δ U1=0 Electric signal disturbance, formed have Δ φ=0 light pulse.
6. a kind of cryptographic key distribution method of MDI-QKD system based on light injection as claimed in claim 5, which is characterized in that The pulse generates the intensity modulated of laser and includes time encoding modulation or/and state is inveigled to modulate.
7. a kind of cryptographic key distribution method of MDI-QKD system based on light injection as claimed in claim 6, which is characterized in that When Systematic selection phase code basic vector encoding ratio paricular value, pulse generates laser and normally provides the triggering electricity of two pulses of front and back Signal；
When Systematic selection time encoding basic vector encoding ratio paricular value, pulse generates laser and carries out time encoding modulation, time Basic vector Z is encoded, basic vector Z contains the intensity distribution state 0 or 1 that two kinds of pulses generate laser transmitting light pulse pair, modulates pulse The triggering electric signal for generating laser, when the coding to bit value 0, closing timing is distributed the triggering telecommunications of the light pulse of front Number, make its light intensity 0, the trigger voltage signal of subsequent light pulse is normally provided, makes its light intensity normal value；When to bit value When 1 coding, closing timing is distributed the triggering electric signal of subsequent light pulse, makes its light intensity 0, normal to provide the light arteries and veins of front The trigger voltage signal of punching makes its light intensity normal value；
When system carries out inveigling state modulation, the phase code basic vector coding and time encoding of laser effect are generated for pulse The light pulse of basic vector coding, on all luminous timing positions, modulation pulse generates the triggering electric signal of laser, makes pulse The light pulse for generating laser transmitting has different intensity values, to form and inveigle the light arteries and veins of each state respective strengths in state scheme Punching.
8. a kind of cryptographic key distribution method of MDI-QKD system based on light injection as claimed in claim 5, which is characterized in that The synchronization module includes that the path selection module and and phase that the end Alice and the end Bob are arranged after intensity attenuators is arranged in Prepare the time synchronization module that laser generates laser with pulse while being connected, the path selection module and intensity attenuators Between a wavelength-division recombiner is set, the wavelength-division recombiner is connected by a photodetector with the time synchronization module, institute The end Alice path selection module is stated to be connected with the path selection module at the end Bob；
The second fiber annular is separately arranged in the end Charlie on polarization-maintaining fiber coupler all the way to single-photon detector transmission line Device, the second optical fiber circulator are connected with polarization-maintaining fiber coupler, single-photon detector, and connect a synchronous radiant, and described the Two optical fiber circulator transmission directions from synchronous radiant to polarization-maintaining fiber coupler, from polarization-maintaining fiber coupler to single photon detection Device；The path selection module is directly exported to common end Charlie when exporting the light pulse that modulated light source issues, and is being transmitted The light pulse of arrival is transmitted to another path selection module when the pulse of synchronous radiant, another path selection module again should Pulse signal is transmitted to photodetector by wavelength division multiplexer, and photodetector transmits a signal to time synchronization module again, Time synchronization module prepares laser according to signal phase-triggered and pulse generates laser works.
9. a kind of networking MDI-QKD system based on light injection, which is characterized in that the system comprises 2 and 2 or more to use Family end and a public-measurement end, each user terminal include modulated light source, and the modulated light source includes:
Phase prepares laser, and the phase prepares laser by generating light pulse after phase premodulated；
Optical fiber circulator, the optical fiber circulator first port connect the phase and prepare laser, close on first port Second port connects pulse and generates laser, and the light pulse of the phase preparation laser modulation passes through the optical fiber circulator Second port injection
Pulse generates laser, and the pulse generates the light pulse excitation that the phase that laser is injected prepares laser generation, Make the modulated light pulse of modulated light source output phase；The pulse generates the phase that laser production is injected and prepares laser life Light pulse excitation and its self-strength modulation, make the modulated light pulse of modulated light source output intensity；The modulated light source is defeated The light pulse after phase-modulation and intensity modulated is extremely out
Public-measurement end, the public-measurement end is as Bell's state measuring device, transmission of the public-measurement end in user terminal It is disposed with photoswitch and filter on line, polarization control unit is set after filter, the photoswitch is needed for selecting It is switched to the user terminal at public-measurement end；
The user terminal is additionally provided with synchronization module comprising time synchronization module and path selection module, the time synchronization Module prepares laser with phase and pulse generates laser and is connected, and a wavelength-division recombiner, the wavelength-division recombiner one is arranged Road connects modulated light source, and another way is connect by photodetector with time synchronization module, compound rear connection path selecting module, The path selection module is connect with quantum channel again；
The second light is separately arranged on polarization-maintaining fiber coupler all the way to a single-photon detector transmission line in the public-measurement end Fine circulator, the second optical fiber circulator are successively connected with polarization-maintaining fiber coupler, single-photon detector and synchronous radiant respectively, The outbound course of second optical fiber circulator be synchronous radiant to polarization-maintaining fiber coupler direction, polarization-maintaining fiber coupler to Single-photon detector direction；The light pulse that the synchronous radiant generates is distinguished by optical fiber circulator through polarization-maintaining fiber coupler It is transmitted to the path selection module of user terminal, which is turned to the path for being transmitted to communication counterpart by the path selection module Respective time synchronization module is arrived after selecting module again and realizes synchronization.
10. a kind of networking MDI-QKD system based on light injection according to claim 9, which is characterized in that the public affairs Measurement end includes: altogether
Polarization control unit group, for receiving light pulse and unified and stable two-way by the quantum channel transmission of user terminal respectively The polarization state of light pulse；
Polarization-maintaining fiber coupler, for receiving the light pulse by polarization control unit output and forming interference；And
Two single-photon detectors carry out not for being formed by result of interference to the light pulse in the polarization-maintaining fiber coupler Same response.
11. a kind of networking MDI-QKD system based on light injection according to claim 10, which is characterized in that described The light pulse that pulse generates laser output decays to single photon level by intensity attenuators and is transmitted to public-measurement end again；Institute It states public-measurement end and is provided with photoswitch on the transmission line after quantum channel, polarization control unit is set after photoswitch.
12. a kind of networking MDI-QKD system based on light injection according to claim 9, which is characterized in that the public affairs Measurement end only allows two-way user terminal to access when in use altogether.
13. a kind of networking MDI-QKD system based on light injection according to claim 12, which is characterized in that user The path selection module at end is connected to a gating module simultaneously, and what the corresponding photoswitch of gating module connection was connected needs to connect To the path selection module of the two-way user terminal at public-measurement end.
14. being distributed according to a kind of key of any networking MDI-QKD system based on light injection of claim 9-13 Method, which is characterized in that the quantum key delivering method the following steps are included:
S101 phase prepares laser and generates by generating light pulse after phase premodulated, and by optical fiber circulator injected pulse Laser；
Pulse described in S102 generates the light pulse excitation that the phase that laser is injected prepares laser generation, keeps modulated light source defeated Light pulse after phase-modulation out；The pulse generates the light pulse excitation that the phase that laser is injected prepares laser generation And its self-strength modulation, make the modulated light pulse of modulated light source output intensity, so far, the light pulse warp that modulated light source generates Optical fiber circulator output, and single photon level is decayed to by intensity attenuators, the light pulse of user terminal is passed through by synchronization module Quantum channel simultaneous transmission to public-measurement end polarization control unit；
The polarization state of light pulse from user terminal is carried out unified and stablized by polarization control unit group described in S103 respectively, and is united One, which is transmitted to the interference of formation high contrast, different result of interference in polarization-maintaining fiber coupler, will cause two single-photon detectors Different responses, to judge whether to produce legal Bell's state；
Legal Bell's state information is sent to user terminal by disclosed classic network by S104 public-measurement end, user terminal according to The processing of MDI-QKD protocol contents generates final security key.
15. a kind of cryptographic key distribution method of networking MDI-QKD system based on light injection according to claim 14, It is characterized in that, photoswitch is provided on the transmission line at the user terminal and public-measurement end, to control whether user terminal accesses Public-measurement end, the public-measurement end only allow two-way user terminal to access when in use.
16. a kind of cryptographic key distribution method of networking MDI-QKD system based on light injection according to claim 14, It is characterized in that, the light pulse that the synchronous radiant generates is transmitted by the second optical fiber circulator through polarization-maintaining fiber coupler respectively The Path selection for the two-way user terminal for needing to be connected to public-measurement end connected to the correspondence photoswitch connected by gating module Light pulse steering is transmitted to after the path selection module of other side that arrive the respective time again same by module, the path selection module It walks module and realizes synchronization.
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