CN114499838B - Centrosymmetric QKD ring-type multi-user system and key distribution method thereof - Google Patents

Centrosymmetric QKD ring-type multi-user system and key distribution method thereof Download PDF

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CN114499838B
CN114499838B CN202111668161.4A CN202111668161A CN114499838B CN 114499838 B CN114499838 B CN 114499838B CN 202111668161 A CN202111668161 A CN 202111668161A CN 114499838 B CN114499838 B CN 114499838B
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bob
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CN114499838A (en
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郭邦红
赵韬
胡敏
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Guangdong Yukopod Technology Development Co ltd
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South China Normal University
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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
    • H04L9/0858—Details about key distillation or coding, e.g. reconciliation, error correction, privacy amplification, polarisation coding or phase coding
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/25—Arrangements specific to fibre transmission
    • H04B10/2507—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion
    • H04B10/2543—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion due to fibre non-linearities, e.g. Kerr effect
    • H04B10/2563—Four-wave mixing [FWM]
    • 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
    • H04B10/27—Arrangements for networking
    • H04B10/275—Ring-type networks
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
    • Y02D30/00—Reducing energy consumption in communication networks
    • Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks

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Abstract

The invention provides a central symmetry QKD ring type multi-user system and a key distribution method thereof, wherein the system is realized based on a Sagnac ring, the network structure is simpler, and the technology is mature; meanwhile, each user stabilizes the light polarization state through the polarization controller, so that the system has better stability; the two multi-user terminals can expand the number of network users according to actual conditions, and the quantum key distribution of the users and a plurality of receiving users at the receiving terminal can be realized through the wavelength division multiplexing/demultiplexing device; each multi-user end shares a multi-wavelength laser generating device, and a group of detectors are shared through the arrangement of the adjustable delay line, so that the network structure is simplified, and the network cost is saved; the multi-wavelength laser generating device selectively generates multi-wavelength light pulses with certain wavelength intervals, so that signal crosstalk caused by a four-wave mixing effect can be reduced, and the error rate is reduced.

Description

Centrosymmetric QKD ring-type multi-user system and key distribution method thereof
Technical Field
The invention relates to the technical field of quantum secret communication and optical communication, in particular to a central symmetry QKD ring-type multi-user system and a key distribution method thereof.
Background
Quantum secret communication is different from classical communication, and instead of relying on mathematical computation complexity to increase eavesdropping difficulty of an eavesdropper in a limited time, eavesdropping is found based on the basic principle and characteristics of quantum mechanics, so that encrypted information of both legal communication parties has unconditional security in theory. With the development of information technology and the popularization of internet application, quantum secret communication has become a research hotspot of the national and international quantum physics and information science interdisciplines.
The research directions of quantum secret communication mainly comprise: quantum key distribution, quantum secret sharing, quantum invisible transmission state and quantum relay. Among them, quantum Key Distribution (QKD) has been receiving attention since its proposal as an application field in which quantum secret communication is most rapidly developed and the degree of engineering is highest. The quantum key distribution refers to a key distribution method that two communication parties negotiate a key through a quantum channel by taking a quantum state as a carrier of information. Since the first quantum key distribution protocol, the BB84 protocol, many experimental schemes have demonstrated the correctness and feasibility of QKD. Currently, QKD technology is relatively mature and is gradually moving to practical application.
At present, the point-to-point QKD system is well established. To cope with the wider communication demands, the large-scale networking of QKD is a problem to be solved. Since 2004, internationally related organizations or institutions have successively deployed many typical multi-node quantum security communication networks, such as DARPA quantum communication network in the united states, SECOQC quantum communication network in the european union, tokyo quantum key distribution network in japan, and head-end quantum communication network in korea. The quantum communication network of China also goes in the front of the world, and four-user quantum communication networks are successfully built in 2007, so that a metropolitan area quantum communication network covering tens of nodes can be realized at present.
The first multi-user quantum communication network experiment was done by Townsend in 1997, which demonstrated a passive star QKD network based on beam splitters. Thereafter, ring QKD networks based on a Sagnac ring, switchable QKD networks based on optical switches, WDM-based wavelength division multiplexing networks have been proposed. The above networks can realize multi-user quantum key distribution, and have simpler structure, but have certain defects. The photon utilization rate of the passive star network is low, and as the number of users increases, the uncertainty of each user receiving the photon signal also increases. Other multi-user QKD schemes are improved, but one optical pulse can only be utilized by one user at a time, and in fact, still a one-to-one multi-user QKD scheme is still available, and the control end has only one user, which is easy to cause network breakdown. These problems not only limit the expansion of the number of users, but also lead to problems of low light pulse utilization. In addition, in the scheme, both transmitting and receiving sides are fixed, and only quantum key distribution in one direction can be performed.
Disclosure of Invention
The invention provides a central symmetry QKD ring type multi-user system which can realize quantum key distribution between a transmitting end user and a plurality of users.
It is yet another object of the present invention to provide a key distribution method for the above-described centrosymmetric QKD-ring multi-user system.
In order to achieve the technical effects, the technical scheme of the invention is as follows:
a central symmetry QKD ring type multi-user system comprises an Alice multi-user end, a Bob multi-user end and an optical fiber link; the optical fiber link comprises an Alice multi-user end-based Sagnac ring optical fiber link, a Bob multi-user end-based Sagnac ring optical fiber link and a public optical fiber link; the Alice multi-user terminal is connected with the Bob multi-user terminal through a public optical fiber link;
the Alice multiuser terminal comprises n Alice users, an optical path gating device A, alice terminal coupling unit and an Alice multiuser terminal phase modulator A; the n Alice users are sequentially connected into an Alice multi-user terminal fiber link based on a Sagnac ring; the optical path gating device A and the Alice end coupling unit are sequentially connected into a common optical fiber link and are connected with an Alice multi-user end optical fiber link based on a Sagnac ring, wherein n is more than or equal to 2 and n is an integer;
Each Alice user of the Alice multi-user terminal comprises an Alice intensity modulator, an Alice polarization controller, a first wavelength division multiplexing/demultiplexing device, a tunable optical delay line, an Alice phase modulator, a second wavelength division multiplexing/demultiplexing device and a variable optical attenuator which are sequentially connected, and the Alice multi-user terminal is accessed into an optical fiber link of the Alice multi-user terminal based on a Sagnac ring; the Alice adjustable light delay line is connected with the Alice first wavelength division multiplexing/demultiplexing device, and the Alice phase modulator is connected with the Alice second wavelength division multiplexing/demultiplexing device; the adjustable delay line and the phase modulator of each Alice user are arranged on a pulse link with corresponding wavelength between the first wavelength division multiplexing/demultiplexing device and the second wavelength division multiplexing/demultiplexing device;
the Alice end coupling unit comprises a multi-wavelength laser generating device A, a third detector, a fourth detector, a third circulator and a fourth circulator; the multi-wavelength laser generating device A, the coupler A and the third detector are respectively connected to one end of the third circulator; the fourth detector is connected to one end of the fourth circulator; the multi-wavelength laser generating device A is used for simultaneously generating a plurality of optical pulses with proper wavelength intervals so as to reduce the influence of the four-wave mixing effect on signal transmission;
The Bob multi-user terminal comprises n Bob users, an optical path gating device B, bob terminal coupling unit and a Bob multi-user terminal phase modulator B; the n Bob users are sequentially connected into the fiber links of the Bob multi-user end based on the Sagnac ring; the optical path gating device B and the Bob end coupling unit are sequentially connected into a common optical fiber link and are connected with the optical fiber link of the Bob multi-user end based on the Sagnac ring;
each Bob user of the Bob multi-user terminal comprises a Bob intensity modulator, a Bob multi-user terminal polarization controller, a first wavelength division multiplexing/demultiplexing device, an adjustable optical delay line, a Bob phase modulator, a second wavelength division multiplexing/demultiplexing device and a variable optical attenuator which are connected in sequence, and the Bob multi-user terminal is connected into an optical fiber link of the Bob multi-user terminal based on a Sagnac ring; the Bob adjustable light delay line is connected with a Bob first wavelength division multiplexing/demultiplexing device, and the Bob phase modulator is connected with a Bob second wavelength division multiplexing/demultiplexing device; the adjustable delay line and the phase modulator of each Bob user are arranged on a pulse link of corresponding wavelength between the first wavelength division multiplexing/demultiplexing device and the second wavelength division multiplexing/demultiplexing device;
the Bob end coupling unit comprises a multi-wavelength laser generating device B, a first detector, a second detector, a first circulator and a second circulator; the multi-wavelength laser generating device B, the coupler B and the first detector are respectively connected to one end of the first circulator; the second detector is connected to one end of the second circulator; the multi-wavelength laser generating device B is used for simultaneously generating a plurality of optical pulses with proper wavelength intervals so as to reduce the influence of the four-wave mixing effect on signal transmission.
Further, the third circulator and the fourth circulator are three-port circulators, and each circulator comprises a first port, a second port and a third port, signals input by the first port are output only by the second port, and signals input by the second port are output only by the third port; the first port of the third circulator is connected with the multi-wavelength laser generating device A, the second port of the third circulator is connected with the first input end of the coupler A, and the third port of the third circulator is connected with the third detector; the first port of the fourth circulator is connected to a common optical fiber link, the second port of the fourth circulator is connected with the second input end of the coupler A, and the third port of the fourth circulator is connected with the fourth detector; the first circulator and the second circulator are three-port circulators, and comprise a first port, a second port and a third port, wherein signals input by the first port are only output by the second port, and signals input by the second port are only output by the third port; the first port of the first circulator is connected with the multi-wavelength laser generating device B, the second port of the first circulator is connected with the first input end of the coupler B, and the third port of the first circulator is connected with the first detector; and the first port of the second circulator is connected to the common optical fiber link, the second port of the second circulator is connected with the second input end of the coupler B, and the third port of the second circulator is connected with the second detector.
Further, the third detector and the fourth detector detect interference photon pulse signals output by the Alice multi-user end based on the fiber link of the Sagnac loop through the coupler A; the Alice multiuser end phase modulator A is accessed to one side of an optical fiber link of the Bob multiuser end based on a Sagnac ring, and modulates the phase of each Alice user optical pulse from the Alice multiuser end; the optical path gating device A is used for gating the output direction of the light pulse flowing into the optical path gating device A; the first detector and the second detector detect interference photon pulse signals output by the fiber links of the Bob multi-user end based on the Sagnac loop through the coupler B; the phase modulator B of the Bob multi-user end is connected to one side of an optical fiber link of the Alice multi-user end based on a Sagnac ring, and modulates the phase of each Bob user optical pulse from the Alice multi-user end; the optical path gating device B is used for gating the output direction of the light pulse flowing into the optical path gating device B.
Further, if the Alice multi-user end is used as the control end of the whole system, the Bob multi-user end is used as the receiving end of the whole system:
when the mth user Alice m of n Alice users and the n Bob users of the Bob multi-user end simultaneously carry out quantum key distribution, m is more than or equal to 1 and less than or equal to n, and the multi-wavelength laser generating device A simultaneously generates multiple wavelengths lambda 1 、λ 2 、…、λ n Through which the light pulse passesThe coupler A flows into the optical path gating device A, the optical path gating device A allows light pulses to enter from only one end of the Alice multi-user end based on an optical fiber link of the Sagnac ring, and the light pulses sequentially pass through Alice users and the Bob multi-user end phase modulator B along the anticlockwise direction; when the light pulse passes through the Alice m user, the Alice m intensity modulator carries out decoy state modulation, the Alice m polarization controller is used for stabilizing the light polarization state, the Alice m first wavelength division multiplexing/demultiplexing device is used for demultiplexing the multi-wavelength light pulse onto a corresponding wavelength link, the Alice m adjustable light delay line does not modulate delay, the Alice m phase modulator allows the multi-wavelength light pulse to pass through the optical link without interference, the Alice m second wavelength division multiplexing/demultiplexing device multiplexes the multi-wavelength light pulse into an optical fiber link, and the Alice m variable light attenuator attenuates the light pulse to a proper average photon number mu per pulse so as to obtain a photon pulse with a single photon level; each device in other n-1 Alice users not participating in communication and the Bob multi-user end phase modulator B allow the multi-wavelength light pulse to pass through without interference; the multi-wavelength photon pulse flows out of the other end of the fiber link of the Alice multi-user end based Sagnac ring, flows out of the first port through the optical path gating device A instead of flowing back into the coupler A, and then flows into the optical path gating device B through the circulator and the coupler B after entering the public fiber link, and the optical path gating device B allows the photon pulse to enter from the two ends of the fiber link of the Bob multi-user end based Sagnac ring.
Further, the photon pulse is divided into two beams by the coupler B according to the proportion of 50:50, and the two beams respectively enter up>A CW-A optical fiber link in the clockwise direction and up>A CCW-A optical fiber link in the anticlockwise direction in the optical fiber link of the Sagnac ring based on the Bob multiuser end to form up>A clockwise photon pulse and an anticlockwise photon pulse;
clockwise CW-up>A photon pulse: the clockwise photon pulse sequentially passes through the Alice multi-user end phase modulator A and each Bob user in the forward direction; the Alice multiuser end phase modulator A modulates the clockwise photon pulse to generate additional phaseWhen the clockwise photon pulses sequentially pass through each Bob user, the variable optical attenuator of each Bob user allows the clockwise photon pulses to pass through without interference, the second wavelength division multiplexing/demultiplexing device is used for demultiplexing the multi-wavelength photon pulses onto the corresponding wavelength link, the phase modulator allows the clockwise photon pulses with corresponding wavelengths to pass through without interference, and the adjustable delay line of each Bob user only modulates the photon pulses with corresponding wavelengths to a proper delay value T 1 、T 2 ……T n Then each wavelength clockwise photon pulse enters a first wavelength multiplexing/demultiplexing device to be multiplexed into a multi-wavelength clockwise photon pulse, a polarization controller stabilizes the light polarization state of the photon pulse, an intensity modulator does not modulate the photon pulse, and finally the multi-wavelength clockwise photon pulse returns to the coupler B through the light path gating device B to be output;
CCW-A photon pulse in counter-clockwise direction: the anticlockwise photon pulse sequentially reversely passes through each Bob user and the Alice multiuser end phase modulator A; specifically, when the counter-clockwise photon pulses sequentially pass through each Bob user, the intensity modulator of each Bob user does not modulate the photon pulses, the polarization controller stabilizes the light polarization state of the photon pulses, and the first wavelength division multiplexing/demultiplexing device is used for demultiplexing the multi-wavelength photon pulses onto the corresponding wavelength links, and the tunable delay lines of each Bob user modulate the corresponding wavelength photon pulses only to a proper delay value T 1 、T 2 ……T n The phase modulator modulates the photon pulse to generate additional phaseThen the anticlockwise photon pulses with each wavelength enter a second wavelength division multiplexing/demultiplexing device for multiplexing, and the variable optical attenuator allows the anticlockwise photon pulses to pass through without interference; the Alice multi-user end phase modulator A allows the anticlockwise photon pulse to pass through without interference, and finally the anticlockwise photon pulse returns to the coupler B through the optical path gating device B and interferes with the clockwise photon pulse which arrives at the same time; .
Further, the first detector and the second detector are based on the phase differenceResponding to the interference result of the clockwise photon pulse and the anticlockwise photon pulse;
The adjustable optical delay line of each Bob user only modulates the photon pulse with the corresponding wavelength to a proper delay value;
because each Bob user shares the photon interference signal detector group B, when the adjustable delay line of each Bob user modulates the photon pulse with the corresponding wavelength, the adjustable delay line of each Bob user should be modulated into proper and different delay values so as to ensure that the clockwise photon pulse and the anticlockwise photon pulse with each wavelength do not interfere at the coupler B at the same time; meanwhile, the adjustable delay line of each Bob user is used for controlling the clockwise CW-up>A photon pulse and the counterclockwise CCW-up>A photon pulse to be not simultaneously present in the Alice multi-user-side phase modulator up>A.
Further, if the Bob multi-user terminal is used as the control terminal of the whole system, the Alice multi-user terminal is used as the receiving terminal of the whole system:
when the kth user Bob k in the n Bob users and the n Alice users of the Alice multi-user terminal simultaneously carry out quantum key distribution, k is more than or equal to 1 and less than or equal to n, and the multi-wavelength laser generating device B simultaneously generates multiple wavelengths lambda 1 、λ 2 、…、λ n The optical pulse flows into the optical path gating device B through the first circulator and the coupler B, the optical path gating device B allows the optical pulse to enter only from one end of the optical fiber link based on the Sagnac loop of the Bob multi-user end, and the optical pulse sequentially passes through each Bob user and Alice multi-user end phase modulator A along the anticlockwise direction; when the light pulse passes through the Bob k user, the Bob k intensity modulator carries out decoy state modulation, the Bob k polarization controller is used for stabilizing the light polarization state, the Bob k first wavelength division multiplexing/demultiplexing device is used for demultiplexing the multi-wavelength light pulse onto the corresponding wavelength link, the Bob k adjustable light delay line does not modulate delay, the Bob k phase modulator allows the multi-wavelength light pulse to pass through without interference, the Bob k second wavelength division multiplexing/demultiplexing device multiplexes the multi-wavelength light pulse into the optical fiber link, the Bob k variable light attenuator attenuates the light pulse to a proper average photon number mu per pulse so as to obtain single light Sub-level photon pulses; each device in other n-1 Bob users which do not participate in communication and the Alice multi-user end phase modulator A allow the multi-wavelength light pulse to pass through without interference; the multi-wavelength photon pulse flows out of the other end of the fiber link of the Bob multi-user end based on the Sagnac loop, flows out of the first port through the optical path gating device B instead of flowing back into the coupler B, and then enters the public fiber link and flows into the optical path gating device a through the fourth circulator and the coupler a, wherein the optical path gating device a allows the photon pulse to enter from the two ends of the fiber link of the Alice multi-user end based on the Sagnac loop.
Further, the photon pulse is divided into two beams by the coupler A according to the proportion of 50:50, and enters a CW-B optical fiber link in the clockwise direction and a CCW-B optical fiber link in the anticlockwise direction in the optical fiber link of the Alice multiuser end based on the Sagnac ring respectively to form a clockwise photon pulse and an anticlockwise photon pulse;
clockwise CW-B photon pulse: the clockwise photon pulse sequentially passes through the Bob multi-user end phase modulator B and each Alice user in the forward direction; the Bob multiuser end phase modulator B modulates the clockwise photon pulse to generate additional phase When the clockwise photon pulses sequentially pass through all Alice users, the variable optical attenuator of each Alice user allows the clock pulse to pass through without interference, the second WDM/DEMUX device is used for de-multiplexing the multi-wavelength photon pulses onto the corresponding wavelength link, the phase modulator allows the clockwise photon pulses with corresponding wavelengths to pass through without interference, and the tunable optical delay line of each Alice user only modulates the photon pulses with corresponding wavelengths to a proper delay value T 1 、T 2 ……T n Then each wavelength clockwise photon pulse enters a first wavelength multiplexing/demultiplexing device to be multiplexed into a multi-wavelength clockwise photon pulse, a polarization controller stabilizes the light polarization state of the photon pulse, an intensity modulator does not modulate the photon pulse, and finally the multi-wavelength clockwise photon pulse returns to the coupler A through the light path gating device A to be output;
CCW-B photon pulse in counter-clockwise direction: the anticlockwise photon pulse sequentially reversely passes through each Alice user and the Bob multiuser end phase modulator B; specifically, when the counter-clockwise photon pulse sequentially passes through each Alice user, the intensity modulator of each Alice user does not modulate the photon pulse, the polarization controller stabilizes the light polarization state of the photon pulse, and the first wavelength division multiplexing/demultiplexing device is used for demultiplexing the multi-wavelength photon pulse onto the corresponding wavelength link, and the tunable delay line of each Bob user modulates only the photon pulse of the corresponding wavelength to a suitable delay value T 1 、T 2 ……T n The phase modulator modulates the photon pulse to generate additional phaseThen the anticlockwise photon pulses with each wavelength enter a second wavelength division multiplexing/demultiplexing device for multiplexing, and the variable optical attenuator allows the anticlockwise photon pulses to pass through without interference; the Bob multi-user end phase modulator B allows the anticlockwise photon pulse to pass through without interference, and finally the anticlockwise photon pulse returns to the coupler A through the optical path gating device A and interferes with the clockwise photon pulse which arrives at the same time;
further, the first detector and the second detector are based on the phase differenceResponding to the interference result of the clockwise photon pulse and the anticlockwise photon pulse;
the tunable optical delay line of each Alice user only modulates the photon pulse with the corresponding wavelength to a proper delay value;
because each Alice user shares the photon interference signal detector group A, when the adjustable delay line of each Alice user modulates the photon pulse with the corresponding wavelength, the adjustable delay line should be modulated into proper and different delay values so as to ensure that the clockwise photon pulse and the anticlockwise photon pulse with the wavelengths do not interfere at the coupler A at the same time; meanwhile, the tunable optical delay line of each Alice user is used for controlling the CW-B photon pulse in the clockwise direction and the CCW-B photon pulse in the counterclockwise direction to be not simultaneously present in the Bob multi-user-side phase modulator B.
A key distribution method for a centrosymmetric QKD-ring multi-user system, comprising the steps of:
s1: establishing identities of both communication parties: confirming that one end of the Alice multiuser end or the Bob multiuser end is a control end and the other end is a multiuser receiving end through a public channel; after the multi-user control end is determined, a certain user of the control end is confirmed as a control user according to the communication requirement, and the control user can carry out quantum key distribution with a plurality of users of another multi-user receiving end at the same time;
s2: generating a multi-wavelength light pulse: confirming the control user of the multi-user control end and the multi-user receiving end through the public channel again, and if the control user and the multi-user receiving end are mutually confirmed, simultaneously generating light pulses with various wavelengths (lambda 1, lambda 2, … and lambda n) by the multi-wavelength laser generating device of the multi-user control end; maintaining a suitable wavelength separation between the wavelengths to minimize signal crosstalk due to the four-wave mixing effect;
s3: setting the delay line length of each user of the multi-user receiving end: according to the actual length of the optical fiber link, the delay line length of each user of the multi-user receiving end is adjusted to ensure that the clockwise CW photon pulse and the counterclockwise CCW photon pulse in the optical fiber link of the Sagnac ring of the multi-user receiving end do not exist in the multi-user receiving end phase modulator at the same time, and ensure that the clockwise photon pulse and the counterclockwise photon pulse of the corresponding wavelength of each receiving user of the multi-user receiving end do not interfere at the coupler at the same time;
S4: modulating the multi-wavelength light pulses: the generated multi-wavelength light pulse is subjected to random intensity modulation by controlling an intensity modulator of a user to become a signal state, a decoy state or a vacuum state; attenuating the multi-wavelength light pulses to a suitable average photon number per pulse by a variable light attenuator to obtain photon pulses for quantum key distribution;
s5: photon pulse interference: the multi-wavelength photon pulse is divided into a CW photon pulse in a clockwise direction and a CCW photon pulse in a counterclockwise direction through a coupler of a multi-user receiving end; clockwise multi-wavelength photon pulse controlled end phaseModulator modulation to generate additional phaseThe counter-clockwise multi-wavelength photon pulses are demultiplexed onto corresponding wavelength links by first wavelength division multiplexing/demultiplexing means of each receiving user, and the phase modulator of each receiving user modulates the counter-clockwise photon pulses of the corresponding wavelength to generate an additional phase +.>Finally, two paths of photon pulses interfere at a coupler of a multi-user receiving end;
s6: interference signal detection and screening coding: after the first detector and the second detector (the third detector and the fourth detector) detect the interference result of the first receiving user, the interference results of the second receiving user and the third … … nth receiving user are sequentially detected according to the delay line length of each receiving user, each receiving user records a code value according to the response results of the first detector and the second detector (the third detector and the fourth detector), performs base pairing with the control user, discards different data, and reserves the same data to obtain a screening key; judging whether the error rate exceeds a set threshold value through corresponding error rate calculation, if the error rate does not exceed the set threshold value, controlling the users and each receiving user to perform data post-processing processes including data coordination, confidentiality enhancement and the like, finally obtaining the same security key, and completing the quantum key distribution process of the controlling users and each receiving user; if the error rate exceeds the set threshold, the communication is terminated and restarted.
Compared with the prior art, the technical scheme of the invention has the beneficial effects that:
the invention is realized based on the Sagnac ring, has simpler network structure, mature technology and easy realization; because the clockwise light path and the anticlockwise light path of the receiving end based on the Sagnac ring structure are completely consistent, the phase jitter can be greatly reduced; meanwhile, each user stabilizes the light polarization state through the polarization controller, so that the system has better stability; the two multi-user terminals can expand the number of network users according to actual conditions, and the quantum key distribution of the users and a plurality of receiving users at the receiving terminal can be realized through the wavelength division multiplexing/demultiplexing device; each multi-user end shares a multi-wavelength laser generating device, and a group of detectors are shared through the arrangement of the adjustable delay line, so that the network structure is simplified, and the network cost is saved; the multi-wavelength laser generating device selectively generates multi-wavelength light pulses with a certain wavelength interval, so that signal crosstalk caused by a four-wave mixing effect can be reduced, and the error rate is reduced; a bidirectional quantum key distribution method of a multi-user system based on a Sagnac loop is provided by using an optical path gating device.
Drawings
FIG. 1 is a diagram of the overall structure of the present invention;
FIG. 2 is a schematic diagram of the structure of each Alice user at Alice multi-user end in the present invention;
FIG. 3 is a schematic diagram of the structure of each Bob user at the multi-user end of Bob in the present invention;
FIG. 4 is a schematic diagram of a multi-user end-to-end Alice coupling unit according to the present invention;
FIG. 5 is a schematic diagram of a Bob multi-user end coupling unit according to the present invention;
FIG. 6 is a structural frame diagram of an embodiment of the present invention;
fig. 7 is a flow chart of the present invention.
Detailed Description
The drawings are for illustrative purposes only and are not to be construed as limiting the present patent;
for the purpose of better illustrating the embodiments, certain elements of the drawings may be omitted, enlarged or reduced and do not represent the actual product dimensions;
it will be appreciated by those skilled in the art that certain well-known structures in the drawings and descriptions thereof may be omitted.
The technical scheme of the invention is further described below with reference to the accompanying drawings and examples.
Example 1
As shown in fig. 1, a central-symmetric QKD-ring multi-user system includes Alice multi-user end 1, bob multi-user end 2, and an optical fiber link; the optical fiber links comprise an Alice multi-user end based on a Sagnac ring optical fiber link 104, a Bob multi-user end based on a Sagnac ring optical fiber link 204 and a public optical fiber link 3; the Alice multiuser end 1 is connected with the Bob multiuser end 2 through a public optical fiber link 3;
The Alice multiuser terminal 1 comprises n (n is more than or equal to 2 and n is an integer) Alice users, an optical path gating device A100, alice terminal coupling units and Alice multiuser terminal phase modulators A103;
as shown in fig. 2 and 6, each Alice user includes an Alice intensity modulator, an Alice polarization controller, a first wavelength division multiplexing/demultiplexing device, a tunable optical delay line, an Alice phase modulator, a second wavelength division multiplexing/demultiplexing device, and a variable optical attenuator connected in sequence, and is connected to an Alice multi-user end-based optical fiber link 104 of a Sagnac loop; the Alice adjustable light delay line is connected with the Alice first wavelength division multiplexing/demultiplexing device, and the Alice phase modulator is connected with the Alice second wavelength division multiplexing/demultiplexing device; the adjustable delay line and the phase modulator of each Alice user are arranged on a pulse link with corresponding wavelength between the first wavelength division multiplexing/demultiplexing device and the second wavelength division multiplexing/demultiplexing device; for example, the Alice 1 user includes Alice 1 intensity modulator 111, alice 1 polarization controller 112, alice 1 first wavelength division multiplexing/demultiplexing device 113, alice 1 tunable optical delay line 114, alice 1 phase modulator 115, alice 1 second wavelength division multiplexing/demultiplexing device 116, and Alice 1 variable optical attenuator 117, and Alice 1 user's Alice 1 tunable optical delay line 114 and Alice 1 phase modulator 115 are placed at a wavelength λ between Alice 1 first wavelength division multiplexing/demultiplexing device 113 and Alice 1 second wavelength division multiplexing/demultiplexing device 116 1 Is connected to the pulse link of (2); the Alice 2 user comprises an Alice 2 intensity modulator 121, an Alice 2 polarization controller 122, an Alice 2 first wavelength division multiplexing/demultiplexing device 123, an Alice 2 tunable optical delay line 124, an Alice 2 phase modulator 125, an Alice 2 second wavelength division multiplexing/demultiplexing device 126 and an Alice 2 variable optical attenuator 127, wherein the Alice 2 tunable optical delay line 124 and the Alice 2 phase modulator of the Alice 2 user are arranged 125 in the Alice 2 first wavelength division multiplexing/demultiplexing device 123 and the Alice 2 second wavelength division multiplexing/demultiplexing device 126The wavelength lambda between the devices 126 2 … … on the pulse link of (c) and so on;
as shown in fig. 4 and 6, the Alice end coupling unit includes a multi-wavelength laser generating device a102, a third detector 119, a fourth detector 129, a third circulator 118, and a fourth circulator 128; the multi-wavelength laser generating device a102, the coupler a101 and the third detector 119 are respectively connected to one end of the third circulator 118; the fourth detector 129 is connected to one end of the fourth circulator 128;
the multi-wavelength laser generating device A102 is used for simultaneously generating a plurality of optical pulses (lambda) with proper wavelength interval 1 、λ 2 、…、λ n ) To reduce the influence of the four-wave mixing effect on signal transmission;
The third circulator 118 and the fourth circulator 128 are all three-port circulators, and include a first port, a second port and a third port, wherein a signal input by the first port is only output by the second port, and a signal input by the second port is only output by the third port; a first port of the third circulator 118 is connected to the multi-wavelength laser generating device a102, a second port is connected to the first input end of the coupler a101, and a third port is connected to the third detector 119; the first port of the fourth circulator 128 is connected to the common optical fiber link 3, the second port is connected to the second input end of the coupler a101, and the third port is connected to the fourth detector 129; a step of
The third detector 119 and the fourth detector 129 are configured to detect an interference photon pulse signal output by the Alice multiuser end based on the optical fiber link 104 of the Sagnac loop via the coupler a 101;
the Alice multiuser end phase modulator A103 is connected to one side of an optical fiber link 204 of the Bob multiuser end based on a Sagnac loop and is used for modulating the phase of each Alice user optical pulse from the Alice multiuser end;
the optical path gating device A100 is used for gating the output direction of the light pulse flowing into the optical path gating device A;
Similarly, as shown in fig. 3, 5 and 6, each Bob user structure of the Bob multi-user terminal 2 and the connection manner of the devices contained in the Bob multi-user terminal 2 are completely consistent with those of the Alice multi-user terminal 1;
to better describe the two-way quantum key distribution method of the multi-user system, the following is developed in two cases:
1. if the Alice multi-user end is used as the control end of the whole system, the Bob multi-user end is used as the receiving end of the whole system:
specifically, it is assumed that Alice 1 users of the n Alice users and n Bob users of the Bob multi-user terminal 2 perform quantum key distribution at the same time, where Alice 1 users are control users, and n Bob users are receiving users; taking the quantum key distribution process of the Alice 1 user and the n Bob users as an example, the transmission process of the light pulse is described in detail, and the transmission process of the light pulse in the quantum key distribution process of any Alice m (m is more than or equal to 1 and less than or equal to n) user and the n Bob users is similar to the following process;
as shown in fig. 6, the multi-wavelength laser generating device a102 generates a plurality of wavelengths (λ simultaneously 1 、λ 2 、…、λ n ) The optical pulse flows into the optical path gating device a100 through the third circulator 118 and the coupler a101, the optical path gating device a100 gates the first port and the third port, only the optical pulse is allowed to enter from the upper end of the Alice multi-user end based optical fiber link 104 of the Sagnac loop, and the optical pulse sequentially passes through each Alice user and Bob multi-user end phase modulator B203 in a counterclockwise direction; when the light pulse passes through the Alice 1 user, the Alice 1 intensity modulator 111 performs decoy state modulation, the Alice 1 polarization controller 112 is used for stabilizing the light polarization state, the Alice 1 first wavelength division multiplexing/demultiplexing device 113 is used for demultiplexing the multi-wavelength light pulse onto the corresponding wavelength link, the Alice 1 tunable optical delay line 114 does not modulate the delay, the Alice 1 phase modulator 115 allows the multi-wavelength light pulse to pass through without interference, the Alice 1 second wavelength division multiplexing/demultiplexing device 116 multiplexes the multi-wavelength light pulse into the optical fiber link, and the Alice 1 variable optical attenuator 117 attenuates the light pulse to a suitable average photon number mu per pulse to obtain a photon pulse with a single photon level; each of the other (n-1) Alice users not participating in the communication and the Bob multiuser-side phase modulator B203 are allowed to do so without interference The multi-wavelength light pulse passes through; the multi-wavelength photon pulse flows out of the lower end of the fiber link 104 based on the Sagnac ring from the Alice multi-user end, flows out of the first port through the third port of the optical path gating device A100, flows back into the coupler A101 instead of flowing out of the second port, and then flows into the optical path gating device B200 from the public fiber link through the second circulator 228 and the coupler B201, and the optical path gating device B200 gates the second port and the third port to allow the photon pulse to enter from the two ends of the fiber link 204 based on the Sagnac ring from the Bob multi-user end;
the photon pulse is divided into two beams by the coupler B201 according to the proportion of 50:50, and respectively enters up>A CW-A optical fiber link in the clockwise direction and up>A CCW-A optical fiber link in the anticlockwise direction in the optical fiber link 204 based on the Sagnac ring of the Bob multiuser end to form up>A clockwise photon pulse and an anticlockwise photon pulse;
clockwise CW-up>A photon pulse: the clockwise photon pulse sequentially passes through the Alice multi-user end phase modulator A103 and each Bob user in the forward direction; specifically, the Alice multi-user side phase modulator a103 modulates the clockwise photon pulse to generate an additional phase When the clockwise photon pulses pass through each Bob user in turn, the variable optical attenuator of each Bob user allows the clockwise photon pulses to pass through without interference, the second wavelength division multiplexing/demultiplexing device is used for demultiplexing the multi-wavelength photon pulses onto the corresponding wavelength link, the phase modulator allows the clockwise photon pulses with corresponding wavelengths to pass through without interference, and the adjustable delay line of each Bob user only modulates the photon pulses with corresponding wavelengths to a proper delay value (T 1 、T 2 ……T n ) Then each wavelength clockwise photon pulse enters a first wavelength multiplexing/demultiplexing device to be multiplexed into a multi-wavelength clockwise photon pulse, a polarization controller stabilizes the light polarization state of the photon pulse, an intensity modulator does not modulate the photon pulse, and finally the multi-wavelength clockwise photon pulse returns to the coupler B201 through the light path gating device B200 to be output;
CCW in counter-clockwise directionA photon pulse: the anticlockwise photon pulse sequentially reversely passes through each Bob user and the Alice multi-user end phase modulator A103; specifically, when the counter-clockwise photon pulses sequentially pass through each Bob user, the intensity modulator of each Bob user does not modulate the photon pulses, the polarization controller stabilizes the light polarization state of the photon pulses, and the first wavelength division multiplexing/demultiplexing device is used for demultiplexing the multi-wavelength photon pulses onto the corresponding wavelength links, and the tunable delay line of each Bob user modulates only the photon pulses of the corresponding wavelength to a suitable delay value (T 1 、T 2 ……T n ) The phase modulator modulates the photon pulse to generate additional phaseThen the anticlockwise photon pulses with each wavelength enter a second wavelength division multiplexing/demultiplexing device for multiplexing, and the variable optical attenuator allows the anticlockwise photon pulses to pass through without interference; the Alice multi-user end phase modulator A allows the anticlockwise photon pulse to pass through without interference, and finally the anticlockwise photon pulse returns to the coupler B201 through the optical path gating device B200 and interferes with the clockwise photon pulse which arrives at the same time;
the first detector 219 and the second detector 229 are based on a phase differenceResponding to the interference result of the clockwise photon pulse and the anticlockwise photon pulse;
the tunable optical delay line of each Bob user modulates only the photon pulse of the corresponding wavelength to the appropriate delay value, e.g., bob 1 user modulates only the wavelength λ 1 To a delay value T 1 Bob 2 user modulates only wavelength lambda 2 To a delay value T 2 … … Bob n user modulates wavelength only to lambda n To a delay value T n ；
2. Similarly, if the Bob multi-user terminal is used as the control terminal of the whole system, the Alice multi-user terminal is used as the receiving terminal of the whole system:
Specifically, it is assumed that Bob 1 users of the n Bob users and the n Alice users of the Alice multi-user terminal 1 perform quantum key distribution at the same time, where the Bob 1 users are control users, and n Alice users are receiving users; taking the quantum key distribution process of the Bob 1 user and the n Alice users as an example, the transmission process of the light pulse is described in detail, and the transmission process of the light pulse in the quantum key distribution process of any other Bob k (k is more than or equal to 1 and less than or equal to n) user and the n Alice users is similar to the following process;
as shown in fig. 6, the multi-wavelength laser generating device B202 generates a plurality of wavelengths (λ simultaneously 1 、λ 2 、…、λ n ) The optical pulse flows into the optical path gating device B200 through the first circulator 218 and the coupler B201, the optical path gating device B200 gates the first port and the third port, and only allows the optical pulse to enter from the Bob multi-user end based on the lower end of the optical fiber link 204 of the Sagnac loop, and the optical pulse sequentially passes through each Bob user and Alice multi-user end phase modulator a103 in a counterclockwise direction; when the light pulse passes through the Bob 1 user, the Bob 1 intensity modulator 211 performs decoy state modulation, the Bob 1 polarization controller 212 is used for stabilizing the light polarization state, the Bob 1 first wavelength division multiplexing/demultiplexing device 213 is used for demultiplexing the multi-wavelength light pulse onto the corresponding wavelength link, the Bob 1 adjustable light delay line 214 does not modulate the delay, the Bob 1 phase modulator 215 allows the multi-wavelength light pulse to pass through without interference, the Bob 1 second wavelength division multiplexing/demultiplexing device 216 multiplexes the multi-wavelength light pulse into the optical fiber link, and the Bob 1 variable optical attenuator 217 attenuates the light pulse to a suitable average photon number mu per pulse to obtain a photon pulse with a single photon level; each device in other (n-1) Bob users not participating in communication and the Alice multi-user-side phase modulator a103 allow the multi-wavelength light pulse to pass through without interference; the multi-wavelength photon pulse flows out of the upper end of the Bob multiuser end Sagnac loop-based fiber link 204, out of the first port via the third port of the optical gating device B200, instead of flowing back into the coupler B201 from the second port, and then into the optical gating device a100 via the fourth circulator 128, the coupler a101, next to the common fiber link, the optical gating device a100 gating the second port and the third port, Allowing photon pulses to enter from both ends of the Alice multiuser end Sagnac loop-based fiber link 104;
the photon pulse is divided into two beams by the coupler A101 according to the proportion of 50:50, and enters a CW-B optical fiber link in the clockwise direction and a CCW-B optical fiber link in the anticlockwise direction in the fiber link 104 based on the Sagnac ring of the Alice multiuser end to form a clockwise photon pulse and an anticlockwise photon pulse;
clockwise CW-B photon pulse: the clockwise photon pulse sequentially passes through the Bob multi-user end phase modulator B203 and all Alice users in the forward direction; specifically, the Bob multiuser-side phase modulator B203 modulates the clockwise photon pulse to generate an additional phaseWhen the clockwise photon pulses sequentially pass through the Alice users, the variable optical attenuator of each Alice user allows the clock pulse to pass through without interference, the second wavelength division multiplexing/demultiplexing device is used for demultiplexing the multi-wavelength photon pulses onto the corresponding wavelength link, the phase modulator allows the clockwise photon pulses with corresponding wavelengths to pass through without interference, and the tunable optical delay line of each Alice user modulates only the photon pulses with corresponding wavelengths to a proper delay value (T 1 、T 2 ……T n ) Then each wavelength clockwise photon pulse enters a first wavelength multiplexing/demultiplexing device to be multiplexed into a multi-wavelength clockwise photon pulse, a polarization controller stabilizes the light polarization state of the photon pulse, an intensity modulator does not modulate the photon pulse, and finally the multi-wavelength clockwise photon pulse returns to the coupler A101 through the light path gating device A100 to be output;
CCW-B photon pulse in counter-clockwise direction: the counter-clockwise photon pulse sequentially reversely passes through each Alice user and the Bob multi-user end phase modulator B203; specifically, when the counter-clockwise photon pulse sequentially passes through all Alice users, the intensity modulator of each Alice user does not modulate the photon pulse, the polarization controller stabilizes the light polarization state of the photon pulse, and the first wavelength division multiplexing/demultiplexing device is used for demultiplexing the multi-wavelength photon pulse onto the corresponding wavelength link, and the tunable optical delay of each Alice userThe time line modulates only the photon pulses of the corresponding wavelength to a suitable delay value (T 1 、T 2 ……T n ) The phase modulator modulates the photon pulse to generate additional phaseThen the anticlockwise photon pulses with each wavelength enter a second wavelength division multiplexing/demultiplexing device for multiplexing, and the variable optical attenuator allows the anticlockwise photon pulses to pass through without interference; the Bob multi-user end phase modulator B allows the anticlockwise photon pulse to pass through without interference, and finally the anticlockwise photon pulse returns to the coupler A101 through the optical path gating device A100 and interferes with the clockwise photon pulse which arrives at the same time;
the third detector 119 and the fourth detector 129 are based on the phase differenceResponding to the interference result of the clockwise photon pulse and the anticlockwise photon pulse;
Preferably, each Alice user's tunable delay line modulates only the corresponding wavelength photon pulse to the appropriate delay value, e.g., alice 1 user modulates only the wavelength λ 1 To a delay value T 1 Alice 2 users modulate only wavelength lambda 2 To a delay value T 2 … … Alien users modulate wavelength only to lambda n To a delay value T n ；
The above is the transmission process of the light pulse of two cases respectively.
Specifically, for both cases described above, the first detector 219 and the second detector 229 (the third detector 119 and the fourth detector 129) are based on the phase differenceIs responsive to the interference result of the clockwise photon pulse and the counter-clockwise photon pulse. The receiving end user records the code values according to the response results of the first detector 219 and the second detector 229 (the third detector 119 and the fourth detector 129) in sequence and controlsThe user performs base pairing, discards different data and reserves the same data to obtain a screening key; and then controlling the users and each receiving user to perform a data post-processing process comprising data coordination, confidentiality enhancement and the like, finally obtaining the same security key, and completing a quantum key distribution process of the controlling users and each receiving user. / >
According to the BB84 protocol of quantum key distribution phase encoding, the light intensity of two photon pulses at the first detector (third detector) is determined by the following equation:
or (b)
Wherein I is 1 For the output intensity at the first detector (third detector), I 0 Is the input light intensity.
Controlling user modulation phasePi or +.>Receiving user modulation phase->Or->Wherein the phase takes 0 and pi as a group of orthogonal bases, and the phase takes +.>And->As another set of orthogonal substrates; when controlling user adjustmentBrake phase->Or->When the transmission code value is 0; when controlling the user modulation phase +.>Or->When this indicates that the transmission code value is 1. Table 1 will->Andthe corresponding detection results may be listed.
(note:or->In actual communication is +.>Or->Depending on whether Alice multi-user end is the control end or Bob multi-user end is the control end. )
Table 1: correspondence table of different phase values and detector response results
As can be seen from the above table, when the phase differenceWhen the first (third) detector responds, the first (third) detector can code, and the receiving user receives a code value of 0; when the phase difference is->When the second (fourth) detector responds, the code can be formed, and the receiving user receives the code value of 1; when the phase difference is- >Or->When the first detector and the second detector (or the third detector and the fourth detector) may respond, the codes cannot be coded, which is caused by different selection bases when the modulation phases of the control user and the receiving user are different.
Example 2
As shown in fig. 7, the present invention provides a two-way quantum key distribution method of a multi-user system based on a Sagnac loop, which is applied to a QKD loop type multi-user system with central symmetry as described above, and the method includes the following steps:
s1, establishing identities of two communication parties: confirming that one end of the Alice multiuser end or the Bob multiuser end is a control end and the other end is a multiuser receiving end through a public channel; after the multi-user control end is determined, a certain user of the control end is confirmed as a control user according to the communication requirement, and the control user can carry out quantum key distribution with a plurality of users of another multi-user receiving end at the same time;
s2, generating multi-wavelength light pulses: and confirming the control user of the multi-user control end and the multi-user receiving end through the public channel again, and if the control user and the multi-user receiving end are confirmed mutually, generating multi-wavelength laser of the multi-user control endThe green device simultaneously generates multiple wavelengths (lambda) 1 、λ 2 、…、λ n ) Is a light pulse of (2); maintaining a suitable wavelength separation between the wavelengths to minimize signal crosstalk due to the four-wave mixing effect;
S3, setting the delay line length of each user of the multi-user receiving end: according to the actual length of the optical fiber link, the delay line length of each user of the multi-user receiving end is adjusted to ensure that the clockwise CW photon pulse and the counterclockwise CCW photon pulse in the optical fiber link of the Sagnac ring of the multi-user receiving end do not exist in the multi-user receiving end phase modulator at the same time, and ensure that the clockwise photon pulse and the counterclockwise photon pulse of the corresponding wavelength of each receiving user of the multi-user receiving end do not interfere at the coupler at the same time;
s4, modulating multi-wavelength light pulses: the generated multi-wavelength light pulse is subjected to random intensity modulation by controlling an intensity modulator of a user to become a signal state, a decoy state or a vacuum state; attenuating the multi-wavelength light pulses to a suitable average photon number per pulse by a variable light attenuator to obtain photon pulses for quantum key distribution;
s5, photon pulse interference: the multi-wavelength photon pulse is divided into a CW photon pulse in a clockwise direction and a CCW photon pulse in a counterclockwise direction through a coupler of a multi-user receiving end; the clockwise multi-wavelength photon pulse is modulated by the phase modulator at the control end to generate additional phase The counter-clockwise multi-wavelength photon pulses are demultiplexed onto corresponding wavelength links by first wavelength division multiplexing/demultiplexing means of each receiving user, and the phase modulator of each receiving user modulates the counter-clockwise photon pulses of the corresponding wavelength to generate an additional phase +.>Finally, two paths of photon pulses interfere at a coupler of a multi-user receiving end;
s6, interference signal detection and screening coding: after the first detector and the second detector (the third detector and the fourth detector) detect the interference result of the first receiving user, the interference results of the second receiving user and the third … … nth receiving user are sequentially detected according to the delay line length of each receiving user, each receiving user records a code value according to the response results of the first detector and the second detector (the third detector and the fourth detector), performs base pairing with the control user, discards different data, and reserves the same data to obtain a screening key; judging whether the error rate exceeds a set threshold value through corresponding error rate calculation, if the error rate does not exceed the set threshold value, controlling the users and each receiving user to perform data post-processing processes including data coordination, confidentiality enhancement and the like, finally obtaining the same security key, and completing the quantum key distribution process of the controlling users and each receiving user; if the error rate exceeds the set threshold, the communication is terminated and restarted.
The invention can realize the simultaneous quantum key distribution of the control user and a plurality of receiving users, and provides a bidirectional quantum key distribution method of a multi-user system based on a Sagnac ring, which has simple network structure and is easy to realize; based on the structural characteristics of the Sagnac ring and the use of the polarization controller, the system has better stability.
The same or similar reference numerals correspond to the same or similar components;
the positional relationship depicted in the drawings is for illustrative purposes only and is not to be construed as limiting the present patent;
it is to be understood that the above examples of the present invention are provided by way of illustration only and not by way of limitation of the embodiments of the present invention. Other variations or modifications of the above teachings will be apparent to those of ordinary skill in the art. It is not necessary here nor is it exhaustive of all embodiments. Any modification, equivalent replacement, improvement, etc. which come within the spirit and principles of the invention are desired to be protected by the following claims.

Claims (10)

1. A central symmetry QKD ring type multi-user system, which is characterized by comprising an Alice multi-user end, a Bob multi-user end and an optical fiber link; the optical fiber link comprises an Alice multi-user end-based Sagnac ring optical fiber link, a Bob multi-user end-based Sagnac ring optical fiber link and a public optical fiber link; the Alice multi-user terminal is connected with the Bob multi-user terminal through a public optical fiber link;
The Alice multiuser terminal comprises n Alice users, an optical path gating device A, alice terminal coupling unit and an Alice multiuser terminal phase modulator A; the n Alice users are sequentially connected into an Alice multi-user terminal fiber link based on a Sagnac ring; the optical path gating device A and the Alice end coupling unit are sequentially connected into a common optical fiber link and are connected with an Alice multi-user end optical fiber link based on a Sagnac ring, wherein n is more than or equal to 2 and n is an integer;
each Alice user of the Alice multi-user terminal comprises an Alice intensity modulator, an Alice polarization controller, a first wavelength division multiplexing/demultiplexing device, a tunable optical delay line, an Alice phase modulator, a second wavelength division multiplexing/demultiplexing device and a variable optical attenuator which are sequentially connected, and the Alice multi-user terminal is accessed into an optical fiber link of the Alice multi-user terminal based on a Sagnac ring; the Alice adjustable light delay line is connected with the Alice first wavelength division multiplexing/demultiplexing device, and the Alice phase modulator is connected with the Alice second wavelength division multiplexing/demultiplexing device; the adjustable delay line and the phase modulator of each Alice user are arranged on a pulse link with corresponding wavelength between the first wavelength division multiplexing/demultiplexing device and the second wavelength division multiplexing/demultiplexing device;
The Alice end coupling unit comprises a multi-wavelength laser generating device A, a third detector, a fourth detector, a third circulator and a fourth circulator; the multi-wavelength laser generating device A, the coupler A and the third detector are respectively connected to one end of the third circulator; the fourth detector is connected to one end of the fourth circulator; the multi-wavelength laser generating device A is used for simultaneously generating a plurality of optical pulses with proper wavelength intervals so as to reduce the influence of the four-wave mixing effect on signal transmission;
the Bob multi-user terminal comprises n Bob users, an optical path gating device B, bob terminal coupling unit and a Bob multi-user terminal phase modulator B; the n Bob users are sequentially connected into the fiber links of the Bob multi-user end based on the Sagnac ring; the optical path gating device B and the Bob end coupling unit are sequentially connected into a common optical fiber link and are connected with the optical fiber link of the Bob multi-user end based on the Sagnac ring;
each Bob user of the Bob multi-user terminal comprises a Bob intensity modulator, a Bob multi-user terminal polarization controller, a first wavelength division multiplexing/demultiplexing device, an adjustable optical delay line, a Bob phase modulator, a second wavelength division multiplexing/demultiplexing device and a variable optical attenuator which are connected in sequence, and the Bob multi-user terminal is connected into an optical fiber link of the Bob multi-user terminal based on a Sagnac ring; the Bob adjustable light delay line is connected with a Bob first wavelength division multiplexing/demultiplexing device, and the Bob phase modulator is connected with a Bob second wavelength division multiplexing/demultiplexing device; the adjustable delay line and the phase modulator of each Bob user are arranged on a pulse link of corresponding wavelength between the first wavelength division multiplexing/demultiplexing device and the second wavelength division multiplexing/demultiplexing device;
The Bob end coupling unit comprises a multi-wavelength laser generating device B, a first detector, a second detector, a first circulator and a second circulator; the multi-wavelength laser generating device B, the coupler B and the first detector are respectively connected to one end of the first circulator; the second detector is connected to one end of the second circulator; the multi-wavelength laser generating device B is used for simultaneously generating a plurality of optical pulses with proper wavelength intervals so as to reduce the influence of the four-wave mixing effect on signal transmission.
2. The center-symmetrical QKD-ring multi-user system of claim 1, wherein the third and fourth circulators are three-port circulators, each including a first port, a second port, and a third port, signals input from the first port being output only from the second port, signals input from the second port being output only from the third port; the first port of the third circulator is connected with the multi-wavelength laser generating device A, the second port of the third circulator is connected with the first input end of the coupler A, and the third port of the third circulator is connected with the third detector; the first port of the fourth circulator is connected to a common optical fiber link, the second port of the fourth circulator is connected with the second input end of the coupler A, and the third port of the fourth circulator is connected with the fourth detector; the first circulator and the second circulator are three-port circulators, and comprise a first port, a second port and a third port, wherein signals input by the first port are only output by the second port, and signals input by the second port are only output by the third port; the first port of the first circulator is connected with the multi-wavelength laser generating device B, the second port of the first circulator is connected with the first input end of the coupler B, and the third port of the first circulator is connected with the first detector; and the first port of the second circulator is connected to the common optical fiber link, the second port of the second circulator is connected with the second input end of the coupler B, and the third port of the second circulator is connected with the second detector.
3. The central-symmetric QKD ring-type multiuser system according to claim 2, wherein the third and fourth detectors detect interference photon pulse signals output from the Alice multiuser end-based optical fiber link of the Sagnac ring via coupler a; the Alice multiuser end phase modulator A is accessed to one side of an optical fiber link of the Bob multiuser end based on a Sagnac ring, and modulates the phase of each Alice user optical pulse from the Alice multiuser end; the optical path gating device A is used for gating the output direction of the light pulse flowing into the optical path gating device A; the first detector and the second detector detect interference photon pulse signals output by the fiber links of the Bob multi-user end based on the Sagnac loop through the coupler B; the phase modulator B of the Bob multi-user end is connected to one side of an optical fiber link of the Alice multi-user end based on a Sagnac ring, and modulates the phase of each Bob user optical pulse from the Alice multi-user end; the optical path gating device B is used for gating the output direction of the light pulse flowing into the optical path gating device B.
4. The system of claim 3, wherein if the Alice multi-user terminal is used as a control terminal of the whole system, the Bob multi-user terminal is used as a receiving terminal of the whole system:
When the mth user Alice m of the n Alice users and the n Bob users of the Bob multi-user end simultaneously carry out quantum key distributionM is more than or equal to 1 and less than or equal to n, and the multi-wavelength laser generating device A simultaneously generates multiple wavelengths lambda 1 、λ 2 、…、λ n The optical pulse flows into the optical path gating device A through the third circulator A and the coupler A, the optical path gating device A allows the optical pulse to enter only from one end of the fiber link based on the Sagnac ring of the Alice multi-user end, and the optical pulse sequentially passes through each Alice user and the Bob multi-user end phase modulator B along the anticlockwise direction; when the light pulse passes through the Alice m user, the Alice m intensity modulator carries out decoy state modulation, the Alice m polarization controller is used for stabilizing the light polarization state, the Alice m first wavelength division multiplexing/demultiplexing device is used for demultiplexing the multi-wavelength photon pulse onto a corresponding wavelength link, the Alice m adjustable light delay line does not modulate delay, the Alice m phase modulator allows the light pulse to pass through, the Alice m second wavelength division multiplexing/demultiplexing device multiplexes the multi-wavelength photon pulse into an optical fiber link, and the Alice m variable optical attenuator attenuates the light pulse to a proper average photon number mu per pulse so as to obtain a photon pulse with a single photon level; each device in other n-1 Alice users not participating in communication and the Bob multi-user end phase modulator B allow the multi-wavelength photon pulse to pass through without interference; the multi-wavelength photon pulse flows out of the other end of the fiber link of the Alice multi-user end based Sagnac ring, flows out of the first port through the optical path gating device A instead of flowing back into the coupler A, and then flows into the optical path gating device B through the circulator and the coupler B after entering the public fiber link, and the optical path gating device B allows the photon pulse to enter from the two ends of the fiber link of the Bob multi-user end based Sagnac ring.
5. The center-symmetrical QKD ring multi-user system of claim 4, wherein the photon pulses are split by coupler B into two beams in up>A ratio of 50:50, respectively entering up>A clockwise CW-up>A fiber link and up>A counterclockwise CCW-up>A fiber link of the Bob multi-user-based fiber links of the Sagnac ring, forming clockwise and counterclockwise photon pulses;
clockwise CW-up>A photon pulse:the clockwise photon pulse sequentially passes through the Alice multi-user end phase modulator A and each Bob user in the forward direction; the Alice multiuser end phase modulator A modulates the clockwise photon pulse to generate additional phaseWhen the clockwise photon pulses sequentially pass through each Bob user, the variable optical attenuator of each Bob user allows the clockwise photon pulses to pass through without interference, the second wavelength division multiplexing/demultiplexing device is used for demultiplexing the multi-wavelength photon pulses onto the corresponding wavelength link, the phase modulator allows the clockwise photon pulses with corresponding wavelengths to pass through without interference, and the adjustable delay line of each Bob user only modulates the photon pulses with corresponding wavelengths to a proper delay value T 1 、T 2 ……T n Then each wavelength clockwise photon pulse enters a first wavelength multiplexing/demultiplexing device to be multiplexed into a multi-wavelength clockwise photon pulse, a polarization controller stabilizes the light polarization state of the photon pulse, an intensity modulator does not modulate the photon pulse, and finally the multi-wavelength clockwise photon pulse returns to the coupler B through the light path gating device B to be output;
CCW-A photon pulse in counter-clockwise direction: the anticlockwise photon pulse sequentially reversely passes through each Bob user and the Alice multiuser end phase modulator A; specifically, when the counter-clockwise photon pulses sequentially pass through each Bob user, the intensity modulator of each Bob user does not modulate the photon pulses, the polarization controller stabilizes the light polarization state of the photon pulses, and the first wavelength division multiplexing/demultiplexing device is used for demultiplexing the multi-wavelength photon pulses onto the corresponding wavelength links, and the tunable delay lines of each Bob user modulate the corresponding wavelength photon pulses only to a proper delay value T 1 、T 2 ……T n The phase modulator modulates the photon pulse to generate additional phaseThen the anticlockwise photon pulses with each wavelength enter a second wavelength division multiplexing/demultiplexing device for multiplexing, and the variable optical attenuator allows the anticlockwise photon pulses to pass through without interference; the Alice multi-user end phase modulator A allows the anticlockwise photon pulse to pass through without interference, and is the most suitableThe latter counter-clockwise photon pulse returns to the coupler B through the optical path gating device B and interferes with the clockwise photon pulse which arrives at the same time.
6. The centrosymmetric QKD ring multi-user system according to claim 5, wherein the first and second detectors are based on phase differences Responding to the interference result of the clockwise photon pulse and the anticlockwise photon pulse;
the adjustable optical delay line of each Bob user only modulates the photon pulse with the corresponding wavelength to a proper delay value;
because each Bob user shares the photon interference signal detector group B, when the adjustable delay line of each Bob user modulates the photon pulse with the corresponding wavelength, the adjustable delay line of each Bob user should be modulated into proper and different delay values so as to ensure that the clockwise photon pulse and the anticlockwise photon pulse with each wavelength do not interfere at the coupler B at the same time; meanwhile, the adjustable delay line of each Bob user is used for controlling the clockwise CW-up>A photon pulse and the counterclockwise CCW-up>A photon pulse to be not simultaneously present in the Alice multi-user-side phase modulator up>A.
7. The system of claim 6, wherein if the Bob multi-user terminal is used as a control terminal of the whole system, the Alice multi-user terminal is used as a receiving terminal of the whole system:
when the kth user Bob k in the n Bob users and the n Alice users of the Alice multi-user terminal simultaneously carry out quantum key distribution, k is more than or equal to 1 and less than or equal to n, and the multi-wavelength laser generating device B simultaneously generates multiple wavelengths lambda 1 、λ 2 、…、λ n The optical pulse flows into the optical path gating device B through the first circulator and the coupler B, the optical path gating device B allows the optical pulse to enter from only one end of the optical fiber link based on the Sagnac ring of the Bob multi-user end, and the optical pulse sequentially passes through each Bob user and each Bob user in the anticlockwise directionAlice multi-user end phase modulator a; when the light pulse passes through the Bob k user, the Bob k intensity modulator carries out decoy state modulation, the Bob k polarization controller is used for stabilizing the light polarization state, the Bob k first wavelength division multiplexing/demultiplexing device is used for demultiplexing the multi-wavelength photon pulse onto a corresponding wavelength link, the Bob k adjustable light delay line does not modulate delay, the Bob k phase modulator allows the light pulse to pass through, the Bob k second wavelength division multiplexing/demultiplexing device multiplexes the multi-wavelength photon pulse into an optical fiber link, and the Bob k variable light attenuator attenuates the light pulse to a proper average photon number mu per pulse so as to obtain a photon pulse with a single photon level; each device in other n-1 Bob users which do not participate in communication and the Alice multi-user end phase modulator A allow the multi-wavelength photon pulse to pass through without interference; the multi-wavelength photon pulse flows out of the other end of the fiber link of the Bob multi-user end based on the Sagnac loop, flows out of the first port through the optical path gating device B instead of flowing back into the coupler B, and then enters the public fiber link and flows into the optical path gating device a through the fourth circulator and the coupler a, wherein the optical path gating device a allows the photon pulse to enter from the two ends of the fiber link of the Alice multi-user end based on the Sagnac loop.
8. The center-symmetrical QKD ring multi-user system of claim 7, wherein the photon pulses are split by the coupler a into two beams in a ratio of 50:50, respectively entering a clockwise CW-B fiber link and a counterclockwise CCW-B fiber link of the Alice multi-user end-based Sagnac ring fiber links, forming clockwise and counterclockwise photon pulses;
clockwise CW-B photon pulse: the clockwise photon pulse sequentially passes through the Bob multi-user end phase modulator B and each Alice user in the forward direction; the Bob multiuser end phase modulator B modulates the clockwise photon pulse to generate additional phaseWhen the clockwise photon pulse sequentially passes through all Alice users, the variable optical attenuator of each Alice user has no interferenceThe second wavelength division multiplexing/demultiplexing device is used for demultiplexing the multi-wavelength photon pulses onto the corresponding wavelength chains, the phase modulator allows the clockwise photon pulses with corresponding wavelengths to pass through without interference, and the adjustable delay line of each Alice user only modulates the photon pulses with corresponding wavelengths to a proper delay value T 1 、T 2 ……T n Then each wavelength clockwise photon pulse enters a first wavelength multiplexing/demultiplexing device to be multiplexed into a multi-wavelength clockwise photon pulse, a polarization controller stabilizes the light polarization state of the photon pulse, an intensity modulator does not modulate the photon pulse, and finally the multi-wavelength clockwise photon pulse returns to the coupler A through the light path gating device A to be output;
CCW-B photon pulse in counter-clockwise direction: the anticlockwise photon pulse sequentially reversely passes through each Alice user and the Bob multiuser end phase modulator B; specifically, when the counter-clockwise photon pulse sequentially passes through each Alice user, the intensity modulator of each Alice user does not modulate the photon pulse, the polarization controller stabilizes the light polarization state of the photon pulse, and the first wavelength division multiplexing/demultiplexing device is used for demultiplexing the multi-wavelength photon pulse onto the corresponding wavelength link, and the tunable delay line of each Alice user modulates only the photon pulse with the corresponding wavelength to a proper delay value T 1 、T 2 ……T n The phase modulator modulates the photon pulse to generate additional phaseThen the anticlockwise photon pulses with each wavelength enter a second wavelength division multiplexing/demultiplexing device for multiplexing, and the variable optical attenuator allows the anticlockwise photon pulses to pass through without interference; the Bob multi-user end phase modulator B allows the anticlockwise photon pulse to pass through without interference, and finally the anticlockwise photon pulse returns to the coupler A through the optical path gating device A and interferes with the clockwise photon pulse which arrives at the same time.
9. The centrosymmetric QKD ring multi-user system according to claim 8, wherein the third and fourth detectors are based on phase differences Responding to the interference result of the clockwise photon pulse and the anticlockwise photon pulse;
the tunable optical delay line of each Alice user only modulates the photon pulse with the corresponding wavelength to a proper delay value;
because each Alice user shares the photon interference signal detector group A, when the adjustable delay line of each Alice user modulates the photon pulse with the corresponding wavelength, the adjustable delay line should be modulated into proper and different delay values so as to ensure that the clockwise photon pulse and the anticlockwise photon pulse with the wavelengths do not interfere at the coupler A at the same time; meanwhile, the tunable optical delay line of each Alice user is used for controlling the CW-B photon pulse in the clockwise direction and the CCW-B photon pulse in the counterclockwise direction to be not simultaneously present in the Bob multi-user-side phase modulator B.
10. A key distribution method for a centrosymmetric QKD-ring multi-user system as claimed in claim 9, comprising the steps of:
s1: establishing identities of both communication parties: confirming that one end of the Alice multiuser end or the Bob multiuser end is a control end and the other end is a multiuser receiving end through a public channel; after the multi-user control end is determined, a certain user of the control end is confirmed as a control user according to the communication requirement, and the control user can carry out quantum key distribution with a plurality of users of another multi-user receiving end at the same time;
S2: generating a multi-wavelength sub-optical pulse: confirming the control user of the multi-user control end and the multi-user receiving end through the public channel again, and if the control user and the multi-user receiving end are mutually confirmed, simultaneously generating light pulses with various wavelengths by the multi-wavelength laser generating device of the multi-user control end, wherein the wavelengths are respectively lambda 1, lambda 2, … and lambda n; maintaining a suitable wavelength separation between the wavelengths to minimize signal crosstalk due to the four-wave mixing effect;
s3: setting the delay line length of each user of the multi-user receiving end: according to the actual length of the optical fiber link, the delay line length of each user of the multi-user receiving end is adjusted to ensure that the clockwise CW photon pulse and the counterclockwise CCW photon pulse in the optical fiber link of the Sagnac ring of the multi-user receiving end do not exist in the multi-user receiving end phase modulator at the same time, and ensure that the clockwise photon pulse and the counterclockwise photon pulse of the corresponding wavelength of each receiving user of the multi-user receiving end do not interfere at the coupler at the same time;
s4: modulating the multi-wavelength sub-optical pulses: the generated multi-wavelength photon pulse is subjected to random intensity modulation by controlling an intensity modulator of a user to become a signal state, a decoy state or a vacuum state; attenuating the multi-wavelength photon pulses to a suitable average photon number per pulse by a variable optical attenuator to obtain photon pulses for quantum key distribution;
S5: photon pulse interference: the multi-wavelength photon pulse is divided into a CW photon pulse in a clockwise direction and a CCW photon pulse in a counterclockwise direction through a coupler of a multi-user receiving end; when Alice multiuser terminal is used as control terminal and Bob multiuser terminal is used as receiving terminal, the clockwise multi-wavelength photon pulse is modulated by control terminal phase modulator to generate additional phaseThe counter-clockwise multi-wavelength photon pulses are demultiplexed onto corresponding wavelength links by first wavelength division multiplexing/demultiplexing means of each receiving user, and the phase modulator of each receiving user modulates the counter-clockwise photon pulses of the corresponding wavelength to generate an additional phase +.>Finally, two paths of photon pulses interfere at a coupler of a multi-user receiving end; when the Bob multi-user terminal is used as the control terminal and the Alice multi-user terminal is used as the receiving terminal, the clockwise multi-wavelength photon pulse is modulated by the phase modulator of the control terminal to generate additional phase +.>The counter-clockwise multi-wavelength photon pulses are demultiplexed onto corresponding wavelength links by first wavelength division multiplexing/demultiplexing means of each receiving user, and the phase modulators of each receiving user modulate counter-clockwise photon pulses of corresponding wavelengths to generateAdditional phase->Finally, two paths of photon pulses interfere at the coupler of the multi-user receiving end
S6: interference signal detection and screening coding: when Alice multi-user terminal is used as a control terminal and Bob multi-user terminal is used as a receiving terminal, after the first detector and the second detector detect interference results of a first receiving user, interference results of a second receiving user and a third receiving user … … n are sequentially detected according to the delay line length of each receiving user, each receiving user records a code value according to response results of the first detector and the second detector, performs pairing with the control user, discards different data, and retains the same data to obtain a screening key; judging whether the error rate exceeds a set threshold value through corresponding error rate calculation, if the error rate does not exceed the set threshold value, controlling the users and each receiving user to perform a data post-processing process, including data coordination and confidentiality enhancement, finally obtaining the same security key, and completing a quantum key distribution process of the controlling users and each receiving user; if the error rate exceeds the set threshold, terminating the communication and restarting; when the Bob multi-user terminal is used as a control terminal and the Alice multi-user terminal is used as a receiving terminal, after the third detector and the fourth detector detect interference results of a first receiving user, interference results of a second receiving user and a third … … nth receiving user are sequentially detected according to the delay line length of each receiving user, each receiving user records a code value according to response results of the third detector and the fourth detector, performs pairing with the control user, discards different data, and retains the same data to obtain a screening key; judging whether the error rate exceeds a set threshold value through corresponding error rate calculation, if the error rate does not exceed the set threshold value, controlling the users and each receiving user to perform a data post-processing process, including data coordination and confidentiality enhancement, finally obtaining the same security key, and completing a quantum key distribution process of the controlling users and each receiving user; if the error rate exceeds the set threshold, the communication is terminated and restarted.
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