CN106850073A - User terminal, MDI QKD systems and method and network system in quantum key distribution system - Google Patents

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

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CN106850073A
CN106850073A CN201710032153.8A CN201710032153A CN106850073A CN 106850073 A CN106850073 A CN 106850073A CN 201710032153 A CN201710032153 A CN 201710032153A CN 106850073 A CN106850073 A CN 106850073A
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phase
laser
light pulse
light
pulse
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CN106850073B (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 invention provides the user terminal in a kind of quantum key distribution system, it includes modulated light source, and the modulated light source prepares laser, optical fiber circulator and pulses generation laser including phase.Present invention also offers MDI QKD systems, it includes user terminal and public-measurement end, and the user terminal includes Alice ends and Bob ends, and the public-measurement end is Charlie ends, and the Alice ends and Bob ends include modulated light source.Invention further provides the cryptographic key distribution method and networking MDI QKD systems of the above-mentioned MDI QKD systems based on light injection.User terminal of the invention simplifies the structure of conventional phase modulation laser and pulses generation laser, without setting phase feedback system.MDI QKD systems of the invention realize light source and phase-modulator, the integrated morphology of intensity modulator, relieve the limitation of phase-modulator, intensity modulator to system high-speed application；Modulated light source can directly generate the light pulse with pure phase information, be capable of achieving light pulse phase reference uniformity control between multi-user.

Description

User terminal, MDI-QKD system and methods and network in quantum key distribution system System
Technical field
The present invention relates to the communications field, it is related to include the user terminal of quantum key distribution system, more particularly to MDI-QKD systems System, and the cryptographic key distribution method in Optical Fiber Transmission Quantum Secure Communication field and quantum secret communication.
Background technology
Lo in 2012 et al. proposes the unrelated quantum-key distribution (measurement-device- of measuring apparatus Independent QKD, MDI-QKD) agreement, light pulses are to untrusted the 3rd 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, and substantially increases the reality of QKD system Security.
MDI-QKD systems based on phase code, because the phase-modulation of light pulse transmits strong antijamming capability in a fiber, Result of detection that system can be stablized and higher into code check, so being especially suitable for the secure communication of long range both sides. Main being achieved in that of light pulse phase code carry out external modulation, common base using phase-modulator in MDI-QKD systems In the phase-modulator of LiNbO3 crystal.In the moment that light pulse is reached, phase-modulator adds a pulse voltage, by electricity The refractive index of field change 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 speeds, it is desirable to which phase-modulator pulse voltage equally has nanosecond Narrow pulse bandwidth, and phase-modulator needs half-wave voltage higher in itself, therefore in the phase-modulation using LiNbO3 crystal During device, the circuit that system needs design complicated is driven control.The key such as analog switch, delay chip device in circuit driven The performance limitation of part, phase-modulator is extremely difficult to i.e. high speed and the ideal Modulated effect of high-voltage value, the arteries and veins that can actually reach The voltage band high-speed applications for limiting system wide are rushed, and its waviness phenomena of pulse voltage of generation can not to finally having into code check The influence of ignorance.Complicated drive circuit also results in the heaviness of user's end structure, increased the design cost of system.
No matter theory discuss or in practical operation, the MDI-QKD agreements based on phase code generally with trick 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 to use intensity to adjust Device processed is modulated by force to light pulse, the common Mach-Zehnder electrooptic modulators based on LiNbO3 crystal.Intensity modulator Modulation and the needs half-wave voltage higher of pulse voltage, its complicated drive circuit and phase-modulator can only equally be received Drive circuit has the shortcomings that similar.And Mach-Zehnder electrooptic modulators have periodic transfer function, to avoid letter Number distortion, it is necessary to make modulator be operated in just bias point, i.e., control strong when being taken in the application of quantum key distribution system Spend the bias point of modulator.But due to being optical fiber insertion and coupling loss by time drift, environment temperature, system laser power It is actual to be difficult control bias point stabilization Deng factors influence, cause intensity modulator output signal to deteriorate.Bias point control Further increase the structural burden of user terminal.
In the MDI-QKD systems based on phase code, in addition to said modulator brings problem, system also faces list The problem of the front and rear two light pulses phase basic vector calibration that individual user terminal sends.In systems, phase code process generally uses one Individual 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 Extra transmission phase difference, and interferometer arm length difference are caused between former and later two subpulses for going out easily by environment temperature, stress etc. The influence of factor and change, cause to transmit the drift of phase difference between two subpulses.The presence for transmitting phase difference destroys two The uniformity of subpulse phase reference, has influence on the interference contrast and result of detection at public-measurement end.For controlling transmission phase The drift of potential difference is simultaneously stablized in 0 value, it is necessary to human intervention environmental factor carries out stably, interferometer such as being sealed in into narrow and small sky Between, interferometer is isolated using internal high heat conduction, insulating back-up material；Or need by adding active feedback in systems Module is controlled, and phase shifter and its attached reponse system are inserted such as in an arm of interferometer, by it is slow become it is anti- Feedback signal changes phase shifter voltage, poor with the 0 value transmission of phase for ensureing stabilization.Equally, the front and rear arteries and veins for being sent to unique user end Rushing the control of phase reference uniformity makes that MDI-QKD system architectures are more complicated, and design cost is higher.
To sum up, there is following defect in the prior art：
1. existing MDI-QKD systems light pulse phase code needs the phase-modulator, intensity modulation to need intensity modulated Device, the use of two kinds of modulation devices not only limit the high-speed applications of system, and both complicated drive circuits make user terminal Structure bulky, cost increase, and are unfavorable for the networking extension of MDI-QKD.
2. the phase reference uniformity of the front and rear light pulse that existing MDI-QKD systems unique user end sends needs phase Position reponse system ensures, engineering is designed in networked system huge.
Above-mentioned two big defect constrains the application of the MDI-QKD system networkings based on phase code, more particularly to simultaneously Between guarantee multi-user during the problem of light pulse phase reference uniformity, the phase feedback system of whole network will be one great Engineering design.
The content of the invention
The invention provides the user terminal in a kind of quantum key distribution system, the user terminal simplifies conventional phase modulation The structure of laser and pulses generation laser, without setting phase feedback system, has saved cost.
Therefore, the present invention uses following technical scheme：
The user terminal includes modulated light source, and the modulated light source includes：
Phase prepares laser, optical fiber circulator and pulses generation laser.
The phase prepares laser by producing light pulse after phase premodulated；
The fiber optical circulator first port connects the phase and prepares laser, the second port closed on first port Connection pulses generation laser, the phase prepares the second port that the light pulse of laser modulation passes through the optical fiber circulator The pulses generation laser is injected,
Particularly, the light pulse that the phase that the pulses generation laser is injected prepares laser generation is excited and its oneself Body intensity modulated produces light pulse, the light pulse after the modulated light source output phase modulation and intensity modulated.So far, in modulation Light source internal completes the phase code and intensity modulated of light pulse.
Preferably, the intensity modulated includes that time encoding is modulated or/and inveigles state modulation.
The trick state signal includes the pulse of signal state, inveigles state pulse and vacuum state pulse, and sets varying strength The dutycycle of light pulse.
Invention further provides a kind of MDI-QKD systems based on light injection, the system realizes light source and phase-modulation The integrated morphology of device, intensity modulator, simplifies system architecture, 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, without phase feedback system, can be real Light pulse phase reference uniformity control between existing multi-user.
Therefore, the present invention uses following technical scheme：
The MDI-QKD systems include user terminal and public-measurement end, and the user terminal includes Alice ends and Bob ends, institute Public-measurement end is stated for Charlie ends, the Alice ends and Bob ends include modulated light source, and the modulated light source includes：
Phase prepares laser, and the phase prepares laser by producing light pulse after phase premodulated；
Optical fiber circulator, the fiber optical circulator first port connects the phase and prepares laser, faces with first port Near second port connection
Pulses generation laser, the light pulse that the phase prepares laser modulation passes through the second of the optical fiber circulator The pulses generation laser is injected in port, and the phase that the pulses generation laser is injected prepares the light arteries and veins of laser generation Impulse is sent out, the light pulse after modulating modulated light source output phase；The phase that the pulses generation laser is injected is prepared and swashed The light pulse that light device is produced is excited and its self-strength is modulated, the light pulse after modulating modulated light source output intensity；The tune The light pulse of light source output processed is exported and via quantum by the 3rd port closed on second port of the fiber optical circulator , to the Charlie ends, the Charlie ends are used as Bel's state measuring apparatus for transmission；The transmission of the optical fiber circulator Direction is first port to second port, second port to the 3rd port.
Preferably, used as Bel's state measuring apparatus, it includes at the Charlie ends：
Polarization control unit group, for receive respectively by Alice ends and Bob ends quantum channel transmit light pulse and unite One and stablize the polarization state of two-way light pulse；
Polarization-maintaining fiber coupler, for receive by polarization control unit export light pulse and form interference；And two lists Photon detector, the result of interference for being formed to the light pulse in the polarization-maintaining fiber coupler carries out different responses.
Preferably, the intensity modulated of the pulses generation laser includes that time encoding is modulated or/and inveigles state modulation
Preferably, the phase prepares laser and pulses generation laser forms transmission channel by optical fiber circulator.
Preferably, the optical fiber circulator is provided with three ports, and the phase prepares laser connection first port, described Pulses generation laser connects second port, and the 3rd port connects quantum channel.
Preferably, the Alice ends and the Bob ends set strength retrogression in the output end of pulses generation laser Device, for the light pulse after coding to be decayed into single photon level.The user terminal makes two-way light pulse same by synchronization module When reach Charlie ends.
Preferably, the phase prepares laser and the light pulse of pulses generation laser generation and includes signal state, inveigles State and vacuum state, and the dutycycle of varying strength light pulse is set.
Preferably, the Alice ends and Bob ends are provided with randomizer, respectively produce one group of random number sequence conduct Both random bit value, and respectively generate another group of random sequence for select encode basic vector, wherein 0 represents phase code base Arrow, 1 represents time encoding basic vector.
Preferably, the Alice ends and Bob ends make two-way light pulse reach Charlie ends simultaneously by synchronization module.Institute State synchronization module include being arranged on path selection module that Alice ends and Bob ends set after intensity attenuators and with phase system The time synchronized module that standby laser is connected simultaneously with pulses generation laser, 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 synchronized module, described The path selection module at Alice ends is connected with the path selection module at Bob ends；
The Charlie ends are another on polarization-maintaining fiber coupler all the way to a single-photon detector transmission line to set second Optical fiber circulator, the second optical fiber circulator connects with polarization-maintaining fiber coupler, single-photon detector and synchronous radiant successively respectively Connect, 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 is produced is by the second optical fiber circulator through polarization maintaining optical fibre coupling Clutch is transmitted separately to the path selection module at Alice ends and Bob ends, and the light pulse is turned to and transmitted by the path selection module Respective time synchronized module is arrived after to other side's path selection module again to realize synchronously；
The path selection module is directly exported when the light pulse that modulated light source sends is exported to common port Charlie, The light pulse for reaching is transmitted to another path selection module in the light pulse of the synchronous radiant of transmission, another Path selection mould Block is again transmitted to photodetector the pulse signal by wavelength division multiplexer, and it is same that photodetector transmits a signal to the time again Step module, time synchronized module prepares laser and pulses generation laser works according to signal phase-triggered, completes synchronous setting Put.
The present invention also needs the technical problem for solving to be to provide the key distributor of the above-mentioned MDI-QKD systems based on light injection Method, it is comprised the following steps：
The phase at S101Alice ends and Bob ends prepares laser by producing light pulse after phase premodulated, and by light Fine circulator injected pulse produces laser；
The light pulse that the phase that pulses generation laser described in S102 is injected prepares laser generation is excited, and makes modulation light Light pulse after the output phase modulation of source；The phase that the pulses generation laser is injected prepares the light pulse of laser generation Excite and its self-strength is modulated, the light pulse after modulating modulated light source output intensity, so far, the light that modulated light source is produced Pulse is exported through optical fiber circulator, and decays to single photon level, the light pulse at Alice ends and Bob ends by intensity attenuators By synchronization module through quantum channel simultaneous transmission to Charlie ends polarization control unit group；
Polarization state of the polarization control unit group respectively by the light pulse from Alice ends and Bob ends is united described in S103 One and stabilization, and high-contrast interference is formed in uniform transmission to polarization-maintaining fiber coupler, different result of interference will cause two The different responses of individual single-photon detector, to judge whether to generate legal Bel's state；
S104 Charlie send to Alice and Bob legal Bel's state information by disclosed classic network, Alice and Bob produces final safe key according to the treatment of MDIQKD protocol contents.
Further, in the step S101, phase prepares laser and enters line phase premodulated process：
Phase prepares laser modulation triggering electric signal, introduces Δ U's within the duration of centre position one of electric signal Electric signal is disturbed, and it is Δ φ to cause not modulated part before and after light pulse to form phase difference, completes phase premodulated, and phase Position prepares the light pulse of laser transmitting, the part of its intermediate phase premodulated respective pulses generation laser when light inject There is light injection effect to pulses generation laser in triggering electric signal interval, part only not modulated before and after it.
Further, in the step S101 and step S102, the Alice ends and Bob ends are provided with random number generation Device, respectively produce one group of random number sequence as both random bit values, 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 is with phase code basic vector encoding ratio paricular value, phase code basic vector is X=[0, π], phase basic vector X Comprising 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 correspondence | 0>Phase states, Δ φ=π correspondences | π>Phase states, the triggering electric signal for making phase prepare laser has Δ U1=0 and Δ U2= UπElectric signal disturbance, the light pulse with Δ φ=0 or Δ φ=π phase premodulated information is formed respectively, injected pulse is produced Raw laser.
When Systematic selection is with 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 pulses generation laser is in intensity modulation process：
When Systematic selection is with phase code basic vector encoding ratio paricular value, pulses generation laser normally provides front and rear two pulses Triggering electric signal；
When Systematic selection is with time encoding basic vector encoding ratio paricular value, pulses generation laser 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 generation lasers launch light pulse pair, modulation The triggering electric signal of pulses generation laser, when the coding to bit value 0, the triggering of closing timing distribution light pulse above Electric signal, makes its light intensity be 0, and the normal trigger voltage signal for providing light pulse below makes its light intensity be normal value；Work as contrast During the coding of paricular value 1, the triggering electric signal of closing timing distribution light pulse below makes its light intensity be 0, normal to provide above The trigger voltage signal of light pulse, makes its light intensity be normal value.
When system carries out inveigling state to modulate, encoded and the time for the phase code basic vector that pulses generation laser is acted on The light pulse of coding basic vector coding, on all luminous timing positions, modulates the triggering electric signal of pulses generation laser, makes It has different intensity levels, to form and inveigle the light pulse of each state respective strengths in state scheme.
Further, synchronization module of the present invention includes that be arranged on Alice ends and Bob ends is set after intensity attenuators Path selection module and prepare laser and pulses generation laser with phase while the time synchronized module being connected, the road One wavelength-division recombiner is set between footpath selecting module and intensity attenuators, and the wavelength-division recombiner passes through a photodetector and institute State time synchronized module to be connected, Alice ends path selection module is connected with the path selection module at Bob ends；
The Charlie ends are another on polarization-maintaining fiber coupler all the way to single-photon detector transmission line to set the second optical fiber Circulator, the second optical fiber circulator is connected with polarization-maintaining fiber coupler, single-photon detector, and connects a synchronous radiant, institute The second optical fiber circulator transmission direction is stated from synchronous radiant to polarization-maintaining fiber coupler, from polarization-maintaining fiber coupler to single photon Detector；The path selection module is directly exported when the light pulse that modulated light source sends is exported to common port Charlie, The light pulse for reaching is transmitted to another path selection module during the pulse of the synchronous radiant of transmission, another path selection module is again The pulse signal is transmitted to photodetector by wavelength division multiplexer, photodetector transmits a signal to time synchronized mould again Block, time synchronized module prepares laser and pulses generation laser works according to signal phase-triggered.
Further, the time location of two single-photon detectors respectively to detecting judges, if two detections Device has response, and in the cycle at the same time, and it is 0, a single photon that a single-photon detector detects time location It is 1 that detector detects time location, then it is assumed that be now legal Bel's state.
In the step S101 and step S102, phase prepares the light pulse bag that laser and pulses generation laser are produced Include signal state, inveigle state and vacuum state, and the dutycycle of varying strength light pulse is set.
The last technical issues that need to address of the invention are to provide a kind of networking MDI-QKD systems based on light injection, The system includes 2 and more than 2 user terminals and a public-measurement end, and each user terminal includes modulated light source, the tune Light source processed includes：
Phase prepares laser, and the phase prepares laser by producing light pulse after phase premodulated；
Optical fiber circulator, the fiber optical circulator first port connects the phase and prepares laser, faces with first port Near second port connection pulses generation laser, the light pulse that the phase prepares laser modulation passes through the fiber annular The second port injection of device
Pulses generation laser, the light pulse that the phase that the pulses generation laser is injected prepares laser generation swashs Hair, the light pulse after modulating modulated light source output phase；The phase that the pulses generation laser is injected prepares laser The light pulse of generation is excited and its self-strength is modulated, the light pulse after modulating modulated light source output intensity, the modulation light Light pulse after source output phase modulation and intensity modulated is extremely
Public-measurement end, used as Bel's state measuring apparatus, the public-measurement end is in user terminal at the public-measurement end Photoswitch and wave filter are disposed with transmission line, polarization control unit is set after wave filter, the photoswitch is used to select 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 unified and stabilization by the quantum channel transmission of user terminal respectively The polarization state of two-way light pulse；
Polarization-maintaining fiber coupler, for receive by polarization control unit export light pulse and form interference；And
Two single-photon detectors, for entering to the result of interference that the light pulse in the polarization-maintaining fiber coupler is formed The different response of row.
Further, the light pulse of the pulses generation laser output decays to single photon level by intensity attenuators Transmit again to public-measurement end；The public-measurement end is disposed with photoswitch, filter on the transmission line after quantum channel Ripple device, sets polarization control unit after wave filter.
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, and it includes time synchronized module and path selection module, The time synchronized module prepares laser with phase and pulses generation laser is connected, and sets a wavelength-division recombiner, described Wavelength-division recombiner connects modulated light source all the way, separately leads up to a photon detector and is connected with time synchronized module, connects after being combined Path selection module is connect, the path selection module is connected with quantum channel again；
The public-measurement end is another on polarization-maintaining fiber coupler all the way to a single-photon detector transmission line to set the 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 is synchronous 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 is produced is coupled by optical fiber circulator through polarization maintaining optical fibre Device is transmitted separately to the path selection module of user terminal, and the light pulse is turned to and transmitted to communication counterpart by the path selection module Path selection module after arrive again respective time synchronized module realize it is synchronous.
Further, the path selection module of user terminal is connected to a gating module simultaneously, and it is right that the gating module is connected Answer photoswitch that the path selection module of the two-way user terminal at public-measurement end is connected to the need for connecting.
The present invention finally provides a kind of cryptographic key distribution method of the networking MDI-QKD systems based on light injection, The quantum key delivering method is comprised the following steps：
S101 phases prepare laser by producing light pulse after phase premodulated, and by optical fiber circulator injected pulse Produce laser；
The light pulse that the phase that pulses generation laser described in S102 is injected prepares laser generation is excited, and makes modulation light Light pulse after the output phase modulation of source；The phase that the pulses generation laser is injected prepares the light pulse of laser generation Excite and its self-strength is modulated, the light pulse after modulating modulated light source output intensity, so far, the light arteries and veins that modulated light source is produced 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 through quantum channel simultaneous transmission to public-measurement end polarization control unit；
Polarization control unit group described in S103 carries out unified and stabilization from the polarization state of the light pulse of user terminal in the future respectively, And high-contrast interference is formed in uniform transmission to 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 generate legal Bel's state；
S104 public-measurements end sends to user terminal, user terminal legal Bel's state information by disclosed classic network Treatment according to MDIQKD protocol contents produces final safe key.
Further, photoswitch is provided with the user terminal and the transmission line at public-measurement end, is used 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 is produced is by the second optical fiber circulator through polarization-maintaining fiber coupler The two-way user terminal at public-measurement end is connected to the need for being transmitted separately to the corresponding photoswitch connection connected by gating module The light pulse is turned to transmit to the path selection module of other side and arrived again each by path selection module, the path selection module Time synchronized module realize it is synchronous.
The present invention combine modulated light source and when both m- phase encoding schemes advantage, omit to phase-modulator and strong Spend the use of modulator, it is not required that the phase reference uniformity of pulse before and after ensureing using phase feedback system, as far as possible The point-to-point MDI-QKD system architectures of simplification and saving design cost, while ensureing that point-to-point MDI-QKD systems have high-contrast Modulated signal, finally allow MDI-QKD systems practical closer to networked instruments, meanwhile, realize phase-modulation and intensity Modulate the half-wave voltage for needing relatively low, be conducive to the high-speed applications of system.Point-to-point MDI-QKD systems of the invention are in networking The huge engineering design that this part is related to can be saved in MDI-QKD systems, system architecture has been obtained great simplification, finally Purpose is to promote networking, the practical development of MDI-QKD.
Brief description of the drawings
(a) of Fig. 1-(e) parts respectively phase prepares the pulse-triggered electric signal of laser, phase and prepares laser hair Long pulse, the light phase evolution process of long pulse, the triggering electric signal of pulses generation laser, the pulses generation laser hair penetrated The short pulse penetrated.
(a) of Fig. 2-(c) parts are respectively triggering electric signal, the triggering of pulses generation laser that phase prepares laser Electric signal, the phase modulated short pulse sequence of modulated light source output.
Fig. 3 is the point-to-point MDI-QKD system light paths figure based on light injection.
(a) of Fig. 4-(c) parts are respectively triggering electric signal, the triggering of pulses generation laser that phase prepares laser Electric signal, modulated light source output through when m- phase code after short pulse sequence.
(a) of Fig. 5-(c) parts are respectively triggering electric signal, the triggering of pulses generation laser that phase prepares 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 Bel's state in embodiment one.
Fig. 7 is the Time Synchronizing exemplary plot of embodiment one.
Fig. 8 is the preferred scheme of path selection module described in embodiment two, i.e., construct this mould using three optical fiber circulators Block.
Fig. 9 is the networking MDI-QKD system light path figures based on light injection.
Figure 10 is the synchronization scenario of the networking MDI-QKD systems that embodiment three is based on light injection.
Figure 11 is the preferred scheme of the gating module.
Specific embodiment
Below in conjunction with accompanying 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 and pulses generation respectively as phase Laser.The light pulse that phase prepares laser output produces laser, pulses generation to swash through the injected pulse of optical fiber circulator 1/6 The light pulse of light device output is outwards exported through optical fiber circulator.The output of modulated light source is substantially the output of pulses generation laser As a result.
Particularly, when phase prepares laser and pulses generation laser works independently, 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 two kinds of cycles of pulse train, makes phase Prepare a pair of bursts periods that each long pulse that laser sends sends on the cycle comprising pulses generation laser.Two The arbitrary neighborhood pulse planted in pulse train all has random phase relation.
Specifically, the core concept of modulated light source is injected for light, phase is prepared the length of the presetting Δ φ phase differences of laser Impulses injection pulses generation laser, can excitation pulse generation laser, a pair of short pulses for launching pulses generation laser Phase difference is Δ φ.
The phase modulation process of modulated light source is as shown in Figure 1.
(a) of Fig. 1-(e) parts respectively phase prepares the pulse-triggered electric signal of laser, phase and prepares laser hair Long pulse, the light phase evolution process of long pulse, the triggering electric signal of pulses generation laser, the pulses generation laser hair penetrated The short pulse penetrated.
As shown in (a) part of Fig. 1, phase modulation prepares the pulse-triggered electric signal of laser, in pulse-triggered telecommunications Number the duration of Δ t of centre position one in introduce the disturbance of Δ U, the pulse-triggered electric signal phase-triggered of this modulation is prepared and swashed Light device launches the long pulse as shown in (b) part 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 change of gain media refractive index, thus changes the frequency of laser output light, for The change of the long pulse of generation this position light frequency to shown in (c) part of linear effect such as Fig. 1 of its phase evolution, i.e. optical frequency Difference causes not modulated fractional phase difference Δ φ before and after long pulse.From (b) part 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, shown in (d) part of such as Fig. 1, prepared by phase into laser triggering telecommunications The triggering electric signal interval of the duration of Δ t alignment pulses generation lasers of number disturbance Δ U, that is, close pulses generation laser To long pulse gain herein, make finally to only have not modulated part before and after long pulse when light injected pulse produces laser Excitation is played, two indistinguishable short pulses are inspired in pulses generation laser, and by pure phase difference Between φ is delivered to two short pulses.(e) part institute of phase modulated two short pulse such as Fig. 1 of final modulated light source transmitting Show.In MDI-QKD systems, using modulated light source directly generate phase it is pure before and after two short pulses, avoid first to phase The use of modulator, secondly need not consider further that entering line phase external modulation by AMZI and phase-modulator brings front and rear two arteries and veins Rush the inconsistent problem of phase reference.Front and rear two pulse will experience identical path arrival public-measurement end after phase code.
It is linear between Δ φ and Δ U, Δ φ can be modulated to arbitrary value by setting Δ U.Fig. 2 be modulated light source only The luminous exemplary plot of two-laser during phase modulation is carried out, (a)-(c) parts of Fig. 2 are respectively the triggering telecommunications that phase prepares laser Number, pulses generation laser triggering electric signal, modulated light source output phase modulated short pulse sequence.Δ U pairs in Fig. 2 Δ φ=π is answered, and when the triggering electric signal disturbance that phase prepares laser is 0, light injection afterpulse produces laser transmitting A pair of phase differences are 0 short pulse.Still there is random phase from after (c) partially visible phase modulation of Fig. 2 between two adjacent short pulses 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 phases modulation Half-wave voltage level (the U of deviceπ4 volts of ≈).It is close that the relatively low half-wave voltage of modulated light source is advantageously implemented high speed, efficient quantum Key is distributed, and it is to light source and the integrated structure for simplifying user terminal of phase-modulator.
As described above, preparing the triggering electric signal of laser by phase modulation, the phase modulation process of modulated light source is capable of achieving. And when the triggering electric signal of modulation pulses generation laser, when pulses generation laser is exported the short pulse of varying strength, just Modulated process of the modulated light source to light intensity is realized, light source is equally beneficial for realizing at a high speed, efficiently with the integrated of intensity modulator Quantum key distribution and simplify the structure of user terminal.
Fig. 3 is the point-to-point MDI-QKD system light paths figure based on light injection, and three nodes are had in figure：User terminal Alice, user terminal Bob and public-measurement end Charlie.The two-way of Alice and Bob to Charlie has identical light path knot Structure, system can be while reach the shellfish of Charlie by the light pulse that synchronization module control Alice and Bob (as shown in Figure 7) sends That state measuring apparatus.
The present invention uses the quantum key distribution scheme of m- phase code when being based on.This scheme does not require to ensure measurement end Relative to the uniformity of user terminal basic vector benchmark, just can generate the detectable signal of high-contrast, there is provided it is higher into code check and Simple system architecture.The present invention is the advantage that make use of this scheme, and combines the advantage of modulated light source, and structural texture is more simple Single MDI-QKD systems.
In the present invention, user terminal Alice and Bob employ phase and prepare laser LD1, pulses generation laser LD2 The modulated light source constituted with optical fiber circulator 1/6, for producing 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 into single photon level.2 and 7 are Quantum channel, for ATT to be decayed after light pulse be transferred to Charlie from Alice and Bob.Charlie ends are used as Bel's state Measuring apparatus, light pulse enters polarization control unit PC in Charlie, with unified and stabilization two-way light pulse polarization state, The two-way light pulse adjusted by polarization control unit PC will form high-contrast in polarization-maintaining fiber coupler 3 and interfere, polarization-maintaining Two output ends of fiber coupler 3 connect single-photon detector 4/5 respectively, 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 relation between bit value can be set to：|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 short pulse phase difference value Δ φ of modulated light source selection output are how many processes, Δ φ=0 Correspondence | 0>Phase states, Δ φ=π correspondences | π>Phase states.According to the corresponding relation of Δ φ and Δ U, two kinds of phases are set and are prepared and swash The triggering electric signal of light device, makes it have Δ U respectively1=0 and Δ U2=UπDisturbance, this two kinds triggering electric signals correspond to respectively Modulated light source output | 0>Phase states and | π>Phase states short pulse pair.
Selection time coding basic vector is Z, and basic vector Z contains two kinds of intensity distribution states of short pulse pair.Timing distribution is gone forward The short pulse intensity in face is 0, and short pulse intensity below is constant, this intensity distribution state encoding ratio paricular value 0；Short pulse above is strong Degree is constant, and short pulse intensity below is 0, this intensity distribution state encoding ratio paricular value 1.The time encoding of system is substantially modulation light The modulated process of electric signal is triggered in source to pulses generation laser, and phase prepares laser triggering electric signal disturbance during time encoding It is 0.The triggering electric signal of pulses generation laser is modulated, when the coding to bit value 0, above short in closing timing distribution The triggering electric signal of pulse, makes its light intensity be 0, the normal trigger voltage signal for providing short pulse below；When to bit value 1 During coding, the triggering electric signal of the short pulse in closing timing distribution below makes its light intensity be 0, the normal short arteries and veins for providing above The trigger voltage signal of punching.
In the present invention, selection can be after Bel's state of the MDIQKD schemes of m- phase code when：Bel's state measurement sets The time location of 2 detectors 4/5 in standby respectively to detecting judges, if 2 detectors have response, and same The individual time cycle, and a detection is that, 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 interval before and after corresponding modulating light source output), then it is assumed that it is now legal Bel's state.
Inside Alice and Bob, randomizer (being not drawn into Fig. 3) respectively produces one group of random number sequence as two The random bit value of person, and respectively generate another group of random sequence for select encode basic vector, wherein 0 represents X basic vectors, 1 represents Z bases Arrow.
As shown in the top sheet of Fig. 4, if the random bit string of Alice generations 0110, and Z, X, Z, X basic vector are selected successively Random bit string is encoded.(a) of Fig. 4-(c) partly illustrates the when m- phase code process of Alice modulated light sources, (a) of Fig. 4-(c) part be respectively phase prepare laser triggering electric signal, the triggering electric signal of pulses generation laser, Modulated light source output through when m- phase code after short pulse sequence.As shown in (a) part of Fig. 4, when Alice uses Z bases During arrow first bit value 0 of coding, it is 0 that phase prepares laser triggering electric signal disturbance；As shown in (b) part 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 sequential point It is forward if the triggering electric signal at a' positions is 0 on cloth, in timing distribution rearward such as b, " the triggering electric signal at position is Normal value.Light injects and two triggering electric signals are shown to (c) part of exercising result such as Fig. 4 of pulses generation laser, right Answer forward such as a in timing distribution " short pulse intensity is 0 at position, in timing distribution rearward such as b, " short pulse is strong at position It is normal value to spend.When Alice encodes the 3rd bit value 1 using Z basic vectors, phase prepares laser triggering electric signal disturbance and is 0, conversely, such as (b) part of Fig. 4 during first bit value 0 of method and coding of modulation pulses generation laser triggering electric signal Triggered at middle e', f' position and the result of light pulse is generated shown in electric signal also in contrast, (c) portion of light pulse result such as Fig. 4 Short pulse in point at e ", f " position is to shown.A pair of short pulses after Z basic vectors coding have random phase with adjacent short pulse Position relation.
As shown in (a) and (b) part of Fig. 4, when Alice encodes second bit value 1 using X basic vectors, to phase system Standby laser tape has disturbance Δ U2Triggering electric signal, be slightly less than normally to pulses generation laser correspondence timing position c'd' places Triggering electric signal.Then the presetting Δ φ of laser is prepared by phase2The long pulse of phase, injected pulse produce laser after C " d " position inspires a pair of short pulses that phase difference is π, as a result as shown in (c) part of Fig. 4.When Alice is compiled using X basic vectors During the 4th bit value 0 of code, shown in (a) and (b) part of such as Fig. 4, preparing laser tape to phase has disturbance Δ U1Triggering Electric signal, to pulses generation laser correspondence timing position g'h', upper two are slightly less than normal triggering electric signal, as a result such as Fig. 4 (c) part shown in, the upper pulses generation laser phase difference output Δ φ of timing position g " h "1=0 a pair of short pulses.At this In the coded system of invention, single short pulse intensity is the half of single short pulse intensity under Z basic vectors coding under X basic vectors coding, This is relevant with the distribution probability of single photon quantum state, does not explain in detail herein.The overall modulation for illustrating Alice in (c) part of Fig. 4 Coding result of the light source to 0110 random bit.
The when m- phase code Principle of Process of Bob modulated light sources is identical with Alice, and no longer citing is repeated herein.Alice In Bob, the short pulse sequence of elapsed time-phase code is exported from modulated light source, and intensity is reached 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 decay Continue to transmit and reach Charlie in quantum channel 2/9.
In the present embodiment, the when m- phase code process of above-mentioned light pulse is not bound with trick state thought, in order that system Listener-in can simultaneously be resisted to attack the leak of imperfect light source, often MDI-QKD and trick state thought is used in combination.This When, modulated light source needs to export the light pulse of varying strength：Signal state, trick state and vacuum state, and varying strength light arteries and veins is set The duty ratio of time of punching.We set identical signal state and lure with two kinds of short pulses under being encoded to Z basic vectors coding and X basic vectors State is deceived, prepares as a example by vacuum state pulse is not encoded using any basic vector to illustrate system time-phase code and inveigle in addition The superposition modulated process of state scheme.If the burst length ratio of signal state, trick state and vacuum state is pμ:pv:p0(pμ+pv+p0= 1) the average pulse number of photons of three kinds of states is respectively μ, v, 0 after, decaying through intensity attenuators ATT.
As it was previously stated, the triggering electric signal of modulation pulses generation laser, makes pulses generation laser export varying strength Short pulse, to realize modulation of the modulated light source to light intensity.Set the lower signal state short pulse of Z basic vectors coding to, inveigle the short arteries and veins of state Rush to the corresponding two kinds of value U of pulses generation laser triggering electric signalμZ、UvZ, make in triggering electric signal UμZTriggering under, arteries and veins Punching produces the signal state short pulse of laser transmitting to that can decay to μ levels through intensity attenuators ATT, in triggering electric signal UvZ's Under triggering, the trick state short pulse of pulses generation laser transmitting through intensity attenuators ATT to that can decay to v levels；Set simultaneously Put the lower signal state of X basic vectors coding, inveigle the corresponding two kinds of value U of pulses generation laser triggering electric signal of stateμX、UvX, make touching Electrical signal UμXTriggering under, pulses generation laser transmitting signal state short pulse to can equally be declined through intensity attenuators ATT μ levels are reduced to, in triggering electric signal UvXTriggering under, pulses generation laser transmitting trick state short pulse to through strength retrogression Device ATT can equally decay to v levels；During vacuum state, phase prepares triggering electric signal of the laser with 0 disturbance, and pulse is produced Raw laser does not work, and short pulse is 0 to intensity.
Fig. 5 is the cataloged procedure of the modulated light source when trick state modulating scheme is added on the basis of Fig. 4.In Figure 5 we The new bit value 1 of addition, is used to describe the modulated process of vacuum state.(a) of Fig. 5-(c) parts are respectively phase and prepare laser Triggering electric signal, the triggering electric signal of pulses generation laser, modulated light source m- phase code and inveigle state scheme when carrying out The short pulse sequence result of superposition modulated.
As shown in the top sheet of Fig. 5, bit 01101 is selected successively Z, X, Z, X, (not selecting basic vector) basic vector coding and Signal state, signal state, trick state, trick state, the intensity modulated of vacuum state.As shown in (a) part of Fig. 5 when m- phase compile Code and inveigle state scheme superposition modulated in, phase prepare laser modulation not by trick state scheme influenceed, with it is foregoing not Plus it is identical during trick state scheme, and provide the triggering electric signal of 0 disturbance in vacuum state modulation.As Fig. 5 (b) part shown in when In the superposition modulated of m- phase code and trick state scheme, when the modulation of signal state is carried out, pulses generation laser is in Z basic vectors There is U respectively on the timing position (such as b' points and 2 points of c', d') of coding and X basic vector encoded luminescentsμZAnd UμXTriggering telecommunications Number, it is still 0 that electric signal is triggered on non-luminous timing position (such as a' points)；When the modulation of state inveigle, pulse is produced Raw laser has U respectively on luminous timing position (such as e' points and 2 points of g', h')vZAnd UvXTriggering electric signal, It is still 0 that electric signal is triggered on non-luminous timing position (such as f' points)；When the modulation of vacuum state is carried out, pulses generation laser Device two timing positions (such as i', j' point) on trigger electric signal all be 0.(c) of Fig. 5 is partly draw plus trick state The output optical pulse sequence of modulated light source afterwards.By the attenuation of intensity attenuators ATT, under Z basic vectors coding and X basic vectors coding The short pulse of signal state, trick state and vacuum state is μ, v and 0 level to being attenuated respectively.Short pulse sequence after decay exists Continue to transmit and reach Charlie in quantum channel 2/9.
Trick state scheme of the invention is not limited to this, and this embodiment is only the tune that pulse strength in state scheme is inveigled in explanation Mode processed, other species into the trick state scheme that code check is higher, security is higher can be implemented using this mode.
In Charlie, Alice and Bob two-way light pulses initially enter polarization control unit PC, PC regulation two-way light arteries and veins The polarization state of punching unifies both polarization states, and ensures that the light pulse of stabilization is polarized by internal feedback system (Fig. 3 is not drawn into) State is adjusted.Interfered on polarization-maintaining fiber coupler 3 by Alice the and Bob two-way light pulse of unified polarization state, interference knot Fruit input single-photon detector 4/5 carries out probe response.Time location to the response of single-photon detector 4/5 is analyzed, with Judge whether to generate legal Bel's state.Shorter pulse times are at intervals of a week before and after two produced when being encoded with modulated light source Time value, and take correspondence of being met twice before and after two pairs of short pulses that Alice and Bob send occur on polarization-maintaining fiber coupler 3 Single-photon detector 4/5 detection timing position be respectively t0、t1, then as shown in the rear selection of Fig. 6 Bel's state measuring apparatus, such as Fruit single-photon detector 4/5 has response within the same cycle, 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 to be now legal Bel's state.Then, Charlie by legal Bel's state information by disclosed classic network be sent to Alice and Bob, Alice and Bob according to The Data Post flow of MDIQKD protocol contents carries out the operations such as basic vector comparison, error correction and privacy amplification to these Bel's states, Produce final safe key.
Embodiment two：
System can be same by the light pulse that synchronization module (being not drawn into Fig. 3) control Alice and Bob sends in embodiment one When reach Charlie Bel's state measuring apparatus.This gives the example of this synchronization module, as shown in Figure 7.Because The synchronization of Alice and Bob two paths of signals light is largely determined by the differentia influence of the separation quantum channel 2 and 7 of two long ranges, utilizes Quantum channel 2 and quantum signal 7 are main path configuration circular path, make both synchronizable optical and flashlight of user terminal Alice Path sum is Chong Die with this circular path, makes both synchronizable optical and flashlight of user terminal Bob path sum equally annular with this The light path of path overlap, i.e. Alice and Bob is all this circular path, then can break away from what both path differences were caused to synchronization Influence.
Fig. 7 is the Time Synchronizing exemplary plot of embodiment one.Synchronous radiant LD3 is accessed using optical fiber circulator 14 Public-measurement end Charlie, the synchronizable optical that light source LD3 sends 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, leaks into monochromatic light through polarization-maintaining fiber coupler 3 through optical fiber circulator 14 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 the bandpass filter BPF of synchronizable optical.
The circular path of Alice：The synchronizable optical of synchronous radiant LD3 transmittings is divided after polarization-maintaining fiber coupler 3 is reached It is two-way, all the way through polarization control unit PC2 (not working now), the laggard access customer end Bob of quantum channel 7.This synchronizable optical according to Secondary B1 ports through user terminal Bob path selection modules B, the A2 ports of B2 ports and user terminal Alice path selection modules A, A3 ports reach the public port of Alice wavelength division multiplexers 10.An output end through wavelength division multiplexer 10 enters photodetection Device 8, photodetector 8 to this synchronous photoresponse and start Alice time synchronized module work, time synchronized module produce system System clock, the phase for triggering Alice prepares the work of laser LD1 and pulses generation laser LD2, and phase prepares laser The course of work of LD1 and pulses generation laser LD2 is identical with embodiment one, no longer repeats herein.Alice modulated light sources are produced Light pulse be flashlight after the decay of intensity attenuators ATT into another output end of wavelength division multiplexer 10, and by ripple The public port of division multiplexer 10 is exported to path selection module A.Enter behind the A3 ports and A1 ports of path selection module A Quantum channel 2, and enter Charlie.Polarization state is adjusted at polarization control unit PC1, polarization maintaining optical fibre coupling is then transmit to Clutch 3.
The circular path of Bob optical signals：Another road that the synchronizable optical of LD3 transmittings is separated by polarization-maintaining fiber coupler 3, through inclined The laggard access customer end Alice of control unit of shaking PC1 (not working now), quantum channel 2.This synchronizable optical is successively through user terminal The A1 ports of Alice path selection modules A, the B2 ports of A2 ports and user terminal Bob path selection modules B, B3 ports reach The public port of Bob wavelength division multiplexers 11.An output end through wavelength division multiplexer 11 enters photodetector 9, photodetection Device 9 to this synchronous photoresponse and start Bob time synchronized module work, time synchronized module generation system clock, trigger Bob Phase prepare the work of laser LD1 and pulses generation laser LD2, phase prepares laser LD1 and pulses generation laser The course of work of device LD2 is identical with embodiment one, no longer repeats herein.The light pulse that Bob modulated light sources are produced is flashlight warp Into another output end of wavelength division multiplexer 11 after the decay of intensity attenuators ATT, and by the common port of wavelength division multiplexer 11 Mouth is exported to path selection module B.B3 ports and the entrance quantum channel 7 of B1 ports through path selection module B, and enter Charlie.Polarization state is adjusted at polarization control unit PC2, polarization-maintaining fiber coupler 3 is then transmit to.
The synchronizable optical and flashlight of Alice and Bob are passed by identical circular path, and both light pulses are in polarization maintaining optical fibre coupling Clutch 3 meets to carry out the measurement of Bell state.Compared with the difference between two long range quantum channels 2 and 7, negligible synchronization herein Light and flashlight the walking path difference inside Alice and Bob cause the time difference to influence.
Fig. 8 is the preferred scheme of path selection module described in the present embodiment, i.e., construct this mould using three optical fiber circulators Block.In this preferred scheme, 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 three ports P1, P2 and P3, for this six optical fiber circulators, light exists Direction of travel therein is all：Two kinds of P1 → P2, P2 → P3.
The connected mode of optical fiber circulator is：In path selection module A, the P1 ports of optical fiber circulator 121, fiber optic loop The P3 ports of shape device 123 P3 ports respectively with optical fiber circulator 122, P1 ports are connected, the P3 ports of optical fiber circulator 121 with The P1 ports of optical fiber circulator 123 are connected, the P2 ports of optical fiber circulator 121, the P2 ports of optical fiber circulator 123 respectively as The A3 ports of path selection module A, A1 ports, the P2 ports of optical fiber circulator 122 as path selection module A A2 ports； In path selection module B, the P1 ports of optical fiber circulator 131, the P3 ports of optical fiber circulator 133 respectively with optical fiber circulator 132 P3 ports, the connection of P1 ports, the P3 ports of optical fiber circulator 131 are connected with the P1 ports of optical fiber circulator 133, optical fiber B3 ports, the B1 ports of the P2 ports of circulator 131, the P2 ports of optical fiber circulator 133 respectively as path selection module B, The P2 ports of optical fiber circulator 132 as path selection module B B2 ports；The P2 ports of optical fiber circulator 132 and fiber optic loop The P2 ports of shape device 122 are connected.P1 → P2's, P2 → P3 according to optical fiber circulator 121-123 and optical fiber circulator 131-133 Direction of travel, you can to realize the circular path and the circular path of Bob of the described Alice of this implementation.
In order to reduce the optics insertion loss such as wavelength division multiplexer 10/11, path selection module A/B inner fiber circulators Deng the influence of the single photon level light pulses exported to intensity attenuators ATT, can be by the intensity attenuators of Alice and Bob two-way ATT is individually positioned on the connecting line between the P1 ports of the P3 ports of optical fiber circulator 121 and optical fiber circulator 123, fiber optic loop On connecting line between the P3 ports of shape device 131 and the P1 ports of optical fiber circulator 133, the monochromatic light for exporting intensity attenuators ATT Sub- level light pulses are by less optics.
Embodiment three：
Fig. 9 is the networking MDI-QKD system light path figures based on light injection.The present embodiment is point-to-point in embodiment one There is the networking extension carried out in system-based, each user terminal identical equipment to constitute and connected mode.User terminal and public The structure of measurement end Charlie, the generation of light pulse, coding, the modulation of trick state, detection method etc. and the basic phase of embodiment one Together, the selection of legal Bell state is identical with embodiment one.Difference is to be added before Charlie polarization control units PC Photoswitch 15 and wave filter BPF (16/17), the switching of photoswitch 15 make two users end of needs by access measurement end Charlie, Two-way filter BFP (16/17) is for filtering the veiling glare in two accessing user's light pulses in Charlie.
Example IV：
Figure 10 is the synchronization scenario of the networking MDI-QKD systems that embodiment three is based on light injection, its synchronous thought and reality The synchronous thought applied in example two is identical, is predominating path with the quantum channel between two communication users and public-measurement end Charlie Construction circular path, it is Chong Die with this circular path that the synchronizable optical and flashlight for making two communication users walk light path sum, makes two logical The light path of credit household is all this circular path, and two communication user path differences are broken away to the synchronous influence for causing with this.
The composition of user terminal is as follows in the synchronization scenario of this networked system：Describe for convenience, 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 synchronized module being attached thereto are set to sending module, and each user terminal composition of the present embodiment removes this sending module It is outer to also have the path selection module being attached thereto.
Because path selection module A and path selection module B in embodiment two actually symmetrical structure, this implementation Path selection module in example can optionally first, and selecting a port of corresponding connected mode, i.e. path selection module (such as A1/B1 in embodiment two) the connection corresponding quantum channel of user terminal, No. three ports (such as embodiment two of path selection module In A3/B3) connection user terminal sending module in wavelength division multiplexer public port.In the whole user side of the present embodiment, One gating module is set to access No. two ports (A2/B2 such as in embodiment two) of all user terminal path selection modules, Function is according to needing to connect two user terminal path selection module No. two ports, make the circular path between two user terminals can There is loop effect to connect, while cut off the connection of other users ends path selection module Two-port netwerk, it is described as needed Two user terminals of connection are two users end of the incision public-measurement of photoswitch 15 end Charlie in example IV.
Figure 11 is the preferred scheme of above-mentioned gating module, as one n*2 photoswitch.1~n inputs of n*2 photoswitches Mouth is sequentially connected No. two ports (the A2/B2 ports such as in embodiment two) of 1~n user terminal path selection modules, n*2 photoswitches Output port P1, P2 be connected with each other.When having an effect, n*2 photoswitches distinguish its certain two input port by system control Connected with two output port P1, P2, because P1, P2 are connected with each other, two input ports opened with n*2 photoswitches connect respectively Circular path is connected between two users end for connecing, and just can be realized such as the synchronization scenario at two communication user ends in embodiment two, institute State the incision public-measurement of photoswitch 15 in certain the two input ports as example IV for being connected with two output port P1, P2 respectively Hold the corresponding ports at two users end of Charlie.
Although embodiments of the invention have been shown and described above, it is to be understood that above-described embodiment is example Property, it is impossible to limitation of the present invention is interpreted as, one of ordinary skill in the art is not departing from principle of the invention and objective In the case of above-described embodiment can be changed within the scope of the invention, change, replace and modification.It is all of the invention Within spirit and principle, any modification, equivalent substitution and improvements made etc. should be included within the scope of the present invention.

Claims (23)

1. the user terminal in a kind of quantum key distribution system, it is characterised in that the user terminal includes modulated light source, the tune Light source processed includes：
Phase prepares laser, and the phase prepares laser by producing light pulse after phase premodulated；
Optical fiber circulator, the fiber optical circulator first port connects the phase and prepares laser, with fiber optical circulator first The fiber optical circulator second port connection that port is closed on
Pulses generation laser, the phase prepares the second port that the light pulse of laser modulation passes through the optical fiber circulator The pulses generation laser is injected, the light pulse that the phase that the pulses generation laser is injected prepares laser generation swashs Hair, the light pulse after modulating modulated light source output phase；The phase that the pulses generation laser is injected prepares laser The light pulse of generation is excited and its self-strength is modulated, the light pulse after modulating modulated light source output intensity.
2. the user terminal in a kind of quantum key distribution system according to claim 1, it is characterised in that the pulse is produced The intensity modulated of raw laser includes that time encoding is modulated or/and inveigles state modulation.
3. a kind of MDI-QKD systems based on light injection, it includes user terminal and public-measurement end, and the user terminal includes Alice ends and Bob ends, the public-measurement end are Charlie ends, it is characterised in that the Alice ends and Bob ends include Modulated light source, the modulated light source includes：
Phase prepares laser, and the phase prepares laser by producing light pulse after phase premodulated；
Optical fiber circulator, the fiber optical circulator first port connects the phase and prepares laser, is closed on first port Second port is connected
Pulses generation laser, the phase prepares the second port that the light pulse of laser modulation passes through the optical fiber circulator The pulses generation laser is injected, the light pulse that the phase that the pulses generation laser is injected prepares laser generation swashs Hair, the light pulse after modulating modulated light source output phase；The phase that the pulses generation laser is injected prepares laser The light pulse of generation is excited and its self-strength is modulated, the light pulse after modulating modulated light source output intensity；Modulated light source is defeated The light pulse for going out is exported by the 3rd port closed on second port of the fiber optical circulator and transmitted via quantum channel To the Charlie ends, the Charlie ends are used as Bel's state measuring apparatus；The transmission direction of the optical fiber circulator is the Single port is to second port, second port to the 3rd port.
4. it is according to claim 3 it is a kind of based on light injection MDI-QKD systems, it is characterised in that the Charlie ends Including：
Polarization control unit group, light pulse that the quantum channel for receiving respectively by Alice ends and Bob ends is transmitted and it is unified with The polarization state of stabilization two-way light pulse；
Polarization-maintaining fiber coupler, for receive by polarization control unit export light pulse and form interference；And
Two single-photon detectors, the result of interference for being formed to the light pulse in the polarization-maintaining fiber coupler is carried out not Same response.
5. it is according to claim 3 it is a kind of based on light injection MDI-QKD systems, it is characterised in that the pulses generation The intensity modulated of laser includes that time encoding is modulated or/and inveigles state modulation.
6. it is according to claim 3 it is a kind of based on light injection MDI-QKD systems, it is characterised in that the user terminal exists An intensity attenuators are set between the port of optical fiber circulator the 3rd and quantum channel, light pulse is decayed into single photon level；Institute State user terminal makes two-way light pulse reach Charlie ends simultaneously by synchronization module.
7. it is according to claim 6 it is a kind of based on light injection MDI-QKD systems, it is characterised in that the synchronization module Laser and the same phase of pulses generation laser are prepared including the path selection module being arranged on after intensity attenuators and with phase Time synchronized module even, sets a wavelength-division recombiner between the path selection module and intensity attenuators, the wavelength-division is answered Clutch is connected by a photodetector with the time synchronized module, path selection module and the Bob ends at the Alice ends Path selection module is connected；
The Charlie ends are another on polarization-maintaining fiber coupler all the way to a single-photon detector transmission line to set the second optical fiber Circulator, the second optical fiber circulator is connected with polarization-maintaining fiber coupler, single-photon detector and synchronous radiant successively respectively, institute The outbound course for stating the second fiber optical circulator be synchronous radiant to polarization-maintaining fiber coupler direction, polarization-maintaining fiber coupler to list Photon detector direction；The light pulse that the synchronous radiant is produced is by the second optical fiber circulator through polarization-maintaining fiber coupler point Supplementary biography transports to the path selection module at Alice ends and Bob ends, and the light pulse is turned to and transmitted to other side by the path selection module Respective time synchronized module is arrived after path selection module again to realize synchronously.
8. it is according to claim 7 it is a kind of based on light injection MDI-QKD systems, it is characterised in that the Path selection Module is directly exported when the light pulse that modulated light source sends is exported to common port Charlie, in the light of the synchronous radiant of transmission The light pulse for reaching is transmitted to another path selection module during pulse, the light pulse that another path selection module will be received again Transmitted to photodetector by wavelength division multiplexer, photodetector transmits a signal to time synchronized module, time synchronized again Module prepares laser and pulses generation laser works according to signal phase-triggered, completes synchronous setting.
9. it is a kind of based on light injection MDI-QKD systems cryptographic key distribution method, the system include user terminal and public-measurement End, the user terminal include Alice ends and Bob ends, the public-measurement end be Charlie ends, it is characterised in that it include with Lower step：
The phase at S101 Alice ends and Bob ends prepares laser by producing light pulse after phase premodulated, and by optical fiber Circulator injected pulse produces laser；
The light pulse that the phase that pulses generation laser described in S102 is injected prepares laser generation is excited, and makes modulated light source defeated The light pulse gone out after phase-modulation；The light pulse that the phase that the pulses generation laser is injected prepares laser generation is excited And its self-strength modulation, the light pulse after modulating modulated light source output intensity；So far, the light pulse warp that modulated light source is produced Optical fiber circulator is exported, and decays to single photon level by intensity attenuators, and the light pulse at Alice ends and Bob ends is by same Walk polarization control unit group of the module through quantum channel simultaneous transmission to Charlie ends；
Polarization control unit group described in S103 respectively the polarization state of the light pulse from Alice ends and Bob ends unify and Stabilization, and high-contrast interference is formed in uniform transmission to polarization-maintaining fiber coupler, different result of interference will cause two lists The different responses of photon detector, to judge whether to generate legal Bel's state；
S104 Charlie legal Bel's state information is sent to Alice and Bob, Alice by disclosed classic network and Bob produces final safe key according to the treatment of MDIQKD protocol contents.
10. the cryptographic key distribution method of a kind of MDI-QKD systems based on light injection as claimed in claim 9, it is characterised in that In the step S101, phase prepares laser and enters line phase premodulated process：
Tidal stress electric signal, introduces electric signal disturbance within the duration of centre position one of electric signal, causes phase to prepare It is Δ φ that not modulated part 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 triggering of part respective pulses generation laser when light injects of its intermediate phase premodulated Electric signal is spaced, and part only not modulated before and after it occurs light injection effect to pulses generation laser.
A kind of 11. cryptographic key distribution methods of the MDI-QKD systems based on light injection as claimed in claim 10, its feature exists In the phase prepares laser during phase premodulated：
When Systematic selection is with phase code basic vector encoding ratio paricular value, phase code basic vector is X=[0, π], and phase basic vector X is included 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 Correspondence | 0 ＞ phase states, Δ φ=π correspondences | π>Phase states, the triggering electric signal for making phase prepare laser has Δ U1=0 or ΔU2=UπElectric signal disturbance, the light pulse with Δ φ=0 or Δ φ=π phase premodulated information is formed respectively；
When Systematic selection is with time encoding basic vector encoding ratio paricular value, the triggering electric signal that phase prepares laser has Δ U1=0 Electric signal disturbance, formed with Δ φ=0 light pulse.
A kind of 12. cryptographic key distribution methods of the MDI-QKD systems based on light injection as claimed in claim 9, it is characterised in that The intensity modulated of the pulses generation laser includes that time encoding is modulated or/and inveigles state modulation.
A kind of 13. cryptographic key distribution methods of the MDI-QKD systems based on light injection as claimed in claim 12, its feature exists In when Systematic selection is with phase code basic vector encoding ratio paricular value, pulses generation laser normally provides touching for front and rear two pulses Electrical signal；
When Systematic selection is with time encoding basic vector encoding ratio paricular value, pulses generation laser carries out time encoding modulation, time Coding basic vector Z, basic vector Z contain the intensity distribution state 0 or 1 that two kinds of pulses generation lasers launch light pulse pair, modulate pulse The triggering electric signal of laser is produced, when the coding to bit value 0, the triggering telecommunications of closing timing distribution light pulse above Number, make its light intensity be 0, the normal trigger voltage signal for providing light pulse below makes its light intensity be normal value；When to bit value During 1 coding, the triggering electric signal of closing timing distribution light pulse below makes its light intensity be 0, the normal light arteries and veins for providing above The trigger voltage signal of punching, makes its light intensity be normal value.
When system carries out inveigling state to modulate, the phase code basic vector coding and time encoding acted on for pulses generation laser The light pulse of basic vector coding, on all luminous timing positions, modulates the triggering electric signal of pulses generation laser, makes pulse Producing the light pulse of laser transmitting has different intensity levels, to form and inveigle the light arteries and veins of each state respective strengths in state scheme Punching.
A kind of cryptographic key distribution method of the 14. MDI-QKD systems based on light injection as described in claim 9 is any, its feature Be, the synchronization module include being arranged on the path selection module that Alice ends and Bob ends set after intensity attenuators and with Phase prepares laser with pulses generation laser while the time synchronized module being connected, and the path selection module declines with intensity Subtract and set between device a wavelength-division recombiner, the wavelength-division recombiner passes through a photodetector and the time synchronized module phase Even, Alice ends path selection module is connected with the path selection module at Bob ends；
The Charlie ends are another on polarization-maintaining fiber coupler all the way to single-photon detector transmission line to set the second fiber annular Device, the second optical fiber circulator is connected with polarization-maintaining fiber coupler, single-photon detector, and connects a synchronous radiant, and described the Two optical fiber circulator transmission directions are 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 when the light pulse that modulated light source sends is exported to common port Charlie, in transmission The light pulse for reaching is transmitted to another path selection module during 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 synchronized module again, Time synchronized module prepares laser and pulses generation laser works according to signal phase-triggered.
15. a kind of networking MDI-QKD systems based on light injection, it is characterised in that the system includes 2 and more than 2 User terminal 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 producing light pulse after phase premodulated；
Optical fiber circulator, the fiber optical circulator first port connects the phase and prepares laser, is closed on first port Second port connects pulses generation laser, and the phase prepares the light pulse of laser modulation by the optical fiber circulator Second port is injected
Pulses generation laser, the light pulse that the phase that the pulses generation laser is injected prepares laser generation is excited, Light pulse after modulating modulated light source output phase；The pulses generation laser produces the phase injected and prepares laser life Light pulse excite and its self-strength modulate, make modulated light source output intensity modulate after light pulse；The modulated light source is defeated The light pulse gone out after phase-modulation and intensity modulated is extremely
Public-measurement end, the public-measurement end is used as Bel's state measuring apparatus, transmission of the public-measurement end in user terminal Photoswitch and wave filter are disposed with line, polarization control unit is set after wave filter, the photoswitch is used to select to need It is switched to the user terminal at public-measurement end.
16. a kind of networking MDI-QKD systems based on light injection according to claim 15, it is characterised in that described Public-measurement end includes：
Polarization control unit group, for receiving light pulse and unified and stabilization two-way by the quantum channel transmission of user terminal respectively The polarization state of light pulse；
Polarization-maintaining fiber coupler, for receive by polarization control unit export light pulse and form interference；And
Two single-photon detectors, the result of interference for being formed to the light pulse in the polarization-maintaining fiber coupler is carried out not Same response.
17. a kind of networking MDI-QKD systems based on light injection according to claim 15, it is characterised in that described The light pulse of pulses generation laser output decays to single photon level and transmits again to public-measurement end by intensity attenuators；Institute State public-measurement end and be provided with photoswitch on the transmission line after quantum channel, polarization control unit is set after photoswitch.
18. a kind of networking MDI-QKD systems based on light injection according to claim 15, it is characterised in that described Public-measurement end only allows two-way user terminal to access when in use.
19. a kind of networking MDI-QKD systems based on light injection according to claim 15, it is characterised in that described User terminal is additionally provided with synchronization module, and it includes time synchronized module and path selection module, the time synchronized module and phase Position prepares laser and is connected with pulses generation laser, and sets a wavelength-division recombiner, and the wavelength-division recombiner connects tune all the way Light source processed, separately leads up to photodetector and is connected with time synchronized module, access path selecting module, the path after being combined Selecting module is connected with quantum channel again；
The public-measurement end is another on polarization-maintaining fiber coupler all the way to a single-photon detector transmission line to set the second light Fine circulator, the second optical fiber circulator is connected with polarization-maintaining fiber coupler, single-photon detector and synchronous radiant successively respectively, The outbound course of the second light 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 is produced is distinguished by optical fiber circulator through polarization-maintaining fiber coupler Transmit to the path selection module of user terminal, the light pulse is turned to and transmitted to the path of communication counterpart by the path selection module Respective time synchronized module is arrived after selecting module again to realize synchronously.
A kind of 20. networking MDI-QKD systems based on light injection according to claim 19, it is characterised in that user The path selection module at end is connected to a gating module simultaneously, and the gating module is connected the need for correspondence photoswitch is connected and connected To the path selection module of the two-way user terminal at public-measurement end.
21. are distributed according to a kind of key of any described networking MDI-QKD systems injected based on light of claim 15-20 Method, it is characterised in that the quantum key delivering method is comprised the following steps：
S101 phases prepare laser by producing light pulse after phase premodulated, and are produced by optical fiber circulator injected pulse Laser；
The light pulse that the phase that pulses generation laser described in S102 is injected prepares laser generation is excited, and makes modulated light source defeated The light pulse gone out after phase-modulation；The light pulse that the phase that the pulses generation laser is injected prepares laser generation is excited And its self-strength modulation, the light pulse after modulating modulated light source output intensity, so far, the light pulse warp that modulated light source is produced Optical fiber circulator is exported, and decays to single photon level by intensity attenuators, and the light pulse of user terminal is passed through by synchronization module Quantum channel simultaneous transmission to public-measurement end polarization control unit；
Polarization control unit group described in S103 carries out unified and stabilization from the polarization state of the light pulse of user terminal in the future respectively, and unites One transmits into polarization-maintaining fiber coupler formation high-contrast interference, and different result of interference will cause two single-photon detectors Different responses, to judge whether to generate legal Bel's state；
S104 public-measurements end sends to user terminal legal Bel's state information by disclosed classic network, user terminal according to The treatment of MDIQKD protocol contents produces final safe key.
A kind of 22. cryptographic key distribution methods of the networking MDI-QKD systems based on light injection according to claim 21, its It is characterised by, photoswitch is provided with the user terminal and the transmission line at public-measurement end, is used to control whether user terminal accesses Public-measurement end, the public-measurement end only allows two-way user terminal to access when in use.
A kind of 23. cryptographic key distribution methods of the networking MDI-QKD systems based on light injection according to claim 21, its It is characterised by, the light pulse that the synchronous radiant is produced is transmitted respectively by the second optical fiber circulator through polarization-maintaining fiber coupler The Path selection of the two-way user terminal at public-measurement end is connected to the need for being connected to the corresponding photoswitch connected by gating module Module, the path selection module turns to the light pulse transmits to the path selection module of other side that to arrive the respective time again same Step module is realized synchronous.
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