CN208445566U - HD-QKD system based on Polarization Modulation time encoding - Google Patents
HD-QKD system based on Polarization Modulation time encoding Download PDFInfo
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- CN208445566U CN208445566U CN201820642979.6U CN201820642979U CN208445566U CN 208445566 U CN208445566 U CN 208445566U CN 201820642979 U CN201820642979 U CN 201820642979U CN 208445566 U CN208445566 U CN 208445566U
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Abstract
The utility model discloses the transmitting terminals to generate the light pulse group of Polarization Modulation based on the mode that light injects, then modulates light pulse group after being encoded via basic vector modulation and trick state, and light pulse group is sent to receiving end after decaying after coding；The receiving end by after the coding of transmitting terminal light pulse group be split after be utilized respectively Z basic vector detecting module and X basic vector detecting module detects.The utility model HD-QKD system using Polarization Modulation time encoding and uses corresponding measuring device, further improves measurement efficiency.
Description
Technical field
The utility model relates to Technique on Quantum Communication field more particularly to a kind of higher-dimensions based on Polarization Modulation time encoding
Quantum key distribution system.
Background technique
With the development of quantum information theory and technology, quantum computer will emerge quickly.Biography based on computational complexity
Uniting public key cryptosyst will be no longer safe.People have known using symmetric cryptography for a long time, and the encryption system of one-time pad from
Be from the point of view of information theory it is safe, this safety is not based on the similar premise such as computational complexity, therefore can't be by
The impact of quantum computer.But such symmetric encryption system needs to carry out real-time security remote key distribution work, and this
It is difficult to accomplish inside classical system.The appearance of quantum key distribution system (QKD), solves in cipher key transmitting process
Safety issue fundamentally solves Communication Security Problem so that the encryption system of one-time pad is achieved.
But existing QKD system has an apparent defect, i.e. code rate is not high (tens kilometers of optical fiber can arrive Mbps).It mentions
Rise the important topic that code rate is QKD functionization.And higher-dimension coding is an effective way for promoting code rate.Traditional QKD system
In, a quantum state carries the information (quantum bit) of a bit, and in higher-dimension QKD system, a quantum state will carry
The information of multiple bits, so that code rate will be promoted.Therefore higher-dimension quantum key distribution system (HD-QKD) is in QKD research
A key areas.
In higher-dimension coded system, X basic vector and Z basic vector have d eigenstate (d indicates system dimensions), therefore each
Sign state corresponds to 0 bit value for arriving d-1.Relationship between X basic vector eigenstate and the eigenstate of corresponding Z basic vector can be used as follows
Formula describes
Wherein | fn> and | tm> it is respectively X basic vector n-th and m-th of eigenstate of Z basic vector.
The form of higher-dimension coding is also varied, and the scheme of mainstream is time encoding；It is more simple on experiment is realized
It is single, thus be widely studied.
In higher-dimension time encoding, the quantum state of d dimension needs the continuous same time interval (τ) corresponding d to constitute
One period (T=d τ) indicates.For time interval, it is marked with 0 to d-1 from left to right.For Z basic vector, times
Anticipate an eigenstate | tn> the concrete form in time encoding are as follows: only have pulse in n-th of time interval and remaining time
There is no pulse in interval.For X basic vector, be not difficult to learn according to formula (1), between different basic vectors the difference is that in time interval
The phase of pulse, and the probability for occurring pulse in each interval is identical.When Fig. 1 gives d=4, | t0> and | f0> time encoding
Form, and for | f0> phase of pulse in each of which interval is labelled with according to above-mentioned formula.
Easy steps such as Fig. 2 of existing higher-dimension time encoding QKD, this is sentenced for dimension d=4, comprising:
The laser at the end 1.Alice generates a series of laser pulse of constant durations；
2. pulse is after the first intensity modulator (IM1) modulation controlled by FPGA, with qxAnd qzProbability respectively to arteries and veins
The modulation of punching group progress X basic vector and Z basic vector；The object of modulation is the pulse group that 4 continuous impulses are constituted；For Z basic vector, pulse
For group by one of equal probabilities Stochastic Modulation to 4 eigenstates, specific implementation is will be in corresponding three time intervals by IM1
Pulse strength be modulated to 0；For needing to carry out the pulse group of X basic vector modulation, IM1 is not modulated.
3. pulse train, which enters phase-modulator (PM), carries out phase-modulation；PM completes X by adjusting the phase of pulse
The modulation of basic vector eigenstate, and the probability for being modulated to any one eigenstate is identical；For the pulse by the modulation of above-mentioned Z basic vector
Group, PM is without modulation.
4. then by the second intensity modulator (IM2) of FPGA control according to probability Stochastic Modulation pulse group intensity to several
Set point value, which, which is referred to as, inveigles state modulation.
5. the intensity of each pulse group is further then decayed to single photon level by the attenuator (ATT) of FPGA control；
Alice completes the preparation of quantum state, it is sent to Bob by optical fiber.
Incident pulse group is sent into a non-equilibrium beam splitter (BS) first by the end 6.Bob, and transmission and reflectivity are pz:px；
The pulse group of transmissive portion enters Z basic vector measuring device, and the pulse group of reflective portion enters X basic vector measuring device.
7.Z basic vector measuring device only needs a photodetector D1, has response in which time interval by detector
Incident quantum state is judged, so that it is determined that bit value.
8.X basic vector measuring device (referring to Fig. 3): it is made of three time delay interferometers and four single-photon detectors；First
A interferometer constitutes (BS1 and BS2) by fiber delay line 1 and two beam splitters；Second interferometer is by fiber delay line 1 and two
A beam splitter constitutes (BS3 and BS4)；Third interferometer is made of fiber delay line phase-modulator (PM) and two beam splitters
(BS5 and BS6)；The measurement result of X basic vector depends on response of 4 detectors in the 3rd time interval, some detector XiAt this
Have counting in time interval, then show that the quantum state received is | fi>.Bob completes the measurement of signal according to above-mentioned measuring device
With record work.
9. by certified classical channel, Alice announces the basic vector and strength information of each quantum state；Bob is according to upper
State the measurement result that information retains corresponding basic vector.
10. the process and the general process for inveigling the discrete scattered variable QKD system of state of the error correction carried out below and privacy amplification
It is identical, therefore be no longer described in detail.
The defect of existing scheme: in the measuring system of higher-dimension time encoding, the measurement of Z basic vector and common quantum bit
It encodes identical when (two dimension)；But the complexity of X basic vector measuring device greatly increases, and its complexity and dimension are positively correlated.It removes
The considerations of going cost and system stability, there is also an apparent defect, above-mentioned X basic vector measurements for higher-dimension X basic vector measuring system
The efficiency and dimension of its measurement of device are inversely proportional, and for 1/d, (value does not include the effect of the loss of device bring and photodetector
Rate), more high-dimensional coding means lower detection efficient, this obviously constrains the reality of higher-dimension time encoding QKD system
Using.
Utility model content
The utility model provides a kind of HD-QKD system, using Polarization Modulation time encoding and corresponding measuring device,
So that the measurement efficiency of X basic vector doubles.
A kind of HD-QKD system based on Polarization Modulation time encoding, it is described including the transmitting terminal to match and receiving end
Transmitting terminal includes:
Polarized pulses group generating means have the light pulse group accordingly polarized for generating each pulse；
Basic vector modulating device, for carrying out basic vector modulation to Polarization Modulation pulse group；
Inveigle state modulating device, for the modulated light pulse of basic vector carry out random strength modulate encoded after light arteries and veins
Rush group；
Attenuator is decayed to single photon level for light pulse group after encoding；
The receiving end includes:
Beam splitting module, for by after the coding of transmitting terminal light pulse group be split；
Z basic vector detecting module, for receiving beam splitting module, wherein output carries out the detection of Z basic vector all the way；
X basic vector detecting module, the another output for receiving beam splitting module carry out the detection of X basic vector.
The unmentioned other component of transmitting terminal can refer to prior art implementation in the utility model.Transmitting terminal is injected based on light
Mode generate the light pulse group of Polarization Modulation, then via basic vector modulate and inveigle state modulate encode after light pulse group, volume
Light pulse group is sent to receiving end after decaying after code；The receiving end by after the coding of transmitting terminal light pulse group divided
It is utilized respectively Z basic vector detecting module after beam and X basic vector detecting module is detected.
When polarized pulses group generating means, basic vector modulating device and mutually indepedent trick state modulating device, i.e., basic vector is modulated
It is all made of external modulation mode with inveigling state to modulate, basic vector modulating device is made of intensity modulator and phase-modulator at this time；It lures
Deceiving state modulating device can be used intensity modulator.
Based on same invention thinking, the utility model also provides a kind of HD-QKD system based on Polarization Modulation time encoding
System, including the transmitting terminal to match and receiving end, the transmitting terminal includes:
Polarized pulses group generating means have the light pulse group accordingly polarized for generating each pulse；It is also used to polarization
It modulates pulse group and carries out basic vector modulation；
Inveigle state modulating device, for the modulated light pulse of basic vector carry out random strength modulate encoded after light arteries and veins
Rush group；
Attenuator is decayed to single photon level for light pulse group after encoding；
The receiving end includes:
Beam splitting module, for by after the coding of transmitting terminal light pulse group be split；
Z basic vector detecting module, for receiving beam splitting module, wherein output carries out the detection of Z basic vector all the way；
X basic vector detecting module, the another output for receiving beam splitting module carry out the detection of X basic vector.
Basic vector modulation at this time uses internal modulation mode, i.e., before in scheme basic vector modulating device function also by inclined
Pulse group generating means of shaking are realized, are more simplified on hardware, without basic vector modulating device is separately configured.Basic vector is modulated via inclined
The driving voltage of each laser is realized in pulse group generating means of shaking；Such as the driving voltage that phase prepares laser is applied special
The short pulse group of relative phase needed for fixed disturbance generates after making its final injected pulse generate laser realizes the modulation of X basic vector.It is right
The modulation for realizing Z basic vector is adjusted in the driving voltage position that pulse generates laser.
The modulation of X basic vector and the modulation of Z basic vector are selected respectively with the likelihood ratio of P/ (1-P) in polarized pulses group generating means.P
Value set according to the actual application, and meet 0 < P < 1.
Preferably, the transmitting terminal includes:
Polarized pulses group generating means have the light pulse group accordingly polarized for generating each pulse；It is also used to polarization
It modulates pulse group and carries out basic vector modulation；Be also used to the modulated light pulse of basic vector carry out random strength modulate encoded after light
Pulse group；
Attenuator is decayed to single photon level for light pulse group after encoding.
The basic vector modulation at this time and trick state modulation are all made of internal modulation mode, i.e., basic vector modulates dress in scheme before
The function of setting, inveigle state modulating device passes through the realization of polarized pulses group generating means, without basic vector modulating device is separately configured
With trick state modulating device, it is further simplified on hardware.Each pulse generates laser and passes through in polarized pulses group generating means
Change its driving voltage to realize and inveigle state modulation.
The polarized pulses group generating means include that phase prepares laser and the first, second pulse generation laser, institute
It states phase and prepares laser for generating long pulse and being injected separately into two pulses generation laser, two pulses generation laser production
The pulse group of raw different polarization states simultaneously is coupled as exporting all the way.
In order to realize the multiplexing of optical path, it is further simplified hardware, preferably, the polarized pulses group generating means are also wrapped
It includes:
Beam splitter is balanced, phase prepares the long pulse that laser generates and is divided into two-way via balance beam splitter；
First optical fiber circulator, that carrys out self-balancing beam splitter wherein enters the first pulse via the first optical fiber circulator all the way
Laser is generated, the first pulse generates laser and generates the light pulse of horizontal polarization and export via the first optical fiber circulator；
Second optical fiber circulator, the another way for carrying out self-balancing beam splitter are produced via the second optical fiber circulator into the second pulse
Raw laser, the second pulse generate laser and generate the light pulse of vertical polarization and export via the second optical fiber circulator；
Polarization beam apparatus, the light pulse from the first optical fiber circulator and the second optical fiber circulator is via the polarization beam apparatus
It is coupled as exporting all the way.
Preferably, the beam splitting module is beam splitter.The splitting ratio of the beam splitter is the likelihood ratio of basic vector modulation.
Preferably, the Z basic vector detecting module is a single-photon detector, to direct impulse group between each time
Every interior distribution；
Or the Z basic vector detecting module includes the fiber coupler of n single-photon detector and a 1:n, n is light arteries and veins
Coding dimension is rushed, incident light pulse is divided into the road n and inputs corresponding single-photon detecting detector, each detection by fiber coupler
Distribution in the specified time interval of device detection.
Preferably, the X basic vector detecting module includes intervention module and quantity single photon corresponding with coding dimension
Detector, each single-photon detector separately detect corresponding result of interference.
The quantity of single-photon detector is corresponding to optical pulse code dimension in X basic vector detecting module, such as optical pulse code
Dimension is n, then needs n single-photon detector.
It can be according to quantity, that is, optical pulse code dimension setting suitable number of single-photon detector in X basic vector detecting module
Interference unit, every primary interference of generation will obtain two-way output, occur if an interference unit is arranged again all the way for every
Primary interference, will obtain more outputs, and so on until quantity Matching with single-photon detector.
Preferably, optical pulse code dimension is 4.
Preferably, the intervention module includes a main interference unit and the son with single-photon detector quantity Matching
Interference unit includes wherein polarization-maintaining polarization beam apparatus, delay line and beam splitter in main interference unit, is incident to main interference unit
Coding after light pulse group via polarization-maintaining polarization beam apparatus be divided into two-way, wherein entering beam splitter all the way, another way is through delay line
Enter beam splitter afterwards, two-way closes beam interferometer in beam splitter and exports.
Such as optical pulse code dimension is 2, i.e., there are two single-photon detector, then main interference unit had two groups it is defeated
Out, different single-photon detectors can directly be entered, then sub- interference unit number is 0, when optical pulse code dimension is 4, son
Interference unit number is 2, i.e. the two of main interference unit group output respectively enters a wherein sub- interference unit again, finally has 4 tunnels
Output, respectively enters different single-photon detectors.
Preferably, the sub- interference unit includes two beam splitters and delay line, into the coding of sub- interference unit
Light pulse group is divided into two-way via beam splitter afterwards, and wherein all the way through delay line, and two-way closes beam interferometer and defeated in another beam splitter
Out.
When optical pulse code dimension is 4, the sub- interference unit is two, and the wherein galianconism (two of a sub- interference unit
No all the way, delay line is in contrast arranged not can be considered long-armed to setting delay line all the way between beam splitter) it is equipped with phase tune
Device processed.
Preferably, the sub- interference unit includes beam splitter, delay line and two faraday rotation mirrors；
Light pulse group is via two-way is divided into after beam splitter after into the coding of sub- interference unit, wherein entering one farad all the way
Revolving mirror, another way enter another faraday rotation mirror after delay line；It is reflected respectively by corresponding faraday rotation mirror again
It interferes and exports along respective original route return beam splitter afterwards.
Polarization drifting problem can be solved by the way that faraday rotation mirror is arranged in sub- interference unit.
Preferably, the X basic vector detecting module includes:
Main interference unit, into the coding of X basic vector detecting module after light pulse group interfered in main interference unit, and it is defeated
First optical signal and the second optical signal out；
First sub- interference unit receives the first optical signal and interferes, third optical signal and the 4th light are exported after interference
Signal；
Second sub- interference unit receives the second optical signal and interferes, the 5th optical signal and the 6th light are exported after interference
Signal；
The quantity of single-photon detector is four in X basic vector detecting module, receives detect the third optical signal, the respectively
Four optical signals, the 5th optical signal and the 6th optical signal.
The multiplexing of multichannel can be realized by modes such as setting optical fiber circulators in the optical path.Preferably, being additionally provided with
Three optical fiber circulators, first optical signal enter the first sub- interference unit via third optical fiber circulator；Third optical signal and
One is directly entered corresponding single-photon detector in 4th optical signal, and another one enters corresponding via third optical fiber circulator
Single-photon detector；
It is additionally provided with the 4th optical fiber circulator, second optical signal enters the second son interference list via the 4th optical fiber circulator
Member；One is directly entered corresponding single-photon detector in 5th optical signal and the 6th optical signal, and another one is via the 4th optical fiber
Circulator enters corresponding single-photon detector；
In first sub- interference unit and the second sub- interference unit, galianconism (beam splitter and the faraday rotation mirror of one of them
Between no all the way, delay line is in contrast arranged not can be considered long-armed to setting delay line all the way) be equipped with phase-modulator.
HD-QKD system of the utility model based on Polarization Modulation time encoding solves existing system X basic vector measurement dress
The relatively low problem of efficiency is set, in transmitting terminal using being further introduced into Polarization Modulation and using corresponding measuring device, to will survey
Amount efficiency promotes one times.
Detailed description of the invention
Fig. 1 (a) is the quantum state form schematic diagram of Z basic vector coding in higher-dimension time encoding；
Fig. 1 (b) is the quantum state form schematic diagram of X basic vector coding in higher-dimension time encoding；
Fig. 2 is the schematic diagram of higher-dimension time encoding QKD system in the prior art；
Fig. 3 is the schematic diagram that X basic vector measures part in Fig. 2；
Fig. 4 is the quantum state form schematic diagram of Polarization Modulation in the utility model；
Fig. 5 is the schematic diagram of HD-QKD system in the utility model；
Fig. 6 is the schematic diagram of pulse generation device in the utility model；
Fig. 7 (a) is the schematic diagram of Z basic vector measuring device in the utility model；
Fig. 7 (b) is the schematic diagram of another embodiment of Z basic vector measuring device in the utility model；
Fig. 8 is the schematic diagram of X basic vector measuring device in the utility model；
Fig. 9 is the schematic diagram of another embodiment of X basic vector measuring device in the utility model；
Figure 10 is variation relation schematic diagram of the key rate with transmission range (fiber lengths)；
Figure 11 is the HD-QKD system schematic of embodiment 1；
The driving voltage schematic diagram of laser when Figure 12 is X basic vector modulation in embodiment 1；
The driving voltage schematic diagram of laser when Figure 13 is Z basic vector modulation in embodiment 1；
Figure 14 is the HD-QKD system schematic of embodiment 2；
Figure 15 is the schematic diagram that state modulating device is inveigled in Figure 14；
Figure 16 is the driving voltage schematic diagram of polarized pulses group generating means in the HD-QKD system of embodiment 3.
Specific embodiment
In the present invention, the rule of Polarization Modulation is (remaining can analogize by taking d=4 as an example): between the first two time
Every the impulse modulation in (the 0,1st time interval) for vertical polarization (V) and in latter two time interval (the 2,3rd time interval)
Impulse modulation is horizontal polarization (H).Referring to Fig. 4.It is, in general, that the impulse modulation of preceding d/2 time interval is V by Polarization Modulation
Then d/2 impulse modulation is V.Certainly modulation is also feasible in turn.The object of next code modulation is exactly such
Polarization Modulation pulse group.
The utility model HD-QKD system and device and step (by taking d=4 as an example) are illustrated below in conjunction with Fig. 5, this is practical
Novel HD-QKD system includes the transmitting terminal (Alice) and receiving end (Bob) being connected by optical fiber, and transmitting terminal successively includes polarization
Pulse group generating means, inveigle state modulating device, attenuator (omitting in figure) at basic vector modulating device, and receiving end includes beam splitter
(BS) and the connected Z basic vector measuring device and X basic vector measuring device of output end corresponding with BS.
The course of work are as follows:
1. polarized pulses group generating means generate the pulse train that above-mentioned polarized pulses group (referring to Fig. 4) is constituted；
2. basic vector modulating device is to each pulse group into the modulation of row stochastic X or Z basic vector；
3. inveigling state modulating device by the intensity Stochastic Modulation of each pulse group to previously selected several values；
The pulse train that modulation is completed is sent to Bob by optical fiber by 4.Alice.
The pulse train received is first passed through a non-equilibrium beam splitter beam splitting by 5.Bob, and transmission and reflectivity are
The end Alice carries out the probability of the probability ratio X basic vector modulation of Z basic vector modulation, and wherein transmissive portion pulse enters Z basic vector measuring device
And corresponding reflective portion enters X basic vector measuring device.
After 6.Bob completes the measurement of all pulses, Alice passes through the classical channel that authenticated for the basic vector tune of each pulse
Information processed and strength information are sent to Bob, and Bob accordingly retains the measurement result of corresponding basic vector.
7. subsequent error correction and privacy amplification process are identical with the existing processing mode for inveigling state QKD, therefore are no longer described in detail.
8. the safe code rate finally retained is provided by phase code rate formula, see below explanation.
Polarized pulses generating means
The utility model polarized pulses generating means are based on light injection technique, adjust for generating a series of polarizations shown in Fig. 4
The pulse group of system is simultaneously completed basic vector simultaneously by way of internal modulation and inveigles the modulation of state.Structure is as shown in fig. 6, include phase
Prepare laser, pulse generate laser 1, pulse generate laser 2, balance beam splitter (BS), the first optical fiber circulator (C1),
Second optical fiber circulator (C2) and polarization beam apparatus (PBS).
Polarization Modulation pulse group is generated using light injection technique, the specific steps are as follows:
1. phase, which prepares laser, generates periodic long pulse；
2. long pulse is through balancing beam splitter (BS) beam splitting；Corresponding reflection long pulse is injected through the first optical fiber circulator (C1)
Pulse generates laser 1；And long pulse is transmitted accordingly and generates laser 2 through (C2) injected pulse of the second optical fiber circulator；
3. pulse generate laser 1 generate horizontal polarization (H) pulse, by adjusting its driving voltage, can make its
Short pulse is generated when time interval 2 and 3；
4. pulse generate laser 2 generate vertical polarization (V) pulse, by adjusting its driving voltage, can make its
Short pulse is generated when time interval 0 and 1；
It is exported all the way 5. the pulse of two-way Polarization Modulation enters after polarization beam apparatus (PBS) is coupled to be formed.
Wherein, it is preferably semiconductor laser diode that pulse, which generates laser,.It is preferably semiconductor that phase, which prepares laser,
Laser diode.
Basic vector modulating device and trick state modulating device
Basic vector modulating device is related to the modulation of pulse group intensity and phase, and state modulating device is inveigled to only relate to pulse group
Intensity modulated.The way of realization of above-mentioned modulation can simply be divided into two kinds: external modulation and internal modulation；External modulation refers to and directly passes through
External phase and intensity modulator realize above-mentioned function, and refer in internal modulation through inner parameters such as the driving voltages of adjusting light source
To modulate pulse needed for directly exporting.
Z basic vector measuring device
By taking d=4 as an example, for Z basic vector measuring device, there is following two structure, the first structure is by shown in Fig. 7 (a), only
It is made of a single-photon detector.It will detect corresponding four time intervals of each pulse group so that it is determined that incidence is Z
Which eigenstate of basic vector.If there are multiple time intervals to respond, a response is randomly selected as a result.
Second of structure the fiber coupler of four single-photon detectors and a 1:4 by being made of shown in Fig. 7 (b)；
Incident light pulse is divided into 4 tunnel pulses and inputs corresponding detector by fiber coupler, and each detector only needs to detect
Specified time interval, such as the 0th detector only need the case where 0 time interval of detection.Equally, if there is multiple detectors to respond,
Then randomly select a response as a result.
X basic vector measuring device
By taking d=4 as an example, following two structure is can be used in X basic vector measuring device, the first X basic vector measuring device such as Fig. 8 institute
Show, X measuring device is made of the interferometer of three time delays and four single-photon detectors.
Interferometer (TDI1) is equivalent to main interference unit, by polarization-maintaining polarization beam apparatus (polarization-maintaining PBS), delay line 1 and balance
Beam splitter (BS1) is constituted；
Interferometer (TDI2) is equivalent to sub- interference unit, by two balance beam splitters (BS2, BS3) and 2 structure of fiber delay line
At the delay time of delay line is τ.
Interferometer (TDI3) is equivalent to sub- interference unit, by two balance beam splitters (BS4, BS5), delay line 3 and phase
Modulator (PM) is constituted；The delay time of delay line is τ.
Two output ends of TDI2 are respectively connected to two single-photon detector (X0And X1), while two output ends of TDI3
Access two single-photon detector (X2And X3)。
Workflow are as follows:
1. pulse group initially enters PBS1, wherein H polarized pulses group is directly transmitted and V polarized pulses group reflects；Reflect arteries and veins
Punching group polarizes rotate to be H simultaneously；Reflected impulse group is delayed through delay line 1.
2. transmission and reflected impulse group divide two-way to be output to TDI2 and TDI3 after BS1 is interfered.
3. the pulse group for entering TDI2 first passes through BS2 beam splitting；Reflected impulse group enters BS3 after the delay of delay line 2, and saturating
It penetrates pulse group and is directly entered BS3；Two-way is divided to export after two-way pulse generation interference, output pulse group is respectively connected to single photon detection
Device X0And X1It measures.
4. the pulse group for entering TDI3 first passes through BS3 beam splitting；Reflected impulse group carries out after the delay of delay line 2 into PM
The phase-modulation of fixed pi/2 enters BS4 with afterpulse group, and transmitted pulse group is directly entered BS4；Two-way pulse generation is dry
Two-way is divided to export after relating to, output pulse group is respectively connected to single-photon detector X2And X3It measures.
Second of X basic vector measuring device is as shown in figure 9, interferometer of the device by three time delays, two fiber optic loops
Shape device (C1, C2) and four single-photon detectors are constituted.
Interferometer (TDI1) is equivalent to main interference unit, by polarization-maintaining polarization beam apparatus (polarization-maintaining PBS), delay line 1 and beam splitting
Device (BS1) composition；
Interferometer (TDI2) is equivalent to sub- interference unit, by beam splitter (BS2), faraday rotation mirror (FM2), delay line 2
It is formed with faraday rotation mirror (FM3)；
Interferometer (TDI3) is equivalent to sub- interference unit, by beam splitter (BS3), faraday rotation mirror (FM4), delay line 3,
Phase-modulator (PM) and faraday rotation mirror (FM5) composition.
Workflow are as follows:
1. incident pulse group, through PBS1 beam splitting, V polarized pulses group is by reflection and H polarized pulses group directly transmits；Reflection
90 degree of polarization overturnings occur simultaneously for pulse group, and polarization becomes H；
2. reflected impulse group enters BS1 after the delay of delay line 1；The delay time of delay line 1 is 2 τ；
3. transmitted pulse group is directly entered BS1, and the reflected impulse group by delay interfere after by BS1 two ends
Mouth output；
4. the pulse group of output all the way exported after BS1 interferes enters TDI2 after C1；Pulse group is first through BS2 beam splitting, instead
It penetrates pulse and returns to BS2 after time-delay mechanism is delayed, and transmitted pulse directly returns to BS2 after FM3 reflects, due to Faraday rotation
The polarization of the effect two-way pulse group of mirror is rotated by 90 °；Two-way pulse group is interfered in BS2, and interference pulse group is through C1 all the way
Into the 0th single-photon detector (X0) measurement, and another way pulse group is directly entered the first single-photon detector (X1) measurement；Prolong
When line 2 delay time be τ/2；
5. the another way pulse group exported after BS1 interferes enters TDI3 through C2；Pulse group is through BS3 beam splitting, and PM is to transmission
The pi/2 phase modulation that pulse group is fixed, subsequent transmitted pulse group return to BS3 after FM5 reflects (polarization is rotated by 90 °)；Instead
It penetrates pulse group and returns to BS3 after time-delay mechanism is delayed, polarization is equally rotated by 90 °；Two-way pulse group is interfered in BS3, wherein
Interference pulse enters the second single-photon detector (X through C2 all the way2) measure, and another way interference pulse group is directly entered
Three single-photon detector (X3) measurement；The delay time of delay line 3 is τ/2.
Preferably, the subsequent all fiber selection polarization maintaining optical fibres of polarization-maintaining PBS.
For an incident pulse group, above two X basic vector measuring device passes through detects between the time for which detector
There is the eigenstate for accordingly differentiating which X basic vector incidence is in 3；If there is multiple detectors to have sound in the time interval
It answers, then randomly selects one as a result.
Measurement efficiency
For in the X basic vector measuring device of the utility model, intervention module can simply be divided into two parts: TDI1
(main interference unit) and other TDI (to interference unit).
The effect of TDI1 is to become energy more after the pulse group that original d time interval is constituted is passed through interference using polarization
The pulse group that d/2 time interval of concentration is constituted, while the pulse group can only be exported from a port of TD1, in the process
In there is no a loss of any energy, therefore its efficiency is 1；And subsequent process can consider with the prior art and measure d/2
The pulse group (two output ends for needing to be respectively connected to TDI1 there are two such device) that time interval is constituted, thus device is whole
Measurement efficiency beOne after another is measured by Polarization Modulation and the corresponding X basic vector measuring device of design to be promoted
One times.
Code rate formula and parameter optimization
For any QKD system, it is necessary to provide the calculation formula of its safe code rate.The formula determines the size of key retained,
The performance of QKD system is demarcated.Each quantum state that code rate herein is defined as Alice transmission is eventually converted into security key
Ratio is indicated with R.The security key formula that d ties up QKD system is as follows, sets total quantum state (pulse of Alice transmitting herein
Group) number is N and finally obtained security key length is L
WhereinThe intensity for indicating the transmitting of the end Alice is a and carries out the quantum state number of Z basic vector modulation；It indicates
Alice sends the quantum state that Z basic vector modulate intensity is a, and i photon ingredient has response in the Z basic vector measuring device of the end Bob
Probability；Indicate the phase error rate of single photon under Z basic vector；
It is the entropy formula of d dimension.
λ simultaneouslyECIndicate the size of key consumed in error correction procedure, expression formula is
Wherein f indicates the efficiency of error correction,Bob is in corresponding Z after indicating the quantum state of Alice transmission Z basic vector modulation a intensity
The error rate of the bit value obtained after the measurement of basic vector measuring device.
In addition g indicates to consider the amendment after limited key (i.e. the quantum state number N that Alice is sent is finite value) combination safety
, expression formula is
Wherein εcorAnd εsecFor correctness and security parameters, value is selected in advance.
By above-mentioned formula, be not difficult to obtain code rate formula be
Theoretical values simulation
The utility model improves the measurement efficiency of X basic vector measuring device, then under square one and prior art phase
Than the measurement data that will obtain more X basic vectors.More data mean in corresponding parameter Estimation, the area of parameter fluctuation
Between it is smaller, system can be made to obtain higher code rate and farther transmission range.
For the superiority for further intuitively illustrating the utility model, chooses following data and carries out numerical simulation:
β indicates the efficiency of transmission of optical fiber, unit dB/km；The measurement efficiency for indicating X basic vector measuring device, using existing
X=1 when having technology and use the utility model when x=2；Indicate the measurement efficiency of Z basic vector measuring device；WithTable
Intrinsic gauging error rate caused by showing X and Z basic vector measuring device due to the problems such as instrument calibration；PdIndicate each photodetection
The dark counting of device；Remaining meaning of parameters has been introduced above, the parameter of the selection of above-mentioned parameter value referring to existing experimental facilities.
The result of numerical simulation gives key rate as the variation of transmission range (fiber lengths) is closed referring to Figure 10 in figure
System.Wherein solid line is the utility model as a result, and dotted line is the result of the prior art.This it appears that using this reality
After New Scheme, code rate is obviously improved all apart from upper, is especially promoted and is become apparent when remote；We simultaneously
Case can also promote the distance of cipher key delivery.
In addition, internal modulation may be implemented by light injection technique, without the various external modulators in prior art,
Structure is simplified；The stability and rate of internal modulation simultaneously are superior to the external modulation scheme of external modulator.Light injection technique is raw
At pulse group between be phase randomization, this meet inveigle state modulation requirement；And prior art will be realized accordingly
Phase randomization it is complex and difficult.
Embodiment 1
Referring to Figure 11, the modulation of basic vector and trick state uses internal modulation mode in the present embodiment, passes through polarized pulses group
Generating means are completed, comprising:
1. generating polarized pulses group using polarized pulses group generating means shown in fig. 6；
2. making the pulse group of output complete basic vector by way of internal modulation and inveigling the modulation (seeing below) of state；
3. the pulse group sequence that modulation is completed is transferred to measurement end by optical fiber；
4. pulse group sequence is first through beam splitter BS beam splitting, transmission and reflectivity are just the probability of Z and X basic vector modulation
Than；
5. transmitted pulse enters Z basic vector measuring device；Preferably, Z basic vector measuring device chooses one in structure shown in Fig. 7
Kind；
6. reflected impulse enters X basic vector measuring device；Preferably, X basic vector measuring device chooses shown in Fig. 8 and Fig. 9 two kinds
One of device；
7. measurement end records measurement result；
8. subsequent step is identical as existing trick state QKD step, therefore is no longer described in detail.
Illustrate to realize basic vector by internal modulation below and inveigle the process of state modulation, the core of internal modulation is to adjust above-mentioned
The driving voltage of three lasers realizes the modulation of pulse strength and phase.
X basic vector is modulated, the driving voltage of laser is shown in Figure 12, the threshold voltage of 0 expression laser in figure；For phase
The long pulse driving voltage for preparing laser applies 3 voltage disturbances in three positions as shown in the figure, which will most
The relative phase being converted between four short pulses eventually, therefore its value depends on needing the eigenstate for the X basic vector modulated；3 are disturbed
Long pulse driving voltage is divided into four sections by dynamic voltage, corresponds to above-mentioned the first two section, and pulse generates there are two lasers 2
The driving voltage of short time, for generating short pulse in time interval 0 and 1；Similarly pulse generates laser 1 in time interval
2 and 3 generate short pulse；Four short pulse intensity of X basic vector are identical, by voltage V0Driving, by adjusting the intensity of the voltage,
The intensity of i.e. adjustable output basic vector, to complete the modulation of trick state.
Z basic vector is modulated, referring to Figure 13.Any disturbance is not applied at this point for long pulse driving voltage；According to required
The Z basic vector eigenstate of modulation applies a short pulse driving voltage V in the corresponding position that pulse generates laser 1 and 20；Together
Reason adjusts V0Size, which can be realized, inveigles state modulation.
Embodiment 2
It is compared referring to Figure 14 with embodiment 1, the present embodiment realizes the modulation for inveigling state by way of external modulation；Base
The internal modulation way of realization and embodiment 1 of arrow are identical, and inveigling the modulation of state in example 2 is no longer by modulating short pulse
Driving voltage V0It realizes, but is realized by external modulator.
Preferably, inveigling state modulating device is intensity modulator；
Preferably, inveigling state modulating device is the intensity modulated device being made of beam splitter and phase-modulator, such as Figure 15
It is shown；Pulse is incident by 1 port of balance beam splitter (BS), and the phase modulation by adjusting phase-modulator (PM) can be
The port 2 of BS obtains the pulse of required intensity through interference.
Device rest part and step and embodiment 1 are identical.
Embodiment 3
Referring to Fig. 5, compared with Example 2, the modulation of the present embodiment basic vector is carried out also by the form of external modulation；Using
The driving voltage that light shown in Fig. 6 injects polarized pulses group generating means is as shown in figure 16；The pulse of device generation Polarization Modulation
Group: there is the pulse of same intensity in four time intervals, and the phase of each pulse is identical.
Intensity modulated device and phase-modulator form basic vector modulating device as shown in Figure 15；
Inveigling state modulating device is structure shown in Figure 15.
Device rest part and step and embodiment 1 are identical.
Disclosed above is only the embodiments of the present invention, but the utility model is not limited to this, this field
Technical staff can carry out various modification and variations without departing from the spirit and scope of the utility model to the utility model.Obviously
These modification and variations should belong in the protection scope protection of the requires of the utility model.In addition, although being used in this specification
Some specific terms, these terms are merely for convenience of description, does not constitute to the utility model any specifically limited.
Claims (12)
1. a kind of HD-QKD system based on Polarization Modulation time encoding, including the transmitting terminal to match and receiving end, feature
It is, the transmitting terminal includes:
Polarized pulses group generating means have the light pulse group accordingly polarized for generating each pulse；
Basic vector modulating device, for carrying out basic vector modulation to Polarization Modulation pulse group；
Inveigle state modulating device, for the modulated light pulse of basic vector carry out random strength modulate encoded after light pulse
Group；
Attenuator is decayed to single photon level for light pulse group after encoding；
The receiving end includes:
Beam splitting module, for by after the coding of transmitting terminal light pulse group be split；
Z basic vector detecting module, for receiving beam splitting module, wherein output carries out the detection of Z basic vector all the way；
X basic vector detecting module, the another output for receiving beam splitting module carry out the detection of X basic vector.
2. a kind of HD-QKD system based on Polarization Modulation time encoding, including the transmitting terminal to match and receiving end, feature
It is, the transmitting terminal includes:
Polarized pulses group generating means have the light pulse group accordingly polarized for generating each pulse；It is also used to Polarization Modulation
Pulse group carries out basic vector modulation；
Inveigle state modulating device, for the modulated light pulse of basic vector carry out random strength modulate encoded after light pulse
Group；
Attenuator is decayed to single photon level for light pulse group after encoding；
The receiving end includes:
Beam splitting module, for by after the coding of transmitting terminal light pulse group be split；
Z basic vector detecting module, for receiving beam splitting module, wherein output carries out the detection of Z basic vector all the way；
X basic vector detecting module, the another output for receiving beam splitting module carry out the detection of X basic vector.
3. a kind of HD-QKD system based on Polarization Modulation time encoding, including the transmitting terminal to match and receiving end, feature
It is, the transmitting terminal includes:
Polarized pulses group generating means have the light pulse group accordingly polarized for generating each pulse；It is also used to Polarization Modulation
Pulse group carries out basic vector modulation；Be also used to the modulated light pulse of basic vector carry out random strength modulate encoded after light pulse
Group；
Attenuator is decayed to single photon level for light pulse group after encoding；
The receiving end includes:
Beam splitting module, for by after the coding of transmitting terminal light pulse group be split；
Z basic vector detecting module, for receiving beam splitting module, wherein output carries out the detection of Z basic vector all the way；
X basic vector detecting module, the another output for receiving beam splitting module carry out the detection of X basic vector.
4. the HD-QKD system as claimed in any one of claims 1 to 3 based on Polarization Modulation time encoding, which is characterized in that
The polarized pulses group generating means include that phase prepares laser and the first, second pulse generation laser, the phase level
Standby laser generates laser for generating long pulse and being injected separately into two pulses, and it is different partially that two pulses generate laser generation
The pulse group of polarization state simultaneously is coupled as exporting all the way.
5. as claimed in claim 4 based on the HD-QKD system of Polarization Modulation time encoding, which is characterized in that the polarization arteries and veins
Punching group generating means further include:
Beam splitter is balanced, phase prepares the long pulse that laser generates and is divided into two-way via balance beam splitter；
First optical fiber circulator carrys out wherein generating all the way via the first optical fiber circulator into the first pulse for self-balancing beam splitter
Laser, the first pulse generate laser and generate the light pulse of horizontal polarization and export via the first optical fiber circulator；
Second optical fiber circulator, the another way for carrying out self-balancing beam splitter enter the second pulse generation via the second optical fiber circulator and swash
Light device, the second pulse generate laser and generate the light pulse of vertical polarization and export via the second optical fiber circulator；
Polarization beam apparatus, the light pulse from the first optical fiber circulator and the second optical fiber circulator are coupled via the polarization beam apparatus
To export all the way.
6. the HD-QKD system as claimed in any one of claims 1 to 3 based on Polarization Modulation time encoding, which is characterized in that
The X basic vector detecting module includes intervention module and quantity single-photon detector corresponding with coding dimension, each single-photon detecting
It surveys device and separately detects corresponding result of interference.
7. as claimed in claim 6 based on the HD-QKD system of Polarization Modulation time encoding, which is characterized in that optical pulse code
Dimension is 4.
8. as claimed in claim 6 based on the HD-QKD system of Polarization Modulation time encoding, which is characterized in that the interference mould
Block includes a main interference unit and the sub- interference unit with single-photon detector quantity Matching, is wherein wrapped in main interference unit
Polarization-maintaining polarization beam apparatus, delay line and beam splitter are included, light pulse group is inclined via polarization-maintaining after being incident to the coding of main interference unit
Vibration beam splitter is divided into two-way, wherein entering beam splitter all the way, another way enters beam splitter after delay line, and two-way is closed in beam splitter
Beam interferometer simultaneously exports.
9. as claimed in claim 8 based on the HD-QKD system of Polarization Modulation time encoding, which is characterized in that the sub- interference
Unit includes two beam splitters and delay line, into the coding of sub- interference unit after light pulse group via beam splitter be divided into two
Road, and wherein all the way through delay line, two-way closes beam interferometer in another beam splitter and exports.
10. as claimed in claim 8 based on the HD-QKD system of Polarization Modulation time encoding, which is characterized in that the son is dry
Relating to unit includes beam splitter, delay line and two faraday rotation mirrors；
Light pulse group is revolved via two-way is divided into after beam splitter wherein entering a faraday all the way after into the coding of sub- interference unit
Tilting mirror, another way enter another faraday rotation mirror after delay line；Again respectively by edge after the reflection of corresponding faraday rotation mirror
Respective original route returns to beam splitter and interferes and export.
11. as claimed in claim 10 based on the HD-QKD system of Polarization Modulation time encoding, which is characterized in that the X base
Swear that detecting module includes:
Main interference unit, into the coding of X basic vector detecting module after light pulse group interfered in main interference unit, and export the
One optical signal and the second optical signal；
First sub- interference unit receives the first optical signal and interferes, third optical signal and the 4th optical signal are exported after interference；
Second sub- interference unit receives the second optical signal and interferes, the 5th optical signal and the 6th optical signal are exported after interference；
The quantity of single-photon detector is four in X basic vector detecting module, receives detect the third optical signal, the 4th light respectively
Signal, the 5th optical signal and the 6th optical signal.
12. as claimed in claim 11 based on the HD-QKD system of Polarization Modulation time encoding, which is characterized in that be additionally provided with
Three optical fiber circulators, first optical signal enter the first sub- interference unit via third optical fiber circulator；Third optical signal and
One is directly entered corresponding single-photon detector in 4th optical signal, and another one enters corresponding via third optical fiber circulator
Single-photon detector；
It is additionally provided with the 4th optical fiber circulator, second optical signal enters the second sub- interference unit via the 4th optical fiber circulator；
One is directly entered corresponding single-photon detector in 5th optical signal and the 6th optical signal, and another one is via the 4th fiber annular
Device enters corresponding single-photon detector；
In first sub- interference unit and the second sub- interference unit, the galianconism of one of them is equipped with phase-modulator.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN108540282A (en) * | 2018-05-02 | 2018-09-14 | 如般量子科技有限公司 | HD-QKD systems based on Polarization Modulation time encoding |
| CN112511301A (en) * | 2021-02-01 | 2021-03-16 | 北京中创为南京量子通信技术有限公司 | Quantum state preparation method, distribution method and device of HD-QKD |
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2018
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN108540282A (en) * | 2018-05-02 | 2018-09-14 | 如般量子科技有限公司 | HD-QKD systems based on Polarization Modulation time encoding |
| CN112511301A (en) * | 2021-02-01 | 2021-03-16 | 北京中创为南京量子通信技术有限公司 | Quantum state preparation method, distribution method and device of HD-QKD |
| CN112511301B (en) * | 2021-02-01 | 2021-07-02 | 北京中创为南京量子通信技术有限公司 | Quantum state preparation method, distribution method and device of HD-QKD |
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