CN208337595U - A kind of quantum key distribution system - Google Patents
A kind of quantum key distribution system Download PDFInfo
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- CN208337595U CN208337595U CN201821164827.6U CN201821164827U CN208337595U CN 208337595 U CN208337595 U CN 208337595U CN 201821164827 U CN201821164827 U CN 201821164827U CN 208337595 U CN208337595 U CN 208337595U
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Abstract
The utility model discloses a kind of quantum key distribution systems, in transmitting terminal, generate light pulse, and polarization and phase combining modulation can be carried out to the light pulse, in receiving end, phase decoding successively is carried out to the light pulse and polarization decodes, after completing polarization decoding, after the fiber channel is supplemented to the disturbance for combining the modulated light pulse, finally the polarization state of the light pulse is detected, in the transmitting terminal, light pulse include | P >, | N >, | R >, | L > } these four polarization states；In the receiving end, each polarization state is detected respectively；Wherein, | P > and | N > be X basic vector eigenstate；| R > and | L > be Y basic vector eigenstate.It realizes to the multiple freedom degrees of single photon while encoding, and system structure is simple.
Description
Technical field
The utility model relates to Quantum Secure Communication fields, more specifically, being related to a kind of quantum key distribution system
System.
Background technique
Quantum key distribution (Quantum Key Distribution, QKD) technology can generate between communicating pair
The key of completely the same unconditional security thus receives significant attention.Since BB84 scheme in 1984 proposes, various reasons
It becomes better and approaching perfection day by day by scheme, technology realization graduallys mature and moves towards practical application.Quantum key distribution (Quantum Key
Distribution, QKD) with the fundamental difference of classic key system it is that it uses single photon or entangled photon pairs as close
The carrier of key, by quantum-mechanical three big basic principles, (Heisenberg uncertainty principle, measurement are collapsed, and theoretical, quantum is unclonable
Law) ensure that can not the eavesdropping of the process, can not the property decoded, to provide a kind of safer key code system.
However in quantum key distribution, the carrier of key is single photon, and under remote transmission conditions, huge channel declines
Subtract and limits final secret-key rate.Many theoretical schemes have been proposed at code rate for how to improve quantum key distribution.Its
In a scheme being concerned be single photon mostly than trick, i.e., using the multiple freedom degrees of single photon simultaneously encoded, make
One photon carries the information of multiple bits, and then effectively improves channel capacity and final security key into code rate.
How a kind of structure simple quantum key distribution system is provided, and realization carries out the multiple freedom degrees of single photon simultaneously
Coding, is a Quantum Secure Communication field problem urgently to be resolved.
Utility model content
To solve the above-mentioned problems, technical solutions of the utility model provide a kind of quantum key distribution system, Ke Yishi
Existing quantum key distribution system encodes the multiple freedom degrees of single photon simultaneously, and system structure is simple.
To achieve the goals above, the utility model provides the following technical solutions:
A kind of quantum key distribution system, the quantum key distribution system include:
Transmitting terminal, the transmitting terminal carry out polarization to the light pulse and phase combining are modulated for generating light pulse；
Receiving end, the receiving end are connect by fiber channel with the transmitting terminal, and the receiving end is used for successively to institute
It states light pulse and carries out phase decoding and polarization decoding, after completion polarization decoding, compensate the fiber channel to combined modulation
The disturbance of the light pulse afterwards, finally detects the polarization state of the light pulse；
In the transmitting terminal, light pulse include | P >, | N >, | R >, | L > } these four polarization states；
In the receiving end, each polarization state is detected respectively；
Wherein, | P > with | N > it is the eigenstate of X basic vector；| R > with | L > it is the eigenstate of Y basic vector.
Preferably, in above-mentioned quantum key distribution system, the transmitting terminal and the receiving end pass through random number
Control realizes non-equilibrium basic vector scheme to use non-equilibrium BB84 agreement.
Preferably, in above-mentioned quantum key distribution system, the transmitting terminal includes:
Laser, the laser is light source, for generating the light pulse；
Polarization encoder module, the polarization encoder module is for carrying out polarization volume to the light pulse of the laser emitting
Code, in the light pulse | R >, | L >, | P > and | a kind of carry out polarization encoder is randomly choosed in N > tetra- kind polarization state；
Phase code module, the phase code module are used to carry out phase code to the light pulse after polarization encoder,
A phase difference is selected to carry out phase code in { 0, pi/2, π, 3 pi/2s } at random；
Adjustable optical attenuator, the adjustable optical attenuator is for decaying to the light pulse that the phase code module is emitted
Single photon magnitude.
Preferably, in above-mentioned quantum key distribution system, the polarization state of the light pulse of the laser emitting is | P >；
The polarization encoder module includes Sagnac interference ring, and the Sagnac interference ring is used for the laser
The polarization converted of the light pulse of outgoing be | P >, | N >, | R >, | L > } these four polarization states.
Preferably, in above-mentioned quantum key distribution system, the polarization encoder module include: the first polarization beam apparatus,
First phase modulator and the first random counting apparatus；
First polarization beam apparatus has first port, second port, third port and the 4th port；Described first
Polarization beam apparatus obtains the light pulse of the laser emitting by its first port, the light pulse is divided into two-way, all the way
It is emitted by its third port, its incident the 4th port, another way pass through its 4th end after the first phase modulator
Mouth outgoing, its incident third port after the first phase modulator, the first phase modulator is to incident two-way
Light pulse carries out phase-modulation, so that generating phase difference between the two-way light pulse；The two-way light pulse returns to described first partially
Vibration beam splitter converges, and the light pulse after its second port forms polarization encoder is sent to the phase code module；
Wherein, the described first random counting apparatus is used to carry out random number to the phase change amount of the first phase modulator
Control.
Preferably, in above-mentioned quantum key distribution system, the phase code module includes: the first beam splitter, first
Faraday rotation mirror, the second faraday rotation mirror, second phase modulator and the second random counting apparatus；
First beam splitter has first port, second port, third port and the 4th port；First beam splitting
Device obtains light pulse after polarization encoder by its first port, and the light pulse is divided into two-way, all the way by its
The outgoing of three ports, incident first faraday rotation mirror, passes through described first farad after the second phase modulator
Its third port of backtracking after revolving mirror reflection, another way is emitted by its 4th port, by second faraday
Its 4th port of backtracking after revolving mirror reflection, the light pulse after phase code are sent to described adjustable by its second port
Optical attenuator；
Wherein, the described second random counting apparatus is used to carry out random number to the phase change amount of the second phase modulator
Control.
Preferably, in above-mentioned quantum key distribution system, the receiving end includes:
Phase decoding module, the phase decoding module are used to carry out phase to the light pulse after combined modulation
Decoding；
Decoder module is polarized, the light pulse that the polarization decoder module is used to be emitted the phase decoding module carries out phase
Position decoding, is also used to compensate the fiber channel for the disturbance of light pulse；
Detector module, the detector module are used for each polarization of the light pulse to the polarization decoder module outgoing
State is detected respectively.
Preferably, in above-mentioned quantum key distribution system, the phase decoding module includes: circulator, delayer,
Three random counting apparatus, the second beam splitter, third phase modulator, third faraday rotation mirror and the 4th faraday rotation mirror；
The circulator has first port, second port and third port；The circulator passes through its first port
Obtain the light pulse of the fiber channel outgoing；
Second beam splitter has first port, second port, third port and the 4th port；Second beam splitting
Device obtains the light pulse of the second port outgoing of the circulator by its first port, and the light pulse is divided into two-way, and one
Road is emitted by its third port, and the incident third faraday rotation mirror, passes through institute after the third phase modulator
State backtracking its third port after the reflection of third faraday rotation mirror, another way is by the outgoing of its 4th port by described the
After its 4th port of backtracking after the reflection of four faraday rotation mirrors, third port and the 4th port obtain reflection simultaneously
Light pulse, the light pulse after reflection go out from its first port and second port respectively after the second beam splitter internal interference
It penetrates, the light pulses of second port outgoing give the polarization decoder module, and the light pulses of first port outgoing are given
After the second port of the circulator, it is sent to the delayer by the third port of the circulator, passes through the delay
Device is sent to the polarization decoder module；
Wherein, the random counting apparatus of the third is used to carry out random number to the phase change amount of the third phase modulator
Control.
Preferably, in above-mentioned quantum key distribution system, the polarization decoder module includes: third beam splitter, first
Polarization Controller, the second Polarization Controller, the second polarization beam apparatus and third polarization beam apparatus；
The third beam splitter has first port, second port, third port and the 4th port；The third beam splitting
Device obtains the light pulse of the second port outgoing of the second beam splitter by its first port, by prolonging described in the acquisition of its second port
When device outgoing light pulse be divided into two-way after the light pulse that the third beam splitter will acquire carries out polarization decoding, pass through all the way
The outgoing of its third port, by incident second polarization beam apparatus of first Polarization Controller, another way by its 4th
Port outgoing, by the incident third polarization beam apparatus of second Polarization Controller；
Incident light pulse is divided into two-way and is sent to the detector module by second polarization beam apparatus；
Incident light pulse is divided into two-way and is sent to the detector module by the third polarization beam apparatus；
Wherein, first Polarization Controller and second Polarization Controller for compensate the fiber channel for
The disturbance of light pulse.
Preferably, in above-mentioned quantum key distribution system, the detector module includes four single-photon detectors,
In two single-photon detectors be used to separately detect the two-way light pulse of the second polarization beam apparatus outgoing, other two
The single-photon detector is used to separately detect the two-way light pulse of the third polarization beam apparatus outgoing.
As can be seen from the above description, the quantum key distribution system that technical solutions of the utility model provide, it is raw in transmitting terminal
At light pulse, and polarization and phase combining modulation can be carried out to the light pulse, in receiving end, successively to the light pulse
Phase decoding and polarization decoding are carried out, after completing polarization decoding, it is modulated described to combining to supplement the fiber channel
After the disturbance of light pulse, finally the polarization state of the light pulse is detected, in the transmitting terminal, light pulse include | P
>, | N >, | R >, | L > } these four polarization states；In the receiving end, each polarization state is detected respectively；Wherein, | P > with | N
> be X basic vector eigenstate；| R > with | L > it is the eigenstate of Y basic vector.It realizes to the multiple freedom degrees of single photon while compiling
Code, and system structure is simple.
Detailed description of the invention
In order to illustrate the embodiment of the utility model or the technical proposal in the existing technology more clearly, below will be to embodiment
Or attached drawing needed to be used in the description of the prior art is briefly described, it should be apparent that, the accompanying drawings in the following description is only
It is the embodiments of the present invention, for those of ordinary skill in the art, without creative efforts, also
Other attached drawings can be obtained according to the attached drawing of offer.
Fig. 1 is a kind of structural schematic diagram of quantum key distribution system provided by the embodiment of the utility model；
Fig. 2 is a kind of process signal of communication means of quantum key distribution system provided by the embodiment of the utility model
Figure；
Fig. 3 is the flow diagram of a kind of polarization provided by the embodiment of the utility model and phase combining modulator approach；
Fig. 4 is a kind of flow diagram of coding/decoding method provided by the embodiment of the utility model.
Specific embodiment
The following will be combined with the drawings in the embodiments of the present invention, carries out the technical scheme in the embodiment of the utility model
Clearly and completely describe, it is clear that the described embodiments are only a part of the embodiments of the utility model, rather than whole
Embodiment.Based on the embodiments of the present invention, those of ordinary skill in the art are without making creative work
Every other embodiment obtained, fall within the protection scope of the utility model.
The multiple freedom degrees of single photon are encoded simultaneously in order to enable quantum key distribution system is realized:
First way is to carry out active polarization modulation after generating photon, in conjunction with BB84 agreement and DPS agreement, by single light
The key generation efficiency of son is promoted to 7/6, single in the agreement such as a kind of highly effective quantum communication protocol that Wang Jindong et al. is proposed
First one of 4 kinds of polarizations such as any 0 °, 90 °, 45 °, -45 ° of selection are encoded a photon, are separated into three pulses and are prolonged
When, selected phase difference is that 0 or π carries out differential phase coding between two adjacent pulses.In receiving end, then first carry out inclined
Vibration decoding, polarization is decoded per phase decoding is carried out again all the way, and interferometer one needed for phase decoding shares 4 at this time.
At this stage, in free space optical path, active polarization modulation is using rotating wave plate or utilizes electro-optical modulation crystal
It realizes.The principle that active polarization modulation is realized by rotating wave plate is to rotate the optical axis of wave plate by electric rotary table, changes wave
Piece angle realizes that by photon polarisation transformation, essence is to realize that rate is very low, is typically only capable to reach kHz by machinery rotation
Magnitude, far from meet current high speed quantum communications easily GHz working frequency the needs of.And master is realized by electro-optical modulation crystal
The principle of dynamic Polarization Modulation is to change the relative index of refraction of o light and e light in crystal by adding voltage signal at crystal both ends,
And then change the polarization state of output laser, although modulation rate is higher in this way, usually MHz magnitude, is far higher by rotation wave plate
Mode can be used in low speed quantum communications, but electro-optic crystal required voltage signal is usually several hundred volts, and
The fast modulation technical difficulty of high-voltage signal is big, therefore not applicable in high speed quantum communications domain variability.In addition, receiving end also uses
Multiple interferometers, increase system complexity.
The second way is improved in above-mentioned first way, and polarization dimension coding makes with phase dimension coding
With BB84 agreement, 4 kinds of polarization quantum states required for polarization encoder are generated respectively using 4 lasers, then pass through polarization beam splitting
Device and polarization-independent beam splitting device carry out conjunction beam.Photon after conjunction beam enters a unbalanced Mech-Zehnder interferometer and is divided into
The front and back two-beam pulse being staggered on time carries out phase code.In decoding end, photon is introduced into a unequal arm Mach-
Zehnder interferometer (Mach-Zehnder interferometer) carries out phase decoding, then carries out polarization solution by beam splitter and polarization beam apparatus
Code, as Zhao cares for the Technique on Quantum Communication scheme that white et al. proposes.
In the second way, the photon of different polarization close enter back into after beam unbalanced Mech-Zehnder interferometer into
Row phase code.Therefore the program is only suitable only for free space optical road, is difficult to realize in fibre system.In optic fibre light path,
In order to improve interference contrast, unbalanced Mech-Zehnder interferometer is constructed usually using polarization maintaining optical fibre.And polarization maintaining optical fibre without
Method is transmitted 4 kinds of polarization states in BB84 agreement and is remained unchanged.
The third mode is the differential phase and polarization encoder possible for any signal dissemination system of efficient stable, combines difference
Divide phase code and polarization state to encode, by introducing faraday mirror structure, and improves conventional system architecture, realize system effectiveness
Higher, stability is more preferable.Photon first carries out active polarization modulation in which, enters back into the interferometer being made of faraday's rotating mirror
In be divided into three beams light pulse carry out differential phase coding.In decoding end, polarization decoding is carried out first and carries out phase decoding again, is caused
Unequal arm interferometer needed for needing multiple phase decodings.And polarization decoding is first using active basic vector selection method to polarization dimension
It is decoded, then ingehious design interferes path, so that phase decoding probability reaches 100% in differential phase agreement.The agreement list
The key generation efficiency of a photon is up to 3/2, is current highest level.But which, in coding side, photon is led
Dynamic Polarization Modulation, usual rate is relatively low (being lower than 1MHz), far from meeting the needs of high speed quantum communications；In decoding end, need
Active basic vector selection is carried out, is modulated usually using rotating wave plate or electro-optic crystal, rate is relatively low (being lower than 1MHz),
Also it is far from satisfying the demand of high speed quantum communications.
To solve the above-mentioned problems, the utility model embodiment provides a kind of quantum key distribution system and its communication party
Method, the quantum key distribution system are the high speed quantum key distribution system of polarization phase combined modulation under non-equilibrium basic vector.It should
When quantum key distribution system carries out polarization encoder, by using a kind of two-port Sagnac interference ring (Sa Ge of ingehious design
Nanogram interference ring) scheme, Polarization Modulation is realized using High speed phase modulators, is solved active polarization modulation rate and is not suitable for slowly
The problem of high speed quantum communications；When carrying out phase code, using the Faraday-Michelson interferometer that compensates automatically of polarization
(faraday-Michelson's interferometer) carries out phase-modulation, avoids inclined using unbalanced Mech-Zehnder interferometer and 4 kinds
The problem of polarization state is not adapted to；When being decoded, using Faraday-Michelson interferometer, phase dimension decoding is first carried out, then
Polarization dimension decoding is carried out, system complexity is reduced, reduces system resources consumption.It is right and in the quantum key distribution system
In polarization encoder and phase code, it is all made of biasing basic vector BB84 agreement, the available coding for leveling off to 2bit/ photon is imitated
Rate.
To keep the above objects, features, and advantages of the utility model more obvious and easy to understand, with reference to the accompanying drawing and have
Body embodiment is described in further detail the utility model.
With reference to Fig. 1, Fig. 1 is a kind of structural schematic diagram of quantum key distribution system provided by the embodiment of the utility model,
Quantum key distribution system shown in Fig. 1 includes: transmitting terminal 11, and the transmitting terminal 11 is for generating light pulse, to the light pulse
Carry out polarization and phase combining modulation；Receiving end 12, the receiving end 12 are connected by fiber channel 13 and the transmitting terminal 11
It connecing, the receiving end 12 is for successively carrying out phase decoding and polarization decoding to the light pulse, after completing polarization decoding,
The disturbance for compensating 13 pairs of the fiber channel modulated light pulses of joint, finally carries out the polarization state of the light pulse
Detection.
In quantum key distribution system described in the utility model embodiment, in the transmitting terminal 11, light pulse include | P
>, | N >, | R >, | L > } these four polarization states；In the receiving end 12, each polarization state is detected respectively.Wherein, | P > with
| N > be X basic vector eigenstate；| R > with | L > it is the eigenstate of Y basic vector.| H > with | V > it is the eigenstate of Z basic vector.
Optionally, the transmitting terminal 11 and the receiving end 12 are controlled by random number, to use non-equilibrium BB84
Agreement realizes non-equilibrium basic vector scheme.
As shown in Figure 1, the transmitting terminal 11 includes: laser LD, the laser LD is light source, for generating the light
Pulse；Polarization encoder module 111, the light pulse that the polarization encoder module 111 is used to be emitted the laser LD carry out inclined
Vibration coding, in the light pulse | R >, | L >, | P > and | a kind of carry out polarization encoder is randomly choosed in N > tetra- kind polarization state；
Phase code module 112, the phase code module 112 are used to carry out phase code to the light pulse after polarization encoder, 0,
Pi/2, π, 3 pi/2s } in select phase difference to carry out phase code at random；Adjustable optical attenuator VOA, the adjustable optical attenuator VOA
Light pulse for the phase code module to be emitted decays to single photon magnitude.
The polarization state of the light pulse of the laser emitting is | P >；The polarization encoder module 111 is dry including Sagnac
Relate to ring, the Sagnac interference ring be used for be by the polarization converted of the light pulse of the laser emitting | P >, | N >, | R
>, | L > } these four polarization states.
As shown in Figure 1, the polarization encoder module 111 includes: the first polarization beam apparatus PBS1, first phase modulator
The random counting apparatus K1 of PM1 and first.It is dry that first polarization beam apparatus PBS1 and first phase modulator PM1 constitutes a Sagnac
Ring structure is related to, random number control is carried out to first phase modulator PM1 by the first random counting apparatus K1.
The first polarization beam apparatus PBS1 has first port a11, second port a12, third port a13 and the 4th
Port a14；The first polarization beam apparatus PBS1 obtains the light pulse of the laser LD outgoing by its first port a11,
The light pulse is divided into two-way, is emitted by its third port a13, is entered after the first phase modulator PM1 all the way
Penetrate its 4th port a14, another way is emitted by its 4th port a14, after the first phase modulator PM1 it is incident its
Third port a13, the first phase modulator PM1 carry out phase-modulation to incident two-way light pulse, so that the two-way light
Phase difference is generated between pulse；The two-way light pulse returns to the first polarization beam apparatus PBS1 and converges, by its second port
A12 is sent to the phase code module 112.
Wherein, the described first random counting apparatus K1 is used to carry out the phase change amount of the first phase modulator PM1
Random number control so that polarization encoder module 111 can be in the light pulse | R >, | L >, | P > and | N > tetra- kind polarization
A kind of carry out polarization encoder is randomly choosed in state.
It should be pointed out that can be added between the laser LD and the port a11 of the first polarization beam apparatus PBS1
One circulator or optoisolator pass through the light intensity that the port a11 inputs the laser LD to reduce polarization encoder later, make
The working condition of the laser LD is more stable, also protects the laser LD, improves device lifetime.In commodity laser LD
Usual integrated optical isolator, at this time without additionally increasing this safeguard measure；If the non-Integrated Light of laser LD used every
It is preferred embodiment using this safeguard measure from device.
As shown in Figure 1, the phase code module 112 include: the first beam splitter BS1, the first faraday rotation mirror FM1,
The random counting apparatus K2 of second faraday rotation mirror FM2, second phase modulator PM2 and second.
The first beam splitter BS1 has first port a21, second port a22, third port a23 and the 4th port
a24；The first beam splitter BS1 obtains the light pulse after polarization encoder by its first port a21, by the light pulse
It is divided into two-way, is emitted all the way by its third port a23, incident first method after the second phase modulator PM2
Revolving mirror FM1 is drawn, backtracking its third port a23 after being reflected by the first faraday rotation mirror FM1, another way warp
Its 4th port a24 outgoing is crossed, its 4th port a24 of backtracking after the second faraday rotation mirror FM2 reflection, phase
Light pulse after the coding of position is sent to the adjustable optical attenuator VOA by its second port a22；
Wherein, the described second random counting apparatus K2 is used to carry out the phase change amount of the second phase modulator random
Number control, so that phase code module 112 can select a phase difference to carry out phase volume at random in { 0, pi/2, π, 3 pi/2s }
Code.
As shown in Figure 1, the receiving end 12 includes: phase decoding module 121, the phase decoding module 121 for pair
The light pulse after combined modulation carries out phase decoding；Decoder module 122 is polarized, the polarization decoder module 122 is used
Carry out phase decoding in the light pulse that is emitted to the phase decoding module 121, be also used to compensate the fiber channel 13 for
The disturbance of light pulse；Detector module 123, the detector module 123 are used for the light being emitted to the polarization decoder module 122
Each polarization state of pulse is detected respectively.In the utility model embodiment, 4 polarization states that when polarization encoder uses and partially
4 polarization state differences using when vibration decoding, are compensated by Polarization Controller, and each polarization state is separately dispensed into pair
The single-photon detector answered, is more applicable for fibre system, is detected respectively for each polarization state, it is easier to detect, increase
System stability is added, has reduced costs.
As shown in Figure 1, the phase decoding module 121 includes: circulator C1, delayer DL1, the random counting apparatus of third
K3, the second beam splitter BS2, third phase modulator PM3, third faraday rotation mirror FM3 and the 4th faraday rotation mirror
FM4。
The circulator C1 has first port a31, second port a32 and third port a33；The circulator C1 is logical
It crosses its first port a31 and obtains the light pulse that the fiber channel 13 is emitted.
The second beam splitter BS2 has first port a41, second port a42, third port a43 and the 4th port
a44.The second beam splitter BS2 obtains the light arteries and veins of the second port a32 outgoing of the circulator C1 by its first port a41
Punching, is divided into two-way for the light pulse, is emitted all the way by its third port a43, after the third phase modulator PM3
The incident third faraday rotation mirror FM3, its third end of backtracking after being reflected by the third faraday rotation mirror FM3
Mouthful a43, another way by its 4th port a44 be emitted after the 4th faraday rotation mirror FM4 reflection backtracking its
4th port a44, third port a43 and the 4th port a44 obtain the light pulse after reflection, the light pulse after reflection simultaneously
After the second beam splitter BS2 internal interference, it is emitted respectively from its first port a41 and second port a42, second port
The light pulses of a42 outgoing give the polarization decoder module 122, and the light pulses of first port a41 outgoing are to described
After the second port a32 of circulator C1, it is sent to the delayer DL1 by the third port a33 of the circulator C1, is passed through
The delayer DL1 is sent to the polarization decoder module 122.
Wherein, the random counting apparatus K3 of the third is used to carry out the phase change amount of the third phase modulator PM3
Random number control measures basic vector selection to control phase decoding module 121 under random number control, randomly chooses phase
Difference.
As shown in Figure 1, the polarization decoder module 122 includes: third beam splitter BS3, the first Polarization Controller PC1,
Two Polarization Controller PC2, the second polarization beam apparatus PBS2 and third polarization beam apparatus PBS3.
The third beam splitter BS3 has first port a51, second port a52, third port a53 and the 4th port
a54；The third beam splitter BS3 obtains the light of the second port a42 outgoing of the second beam splitter BS2 by its first port a51
Pulse obtains the light pulse of the delayer DL1 outgoing by its second port a52, what the third beam splitter BS3 will acquire
After light pulse carries out polarization decoding, it is divided into two-way, is emitted all the way by its third port a53, by first Polarization Control
Device PC1, the incident second polarization beam apparatus PBS2, another way are emitted by its 4th port a54, by second polarization
The incident third polarization beam apparatus PBS3 of controller PC2.Wherein, the first Polarization Controller PC1 and it is described second partially
Vibration controller PC2 is carried out for compensating the fiber channel 13 for the disturbance of light pulse, and by four polarization states of light pulse
Separation, in order to be detected respectively to four polarization states.
Incident light pulse is divided into two-way and is sent to the detector module 123 by the second polarization beam apparatus PBS2.
Incident light pulse is divided into two-way and is sent to the detector module 123 by the third polarization beam apparatus PBS3.
As shown in Figure 1, the detector module 123 includes four single-photon detectors D1, D2, D3 and D4, wherein two
A single-photon detector (D1 and D2) is used to separately detect the two-way light pulse of the second polarization beam apparatus PBS2 outgoing,
Other two described single-photon detector (D3 and D4) is used to separately detect the two-way of the third polarization beam apparatus PBS3 outgoing
Light pulse.Single-photon detector D1-D4 respectively corresponds a polarization state for detecting the light pulse.
In quantum key distribution system shown in Fig. 1, transmitting terminal 11 has laser LD, generates light pulse by laser LD
(photon i.e. described below), output photon polarization state is after impulse modulation is passed through in light pulse | P >.Single photon is in transmitting terminal
11, which first pass through polarization encoder module 111 (Sagnac interference ring), carries out polarization encoder, in cataloged procedure | R >, | L >, | P > and
| a kind of carry out polarization encoder is randomly choosed in N > tetra- kind polarization state.
After polarization encoder, photon carries 1bit polarization information, and then photon passes through phase code module 112
(Faraday-Michelson interferometer) carries out phase code, and a phase difference is selected to carry out at random in { 0, pi/2, π, 3 pi/2s }
Phase code, photon carries 1bit polarization information and 1bit phase information, gross information content 2bit simultaneously after phase code.
Photon after polarization encoder and phase code is transferred to receiving end 12 by fiber channel 13.Then, light
Son is decoded by phase decoding module 121 (Faraday-Michelson interferometer).Using polarization decoder module 122
Carry out polarization decoding.There are two output ports for the tool of phase decoding module 121.If polarized respectively to two output ports
Decoding, needs two polarization decoder modules, is needed altogether using 8 single-photon detectors, system device number is more, resource consumption
It is very big.In the utility model embodiment, phase decoding module 121 be arranged a delayer DL1, to wherein all the way optical signal into
After line delay, then two ways of optical signals is inputted into same polarization decoder module 122 and carries out polarization decoding, reduces detector module 123
The number of middle single-photon detector simplifies system structure and cost.
After polarization decoding, according to the detection result of detector module 123, phase bits information and partially can be obtained simultaneously
Shake bit information.In this way, dibit information can be obtained simultaneously as long as transmitting a photon, improves channel capacity and quantum is logical
Believe key generating rate (code rate).
In the prior art, using the BB84 agreement of standard, selection is different when preparing and measuring different quantum states
The probability of basic vector be it is the same, need to carry out basic vector comparison, that is, abandon general measure basic vector selection mistake detection count, therefore
Waste many resources.
In the utility model embodiment, non-equilibrium BB84 agreement is used, it is possible to reduce the spy abandoned in basic vector comparison process
It surveys device detection to count, improves quantum key generating rate.The realization of non-equilibrium BB84 agreement is used in the utility model embodiment
Principle is: polarization encoder module 111, phase code module 112 and phase decoding module 121 be respectively set one by with
The phase-modulator of machine number control is being prepared and is being surveyed so that quantum key distribution system can use non-equilibrium BB84 agreement
The probability of different basic vectors is selected to be different when measuring different quantum states, therefore quantum provided by the embodiment of the utility model is close
Key dissemination system is the high speed quantum key distribution system of the polarization phase combined modulation under non-equilibrium basic vector.
Specifically, when carrying out polarization encoder, if it is standard BB84 agreement is used, then light pulse is modulated to | R >,
| L >, | P > and | N > these four shape probability of states be it is the same, the outgoing probability of each state is 25%, i.e., existing skill
Art is balance basic vector scheme.The utility model embodiment can basis when carrying out polarization encoder using non-equilibrium BB84 agreement
The outgoing probability of each state is arranged in demand, such as selects | P > or | N > probability (select the general of X basic vector in other words for 45%
Rate is 90% because | P > and | N > is the eigenstate of X basic vector), select | R > and | L > probability be 5% (selection Y basic vector in other words
Probability be 10%, | R > and | L > is the eigenstate of Y basic vector), probability can be arranged as desired, which kind of is specifically chosen each time
State is controlled by random number, i.e., the utility model embodiment is non-equilibrium basic vector scheme.For example, can be set random number be 00 when
Outgoing state is | R >, the state that is emitted when random number is 01 is | L >, the state that is emitted when random number is 10 is | P >, random number 11
When outgoing state be | N >, setting random number 00 occur probability be 5%, random number 01 occur probability be 5%, the two with
The corresponding state of machine number is only Y basic vector eigenstate, and the probability added up is 10%, and the probability that random number 10 occurs is 45%,
And the probability that random number 11 occurs is 45%, the corresponding state of the two random numbers is X basic vector eigenstate, and the probability added up is
90%.
It should be noted that the selection of each polarization state can be set according to demand, also in the utility model embodiment
It is to say, the probability of random number is not limited to mode described in the utility model embodiment.
When carrying out polarization decoding, polarization decoding selects general with polarization encoder in the non-equilibrium basic vector scheme of the utility model
Rate can be identical or different.When the two select probability is identical, at code rate highest.Above-mentioned 90% and 10% is selected when such as encoding
Probability, when decoding can arbitrarily select two probability for 85% and 15%, select two probability for above-mentioned 90% He upon decoding
When 10%, system performance is best, at code rate highest.
When phase code, random number control second phase modulator PM2 selects different phase differences.It uses in the prior art
It is the same for balancing the probability of basic vector Scheme Choice { 0, π/4, pi/2,3 π/4 }；Non-equilibrium base is used in the utility model embodiment
Probability is different in arrow scheme, is 45% (selecting the probability of X basic vector in other words is 90%) as selected the probability of 0 and pi/2,
The probability of π/4 and 3 π/4 is 5% (selecting the probability of Y basic vector in other words is 10%).Select probability setting can be set as desired
It sets.
In the utility model embodiment, in phase code, light pulse phase is changed by second phase modulator PM2
Position, realization principle is: phase-modulator changes the phase of light pulse, the pulse of different pulse voltages under the control of pulse voltage
Amplitude corresponds to different phase change amounts, if light pulse, when by phase-modulator, the voltage of phase-modulator is in height
Pressure condition (different amplitudes correspond to different phase change amounts), the phase of light pulse can change, if phase-modulator
Voltage is in low-pressure state (could also say that and voltage is not added), and the phase of light pulse does not change.The utility model embodiment
In, the corresponding phase difference of the quantum state for needing to select is { 0, pi/2, π, 3 pi/2s }, is realized and is adjusted by second phase modulator PM2
System.
A kind of mode is the longer control pulse voltage of Duration Ratio that adds high pressure to second phase modulator PM2.It is this
In the case of, light pulse needs to pass twice through in outgoing and reflection process the second phase modulator, since high pressure continues
Time is longer so that this twice during second phase modulator be in high pressure conditions, light pulse phase changes two in total
It is secondary, as long as therefore second phase modulator phase difference be set as the corresponding phase difference of the quantum state for needing to select for 0, pi/2,
π, 3 pi/2s } half, i.e., setting second phase modulator PM2 phase change amount be { 0, π/4, pi/2,3 π/4 }.It is another
Kind of embodiment is the duration shorter pulse voltage that adds high pressure to second phase modulator PM2, in this way when light pulse the
When once passing through second phase modulator PM2, second phase modulator PM2 is in high pressure conditions, leads to for second after reflection
When crossing second phase modulator PM2, second phase modulator PM2 is in low-pressure state, therefore can only change a phase, therefore the
It is { 0, pi/2, π, 3 pi/2s } that the phase difference of two phase modulator PM2 setting, which needs phase difference corresponding with the quantum state for needing to select,
It is identical, it needs to be arranged second phase modulator PM2 phase difference with higher in view of which, therefore needs higher control electricity
Pressure, causes power consumption larger, and cost of implementation is higher, is not easy to realize, therefore it is preferred that uses first way.
When phase decoding, random number controls third phase modulator PM3 and selects different measurement basic vectors.Balance basic vector side
In case, select 0 with the probability of π/4 to be as；It is different in non-equilibrium basic vector scheme, is 90% as selected 0 probability,
Selecting the probability of π/4 is 10%.
In quantum key distribution system described in the utility model embodiment, carry out polarization encoder when, usually select 0 ° (i.e. | H
>), 90 ° (i.e. | V >), 45 ° (i.e. | P >) and -45 ° (i.e. | N >) these four polarization states are encoded.In fibre system, if
Need actively to modulate that these four polarization states are relatively difficult, and modulation rate is also relatively low, it is difficult to be suitable for high speed quantum communications field
It closes.In the utility model embodiment, it is contemplated that two eigenstates of Y basic vectorWithIt selects X basic vector and Y basic vector as coding basic vector, BB84 protocol code can also be completed, with selection
X basic vector and Z basic vector have same safety.Wherein, X basic vector, Y basic vector and Z basic vector are the definition in quantum mechanics, often
The matrix of corresponding 2 rows 2 column of a basic vector, according to linear algebra knowledge, the corresponding two special states of each basic vector, referred to as originally
Levy state.
Wherein,
During polarization encoder, ring structure is interfered by the Sagnac of ingehious design, (i.e. using High speed phase modulators
PM1 it) realizes Polarization Modulation, selects polarization X basic vector and the corresponding eigenstate of Y basic vector as polarization encoder state.Laser LD goes out
High-speed optical pulse is penetrated, polarizing is+45 °, i.e.,Incident light pulse is divided into transmission road and anti-by PBS1
Rays two-beam pulse.Two-beam pulse polarization is different, respectively 0 ° polarization (| H >) and 90 ° of polarizations (| V >), then pass through PM1 tune
System | H > and | V > between relative phase difference.Assuming that the phase change amount of PM1 is θ1, then the polarization state exported isWherein, the phase change amount of PM1 is θ1Controlled by random number, { 0, π/4, pi/2,3 π/4 } it
Between randomly choose.It is such as selected as 0, then output polarization state is | P >；π/4 are such as selected as, then output polarization state is | R >；Such as it is selected as
Pi/2, then output polarization state be | N >；3 π/4 are such as selected as, then output polarization state is | L >.
Due in polarization encoder module 111 there is Sagnac to interfere ring structure, so that | H > with | V > corresponding light pulse warp
The path crossed is consistent, contrary, compensates for influence of the fiber channel change for polarization state automatically.
After completing polarization encoder, light pulse is input to phase code module 112 and carries out phase code, there are four types of light may have
Polarization state (| R >, | L >, | P > and | N > one of).In order to improve interference contrast, the prior art generallys use Mach-
Zehnder interferometer is built using polarization maintaining optical fibre, can not be adapted to 4 kinds of polarizations.Faraday- is used in the utility model embodiment
(in phase code module 112, BS1, FM1, FM2 and PM2 constitute a unequal arm Faraday- to Michelson interferometer
Michelson interferometer) solve the problems, such as this.The light pulse of input first passes through BS1 and is divided into two-beam pulse, respectively enters interference
The two-arm of instrument, then reflected respectively by FM1 and FM2, it is output to adjustable optical attenuator VOA.
In phase code module 112, two arm lengths of Faraday-Michelson interferometer are inconsistent, therefore return
Light pulse arrival time is different, and what is exported from BS1 is two adjacent light pulses of front and back, and a light pulse is preceding | t0>, it is another
A light pulse is rear | t1>, delay can rationally be adjusted by controlling two-arm length difference between two light pulses.Interfering
PM2 is arranged in one arm of instrument, and by the way that PM2 is arranged, phase change amount is θ2, output phase statePM2
Phase change amount be θ2It is controlled by random number, is randomly choosed between { 0, π/4, pi/2,3 π/4 }.Such as be selected as 0, then it is defeated
Phase states are outπ/4 are such as selected as, then output phase state isIt is such as selected as pi/2,
Then output phase state is3 π/4 are such as selected as, then output phase state is
In the utility model embodiment, phase code is realized using Faraday-Michelson interferometer, it can be using single
Mode fiber is built, and different input polarization states is easily adapted；It is tied simultaneously using Faraday revolving mirror (faraday rotation mirror)
Structure, can it is birefringent in automatic compensated optical fiber channel caused by polarization variations, keep light pulse polarization state to stablize.
When phase decoding, phase decoding module 121 equally has a Faraday-Michelson interferometer (phase solution
In code module 121, BS2, FM3, FM4 and PM3 equally constitute a unequal arm Faraday-Michelson interferometer) it carries out
Phase dimension decoding.Light pulse is divided into two beams by BS2, respectively enters the two-arm of interferometer, then passes through FM3 and FM4 respectively
It reflects.PM3 is set in an arm of interferometer, one of random selection { 0, π/4 } is as decoding basic vector.Since phase is compiled
Two light pulses are exported after code, and the Faraday-Michelson interferometer in phase decoding module 121 is set in the utility model
With the Faraday-Michelson interferometer arm length difference having the same in phase code module 122, therefore previous light pulse
Reach BS2 simultaneously after interferometer galianconism with the latter light pulse after interferometer is long-armed and carries out interferometry.It is previous
Light pulse of the light pulse and the latter light pulse that light pulse is generated by interferometer galianconism Jing Guo the long-armed generation of interferometer is nothing
The garbage signal is arranged in the work of detecting module 123 by the way that the working time window of detector module 123 is arranged with signal
Make except the time, is not detected by detector module 123.
Since the interference light pulse after phase decoding may may also be from its second port from the first port a41 of BS2
A42 outgoing, it is therefore desirable to polarization decoding all be carried out to the light pulse of two ports output, such conventional design needs two are partially
The decoder module that shakes amounts to 8 single-photon detectors, and resource consumption is big and at high cost.The utility model devises time-multiplexed light
Road, design be delayed after C1, then through DL1 from the light pulse that the first port a41 of BS2 is emitted, in time with BS2
The light pulse of second port a42 outgoing form the delay of preset time, then two-way light pulse is inputted into same polarization decoding mould
Block 122 carries out polarization decoding.In this way, when the single-photon detector (D1-D4) in detector module 123 can be reached from light pulse
Between tell first port a41 or second port a42 of the light pulse from BS2, so that it is determined that the phase information of the light pulse.
Phase decoding module 121 and polarization decoder module 122 share a detector module 123.
, can be consistent with common polarization encoder QKD after the polarization conversion of PBS1, select active polarization decoding side
Formula carries out polarization decoding or passive polarization decoding process carries out polarization decoding.Active polarization decoding process, which refers to, passes through adjuster
Part active selection measurement basic vector, passive polarization decoding process, which refers to, splits the light into two-way by beam splitter, every to respectively represent all the way
Different measurement basic vectors.Passive decoding process may be implemented in the utility model embodiment, and beam splitter BS3 is used when polarizing decoding
Incident light pulse is divided into two-way, polarimetry is carried out by PBS2 and PBS3 respectively.It can also be decoded by active polarization
Mode realizes polarization decoding, polarimetry basic vector is actively selected by the methods of photoswitch or electrooptic modulator, then by inclined
The beam splitter that shakes carries out polarimetry.
The utility model embodiment uses Polarization Modulation (including polarization encoder and polarization decoding) for single photon
With phase-modulation (including phase code and phase decoding), key can be generated into rate and doubled.
Non-equilibrium BB84 agreement is all made of for Polarization Modulation and phase-modulation, to further increase security key rate.
In standard BB84 agreement, when coding with same probability among two coding basic vectors optionally first, compared by basic vector, will
The basic vector for abandoning half selects inconsistent example, therefore the encoding rate of single photon is 1/2, and code efficiency is relatively low.This is practical
In new embodiment, for polarization dimension or phase dimension, when coding, using unbalanced probability in X basic vector and Y basic vector
It is selected.The probability of selection X basic vector and Y basic vector is respectively p and 1-p when note coding, after comparing by basic vector, abandons basic vector
Inconsistent example number is selected, therefore the code efficiency of single photon is p2+(1-p)2=1+2p2-2p.If to be higher than 50%
The one of basic vector of probability selection be higher than standard BB84 agreement then the encoding rate of single photon will be greater than 1/2.If with
Level off to 100% the one of basic vector of probability selection, then single photon code efficiency will be close to 1, secret-key rate will substantially
It improves.
In the utility model embodiment, non-equilibrium basic vector selection realization principle is: in phase modulation process, selection
The probability of { 0, pi/2 } is p1, selecting the probability of { π/4,3 π/4 } is 1-p1, the probability of { 0, pi/2 } is selected during polarization encoder
For p2, selecting the probability of { π/4,3 π/4 } is 1-p2.It is corresponding, during phase decoding, select 0 probability for p1, selection π/
4 probability is 1-p1, it is p that the probability of HV basic vector (i.e. Z basic vector) is selected in polarization decoding process2, select the probability of PN basic vector for
1-p2.If (it is decoded using active polarization, it can be by control random number come control selections probability；If using passive polarization
Decoding, can be by selection BS splitting ratio come control selections probability).Work as p1=0.5 or p2=0.5 is and common QKD scheme
Unanimously；Work as p1≠ 0.5 or p2Higher traffic rate and code efficiency can be obtained when ≠ 0.5；Work as p1→ 0or 1 or p2
→ 0or 1 can be obtained to be promoted close to 100% code efficiency and traffic rate at double.If p1→ 0or 1 while p2→0or
1, it can obtain and be improved close to the code efficiency of 1 photon, 2 bits and 4 times of traffic rates.
As can be seen from the above description, in the utility model embodiment, using non-equilibrium basic vector scheme, the amount of greatly improving
Sub- communication security secret-key rate, under the conditions of same parameter, compared to the standard BB84 agreement of single dimension coding, secret-key rate is improved
About 4 times.
If realizing technical solutions of the utility model on the basis of weak coherent light source, can be combined with that state method is inveigled to mention
The safety of high system.If only simply state method is inveigled in superposition on the basis of the utility model, also belong to practical
New embodiment protection scope.
In the utility model embodiment, laser LD is semiconductor laser, under applied electronic signal control, can be emitted
Light pulse.There are four port, light pulses to be divided into two beams after a11 input, export respectively from a13 and a14 for PBS1 tool, regardless of
The light pulse polarization state of input is how, and the polarization state of light pulse of a13 and a14 output is respectively | H > and | V >, such as can be false
If a13 outgoing polarization state be | H >, a14 outgoing polarization state be | V >.
In quantum key distribution system described in the utility model embodiment, 3 phase-modulator PM1-PM3 are used altogether, respectively
Phase-modulator adjusts the phase of light pulse under the control of applied voltage signal；Three polarization beam apparatus PBS1- are used altogether
PBS3, polarization beam apparatus, which has, outputs and inputs two ports；4 faraday rotation mirror FM1-FM4 are used altogether, and light inputs farad
Can vertically be reflected after revolving mirror, while polarization state changes 90 °, such as incidence | H >, it is emitted after reflection | V >, it is incident | V
>, it is emitted after reflection | H >；Using an adjustable optical attenuator VOA, for optical pulse intensity to be decayed to single photon magnitude；Using
One circulator C1 shares 3 port a31-a33, exports when light is inputted from a31 from a32, export when inputting from a32 from a33；
Three beam splitter BS1-BS3 are used altogether, and there are four port, light to input from a port for strand-separating appts, is finally equally divided into two-way
It is exported from other two port；Using a delayer DL1, for adjusting the arrival time of light pulse；It is controlled using two polarizations
Device PC1-PC2 processed, for adjusting the polarization state of light pulse；4 single-photon detector D1-D4 are used altogether, when a light pulse is defeated
It is fashionable to generate an electric pulse output.
The workflow of quantum key distribution system described in the utility model embodiment is as follows:
Laser LD generates light pulse, and polarization state is | and P >.Light pulse input polarization coding module 111 is modulated into different
Polarization state output.Polarization encoder module 111 is designed to optical fiber Sagnac ring structure, and the light pulse inputted from the a11 of PBS1 is divided into
Two beams are exported from a13 and a14 respectively, and polarization state is respectively | H and | V >.The light pulse exported from a13 passes through again after PM1
A14 returns to PBS1, and the light pulse exported from a14 returns to PBS1 by a13 again after PM1.Passed through due to two-beam pulse
Path is the same, and direction is different, therefore will reach PBS1 simultaneously, and interference is generated in PBS1, exports after interference from a12.Output
Polarization state it is related with the phase that PM1 changes.Assuming that the phase change amount of PM1 is θ1, output polarization state beThe phase change amount of PM1 is controlled by true random number, random between { 0, π/4, pi/2,3 π/4 }
Selection.It is such as selected as 0, then output polarization state is | P >；π/4 are such as selected as, then output polarization state is | R >；It is such as selected as pi/2, then
Output polarization state is | N >；3 π/4 are such as selected as, then output polarization state is | L >.The light pulse being emitted from polarization encoder module 111
It is inputted from the a21 of BS1, is divided into two beams, exported respectively from a23 and a24.The light pulse of a23 output carries out phase tune by PM2
System, after reflecting using FM1, backtracking reaches BS1 by a23.The light pulse of a24 output is directly reflected by FM2, former
Road returns, and reaches BS1 by a24.The corresponding fiber lengths of a23 and a24 are different, and length difference is arranged according to demand.In this way, through
Two light pulses can be exported after crossing phase code module 112, a light pulse is preceding | t0>, another light pulse is rear | t1>,
For phase difference between the two there are a difference value, the difference value is related with the phase difference that PM2 is modulated.Assuming that the phase of PM2 changes
Variable is θ2, output phase stateThe phase change amount of PM2 is θ2It is controlled by random number, 0,
π/4, pi/2,3 π/4 } between randomly choose.It is such as selected as 0, then output phase state isπ/4 are such as selected as,
Then output phase state isIt is such as selected as pi/2, then output phase state isSuch as it is selected as
3 π/4, then output phase state be
After polarizing and phase combining is modulated, the quantum state in light pulse isThere is polarization information and phase information simultaneously.
An adjustable optical attenuator VOA is passed through in the light pulse exported from phase code module 112, and optical pulse intensity is decayed
To single photon magnitude.
The light pulse that fiber channel 13 exports enters phase decoding module 121 and carries out phase decoding.First from circulator C1's
A31 input enters the a41 of BS2 from a32 output.The length of its interferometer is passed through in first light pulse of phase decoding module 121
Arm exports, the incidence FM3 after PM3 from a43, backtracking is to a43 after being reflected by FM3；Second light pulse passes through it
Interferometer galianconism exports, the backtracking a44 after FM4 reflects from a44.Due to interferometer in phase decoding module 121
Arm length difference is equal with the arm length difference of interferometer in phase code module 112, and two light pulses will reach simultaneously BS2 and interfere,
It is exported respectively from the a41 of BS2 and a42 after interference.PM3 measures basic vector selection under the control of random number, randomly chooses phase
Potential difference is { 0, π/4 }.Polarization decoder module 122 is directly entered by the light pulse that a42 is exported and carries out polarization decoding, by a41
The light pulse of output is inputted from the a32 of C1, is exported from the a33 of C1, is entered polarization decoder module 122 using DL1 and is polarized
Decoding.The effect of DL1 is the preset length that is staggered the time for reaching two light pulses, to guarantee the same detector module
123 correctly can detect and differentiate the two light pulses.DL1 can be stored by the optical fiber or quantum that appropriate length is arranged
Etc. modes realize.By this time-multiplexed mode, the quantity and single-photon detecting of polarization decoder module 122 can be effectively reduced
The quantity of device is surveyed, the circuit structure of polarization decoder module 122 is simplified, reduces resource consumption, saves system cost.It needs to illustrate
It is the time window for needing rationally to be arranged detector, only interference light pulse is measured.In the utility model embodiment, partially
Vibration decoder module 122 and phase decoding module 121 share the same detector module 123.
After the completion of phase decoding, light pulse is input to polarization decoder module 122 and carries out polarization decoding.Light pulse first passes through
BS3 is divided into two light pulses and passes through a53 and a54 output respectively, and the light pulse of a53 output first passes through PC1, using PBS2, into
The light pulse of the detection of two polarization states of row, a54 output first passes through PC2, and the spy of other two polarization state is carried out using PBS3
It surveys.Detector module 123 respectively detects four polarization states of light pulse by single-photon detector D1-D4.
As can be seen from the above description, in quantum key distribution system described in the utility model embodiment, in non-equilibrium BB84
On the basis of agreement, while Polarization Modulation and phase-modulation are used, obtain the code efficiency of 1 photon, 2 bits, simultaneously will
Quantum communications rate improves four times；State when Polarization Modulation state and last polarimetry is not quite identical；By setting
Sagnac interference ring is counted, is modulated using high-speed phase and realizes high speed Polarization Modulation.
Polarization encoder is realized by phase-modulator in the utility model embodiment.A kind of conventional polarization encoding scheme passes through
Two polarization beam apparatus and a phase-modulator realize polarization encoder, are substantially Mach-Zednder interferometers.This is practical
It is realized in new embodiment using a polarization beam apparatus and a phase-modulator, is substantially Sagnac interference ring, a side
Face, technical solution described in the utility model embodiment reduce device requirement, reduce costs；On the other hand, due to Sagnac
The ideal symmetrical structure of interference ring, so that the path of light pulse experience is identical, it being capable of the environmental factors such as having automatic temp compensating
It is influenced for caused by polarization encoder, it is with good stability, while being greatly reduced processing technology requirement.And tradition is partially
In encoding scheme of shaking, need to keep the stability of interferometer, resource consumption and cost using technologies such as active temperature controls
All higher, adaptation range is smaller；It requires the brachium of interferometer two-arm essentially equal in process simultaneously, just can guarantee output
The quality of light pulse, therefore technique is required very strict.In addition, in technical solution described in the utility model embodiment, it is right
Lower in phase-modulator requirement, the voltage and phase difference of modulation only have the half of conventional polarization encoding scheme, this facilitates
It reduces system power dissipation and improves system operating frequency and stability.
Another conventional polarization encoding scheme constitutes interferometer, the output port of interferometer using single channel polarization beam apparatus
It is the same port with input port, it is therefore desirable to be separated input light and output light using circulator；And the utility model skill
In art scheme, polarization encoder is carried out using binary channels polarization beam apparatus, the input and output port of polarization encoder module 111 is inclined
The different port of vibration beam splitter, on the one hand, reduce number of devices, reduce costs, on the other hand, conventional polarization makes when encoding
Efficiency of transmission and systematic absences ratio can be reduced with circulator, and technical solutions of the utility model can possess higher efficiency of transmission
With systematic absences ratio.
Use single laser as quantum light source in technical solutions of the utility model, conventional QKD system is needed using 4
Laser is as light source, on the one hand, and technical solutions of the utility model simplify light channel structure, have saved cost, on the other hand, phase
Than in the scheme of multi-laser, technical solutions of the utility model can obtain consistent wavelength characteristic, spectral characteristic etc., and reduction is stolen
For hearer for the possibility attack method of light-source system, safety is higher.
Technical solutions of the utility model use active polarization modulation technique, dry by carrying out selection coding basic vector and Sagnac
Ring is related to, completes Polarization Modulation using High speed phase modulators, it is entirely different with traditional passive Polarization Modulation scheme, it can obtain
Higher modulation rate, available longer operating distance and more high safety secret-key rate.
The Faraday-Michelson interferometer designed in technical solutions of the utility model, interference contrast is higher, is applicable in
Range is wider, can realize in free space optical path and optic fibre light path simultaneously.Conventional solution uses Mach-Zednder
Interferometer, therefore free space optical path can only be used to build, and interfere contrast relatively low, it is not available in optic fibre light path.
In technical solutions of the utility model, use | P >, | N >, | R >, | L > } polarization state progress polarization encoder, polarization decoding
Afterwards, four polarization states are detected respectively, in conventional solution polarization decoding use | H >, | V >, | P >, | N > } tool
There were significant differences.Technical solutions of the utility model have both the advantages of optical fiber provides various High Speed Modulations and easy detection simultaneously.
In technical solutions of the utility model, using non-equilibrium BB84 agreement, relative to the technology using standard BB84 agreement
Scheme, key is higher at code rate, and theoretically, single photon code efficiency compares traditional scheme close to 2 in technical solutions of the utility model
Gao Yueyi times.
4 single-photon detectors are only needed in technical solutions of the utility model, conventional solution generally requires 8 monochromatic lights
Sub- detector.Technical solutions of the utility model simplify system light path, reduce number of devices, reduce costs, and improve steady
It is qualitative.
In technical solutions of the utility model, phase-modulation use BB84 scheme, the safety of BB84 scheme at present from
Theoretically by Strict Proof, and the safety of DPS scheme is Partial Proof, therefore compared to the implementation of DPS scheme, safety
Property is higher.
In the phase-modulation stage, technical solutions of the utility model use Faraday-Michelson interferometer, relative to adopting
With the conventional solution of Mach-Zednder interferometer.Technical solutions of the utility model have polarization automatic compensation function, do
It is more preferable to relate to performance and stability.
In technical solutions of the utility model, carry out only needing an interferometer when phase code, light channel structure is simple, system
Performance and stability are more preferable.Polarization Modulation function is realized by phase-modulator, it is with good stability.In phase decoding
It only needs interferometer to carry out phase decoding, four interferometers is needed to carry out phase decodings in conventional solution, therefore this reality
Light channel structure is simplified with new technique scheme, improves system performance and stability.
In technical solutions of the utility model, phase decoding is realized by Faraday-Michelson interferometer, compared to adopting
With Mach-Zednder interferometer conventional solution, the interferometer of technical solutions of the utility model has the automatic compensation function of polarization
Can, interference performance and stability are more preferable.
Based on above-mentioned quantum key distribution system embodiment, it is close that another embodiment of the utility model additionally provides a kind of quantum
The communication means of key dissemination system, for quantum key distribution system described in above-described embodiment, the communication means such as Fig. 2 institute
Show, Fig. 2 provides a kind of flow diagram of the communication means of quantum key distribution system for the utility model embodiment, described logical
Letter method includes:
Step S11: light pulse is generated in the transmitting terminal, polarization is carried out to the light pulse and phase combining is modulated.
Step S12: polarization and the modulated light pulses of phase combining will be carried out to institute by the fiber channel
State receiving end.
Step S13: in the receiving end, phase decoding successively is carried out to the light pulse and polarization decodes, is completed
After polarization decoding, disturbance of the fiber channel to the modulated light pulse is combined is compensated, finally to the light pulse
Polarization state is detected.
As described in above-described embodiment, the transmitting terminal include: laser, polarization encoder module, phase code module and
Adjustable optical attenuator.
In the communication means, the light pulse that the transmitting terminal generates include | P >, | N >, | R >, | L > } these four are partially
Polarization state.Each polarization state is detected respectively in the receiving end.
As described in above-described embodiment, communication means described in the utility model embodiment can control the hair by random number
End and the receiving end are penetrated, to use non-equilibrium BB84 agreement, realizes non-equilibrium basic vector scheme.
Optionally, described to generate light pulse in the transmitting terminal, polarization and phase combining tune are carried out to the light pulse
System is as shown in figure 3, Fig. 3 is the process signal of a kind of polarization provided by the embodiment of the utility model and phase combining modulator approach
Figure, this method comprises:
Step S21: the light pulse is generated by the laser.
Step S22: polarization encoder is carried out to the light pulse of the laser emitting by the polarization encoder module, in institute
State light pulse | R >, | L >, | P > and | a kind of carry out polarization encoder is randomly choosed in N > tetra- kind polarization state.
Step S23: carrying out phase code to the light pulse after polarization encoder by the phase code module, 0, π/
2, π, 3 pi/2s } in select phase difference to carry out phase code at random.
Step S24: the light pulse that the phase code module is emitted is decayed to by monochromatic light by the adjustable optical attenuator
Sub- magnitude.
As described in above-described embodiment, the receiving end includes: phase decoding module, polarization decoder module and detector mould
Block.
Optionally, described in the receiving end, phase decoding successively is carried out to the light pulse and polarization decodes, complete
After polarization decoding, disturbance of the fiber channel to the modulated light pulse is combined is compensated, finally to the light pulse
Polarization state detected as shown in figure 4, Fig. 4 is a kind of process signal of coding/decoding method provided by the embodiment of the utility model
Figure, this method comprises:
Step S31: phase decoding is carried out to the light pulse after combined modulation by the phase decoding module.
Step S32: phase solution is carried out to the light pulse that the phase decoding module is emitted by the polarization decoder module
Code, compensates the fiber channel for the disturbance of light pulse.
Step S33: by the detector module to each polarization state of the light pulse of the polarization decoder module outgoing
It is detected respectively.
Finally, step S34: assisting lower progress data subsequent processing by classical channel, generated in transmitting terminal and receiving end
The quantum key of safety.
As described in above-mentioned QKD embodiment, communication means described in the utility model embodiment can pass through in the transmitting terminal
Sagnac interference ring is by the polarization state of the light pulse of the laser emitting | P > be converted to | P >, | N >, | R >, | L > } this four
Kind polarization state.
Communication means described in the utility model embodiment is for quantum key distribution system described in above-described embodiment, realization side
Formula is simple, at the same using Polarization Modulation (including polarization encoder and polarization decoding) and phase-modulation (including phase code and
Phase decoding), key can be generated into rate and doubled.
Each embodiment in this specification is described in a progressive manner, the highlights of each of the examples are with other
The difference of embodiment, the same or similar parts in each embodiment may refer to each other.For being communicated disclosed in embodiment
For method, since it is corresponding with quantum key distribution system disclosed in embodiment, so be described relatively simple, correlation
Place illustrates referring to quantum key distribution system part.
The foregoing description of the disclosed embodiments can be realized professional and technical personnel in the field or using originally practical new
Type.Various modifications to these embodiments will be readily apparent to those skilled in the art, and determine herein
The General Principle of justice can be realized in other embodiments without departing from the spirit or scope of the present utility model.Cause
This, the present invention will not be limited to the embodiments shown herein, and is to fit to and principles disclosed herein
The widest scope consistent with features of novelty.
Claims (10)
1. a kind of quantum key distribution system, which is characterized in that the quantum key distribution system includes:
Transmitting terminal, the transmitting terminal carry out polarization to the light pulse and phase combining are modulated for generating light pulse；
Receiving end, the receiving end are connect by fiber channel with the transmitting terminal, and the receiving end is used for successively to the light
Pulse carries out phase decoding and polarization decoding, and after completing polarization decoding, it is modulated to combining to compensate the fiber channel
The disturbance of the light pulse finally detects the polarization state of the light pulse；
In the transmitting terminal, light pulse include | P >, | N >, | R >, | L > these four polarization states；
In the receiving end, each polarization state is detected respectively；
Wherein, | P > and | N > be X basic vector eigenstate；| R > and | L > be Y basic vector eigenstate.
2. quantum key distribution system according to claim 1, which is characterized in that the transmitting terminal and the receiving end
It is controlled by random number, to use non-equilibrium BB84 agreement, realizes non-equilibrium basic vector scheme.
3. quantum key distribution system according to claim 1 or 2, which is characterized in that the transmitting terminal includes:
Laser, the laser is light source, for generating the light pulse；
Polarization encoder module, the polarization encoder module are used for the light pulse to the laser emitting and carry out polarization encoder,
The light pulse | R >, | L >, | P > and | a kind of carry out polarization encoder is randomly choosed in tetra- kinds of polarization states of N >；
Phase code module, the phase code module are used to carry out phase code to the light pulse after polarization encoder, 0, π/
2, π, 3 pi/2s } in select phase difference to carry out phase code at random；
Adjustable optical attenuator, the adjustable optical attenuator are used to the light pulse that the phase code module is emitted decaying to monochromatic light
Sub- magnitude.
4. quantum key distribution system according to claim 3, which is characterized in that the light pulse of the laser emitting
Polarization state is | P >；
The polarization encoder module includes Sagnac interference ring, and the Sagnac interference ring is used for the laser emitting
Light pulse polarization converted be | P >, | N >, | R >, | L > these four polarization states.
5. quantum key distribution system according to claim 3, which is characterized in that the polarization encoder module includes:
One polarization beam apparatus, first phase modulator and the first random counting apparatus；
First polarization beam apparatus has first port, second port, third port and the 4th port；First polarization
Beam splitter obtains the light pulse of the laser emitting by its first port, and the light pulse is divided into two-way, is passed through all the way
The outgoing of its third port, its incident the 4th port, another way go out by its 4th port after the first phase modulator
It penetrates, its incident third port after the first phase modulator, the first phase modulator is to incident two-way light arteries and veins
Row phase-modulation is rushed in, so that generating phase difference between the two-way light pulse；The two-way light pulse returns to first polarization point
Beam device converges, and the light pulse after its second port forms polarization encoder is sent to the phase code module；
Wherein, the described first random counting apparatus is used to carry out random numerical control to the phase change amount of the first phase modulator
System.
6. quantum key distribution system according to claim 3, which is characterized in that the phase code module includes:
One beam splitter, the first faraday rotation mirror, the second faraday rotation mirror, second phase modulator and the second random counting apparatus；
First beam splitter has first port, second port, third port and the 4th port；First beam splitter is logical
It crosses its first port and obtains the light pulse after polarization encoder, the light pulse is divided into two-way, pass through its third end all the way
Mouth outgoing, incident first faraday rotation mirror after the second phase modulator, passes through first faraday and revolves
Its third port of backtracking after tilting mirror reflection, another way is emitted by its 4th port, by second Faraday rotation
Its 4th port of backtracking after mirror reflection, the light pulse after phase code are sent to the adjustable light decay by its second port
Subtract device；
Wherein, the described second random counting apparatus is used to carry out random numerical control to the phase change amount of the second phase modulator
System.
7. quantum key distribution system according to claim 1 or 2, which is characterized in that the receiving end includes:
Phase decoding module, the phase decoding module are used to carry out phase solution to the light pulse after combined modulation
Code；
Decoder module is polarized, the light pulse that the polarization decoder module is used to be emitted the phase decoding module carries out phase solution
Code, is also used to compensate the fiber channel for the disturbance of light pulse；
Detector module, the detector module are used for each polarization state point of the light pulse to the polarization decoder module outgoing
It is not detected.
8. quantum key distribution system according to claim 7, which is characterized in that the phase decoding module includes: ring
The random counting apparatus of shape device, delayer, third, the second beam splitter, third phase modulator, third faraday rotation mirror and the 4th
Faraday rotation mirror；
The circulator has first port, second port and third port；The circulator is obtained by its first port
The light pulse of the fiber channel outgoing；
Second beam splitter has first port, second port, third port and the 4th port；Second beam splitter is logical
The light pulse that its first port obtains the second port outgoing of the circulator is crossed, the light pulse is divided into two-way, a-road-through
The outgoing of its third port is crossed, the incident third faraday rotation mirror after the third phase modulator passes through described the
Its third port of backtracking, another way pass through the 4th method by the outgoing of its 4th port after the reflection of three faraday rotation mirrors
Its 4th port of backtracking after drawing revolving mirror to reflect, third port and the 4th port obtain the light arteries and veins after reflection simultaneously
Punching, the light pulse after reflection are emitted from its first port and second port respectively after the second beam splitter internal interference,
The light pulses of second port outgoing give the polarization decoder module, and the light pulses of first port outgoing give the ring
After the second port of shape device, it is sent to the delayer by the third port of the circulator, is sent by the delayer
To the polarization decoder module；
Wherein, the random counting apparatus of the third is used to carry out random numerical control to the phase change amount of the third phase modulator
System.
9. quantum key distribution system according to claim 8, which is characterized in that the polarization decoder module includes:
Three beam splitters, the first Polarization Controller, the second Polarization Controller, the second polarization beam apparatus and third polarization beam apparatus；
The third beam splitter has first port, second port, third port and the 4th port；The third beam splitter is logical
The light pulse that its first port obtains the second port outgoing of the second beam splitter is crossed, the delayer is obtained by its second port
The light pulse of outgoing is divided into two-way after the light pulse that the third beam splitter will acquire carries out polarization decoding, all the way by its
The outgoing of three ports, by incident second polarization beam apparatus of first Polarization Controller, another way passes through its 4th port
Outgoing, by the incident third polarization beam apparatus of second Polarization Controller；
Incident light pulse is divided into two-way and is sent to the detector module by second polarization beam apparatus；
Incident light pulse is divided into two-way and is sent to the detector module by the third polarization beam apparatus；
Wherein, first Polarization Controller and second Polarization Controller are for compensating the fiber channel for light arteries and veins
The disturbance of punching.
10. quantum key distribution system according to claim 9, which is characterized in that the detector module includes four
Single-photon detector, single-photon detector described in two of them are used to separately detect the two-way of the second polarization beam apparatus outgoing
Light pulse, other two described single-photon detector are used to separately detect the two-way light arteries and veins of the third polarization beam apparatus outgoing
Punching.
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