A kind of high speed of external modulation inveigles the device of state quantum light source
Technical field
The utility model relates to field of quantum secure communication, and as the quantum state light source in its high speed quantum key distribution system, specifically a kind of high speed of external modulation inveigles the device of state quantum light source.
Background technology
Quantum mechanics is set up at the beginning of last century, greatly promote physical development, moreover, it is found that quantum mechanics and facing Information Science combine, the quantum information subject developed can complete the task that classical information subject cannot complete, as quantum key distribution (QKD), its fail safe is ensured by basic physics theory, therefore this communication mode has the absolute safety that cannot be cracked.
The quantum key distribution scheme obtaining extensively accreditation at present in the world comprises phase encoding scheme, polarization encoder scheme, Entangled State scheme etc.QKD system based on entangled photon pairs also rests on laboratory stage at present, also has a segment distance from practical.Phase encoding scheme core is the single photon path in stellar interferometer, according to the interference of photons situation screening key under out of phase.But phase encoding scheme needs to carry out accurately controlling to keep interference visibility to light path in systems in practice, and also needs in one-way system to ensure polarization-stable, and system needs the unit module of ACTIVE CONTROL more.For this problem, two-way " plug-play " system proposed by Gisin group utilizes faraday's speculum to achieve automatic path and polarization compensation, there is very strong antijamming capability, higher Single-photon interference stability just can be reached without the need to ACTIVE CONTROL, but this scheme is a kind of two-way PE system, quantum state light source and single-photon detector are at receiving terminal, phase-modulation is positioned at transmitting terminal, for overcoming the polarization correlated of phase-modulator, modulation must be implemented to by two orthogonal polarization orientation before and after faraday's speculum, the pulse be carried on phase-modulator at least needs to cover the light path back and forth between faraday's speculum and phase-modulator, information is caused to load the limited speed of sequential, in addition, the light echo scattering that the intense light pulse sent from receiving terminal to transmitting terminal produces optical fiber circuit covers regular hour width, the single photon detection of receiving terminal is had a negative impact, and single-photon detector also has regular hour shake, so kind scheme is not suitable for the high speed QKD system of more than GHz.
The scheme of polarization encoder is then utilize photon polarity to carry out quantum secret communication, and the experiment of first time quantum communications in history is also utilize this coded system.Compared with phase system, polarization encoder can use passive modulation and demodulation device, and without the need to ACTIVE CONTROL, the insertion loss of its device is also smaller.Because in the QKD scheme of polarization encoder, quantum light source and single-photon detector are positioned at channel two ends, therefore there is not Problems existing in " plug-play " scheme, therefore be applicable to the high speed QKD system of more than GHz.
Due to the restriction of experimental facilities in reality, strict single-photon source cannot be produced, the quantum light source used is generally the weak coherent light after overdamping, attack because unavoidable multi-photon pulses causes listener-in Eve that number of photons can be adopted to be separated (PNS) in light source, tackle photon when communicating pair is not perceiveed, this defect result in key rate and maximum safe distance is all affected.In communication process, if both sides can know the ratio of single photon pulses, carry out by collaborative amplification of maintaining secrecy, key can be compressed and make Eve cannot obtain any information.Like this, the fail safe of system just can be ensured by the operation of subsequent process.The accuracy rate of single photon Ratio Estimation directly affects the efficiency of maintaining secrecy and amplifying, so the accurate estimation of single photon pulses ratio in the pulse sent light source is the key of quantum-key distribution.2003, Hwang proposition employing trick state method better estimated the single photon ratio in pulse, and this makes the key rate of QKD system and maximum safe distance all be significantly increased.2005, Wang and Lo proposed complete trick state QKD scheme respectively, 2007, research group's Combined Trials of China, completed the experimental verification of inveigling state QKD scheme.Subsequently, numerous QKD scheme and experiment have researcher all over the world to complete, and have been proved to be to resist the most effective scheme that PNS attacks.And polarization correlated, namely different to different polarization states light intensity modulation result due to intensity modulator in phase encoding scheme, historical facts or anecdotes now trick state light source is at a high speed very difficult.
The basic idea of trick state scheme is: the trick state pulse that Alice intensity is different replaces the pulse of a part of signal state.Inveigle state and signal state to be identical in physical essence, they are all the weak coherent states sent by light source, and just intensity is different, namely has different average photon numbers.Eve cannot distinguish and inveigle state and signal state, makes no exception to two kinds of signals when carrying out PNS attack.But owing to inveigling state different with signal state intensity, therefore percent of pass can be different with error rate.
At present in most of polarization encoder QKD scheme, carry out manual adjustments with four semiconductor lasers by Polarization Controller and go out four kinds of polarization states, be i.e. a pair inclined base of line (45 ° of line polarisations and 135 ° of line polarisations) and a pair inclined base of circle (left circularly polarized light and right-circularly polarized light) totally four kinds of polarization states.Inveigle state light source to realize, also need the light exported by each laser to realize respectively inveigling state and signal state by beam splitting, this adds redundancy and the cost of system undoubtedly, is unfavorable for the integrated of system; And due to the centre wavelength and live width etc. of different laser diode, all there is some difference, can bring leak to whole system.
Also internal modulation method can be used to prepare the quantum state of inveigling three kinds of every average pulse number of photons of difference in state, namely the electric impulse signal amplitude by controlling driving laser diode controls the amplitude size of output laser pulse, the electric impulse signal of this kind of method driving laser diode is supershort electric pulse, and be AC signal, there is certain negative sense bias voltage, can use when medium and low frequency section, but at high frequency, when particularly frequency reaches more than GHz, this exist the shape that electric impulse signal that negative sense is biased can cause output laser pulse, amplitude, the a series of problem of inconsistency such as pulsewidth, the security breaches in communication process can be caused.
Utility model content
The purpose of this utility model is the device that the method for a kind of external modulation provided for prior art Problems existing produces that polarization encoder inveigles state quantum light source, this device adopts the intensity of the mode modulating light pulse of external modulation, the light pulse of the different quantum states modulated has good consistency, overcomes internal modulation due to optical pulse shape, amplitude, the inconsistent problem causing security breaches of pulsewidth.
The purpose of this utility model is achieved in that
The high speed of external modulation inveigles a device for state quantum light source, feature to be that this device is produced light path, high-speed light phase modulation module, optical attenuator and high speed logic control chip formed by ultrashort pulse laser, high-speed light intensity modulated module, polarization state; Wherein, ultrashort pulse laser connects high-speed light intensity modulated module, high-speed light intensity modulated model calling polarization state produces light path, polarization state produces light path one end and connects high-speed light phase modulation module, one end connects optical attenuator, and high speed logic control chip connects ultrashort pulse laser, high-speed light intensity modulated module and high-speed light phase modulation module respectively.
Described ultrashort pulse laser is the semiconductor laser diode that electric pulse drives, and the repetition rate of the laser pulse sent can reach GHz, and light impulse length is picosecond magnitude.
Described high-speed light intensity modulated module, be made up of high-speed light intensity modulator and its drive circuit, be connected with described ultrashort pulse laser by optical fiber, intensity modulated is carried out to the ultrashort light pulse that it produces, described high-speed light intensity modulator is the light intensity modulator based on electro optic effect, and extinction ratio requires higher; Described drive circuit is made up of two-way, and each clock cycle selects random drive one road or two-way all not to trigger by high speed logic control chip, produces I respectively
1, I
2, 0 three kinds of light intensity, wherein I
1: I
2=3:1, respectively respective signal state and trick state.
Described polarization state produces optical routing optical fibre device composition, can be Sagnac (Sagnac) interference ring or the light path based on " plug-play " etc., incident light can be divided into two bunch polarised lights mutually to interfere by this light path, wherein a route polarised light passes through phase-modulator, produce phase difference with another linearly polarized light, two-beam modulates the inclined base of outlet (45 ° of line polarisations and 135 ° of line polarisations) and circle inclined base (left circularly polarized light and right-circularly polarized light) totally four kinds of polarization states after interfering.
Described high-speed light phase modulation module is made up of High speed phase modulators and its drive circuit, described phase-modulator is the modulator based on electro optic effect, modulator crystal used can be KDP crystal or lithium columbate crystal etc., when being added to the electric field on crystal and changing, crystal medium refractive index linear change thereupon, thus realize the modulation to light; Described drive circuit is made up of (respectively the phase shift of correspondence 0, pi/2, π, 3 pi/2s), by any road of high speed logic control chip random drive four roads.
Described high speed logic control chip can be field programmable gate array (Field Programmable Gate Array, or integrated circuit ASIC (Application Specific Integrated Circuits FPGA), the logical block such as ASIC), described asic chip is the integrated circuit by system requirements processing and fabricating, because it can be customized therefore than the FPGA execution speed block of equal technique, due to some logical resources do not used that can save in FPGA thus large-scale production time cost very low.
Described optical attenuator is a kind of adjustable optical fibre device of decaying, produce light path by polarization maintaining optical fibre and polarization state to be connected, light pulse signal after modulation is decayed to quantum state level, produce totally nine kinds of quantum states: three kinds of intensity light pulse, average every pulsed light subnumber is respectively μ=0, μ=0.2, μ=0.6, i.e. zero photon state, trick state and signal state (number ratio is 1:1:3); Wherein average every pulsed light subnumber is μ=0.2, two kinds of light pulse signals of μ=0.6 comprise again four kinds of polarization states (45 ° of line polarisations, 135 ° of line polarisations, left circularly polarized light and right-circularly polarized lights) respectively.
The beneficial effects of the utility model:
(1), the utility model adopts laser diode modulation kind quantum state coldest days of the year end, is conducive to the integrated of engineering.
(2), the utility model adopts the intensity of method modulating light pulse of external modulation, and the light pulse of the different quantum states modulated has good consistency, overcomes internal modulation due to optical pulse shape, amplitude, the inconsistent problem causing security breaches of pulsewidth.
(3), the quantum state that adopts of the utility model produces scheme and is easy to control and synchronous, and at high band such as GHz, even hyperfrequency is applicable equally.
(4), the utility model adopts high speed logic control chip to make system have the reliability and stability of height as master controller.
(5), the utility model adopts and first carries out to light pulse intensity modulated produces four kinds of polarization states again method through polarization state generation light path, avoid the polarization correlated of intensity modulator, namely avoid when different polarization state enters intensity modulator and occur different intensity modulated results, further increase the fail safe of system.
Accompanying drawing explanation
Fig. 1 is the utility model apparatus structure schematic diagram;
Fig. 2 is the synchronous schematic diagram of FPGA in the utility model embodiment;
Fig. 3 is the synchronous schematic diagram of asic chip in the utility model embodiment;
Fig. 4 is the utility model example structure schematic diagram;
Fig. 5 is the ultrashort laser pulse sequential chart of the utility model embodiment;
Fig. 6 is the high-speed light intensity modulated module diagram of the utility model embodiment;
Fig. 7 is the high-speed light intensity modulated module optical pulse intensity modulation timing figure of the utility model embodiment;
Fig. 8 is light pulse phase-modulation sequential chart in the high-speed light phase modulation module of the utility model embodiment;
Fig. 9 is that the polarization state of the utility model embodiment produces light path schematic diagram.
Embodiment
Below in conjunction with drawings and Examples, the utility model is described in detail, but is not limited only to following examples.
Embodiment
Consult Fig. 4, centered by the present embodiment lasing light emitter, wavelength 1550nm, repetition rate are the ultrashort pulse laser of 1.25GHz, pulsewidth, at about 30ps, produces the trick state light source that comprise nine kind quantum states after producing light path and optical attenuator successively by high-speed light intensity modulator module and polarization state.
Consult Fig. 2 and Fig. 3, the random data signal of 1.25GHz will be used in the present embodiment, exported by logic chip and and the triggering signal of ultrashort pulse laser synchronous, the true random number based on white noise is produced by random number chip, send into after logic chip processes and give light intensity modulation module and the use of light phase modulation module by random data signal, logic chip exports 1.25GHz triggering signal to ultrashort pulse laser simultaneously, and carries out synchronous with random data signal.
Consult Fig. 5, the light pulse that ultrashort pulse laser sends is linearly polarized light, is spaced apart 800ps, then enters light intensity modulation module, carries out the Stochastic Modulation of three kinds of luminous intensities.The intensity modulator used requires very high extinction ratio and very wide bandwidth, uses the lithium niobate intensity modulator that extinction ratio is 12GHz for 30dB bandwidth herein; As shown in Figure 6, the half-wave voltage of this intensity modulator is 6.5V for intensity modulator and its peripheral drive circuit, the size of namely added DC offset voltage.Whole intensity modulated module is controlled by logic chip and synchronously, logic chip each clock cycle produces three kinds of two random numbers 00,01,10, and the ratio controlling these three kinds of random numbers is 1:3:1, and shaping pulse amplification module 1 and 2 is corresponding I respectively
1and I
2(wherein I
1: I
2=3:1), triggered by random number 01 and 10 respectively, when producing 00 random number, two-way does not all trigger, now without light output, corresponding zero photon state, so time I
1, I
2, 0 three kinds of light intensity light pulse quantity ratio be 3:1:1; Wherein the modulated voltage signal of shaping pulse amplification module 1 and 2 output is by broadband power synthesizer coupling rear drive intensity modulator.As shown in Figure 7, three kinds of modulation voltage pulses that the random number produced by logic chip triggers at random modulate each light pulse signal respectively to the modulation timing of signal after synchronous, then export I at random
1, I
2, 0 three kinds of light intensity (wherein I
1: I
2=3:1 and three kinds of light intensity number of pulses are than being 3:1:1).
Then the light pulse comprising three kinds of different light intensity enters four mouthfuls of PBS after optical circulator, as shown in Figure 9, each light pulse is divided into the mutually perpendicular A light in polarization direction and B light, A light is successively by again arriving PBS after phase modulation module, PBS and faraday's speculum FM, now have rotated 90 ° because A light retrodeviates polarization state by faraday's tilting mirror, therefore meeting transmission when again entering PBS; The path of B light is then contrary, again arrives PBS successively after FM, PBS, phase modulation module.Because two light transmission paths are identical, so time A light and B light again interfere in the convergence of PBS place.Wherein only phase-modulation is carried out to A light, sequential as shown in Figure 8, modulating pulse is alignd with the pulse train of A light respectively in each cycle, and guarantee that the B light simultaneously injected with A light is by turning off modulating pulse before phase-modulator, namely the path length difference that the length adjusting optical fiber makes A light and B light pass through when arriving phase-modulator is L, and light in a fiber propagation velocity is 2 × 10
8m/s, makes B pulse just in time middle by modulator two A pulses, even if A and B two pulse is 400ps by the time delay of modulator, then
L=2×10
8m/s×400ps=8cm
And modulate the width control system of electric pulse at about 300ps, can guarantee only to modulate A light.Except the optical fiber connecting FM and PBS is that except monomode fiber, all the other optical fiber are polarization maintaining optical fibre in this light path.
The circuit of phase-modulation electric impulse signal has four tunnels, as shown in Figure 9, corresponding phase modulators modulate produces 0 respectively, pi/2, π, 3 pi/2 phase shift required voltages, then by broadband power synthesizer, the modulation voltage of each clock cycle is synthesized a road rear drive phase-modulator (similar with intensity modulator drive circuit), the relative B light of A light is made to produce 0 respectively, pi/2, π, the phase difference of 3 pi/2s, then interfere when PBS converges again, produce 45 ° of line polarisations respectively, left circularly polarized light, 135 ° of linearly polarized lights and right-circularly polarized light be totally four kinds of polarization states.Wherein exported the random number of 1.25GHz by logic chip, trigger a road drive circuit at random in each clock cycle, namely can produce four kinds of polarization states by this light path.
Then light pulse signal decays to single photon level by arriving the adjustable optical attenuator of decay after optical circulator, totally three kinds of intensity light pulse, average every pulsed light subnumber is respectively μ=0, μ=0.2, μ=0.6, i.e. zero photon state, trick state and signal state (number ratio is 1:1:3); Wherein average every pulsed light subnumber is μ=0.2, two kinds of light pulse signals of μ=0.6 comprise again four kinds of polarization states (45 ° of line polarisations, 135 ° of line polarisations, left circularly polarized light and right-circularly polarized lights) respectively, so time obtain the trick state light source comprising nine kinds of quantum states.