CN1317598C - Geraerating method of communication band single photon source - Google Patents

Geraerating method of communication band single photon source Download PDF

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CN1317598C
CN1317598C CNB2004100846223A CN200410084622A CN1317598C CN 1317598 C CN1317598 C CN 1317598C CN B2004100846223 A CNB2004100846223 A CN B2004100846223A CN 200410084622 A CN200410084622 A CN 200410084622A CN 1317598 C CN1317598 C CN 1317598C
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light
frequency
photon source
pump light
nonlinear crystal
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CN1624558A (en
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曾和平
周春源
吴光
韩晓红
潘海峰
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East China Normal University
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East China Normal University
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Abstract

The present invention relates to the class of quantum secret communication, particularly to a method for obtaining an optical fibre communication wave-band single photon source which can be used for quantum secret communication of optical fibers by frequency conversion. In the method, single photons used as signal light are transmitted into a nonlinear crystal which is pumped by light, and the frequency of pumping light is smaller than that of the single photon source to generate a difference frequency between the signal light and the pumping light for generating communication wave-band photons. The present invention has the advantage that the method can obtain ideal communication wave-band single photon sources; the present invention also has the advantages of high conversion efficiency, high stability, good directivity and little probability of containing multiple photons in each pulse.

Description

A kind of production method of communication band single-photon source
Technical field
The present invention relates to the quantum secret communication class, relate to concretely a kind ofly obtain the method that can be used for the optical fiber Single Photon Source of Quantum Secure Communications, obtain the single-photon source of optical fiber communication wave band by frequency inverted.
Background technology
Quantum secret communication is based on the cipher key communication of light quantum, information loads on the single photon, and transmit by single photon, unknown quantum state can not be cloned, measure quantum and can change quantum state, the listener-in just can not obtain information and not be found like this, therefore in quantum secret communication, cipher key communication is perfectly safe, and is wherein most important as the single photon of information carrier.
It is near-infrared band about 1.3 μ m and 1.5 μ m that optical communicating waveband refers to wavelength, because compare with other wave band, the light of these two wave bands is subjected to the minimum that influences of fibre loss and chromatic dispersion, is specially adapted to faint optical signal and transmits at the optical fiber middle and long distance.
Single photon in order to load information in the existing quantum secret communication system obtains after pulse decays to weak laser mostly, thereby make light when leaving the key transmit leg, decay to the single photon level, generally decay to every average pulse and contain 0.1 photon, thereby guarantee lower multi-photon pulse, guarantee being perfectly safe of cipher key communication, but so useful photon generation efficient is just very low, and the probability that the situation that multi-photon occurs accounts for total bright dipping situation does not change thereupon, has limited the critical distance and the key generating rate of quantum secret communication.
Quantum secret communication just will develop must use effective single-photon source.There is the true single-photon source of 4 classes in the laboratory, to realize at present.Adopt quantum well, quantum dot, optical pumping colour centre crystal, the parameter method of conversion down respectively.
Adopting the method for quantum well is to utilize the PN semiconductor structure, and all there is quantum well at the PN junction two ends, and its semiconductor layer is very narrow, applying under the situation of small voltage very, just have the electron hole and enter P district and N district respectively, thus compound generation single photon.But adopt the method for quantum well, require working temperature very low,, be difficult for realizing in mK (per mille Kelvin) magnitude; And the direction of light of its generation is relatively poor.
Adopt the quantum dot method, quantum dot can be regarded " artificial " atom that methods such as utilizing the chemical evapn precipitation is synthesized as, under the enough little situation of density between quantum dot, only excite a quantum dot in the time of can guaranteeing the pump light irradiation, thereby only send a photon, when adopting the method for quantum dot usually, all can press narrow linewidth with microcavity, so narrow with the common live width of single photon that the method for quantum dot is obtained, experimental provision is relatively complicated simultaneously.
Adopting optical pumping colour centre crystal method, is example with nitrogen defective diamond crystal, participates in nitrogen-atoms during artificially synthesizing diamond, and under certain growing environment, diamond crystal structures can produce the i.e. carbon atom of a nitrogen-atoms replacement of lattice imperfection.When the optical pumping meeting generation fluorescence on defective with 532nm, its centre wavelength is 637nm, uses the lower crystal of small spot pumping defect density, can realize a pumping individual defect, thereby obtains the output of single photon fluorescence.This method directivity is better, and efficient is also higher.Because the centre wavelength of the single photon that produces is 637nm, is not suitable for the optical fiber quantum secret communication.
Adopt the parameter method of conversion down, parameter conversion down is a nonlinear effect of utilizing crystal, when a high-frequency pump light is injected wherein, utilize the second order nonlinear effect of crystal, the direction spontaneous radiation of satisfying certain phase condition goes out two photons that frequency is lower, new two photon frequency sums that produce equal the pump photon frequency, produce the efficient of new photon by the nonlinear factor of crystal, with the action length and the pump light intensities decision of pump light, the photon that is produced is followed Poisson distribution, still is difficult to eliminate the multi-photon situation.And even use pulse pump light, also there is certain uncertainty the time that the parameter single photon produces, and the direction of light of its generation is also relatively poor.
Summary of the invention
The objective of the invention is at above-mentioned the deficiencies in the prior art part, a kind of production method of communication band single-photon source is provided, this method can obtain the desirable single-photon source of effective communication band, this method is utilized existing non-communication band single-photon source, by non-linear (difference frequency) thus conversion obtains the communication band single photon.
The object of the invention realizes being finished by following technical scheme:
A kind of production method of communication band single-photon source, it is characterized in that this method is that the non-communication band single-photon incident as flashlight is advanced nonlinear crystal, this nonlinear crystal is optically pumped, pumping light frequency wherein is less than the frequency of single-photon source, adjusting flashlight then overlaps in nonlinear crystal with intracavity pump light, and satisfy phase-matching condition, because the second order nonlinear effect of crystal, make as signal light frequency higher single-photon source and the lower pump light generation difference frequency of frequency, thereby produce the photon of communication band that a frequency is the difference of flashlight and pump light frequency.
Above-mentioned nonlinear crystal has referred to second order nonlinear effect, and logical optical band comprises pump light, the nonlinear crystal of incoming signal light and conversion back signal light wavelength.Wavelength as the single photon of flashlight should be less than the optical communicating waveband wavelength.
Pump light can be continuous or impulse form, and the pumping light intensity should make nonlinear crystal produce nonlinear polarization at least, but can not surpass the damage threshold of nonlinear crystal.Above-mentioned nonlinear crystal can place an external resonator cavity interior (external cavity type) that the power humidification is arranged, and also can place in the active resonant cavity that produces pump light (intracavity).
Described phase-matching condition is meant angular phase coupling or accurate phase matching, angular phase coupling wherein is to select specific nonlinear crystal cutting angle, make that in nonlinear crystal pump light equates with the wave vector of conversion back flashlight with the wave vector stack back of incoming signal light; Accurate phase matching wherein is nonlinear crystal to be made period polarized, specific polarization cycle can correspondingly realize the pump light of specific wavelength and the phase matching of incoming signal light.
The invention has the advantages that, can obtain the desirable single-photon source of communication band, the conversion efficiency height, good stability, good directionality, the probability that each pulse contains multi-photon is little.
Summary of drawings
Accompanying drawing 1 utilizes outer-cavity structure for the embodiment of the invention 1 and realizes the light channel structure synoptic diagram of frequency inverted;
Accompanying drawing 2 utilizes under inner-cavity structure, the situation of pump light for continuous light for the embodiment of the invention 2, realizes the light channel structure synoptic diagram of frequency inverted;
Accompanying drawing 3 utilizes under inner-cavity structure, the situation of pump light for pulsed light for the embodiment of the invention 3,4, realizes the structured flowchart of frequency inverted;
Accompanying drawing 4 utilizes under inner-cavity structure, the situation of pump light for pulsed light for the embodiment of the invention 3,4, realizes the light channel structure synoptic diagram of frequency inverted.
Concrete technical scheme
Feature of the present invention and other correlated characteristic are described in further detail by embodiment below in conjunction with accompanying drawing, so that technician's of the same trade understanding:
Optical communicating waveband 1.5 μ m are example with 1550nm in the following embodiments, and its all band is the implementation method unanimity of wave band therewith.
The single photon signal light wavelength is 631nm in our embodiment, and the pump light wavelength that is used for frequency inverted is 1064nm, and difference frequency light (the single photon signal that obtains after the frequency inverted) wavelength is 1550nm, i.e. the desirable single-photon source of communication band.
Embodiment 1:
In order to realize effective non-linear frequency conversion, the pump light intensities that as far as possible improves effective incident nonlinear crystal is necessary.As shown in Figure 1, the method that this programme adopts is, pump light is injected external four mirrors, 8 word ring resonators (perhaps other structure suitable cavity), with servo-control system control one side chamber mirror wherein, make the resonance frequency and the pumping light frequency of resonator cavity be complementary, reach the effect that intracavity power strengthens, thereby make the nonlinear crystal that is placed in this exocoel can obtain to be several times as much as effective incident intensity of pump light.
The experimental provision of label 1-15 is described below among Fig. 1:
Pump light 1, the laser instrument that is met the pump light wavelength of phase matching in the nonlinear interaction by emergent light provides, as solid neodymium ion laser instrument etc., adjustable power;
Coupling input cavity mirror 2, the planar laser catoptron is at pump light wave band reflectivity 95%;
Planar cavity mirror 3, pump light wave band of laser high reflective mirror, reflectivity is greater than 99.9%;
Piezoelectric ceramics 4, bonding with planar cavity mirror 3, can change laser cavity length by changing its operating voltage;
Servo-control system 5, servo control circuit, the operating voltage of control piezoelectric ceramics 4;
Power monitoring meter 6, monitoring shoot laser power is delivered to servo-control system 5 with the variable power signal;
Single photon signal 7 for existing centre wavelength is the single-photon source of 637nm, can obtain the single-photon source that wavelength is 631nm after filtration behind the electro-optical device 12;
Concave surface laser mirror 8, radius of curvature R=-75mm, the high-reflecting film of curved surface plating pump light wave band, R>99.9%, the anti-reflection film of two sides plating flashlight and difference frequency light wave band;
Nonlinear crystal 9, satisfy phase-matching condition, can realize the nonlinear crystal of the flashlight frequency translation among the present invention, such as BIBO (bismuth boracic acid) crystal, PPLN (period polarized lithium niobate) crystal or PP-MgO:LN (mixing the period polarized lithium niobate of magnesium) crystal etc., working temperature is accurately controlled, and two surfaces of crystal are coated with the anti-reflection film of pump light, flashlight and three wave bands of difference frequency light;
Concave surface laser mirror 10, radius of curvature R=-75mm, the high-reflecting film of curved surface plating pump light wave band, R>99.9%, the anti-reflection film of two sides plating difference frequency light wave band;
Amici prism 11, the Brewster angle quartz prism;
Filter system 12 comprises with the flashlight frequency being the spike interference filter a slice at center, plane mirror a slice of the anti-reflection film of two sides plating flashlight and difference frequency light wave band;
Lens 13, about focal length 100mm, two sides plating flashlight wave band anti-reflection film;
Diaphragm 14, slit diaphragm;
Filter system 15 comprises that with the difference frequency light frequency be the high-reflecting film of the spike interference filter a slice at center and 0 ° of incident pump light wave band of plating, plane mirror a slice that the anti-reflection film of difference frequency light wave band is plated on the two sides.
The laserresonator that adopts in this programme is four mirror ring resonators that are made of planar cavity mirror 2,3 and sphere chamber mirror 8,10, satisfy the resonator cavity stable condition, wherein the distance between the planar cavity mirror 2 and 3 is 30mm, distance between the sphere chamber mirror 8 and 10 is 140mm, chamber mirror 2 and 8,3 equates with 10 distance, is 120mm.Coupling input cavity mirror 2 is plane 1064nm laser mirrors, and reflectivity is 95%.Pump light can be provided by the solid neodymium ion laser instrument of semiconductor diode pump, and output laser is linear polarization.By coupling input cavity mirror 2 pump energy is injected the chamber.Planar cavity mirror 3 is bonded together with piezoelectric ceramics 4, and piezoelectric ceramics is flexible can adjust cavity length and pump light resonance.The voltage signal of control piezoelectric ceramics is provided by servo-control system 5.Power monitoring meter 6 obtains the signal of output power fluctuation, delivers to servo-control system, controls the flexible of piezoelectric ceramics then, and the latch well internal power is in maximal value.Power in the chamber can be than high 1 to 2 order of magnitude of pumping light power at this moment.Regulate the pumping light intensity, guarantee that conversion efficiency reaches quantum state and shifts.Nonlinear crystal is placed chamber such as figure position, accurately control crystal temperature effect and satisfying on the working temperature of phase matching.
The PPLN crystal has utilized accurate phase matching to interact, and has selected specific polarization cycle to realize that pump light 1064nm and the interaction of incoming signal light 631nm difference frequency obtain changing back flashlight 1550nm, and effective nonlinear coefficient is about 16pm/V.The polarization cycle of the PPLN crystal that adopts in the present embodiment is 11.80 μ m or 12.0 μ m.Incoming signal polarisation of light direction, consistent with the pump light polarization direction in the chamber, satisfy I class phase-matching condition.The single photon signal of 637nm is after filtration behind the photosystem 12, obtain the flashlight of 631nm, by being coupled in the nonlinear crystal after lens 13 focusing, accurately the locus of conditioning signal light overlaps in nonlinear crystal with pump light, and purpose is to make their sufficient interactions.The nonlinear crystal that uses in the present embodiment is the PPLN crystal, length 40mm.The anti-reflection film that nonlinear crystal two surfaces are coated with pump light 1064nm, incoming signal light 631nm and outgoing difference frequency light 1550nm wave band can reduce the loss of single photon signal, also can reduce the insertion loss of nonlinear crystal to resonator cavity.Comprised pump light and difference frequency light by chamber mirror 10 emitting lasers, by Amici prism 11 separately, done spatial filtering, only allowed difference frequency light to pass through with slit diaphragm 14 with different compositions.Filter system 15 comprises with 1550nm being the narrow band pass filter at center and the 1064nm high reflective mirror of two sides plating 1550nm anti-reflection film, and purpose is in order further to leach the 1550nm difference frequency light.Thereby obtain the single photon signal that we need.
Embodiment 2:
As shown in Figure 2, compare with embodiment 1, in the present embodiment, we have invented the power that a kind of comparatively simple method increases effective incident nonlinear crystal, can significantly reduce the complexity of system and the adjustment difficulty of light path.Producing wavelength is the resonator cavity of the pump light of 1064nm, and the transmissivity of its outgoing mirror is generally a few percent or tens percent, and then the light intensity in the resonator cavity can reach tens times even tens times of output intensity.Nonlinear crystal is placed in this resonator cavity, can obtain being higher than effective incident intensity of 1-2 the order of magnitude of emergent light intensity equally.Because nonlinear crystal is placed the active cavity of pump light, the device that does not need to add just can obtain the incident pumping light power of high stable, and this has also improved the degree of stability of frequency inverted greatly.Because continuous pump light is difficult to reach very high power, so this moment, the effective nonlinear coefficient to the nonlinear crystal that is used for frequency inverted required than higher, as the accurate phase matching non-linear crystal of cycles such as PPLN (period polarized lithium niobate) crystal, PP-MgO:LN (lithium niobate of period polarized doped with magnesia) crystal polarization.
The experimental provision of label 1-12 is described below among Fig. 2:
Single photon signal 1, promptly existing centre wavelength are the single-photon source of 637nm, can obtain the single-photon source that wavelength is 631nm after filtration behind the electro-optical device 2;
Filter system 2 comprises with the incoming signal light frequency being the spike interference filter a slice at center, plane mirror a slice of the anti-reflection film of two sides plating incoming signal optical band;
Lens 3, about focal length 500mm, two sides plating incoming signal optical band anti-reflection film;
Concave surface laser cavity catoptron 4, the anti-reflection film of two sides plating incoming signal optical band, the high-reflecting film of curved surface plating intracavity pump optical band, reflectivity is 98%, radius of curvature R=-500mm;
Planar laser cavity reflection mirror 5, the anti-reflection film of two sides plating difference frequency light wave band, close nonlinear crystal simultaneously plates the high-reflecting film of pump light wave band;
Nonlinear crystal 6 satisfies phase-matching condition, can realize the nonlinear crystal of flashlight frequency translation of the present invention, and such as BIBO crystal, PPLN crystal or PP-MgO:LN crystal etc., working temperature is accurately controlled;
Laser gain crystal 7 is mixed Nd 3+The ion laser gain media is (as Nd 3+: GdVO 4, Nd 3+: YVO 4) length is 3mm, the anti-reflection film of two sides plating intracavity pump laser wavelength, doping content is 1%;
Concave surface laser cavity catoptron 8, the anti-reflection film of two sides plating 808nm, the high-reflecting film of curved surface plating pumping laser wavelength, radius of curvature R=-100mm;
Pumping source 9, the LD (semiconductor laser diode laser instrument) of optical fiber coupling output.Emission wavelength is 808nm, peak power output 20W.Be coupled on the gain medium by optical focusing system;
Amici prism 10, the Brewster angle quartz prism;
Diaphragm 11, slit diaphragm;
Filter system 12 comprises that with the difference frequency light wavelength be each a slice of plane mirror that the spike interference filter at center and high-reflecting film, the two sides of plating 0 ° of incident pump light wave band are coated with the anti-reflection film of difference frequency light wavelength.
As shown in Figure 2, among the embodiment, the pump light of 1064nm is produced by solid neodymium ion laser instrument.It is that the laser 9 of 20W is focused on the neodymium ion laser gain crystal 7 by optical system that the semiconductor diode laser of optical fiber coupling output produces maximum emergent power, realizes laser generation in the laserresonator of L type.The laserresonator of L type is to be made of two sides concave surface laser cavity catoptron 4 and 8 and planar laser cavity reflection mirrors 5, and the angle between two arms is approximately 18 °.Distance between the laser cavity catoptron 8 and 4 is about 600mm, and the distance between the laser cavity catoptron 5 and 4 is about 480mm, to satisfy stable resonator cavity condition.The reflectivity of 4 pairs of 1064nm laser of concave surface laser cavity catoptron is 98%, owing to along the direction of resonator cavity two arms laser emitting is arranged all, its total coupling output rating is about 3%, and endovenous laser is a linear polarization.When if the 1064nm Output optical power of resonator cavity is 3W, then the power in the chamber is 100W.The size of 1064nm laser power can be regulated by changing 808nm pump light 9 power that sent by LD in the chamber.
Because the spot size of resonator cavity inner light beam is smaller on the close position of planar laser cavity reflection mirror 5, nonlinear crystal 6 is positioned over obtains bigger incident optical power density herein.The long nonlinear crystal PPLN of the 40mm that uses in this scheme two sides is coated with the anti-reflection film at 631nm, 1064nm and 1550nm wave band, has both reduced low light level loss of signal, has also reduced the insertion loss of resonator cavity.
The PPLN crystal has utilized accurate phase matching to interact, and has selected specific polarization cycle to realize that pump light 1064nm and the interaction of incoming signal light 631nm difference frequency obtain changing back flashlight 1550nm, and effective nonlinear coefficient is about 16pm/V.Polarization cycle is identical with embodiment 1.The single photon signal of 631nm is that the single-photon source by 2 couples of 637nm of filtering apparatus filters and obtains, and flashlight is consistent with the interior 1064nm laser light field polarization of resonator cavity, satisfies I class phase-matching condition.After lens 3 focusing, incide on the nonlinear crystal 6, the focus of focusing drops on the centre position of nonlinear crystal.The temperature of nonlinear crystal is accurately controlled, and deviation is less than 0.1 ℃.The careful position of adjusting incident light, make incident light in nonlinear crystal with resonator cavity in the 1064nm light field well overlap.Like this, 1064nm pump light and 631nm flashlight interact in nonlinear crystal, are converted to the difference frequency light of 1550nm under the flashlight frequency of the 631nm of incident.The pump light intensities of effective incident nonlinear crystal in the control chamber makes conversion efficiency reach maximum, has also realized the quantum state transfer simultaneously.In order to reduce low light level signal (comprising the incoming signal light of 631nm and the difference frequency light of 1550nm) loss, on the element of its process, all be coated with corresponding anti-reflection film.1064nm pump light and 1550nm difference frequency light are through outside planar laser cavity reflection mirror 5 output cavities, and this moment, they spatially still overlapped basically.Through behind the Amici prism 10, pump light and difference frequency light spatially are separated.Do spatial filtering with slit diaphragm 11, only allow difference frequency light to pass through.Filter system 12 comprises with 1550nm being the narrow band pass filter at center and the 1064nm high reflective mirror of two sides plating 1550nm anti-reflection film, and purpose is in order further to leach the 1550nm difference frequency light.Thereby obtain the single photon output of we required 1550nm.
Embodiment 3:
As shown in Figure 3, pump light is pulse, the single photon signal of a incident also is pulse, in order to make pump light and flashlight reach synchronous in time, here with the e clock control the triggering of single photon signal and pulse pump light the triggering detection system triggering constantly, and consider the priority that incident takes place, add time-delay, purpose is assurance pump light pulse and signal pulse time to go up inregister.Because pulse pump light can have very high peak power, relative, the effective nonlinear coefficient of nonlinear crystal does not need very high, as BIBO (bismuth boracic acid) crystal.
Present embodiment light channel structure synoptic diagram as shown in Figure 4,13 is the acousto-optic or the electric-optically Q-switched element of operation wavelength and pump light consistent wavelength among the figure, other element is all identical with Fig. 2.Q switched element can be used for regulating the loss of laser cavity.Transfer the process of Q to be described below: in laser pump (ing) just at first, Q switched element produces very high loss, makes the laser output of can't vibrating.Because continue pumping, energy is stored.This moment, Q switched element reduced the wastage suddenly, in the extremely short time energy stored was discharged, and promptly formed a strong laser pulse.The Q pulse has very high peak power, short pulse width.
Compare with embodiment 2, present embodiment has adopted the working method of pulse.Cavity resonator structure that adopts in the present embodiment and embodiment 2 basically identicals.For pump light is moved under pulse mode, we have inserted the Q switched element (can be acousto-optic Q modulation element or electric-optically Q-switched element) of 1064nm in the chamber.The triggering frequency lock 1064nm pump light repetition frequency of Q switched element is consistent with the repetition frequency of flashlight.The 631nm single photon flashlight of incident also is pulse, and pulsewidth is about 1 ns (10 -9S).As described in Figure 3, flashlight and Q-switch element be all by the control of time clock, and suitably introduce time-delay, guarantees flashlight and pump light pulse overlapping in time.
Nonlinear crystal 6 can use the low slightly crystal of effective nonlinear coefficient, BIBO crystal such as length 10mm, the cutting angle of crystal is: θ=7.7 °, the angular phase matching condition that in the time of 1064nm pump light and the incident of 631nm incoming signal light positive difference frequency obtains 1550nm outgoing flashlight is satisfied in =0 °.The crystal two sides is coated with the anti-reflection film of 631nm, 1064nm, 1550nm equally.Q impulse width in the chamber is in the 10ns magnitude, pulse width than the big magnitude of signal pulse about with bonding photon signal light fully by frequency inverted.Adjusting the power of 808nm pumping source and the width (adjusting Q-switch) of Q pulse makes the peak power (several kW magnitude) of pumping pulse satisfy the requirement of frequency inverted.The single photon signal of 631nm is that the single-photon source by 2 couples of 637nm of filtering apparatus filters and obtains, and flashlight is consistent with the interior 1064nm laser light field polarization of resonator cavity, satisfies I class phase-matching condition.Through behind the condenser lens 3, incide on the nonlinear crystal 6, the focus of focusing drops on the centre position of nonlinear crystal.The careful position of adjusting incident light, make incident light in nonlinear crystal with resonator cavity in the 1064nm light field well overlap.Under the nonlinear difference effect, be converted to the difference frequency light of 1550nm under the flashlight frequency of the 631nm of incident.In order to reduce low light level signal (comprising the incoming signal light of 631nm and the difference frequency light of 1550nm) loss, on the element of its process, all be coated with corresponding anti-reflection film.1064nm pump light and 1550nm difference frequency light are through outside planar laser cavity reflection mirror 5 output cavities, and this moment, they spatially still overlapped basically.Through behind the Amici prism 10, pump light and difference frequency light spatially are separated.Do spatial filtering with slit diaphragm 11, only allow difference frequency light to pass through.Filter system 12 comprises with 1550nm being the narrow band pass filter at center and the 1064nm high reflective mirror of two sides plating 1550nm anti-reflection film, and purpose is in order further to leach the 1550nm difference frequency light.Thereby obtain the single photon output of we required 1550nm.
Embodiment 4:
The method that has replaced the accent Q among the embodiment 3 in the present embodiment with the method for active mode.Active mode locking technique is to place a modulator in laser cavity, the modulation that this modulator produces an amplitude or phase place to endovenous laser, and purpose is to make the longitudinal mode spacing in the chamber equal fully.Realize coherence stack between each longitudinal mode that equates at interval, so obtain the laser pulse of high-peak power, short pulse width.It is narrow that mode locking pulse has pulse width, and the characteristics that repetition frequency is high can realize the incoming signal light frequency conversion of high repetition frequency on the one hand, also require flashlight to have very narrow pulse width on the other hand.Because the repetition frequency of mode locking pulse is by the length decision of laserresonator, so we design the length numerical value of resonator cavity, make the pump light repetition frequency equal the flashlight repetition frequency, or the integral multiple of flashlight repetition frequency, we are guaranteed that pump light pulse and signal pulse can be corresponding one by one like this, realize in time overlapping.In this programme, the pulse width of pump light is about tens of ps (10 -12S), the tens of MHz of repetition frequency, the signal pulse width of incident is about several ps, and repetition frequency can be up to number MHz even tens of MHz.
As shown in Figure 4, the light channel structure synoptic diagram of active mode and the structural representation basically identical of embodiment 3, difference only is that the element 13 that inserts in the chamber is not the Q-switch element, but produces the acousto-optic or the electrooptic modulator of locked mode modulation, and the operation wavelength of modulator is at 1064nm.As described in Figure 3, flashlight and electric light or acousto-optic modulator are controlled by a time clock, and suitably introduce time-delay, guarantee flashlight and pump light pulse overlapping in time.The accent Q mode basically identical of its working mechanism and embodiment 3.
Those skilled in the art obviously can recognize, the present invention also is not limited to certain specific chamber type, specific nonlinear crystal, the pump light of specific wavelength, promptly can design different laser cavitys satisfying under the condition of frequency inverted, select different nonlinear crystals, 1.3 the single-photon source of other wave band all can obtain by method provided by the present invention near mu m waveband and the 1.5 μ m, pump light and the corresponding resonator cavity that only need choose corresponding wave band get final product.

Claims (7)

1, a kind of production method of communication band single-photon source, it is characterized in that this method is that the non-communication band single-photon incident as flashlight is advanced nonlinear crystal, this nonlinear crystal is optically pumped, pumping light frequency wherein is less than the frequency of single-photon source, adjusting flashlight overlaps in nonlinear crystal with intracavity pump light, and satisfy phase-matching condition, make as signal light frequency higher single-photon source and the lower pump light generation difference frequency of frequency, thereby produce the photon of communication band that a frequency is the difference of flashlight and pump light frequency.
2, the production method of a kind of communication band single-photon source according to claim 1, it is characterized in that described nonlinear crystal has referred to second order nonlinear effect, and logical optical band comprises the nonlinear crystal of pump light, incoming signal light and conversion back signal light wavelength.
3, the production method of a kind of communication band single-photon source according to claim 1 is characterized in that described pump light is continuous or impulse form.
4, the production method of a kind of communication band single-photon source according to claim 1, the wavelength that it is characterized in that described single photon as flashlight is less than the optical communicating waveband wavelength.
5, the production method of a kind of communication band single-photon source according to claim 1 is characterized in that described pumping light intensity should make nonlinear crystal produce nonlinear polarization at least, but can not surpass the damage threshold of nonlinear crystal.
6, the production method of a kind of communication band single-photon source according to claim 1 is characterized in that described nonlinear crystal can place in the external resonator cavity that the power humidification arranged, and also can place in the active resonant cavity that produces pump light.
7, the production method of a kind of communication band single-photon source according to claim 1 is characterized in that described phase-matching condition refers to angular phase coupling or accurate phase matching.
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CN114578628B (en) * 2022-02-18 2023-04-14 山西大学 Down-conversion optical resonant cavity for generating narrow linewidth photon pair

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