CN102255224A - Circulating ultrasonic grating frequency shift nonlinear difference-frequency type broadband tuning terahertz wave generator - Google Patents

Abstract

The invention provides a circulating ultrasonic grating frequency shift nonlinear difference-frequency type broadband tuning terahertz wave generator which comprises a laser, a first circulator, a beam splitter, an ultrasonic grating frequency shift based circulating frequency shift link, a first beam synthesizer, a photoisolator, a nonlinear element and a terahertz wave filter, wherein light output by the laser is split into a first path of light and a second path of light by the beam splitter after passing through the first circulator, the first path of light is used as reference light and the second path of light is input to the circulating frequency shift link to generate circulating frequency shift light, the first beam synthesizer is used for carrying out difference frequency on the reference light and the circulating frequency shift light by the photoisolator in the nonlinear element after the reference light and the circulating frequency shift light are synthesized and then coherent terahertz waves are generated through filtering radiation of the terahertz wave filter. The circulating ultrasonic grating frequency shift nonlinear difference-frequency type broadband tuning terahertz wave generator provided by the invention has the advantages of small volume, less quantity and easiness in integration of optical elements, large tuning range, high tuning efficiency and high terahertz wave generation efficiency.

Description

Circulating ultrasonic grating shift frequency nonlinear difference formula wide-band tuning THz wave generator

Technical field

The present invention relates to the wide-band tuning THz wave device that a kind of difference frequency mode produces, relate in particular to a kind of wide-band tuning THz wave light source based on ultrasonic grating shift frequency, circulation shift frequency and difference frequency principle.

Background technology

Terahertz (THz, 1THz=10 ¹²Hz) ripple is meant that operating frequency is in the electromagnetic wave in 0.1～10THz scope.Why THz wave can cause the research interest that the scientific worker is dense, it is not electromagnetic radiation rarely known by the people because it is mysterious, main is that these unique character have been given Terahertz science application prospects just because it has the character of a lot of uniquenesses.The character of the uniqueness of THz wave mainly shows: perspectivity, fail safe, spectral resolving power.Terahertz emission has good penetrability to a lot of dielectric materials and nonpolar liquid, therefore can carry out perspective imaging to nontransparent object, in addition since the wavelength of Terahertz greater than the yardstick of suspension smoke particle in the air, the Rayleigh scattering loss is minimum, so can penetrate flue dust and thick fog preferably, be the perfect light source of imaging in fire rescue or the travel fatigue environmental monitoring.Compare the photon energy that X ray has kiloelectron-volt, the photon energy of terahertz emission has only the milli electronvolt, this energy is all lower than the bond energy of various chemical bonds, so ionization reaction can not take place, promptly can not destroy molecular structure of compounds, therefore can be applied to places such as safety check and biological detection, this is the embodiment of the fail safe of Terahertz, a large amount of molecules, especially the transition of the vibration of organic molecule and rotation is composed, all be in the Terahertz spectral range, thereby can utilize the spectral resolution characteristic to realize the analysis of object appearance and constituent.

Because THz wave has above-mentioned important application prospects, existing in the world at present a plurality of groups have carried out the scientific research in relevant THz wave field, especially about the research of the generation aspect of tunable relevant THz wave.In Korea S, N.J.Kim group has realized in 2009 based on dual wavelength distributed feedback laser diode (Distributed Feedback Laser Diodes, DFB LDs) the tunable continuous wave terahertz emission of pumping, and expand 0.5THz in the broadness of tuning with THz wave in 2010.In Canada, S.L.Pan group has realized in 2009 based on dual wavelength erbium-doped fiber laser (Erbium-Doped Fiber Laser, adjustable microwave signal output EDFL).In the U.S., Y.J.Ding group has realized that in 2010 (Difference Frequency DF) has produced compact, portable terahertz emission source, and its volume can narrow down to 30.48 * 15.24 * 10.16cm based on the dual wavelength difference frequency ³, unique deficiency be: untunable.In Germany, the I.Breunig group of Bonn University constantly improved based on inner chamber optical parametric oscillator (Internal Cavity Optical Parametric Oscillator during 2007 to 2010, ICOPO) tunable THz wave produces scheme, final its broadness of tuning reaches 2THz, but the temperature stability of heating furnace becomes the key issue of the accurate phase matched of influence (QPM).In France, the J.Mangeney group of French research establishment (CNRS) is devoted to utilize some nonlinear material (as In recent years always _0.53Ga _0.47As) optical mixer (PM) produces the research of tunable continuous THz wave, and maximum broadness of tuning is 0.9THz.In Japan, H.Ito group utilizes UTC-PD (Uni-Traveling-Carrier Photodioed) optical mixer to realize the generation of continuous THz wave, and highest frequency can reach 1.5THz.

The mode that obtains THz wave is a lot, and principle is also different, and the mode that produces tunable relevant THz wave at present roughly can be divided into three major types.The first kind is based on the tunable relevant terahertz emission of research of dual wavelength pumping source and design; Second class is that the pumping source wavelength is fixed, and produces the research and the design of THz wave based on the ICOPO of non-linear cascade process.The 3rd class is based on the tunable terahertz emission source of PM.For the first kind, relate generally to research of tunable relevant terahertz emission source and design at present based on DFB LDs, EDFLs, DF dual wavelength pumping source.The Terahertz tuning range of utilizing DFB LDs to produce is narrower, generally less than 0.5THz; Though the Terahertz tuning range of utilizing the EDFLs mode to produce can reach 0.5THz, its structure is quite complicated; Though and the Terahertz tuning range broad that utilizes the DF mode to produce can reach 20THz, the terahertz emission source apparatus of this mode is quite huge, although 2010 years, Y.J.Ding has realized 30.48 * 15.24 * 10.16cm ³Compact terahertz emission source, however untunable.For second class, though its broadness of tuning can reach 2THz at present, owing to the temperature stability reason, satisfying accurate phase-matching condition is not the part nothing the matter, thereby makes that tuning efficient is lower.For the 3rd class, at present high tuning width is 0.9THz, and obviously its broadness of tuning is narrower.

In a word, said method or broadness of tuning are narrower, or bulky, or tuning efficient is low, or conversion efficiency is low.

Summary of the invention

Technical problem to be solved by this invention provides a kind of compactness, portable, be easy to integrated, the wide-band tuning THz wave device that broad tuning and tuning efficient are high.

The technical scheme that solves the technology of the present invention problem is: a kind of circulating ultrasonic grating shift frequency nonlinear difference formula wide-band tuning THz wave generator is provided, it comprises laser, first circulator, beam splitter, circulation shift frequency link based on the ultrasonic grating shift frequency, first beam synthesis, optical isolator, non-linear element and Terahertz filter plate, the light of described laser output is divided into the first via and the second tunnel by beam splitter after through first circulator, the first via is a reference light, the second the tunnel is input to and produces circulation shift frequency light after the described circulation shift frequency link, described reference light and circulation shift frequency light are after first beam synthesis closes bundle, carry out difference frequency through optical isolator in non-linear element again, filtering gives off relevant THz wave through the Terahertz filter plate at last.

Described laser is semiconductor laser, gas laser, solid state laser or the fiber laser of operation wavelength in the 600nm-2000nm wave band.

Described first circulator is a three-port circulator, and its first port connects laser, and second port connects beam splitter, and the 3rd port connects absorbing load, the reverberation of described absorbing load absorbing light beam splitter.

Described non-linear element is the periodic structure that nonlinear material and linear material are alternately arranged, or alternately arrange the optical superlattice structure that constitutes by nonlinear material and linear material, or alternately arrange the slow variable period structure that constitutes by nonlinear material and linear material, or arrange Fibonacci (Fibonacci) structure that constitutes by nonlinear material and linear material, it satisfies the desired phase-matching condition scope of the pairing nonlinear difference process of Terahertz output wave frequency tuning range of system.

Described Terahertz filter plate is logical transmission-type filter of Terahertz band or Terahertz band resistance reflecting filter; For the logical transmission-type filter of band, transmitted wave is output as THz wave, and the ripple of other wavelength can be reflected by this filter; For band resistance reflecting filter, reflected wave is output as THz wave, and the ripple of other wavelength can see through this filter.

The optimum value of the closed loop gain coefficient of described circulation shift frequency link based on the ultrasonic grating shift frequency is 1, and inferior good value is other positive integer value beyond 1, and good once more value is the reciprocal value of other positive integer beyond 1.

The splitting ratio optimum value of described beam splitter is 1, inferior good value is the reciprocal value of other positive integer beyond 1, good once more value is other positive integer value beyond 1, and the splitting ratio of described beam splitter is a reference light power divided by the input optical power based on the circulation shift frequency link of ultrasonic grating shift frequency.

Described circulation shift frequency link based on the ultrasonic grating shift frequency comprises second beam synthesis, ultrasonic grating, L ₁Lens, L ₂Lens, second circulator, the first reaction type Bragg grating, tunable optic filter, image intensifer and light amplitude fading device, described image intensifer and light amplitude fading device are formed the image intensifer of Gain Adjustable.

Described ultrasonic grating is the transmission ultrasonic grating, is used for phase modulated.

Described second circulator is a three-port circulator, and its first port receives from L ₂The light of lens, second port connect the first reaction type Bragg grating, and the 3rd port connects absorbing load, and described absorbing load absorbs the reverberation of the first reaction type Bragg grating.

Described operational frequency bandwidth based on each parts, first beam synthesis, optical isolator in the circulation shift frequency link of ultrasonic grating shift frequency is not less than the highest frequency of the THz wave of output.

Described circulator, beam splitter, consistent with the service band of laser based on the service band of each parts, first beam synthesis, optical isolator in the circulation shift frequency link of ultrasonic grating shift frequency.

Described tunable optic filter is a narrow band filter, it allows a narrow band light to output to the input of beam synthesis, and the light of other frequency is reflexed to the input of image intensifer, the difference of the arrowband output light frequency of described tunable optic filter and the output light frequency of described laser equals needed Terahertz wave frequency, and the frequency-tuning range of the THz wave of output is not more than the arrowband output light frequency tuning range of tunable optic filter.

Described tunable optic filter is the 1-D photon crystal tunable optic filter or the Bragg grating-completely reflecting mirror assembly of band defect layer.

The forbidden photon band district of described 1-D photon crystal is not less than the frequency tuning range of system's output wave, described 1-D photon crystal comprises the adjustable defect layer of one deck refractive index, the regulative mode of the refractive index of described defect layer comprises that electricity causes and sells off, mangneto is sold off, sound causes to be sold off, photic selling off, power causes sells off or thermic is sold off, described 1-D photon crystal has a defective mould, described defective mould changes with the change of refractive of described defect layer, the surface of described 1-D photon crystal tunable optic filter and its incident wave line of propagation are in angle of 45 degrees, the arrowband transmitted wave of described 1-D photon crystal tunable optic filter enters into the input of beam synthesis, and the reverberation of described 1-D photon crystal tunable optic filter enters into the input of image intensifer.

Described Bragg grating-completely reflecting mirror assembly comprise one with the incident light direction second reaction type Bragg grating and reflecting surface and incident light direction completely reflecting mirror in angle of 45 degrees in angle of 45 degrees, between described second reaction type Bragg grating and completely reflecting mirror is an air or dielectric layer, the narrowband reflection light of the described second reaction type Bragg grating is the arrowband output light of this tunable optic filter, the narrowband reflection light of the described second reaction type Bragg grating enters in first beam synthesis, the reverberation of described completely reflecting mirror enters into the input of image intensifer along another light path, the lattice parameter of the described second reaction type Bragg grating passes through piezoelectric effect, magnetostrictive effect, the effect of expanding with heat and contract with cold, electricity causes to be sold off, mangneto is sold off, sound causes to be sold off, photic selling off, power causes sells off or the thermic mode of selling off is regulated, with the adjusting of the narrowband reflection light frequency of realizing the described second reaction type Bragg grating.

The present invention's beneficial effect compared with prior art is:

(1) compact, portable.Circulating ultrasonic grating shift frequency nonlinear difference formula wide-band tuning THz wave generator utilizes the volume after the commercially available assembly assembling to be no more than 40 * 10 * 35cm ³, weight is no more than 8kg.

(2) light path is simple.In whole device, have only beam splitter and L ₁, L ₂Lens are movable optical element, and other parts are all fixing, and preferred beam synthesis is a fiber coupler.This device makes things convenient for light integrated.

(3) tuning range or broadness of tuning are big.Even if centre wavelength (for example, 1550nm) is subjected to the bandwidth constraints of tunable optic filter and image intensifer.For bandwidth of operation is tunable optic filter and the image intensifer of 40nm, can obtain the broadness of tuning of 5THz THz wave.This broadness of tuning than most of terahertz emission source in the past is all big.Along with the increase of the broadness of tuning of tunable optic filter and bandpass amplifier, the wavelength regulation scope of output THz wave can correspondingly increase.

(4) tuning efficient height.Tuning in this scheme mainly realized frequency shifts by ultrasonic grating, when the signal frequency after regulating reaches the selecting frequency of tunable optic filter, the narrow band light output of tunable optic filter is just exported the input of a narrow band light to first beam synthesis, otherwise flashlight is reflected and enters image intensifer, after amplifying, feed back to the input of ultrasonic grating again, carry out frequency shifts once more through ultrasonic grating.This process does not need artificial or computer intervention, and its tuning efficient is quite high.

(5) Terahertz produces the efficient height.Owing to have the Gain Adjustable part in the circulation shift frequency joint, so the power output of shift frequency light can be than higher, this efficient than any shift frequency mode in the past is all high, and then the conversion efficiency of terahertz emission is also corresponding to higher.

Description of drawings

Fig. 1 is the system configuration schematic diagram of circulating ultrasonic grating shift frequency nonlinear difference formula wide-band tuning THz wave generator of the present invention.

Fig. 2 is the schematic diagram of first kind of execution mode of circulating ultrasonic grating shift frequency nonlinear difference formula wide-band tuning THz wave generator of the present invention.

Fig. 3 is the schematic diagram of the another kind of execution mode of circulating ultrasonic grating shift frequency nonlinear difference formula wide-band tuning THz wave generator of the present invention, and the slanted bar line in the short dash line frame wherein fills frame and black filling frame is respectively reaction type Bragg grating and completely reflecting mirror.

Fig. 4 is the difference frequency schematic diagram of circulating ultrasonic grating shift frequency nonlinear difference formula wide-band tuning THz wave generator of the present invention.

Embodiment

Below in conjunction with accompanying drawing and embodiment the present invention is described in further detail:

The invention provides a kind of circulating ultrasonic grating shift frequency nonlinear difference formula wide-band tuning THz wave generator, as shown in Figure 1, it comprise laser 1, first circulator, beam splitter 3, based on circulation shift frequency link 4, first beam synthesis, optical isolator 6, non-linear element 7 and the Terahertz filter plate 8 of ultrasonic grating shift frequency.The light of laser 1 output is divided into the first via and the second tunnel by beam splitter 3 after through first circulator, the first via is a reference light, the second the tunnel is input to described circulation shift frequency link 4 backs produces circulation shift frequency light, described reference light and circulation shift frequency light are after first beam synthesis closes bundle, carry out difference frequency through optical isolator 6 in non-linear element 7 again, 8 filtering give off relevant THz wave through the Terahertz filter plate at last.

Laser 1 is semiconductor laser, gas laser, solid state laser or the fiber laser of operation wavelength in the 600nm-2000nm wave band.First circulator is a three-port circulator, and its first port connects laser 1, the second port and connects beam splitter 3, the three ports connection absorbing load, the reverberation of described absorbing load absorbing light beam splitter 3.

Circulation shift frequency link 4 based on the ultrasonic grating shift frequency comprises second beam synthesis, ultrasonic grating 42, L ₁Lens 43, L ₂Lens 44, second circulator, the first reaction type Bragg grating 46, tunable optic filter 47, image intensifer 48 and light amplitude fading device 49, image intensifer 48 and light amplitude fading device 49 are formed the image intensifer of Gain Adjustable.First circulator, beam splitter 3, consistent with the service band of laser 1 based on the service band of each parts, first beam synthesis, optical isolator 6 in the circulation shift frequency link 4 of ultrasonic grating shift frequency.

Based on the closed loop gain coefficient of the circulation shift frequency link 4 of ultrasonic grating shift frequency or claim that the optimum value of entire gain coefficient is 1, inferior good value is other positive integer value beyond 1, and good once more value is the reciprocal value of other positive integer beyond 1.Equal the amplitude of reference light based on the amplitude optimum value of the output light of the circulation frequency displacement link 4 of ultrasonic grating shift frequency, the splitting ratio optimum value that is beam splitter 3 is 1, inferior good value is the reciprocal value of other positive integer beyond 1, good once more value is other positive integer value beyond 1, also is the splitting ratio of beam splitter 3 and product optimum value based on the closed loop gain coefficient of the circulation shift frequency link of ultrasonic grating shift frequency is 1.The splitting ratio of beam splitter 3 equals reference light power divided by the input power based on the circulation shift frequency link 4 of ultrasonic grating shift frequency.

Ultrasonic grating 42 is the transmission ultrasonic grating, is used for phase modulated.The frequency displacement principle of ultrasonic grating 42 is: ultrasonic wave will cause the elastic strain of medium when propagating and do cyclic variation on time and the space, and cause the refractive index of medium also to change in transparent medium.If acousto-optic interaction distance hour, light wave causes mainly that by medium space periodicity changes, and the position of final light wave is modulated mutually.Be without loss of generality, the ultrasonic wave of establishing in the acousto-optic medium is the plane compressional wave of propagating along the x direction, and its angular frequency is ω _s, wave vector is k _s(=2 π/λ _s), λ wherein _sBe the ultrasonic wave wavelength; Incident light is the plane wave of propagating along the z direction, and its angular frequency is ω, and wave vector is that (=2 π/λ), wherein λ is an optical wavelength in the vacuum to k.When the elastic strain of medium hour, refractive index n with the variation relation of x and time t is

n(x，t)＝n ₀+(Δn) _msin(ω _st-k _sx) (1)

N wherein ₀The refractive index of medium when representing no ultrasonic wave, (Δ n) _mExpression change of refractive amplitude.When light wave was the ultrasonic grating of L by thickness, the phase change that causes was

ΔΦ(x，t)＝kn(x，t)L＝ΔΦ ₀+ΔΦ _msin(ω _st-k _sx) (2)

ΔΦ wherein ₀Represent the phase difference of no ultrasonic wave time, ΔΦ by L thickness ultrasonic grating _mThe amplitude of variation of expression phasic difference.When supposing light for the first time by ultrasonic grating, the electric vector on the z=-L/2 plane is

E＝Ae ^iωt (3)

Then by behind the ultrasonic grating, the electric vector on the z=L/2 plane is light for the first time

$E={\mathrm{Ae}}^{i[\mathrm{\ωt}-\mathrm{\Δ}{\mathrm{\Φ}}_0-\mathrm{\Δ}{\mathrm{\Φ}}_m\sin ({\mathrm{\ω}}_{s}t-k_{s}x)]---\left(4\right)}$

Utilize the mathematics identity

$e^{\mathrm{i\β}\sin \mathrm{\θ}}=\underset{n=-\∞}{\overset{\∞}{\mathrm{\Σ}}}{J}_n\left(\mathrm{\β}\right)e^{\mathrm{in\θ}},J_{-n}\left(\mathrm{\β}\right)={(-1)}^n{J}_n\left(\mathrm{\β}\right)---\left(5\right)$

(5) in the formula, J _n(β) be Bessel function of the first kind.(5) formula of utilization can be changed to (4) formula

$E={\mathrm{CJ}}_0\left(\mathrm{\β}\right)e^{\mathrm{i\ωt}}$

$+{\mathrm{CJ}}_1\left(\mathrm{\β}\right)e^{i(\mathrm{\ω}-{\mathrm{\ω}}_s)t}-{\mathrm{CJ}}_1\left(\mathrm{\β}\right)e^{i(\mathrm{\ω}+{\mathrm{\ω}}_s)t}$

$+{\mathrm{CJ}}_2\left(\mathrm{\β}\right)e^{i(\mathrm{\ω}-2{\mathrm{\ω}}_s)t}+{\mathrm{CJ}}_2\left(\mathrm{\β}\right)e^{i(\mathrm{\ω}+2{\mathrm{\ω}}_s)t}---\left(6\right)$

$......$

$+{\mathrm{CJ}}_n\left(\mathrm{\β}\right)e^{i(\mathrm{\ω}-{\mathrm{n\ω}}_s)t}+{\mathrm{CJ}}_n\left(\mathrm{\β}\right){(-1)}^n{e}^{i(\mathrm{\ω}+{\mathrm{n\ω}}_s)t}$

Wherein, C=Aexp[i (Δ φ ₀+ k _xX)], β=ΔΦ _mThe plane wave electric vector stack of formula (6) expression n order diffraction.In the above-mentioned in addition deformation process, suppose

k _x＝ksinα＝nk _s (7)

Wherein, α represents the angle of diffraction.If (7) formula is rewritten as

λ _ssinα＝nλ(n＝0，±1，±2，......) (8)

(8) formula of observation can find that this formula is closely similar with the expression formula of the grating equation of knowing, wherein λ _sBe equivalent to grating constant.Can determine relation between ultrasonic grating constant (being the ultrasonic wave wavelength), optical wavelength, not at the same level the angle of diffraction three from this formula.

In conjunction with actual conditions, only get first order diffraction as the circulation object, promptly only be concerned about second row, especially second expression formula in (6) formula.Then the N time electric vector by the HFS of first order diffraction behind the ultrasonic grating of light can be written as-(CJ ₁(β)) ^NExp[i (ω+N ω _s) t], can find N ω from the frequency part _sFrequency increase.

This shows, in circulation shift frequency link, obtain N ω behind N circulation shift frequency of light wave process based on ultrasonic grating _sFrequency shift amount, as long as this frequency shift amount does not make light frequency reach the selecting frequency of tunable optic filter, then light wave can be fed back in the circulation shift frequency link and constantly circulate, till frequency shift amount makes light frequency reach the selecting frequency of filter.

In addition, be sin α=λ/λ owing to there is certain proportionate relationship in the first order angle of diffraction with optical wavelength and ultrasonic grating constant _sSo, the necessary excursion of determining angle when optical wavelength behind the circulation shift frequency changes.Suppose and be defined as 34000nm by ultrasonic grating constant (getting the velocity of sound is 340m/s, ultrasonic frequency is 10MHz), (for example, the excursion of angle is 0.045 to 0.046rad when 1550nm) fluctuating 20nm up and down, i.e. 2.58 ° to 2.65 ° angular ranges from certain value when optical wavelength so.Obviously, the angle of first-order diffraction changes not quite when optical wavelength changes, and this has valuable help to the circulation shift frequency, has avoided the adjusting at any time of optical element, and it is integrated to be beneficial to optics.

Second circulator is a three-port circulator, its first port receives the light from L2 lens 44, second port connects the first reaction type Bragg grating, 46, the three ports and connects absorbing load, and described absorbing load will absorb the reverberation of the first reaction type Bragg grating 46.Described operational frequency bandwidth based on each parts, first beam synthesis, optical isolator 6 in the circulation shift frequency link 4 of ultrasonic grating shift frequency is not less than the highest frequency of the THz wave of output, and promptly operational frequency bandwidth is not less than the maximum frequency shift scope of described circulation shift frequency link based on the ultrasonic grating shift frequency.

Tunable optic filter 47 is a narrow band filter, it allows a narrow band light to output to the input of first beam synthesis, and the light of other frequency is reflexed to the input of image intensifer 48, the difference of the arrowband output light frequency of described tunable optic filter 47 and the output light frequency of described laser 1 equals needed Terahertz wave frequency, the Terahertz wave frequency of output realizes that by the arrowband output light frequency of regulating tunable optic filter 47 frequency-tuning range of THz wave is not more than the arrowband output light frequency tuning range of tunable optic filter 47.

Preferably, tunable optic filter 47 is the 1-D photon crystal tunable optic filter (as shown in Figure 2) or the Bragg grating-completely reflecting mirror assembly (as shown in Figure 3) of band defect layer; The forbidden photon band district of described 1-D photon crystal is not less than the frequency tuning range of the THz wave of system's output, described 1-D photon crystal comprises the adjustable defect layer of one deck refractive index, the regulative mode of the refractive index of described defect layer comprise electricity cause sell off, mangneto is sold off, sound cause sell off, photicly sell off, power causes and sells off or thermic is sold off, described 1-D photon crystal has a defective mould, described defective mould changes with the change of refractive of described defect layer, realizes the function of tunable filtering.Preferably, the surface of described 1-D photon crystal tunable optic filter and its incident wave line of propagation are in angle of 45 degrees, the arrowband transmitted wave of described 1-D photon crystal tunable optic filter enters into the input of beam synthesis 5, and the reverberation of described 1-D photon crystal tunable optic filter enters into the input of image intensifer 48; Described Bragg grating-completely reflecting mirror assembly comprise one with the incident light direction second reaction type Bragg grating and reflecting surface and incident light direction completely reflecting mirror in angle of 45 degrees in angle of 45 degrees, between described second reaction type Bragg grating and completely reflecting mirror is an air or dielectric layer, the narrowband reflection light of the described second reaction type Bragg grating is the arrowband output light of this tunable optic filter, the narrowband reflection light of the described second reaction type Bragg grating enters in first beam synthesis, the reverberation of described completely reflecting mirror enters into the input of image intensifer 48 along another light path, the lattice parameter of the described second reaction type Bragg grating passes through piezoelectric effect, magnetostrictive effect, the effect of expanding with heat and contract with cold, electricity causes to be sold off, mangneto is sold off, sound causes to be sold off, photic selling off, power causes sells off or the thermic mode of selling off is regulated, with the adjusting of the narrowband reflection light frequency of realizing the described second reaction type Bragg grating.

The difference frequency principle: as shown in Figure 4, it is the parametric process of three-wave interaction that optical difference frequency produces; Frequency is respectively ω ₁And ω ₂Pump light in non-linear element, interact, the parameter light frequency of generation is the difference ω of this two bundles pump light frequency ₁-ω ₂As ω of every consumption ₁Photon must produce a ω simultaneously ₂Photon, these three frequencies must satisfy energy conservation relation ω ₃=ω ₁-ω ₂In the difference frequency process, the ω that frequency is higher ₁Light is consumed, the ω that frequency is lower ₂Light will be exaggerated.If produce the difference frequency field effectively, polarized wave must be identical with electromagnetic phase velocity, and promptly interactional three plane waves must satisfy phase-matching condition Δ k=k in the non-linear element ₁-k ₂-k ₃In order to realize the output of wide-band tuning THz wave, need wide phase matched scope, by the periodic structure of alternately arranging by nonlinear material and linear material, or alternately arrange the optical superlattice structure that constitutes by nonlinear material and linear material, or alternately arrange the slow variable period structure that constitutes by nonlinear material and linear material, or, can obtain the desired phase-matching condition scope of the pairing nonlinear difference process of Terahertz output wave frequency tuning range of system by Fibonacci (Fibonacci) structure that nonlinear material and linear material arrangement constitute.

Be each part and the running parameter thereof of a kind of embodiment below.Laser 1 is selected 1550nm super-narrow line width continuous conductor laser for use, the operation wavelength of this laser in the time of 25 ℃ is 1550nm, and power output is 5mW, continuous operation mode, maximum line width is 50kHz, and the output optical fibre type is SMF-28 monomode fiber (9/125 μ m).The acousto-optic medium of ultrasonic grating 42 is a pure water, and operating frequency is 10MHz, and the order of diffraction is inferior can to reach 3 grades, and diffraction efficiency is 96%, and the supersonic frequency maximum can reach 30MHz, and diffraction head volume is 4 * 4 * 2cm ³The broadness of tuning of selected 47 pairs of centre wavelengths of tunable optic filter reaches 40nm, and (1528nm～1610nm), the insertion loss is 4.0dB, and the volume of this filter is 24 * 8.8 * 35cm almost to have covered whole C-band ³The bandwidth of operation of selected image intensifer 48 is 40nm, has covered whole C-band.Selected beam splitter 3 is 10/90 optical element of response 1550nm wavelength, 10 expression reference light parts wherein, 90 expression flashlight parts.The first selected circulator, second circulator are to connect the optics of inhaling carrier load, play the light isolation effect, simultaneously carrier load is inhaled in the light utilization that reflects and absorbed, this device not only plays the light isolation but also plays environmental-protection function, and its response wave length is near 1550nm.Selected 46 couples of carrier wavelength 1550nm of the first reaction type Bragg grating play the reflection inhibitory action.The first selected beam synthesis, second beam synthesis are for responding the fiber coupler of 1550nm wavelength.Selected L ₁Lens 43 and L ₂Lens 44 are convenient to couple the beam in the optical fiber near the beam system that contracts of the wavelength anti-reflection 1550nm.Selected non-linear element 7 is for becoming the periodic polarized lithium columbate crystal of inclined (PPLN) slowly, and Terahertz filter plate 8 is the resin material of response terahertz wave band, total reflection or total transmissivity reference light and shift frequency light.

Beam splitter 3 is divided into two-way with the 1550nm laser of optical fiber output, one the tunnel as reference light, another road is as the modulation signal light of ultrasonic grating 42, ultrasonic grating 42 changes the signal light frequency under the ultrasonic frequency signal drives, the signal light frequency is offset, when the signal light frequency reaches the selecting frequency of tunable optic filter 47, the narrow band light output of tunable optic filter is just exported the input of a narrow band light to first beam synthesis, otherwise flashlight can be reflected to the input of image intensifer 48 along another light path, feeds back to once more and carries out frequency shifts in the ultrasonic grating 42 through entering second beam synthesis after the light amplification.This frequency shifts process constantly repeats, the final frequency shifts of size arbitrarily that obtains, and this is one of key advantages of this programme.The flashlight of reference light and tunable optic filter 47 outputs closes the bundle back through first beam synthesis and carry out difference frequency in non-linear element 7, after 8 filtering of Terahertz filter plate give off the relevant THz wave that frequency-tuning range is 5THz.

In order to guarantee amplitude coherent superposition such as reference light and shift frequency light, connect amplitude fading device 49 at the output of image intensifer 48.

Wide-band tuning Terahertz generator volume provided by the invention is little, and optical element is few thereby easy of integration, and tuning range is big, tuning efficient height, and Terahertz produces the efficient height.

The above the present invention all has improvements in embodiment and range of application, not should be understood to limitation of the present invention.

Claims (16)

1. circulating ultrasonic grating shift frequency nonlinear difference formula wide-band tuning THz wave generator, it is characterized in that: it comprises laser (1), first circulator, beam splitter (3), the circulation shift frequency link (4) based on the ultrasonic grating shift frequency, first beam synthesis, optical isolator (6), non-linear element (7) and Terahertz filter plate (8); The light of described laser (1) output is divided into the first via and the second tunnel by beam splitter (3) after through first circulator, the first via is a reference light, the second the tunnel is input to described circulation shift frequency link (4) back produces circulation shift frequency light, first beam synthesis after optical isolator (6) carries out difference frequency in non-linear element (7), passes through described reference light and circulation shift frequency combiner then Terahertz filter plate (8) filtering and gives off relevant THz wave.

2. according to the described circulating ultrasonic grating of claim 1 shift frequency nonlinear difference formula wide-band tuning THz wave generator, it is characterized in that: described laser (1) is semiconductor laser, gas laser, solid state laser or the fiber laser of operation wavelength in the 600nm-2000nm wave band.

3. according to the described circulating ultrasonic grating of claim 1 shift frequency nonlinear difference formula wide-band tuning THz wave generator, it is characterized in that: described first circulator is a three-port circulator, its first port connects laser (1), second port connects beam splitter (3), the 3rd port connects absorbing load, the reverberation of described absorbing load absorbing light beam splitter (3).

4. according to the described circulating ultrasonic grating of claim 1 shift frequency nonlinear difference formula wide-band tuning THz wave generator, it is characterized in that: described non-linear element (7) replaces the periodic structure of arrangement for nonlinear material and linear material, or alternately arrange the optical superlattice structure that constitutes by nonlinear material and linear material, or alternately arrange the slow variable period structure that constitutes by nonlinear material and linear material, or arrange Fibonacci (Fibonacci) structure that constitutes by nonlinear material and linear material, it satisfies the desired phase-matching condition scope of the pairing nonlinear difference process of Terahertz output wave frequency tuning range of system.

5. according to the described circulating ultrasonic grating of claim 1 shift frequency nonlinear difference formula wide-band tuning THz wave generator, it is characterized in that: described Terahertz filter plate (8) is logical transmission-type filter of Terahertz band or Terahertz band resistance reflecting filter; For the logical transmission-type filter of band, transmitted wave is output as THz wave, and the ripple of other wavelength can be reflected by this filter; For band resistance reflecting filter, reflected wave is output as THz wave, and the ripple of other wavelength can see through this filter.

6. according to the described circulating ultrasonic grating of claim 1 shift frequency nonlinear difference formula wide-band tuning THz wave generator, it is characterized in that: the optimum value of the closed loop gain coefficient of described circulation shift frequency link (4) based on the ultrasonic grating shift frequency is 1, inferior good value is other positive integer value beyond 1, and good once more value is the reciprocal value of other positive integer beyond 1.

7. according to the described circulating ultrasonic grating of claim 1 shift frequency nonlinear difference formula wide-band tuning THz wave generator, it is characterized in that: the splitting ratio optimum value of described beam splitter (3) is 1, inferior good value is the reciprocal value of other positive integer beyond 1, good once more value is other positive integer value beyond 1, and the splitting ratio of described beam splitter (3) is a reference light power divided by the input optical power based on the circulation shift frequency link (4) of ultrasonic grating shift frequency.

8. according to the described circulating ultrasonic grating of claim 1 shift frequency nonlinear difference formula wide-band tuning THz wave generator, it is characterized in that: described circulation shift frequency link (4) based on the ultrasonic grating shift frequency comprises second beam synthesis, ultrasonic grating (42), L ₁Lens (43), L ₂Lens (44), second circulator, the first reaction type Bragg grating (46), tunable optic filter (47), image intensifer (48) and light amplitude fading device (49), described image intensifer (48) and light amplitude fading device (49) are formed the image intensifer of Gain Adjustable.

9. according to the described circulating ultrasonic grating of claim 8 shift frequency nonlinear difference formula wide-band tuning THz wave generator, it is characterized in that: described ultrasonic grating (42) is the transmission ultrasonic grating, is used for phase modulated.

10. according to the described circulating ultrasonic grating of claim 8 shift frequency nonlinear difference formula wide-band tuning THz wave generator, it is characterized in that: described second circulator is a three-port circulator, its first port receives the light from L2 lens (44), second port connects the first reaction type Bragg grating (46), the 3rd port connects absorbing load, and described absorbing load absorbs the reverberation of the first reaction type Bragg grating (46).

11. according to the described circulating ultrasonic grating of claim 8 shift frequency nonlinear difference formula wide-band tuning THz wave generator, it is characterized in that: described operational frequency bandwidth based on each parts, first beam synthesis, optical isolator (6) in the circulation shift frequency link (4) of ultrasonic grating shift frequency is not less than the highest frequency of the THz wave of output.

12., it is characterized in that: described first circulator, beam splitter (3), consistent with the service band of laser (1) based on the service band of each parts, first beam synthesis, optical isolator (6) in the circulation shift frequency link (4) of ultrasonic grating shift frequency according to the described circulating ultrasonic grating of claim 8 shift frequency nonlinear difference formula wide-band tuning THz wave generator.

13. according to the described circulating ultrasonic grating of claim 8 shift frequency nonlinear difference formula wide-band tuning THz wave generator, it is characterized in that: described tunable optic filter (47) is a narrow band filter, it allows the narrow band light of a frequency adjustable to output to the input of first beam synthesis, and the light of other frequency is reflexed to the input of image intensifer (48), the difference of the arrowband output light frequency of described tunable optic filter (47) and the output light frequency of described laser (1) equals needed Terahertz wave frequency, and the frequency-tuning range of the THz wave of output is not more than the arrowband output light frequency tuning range of tunable optic filter (47).

14. according to the described circulating ultrasonic grating of claim 13 shift frequency nonlinear difference formula wide-band tuning THz wave generator, it is characterized in that: described tunable optic filter (47) is the 1-D photon crystal tunable optic filter or the Bragg grating-completely reflecting mirror assembly of band defect layer.

15. according to the described circulating ultrasonic grating of claim 14 shift frequency nonlinear difference formula wide-band tuning THz wave generator, it is characterized in that: the forbidden photon band district of described 1-D photon crystal is not less than the frequency tuning range of the THz wave of system's output, described 1-D photon crystal comprises the adjustable defect layer of one deck refractive index, the regulative mode of the refractive index of described defect layer comprises that electricity causes and sells off, mangneto is sold off, sound causes to be sold off, photic selling off, power causes sells off or thermic is sold off, described 1-D photon crystal has a defective mould, described defective mould changes with the change of refractive of described defect layer, the surface of described 1-D photon crystal tunable optic filter and its incident wave line of propagation are in angle of 45 degrees, the arrowband transmitted wave of described 1-D photon crystal tunable optic filter enters into the input of beam synthesis (5), and the reverberation of described 1-D photon crystal tunable optic filter enters into the input of image intensifer (48).

16. according to the described circulating ultrasonic grating of claim 14 shift frequency nonlinear difference formula wide-band tuning THz wave generator, it is characterized in that: described Bragg grating-completely reflecting mirror assembly comprise one with the incident light direction second reaction type Bragg grating and reflecting surface and incident light direction completely reflecting mirror in angle of 45 degrees in angle of 45 degrees, between described second reaction type Bragg grating and completely reflecting mirror is an air or dielectric layer, the narrowband reflection light of the described second reaction type Bragg grating is the arrowband output light of this tunable optic filter, the narrowband reflection light of the described second reaction type Bragg grating enters in first beam synthesis, the reverberation of described completely reflecting mirror enters into the input of image intensifer (48) along another light path, the lattice parameter of the described second reaction type Bragg grating passes through piezoelectric effect, magnetostrictive effect, the effect of expanding with heat and contract with cold, electricity causes to be sold off, mangneto is sold off, sound causes to be sold off, photic selling off, power causes sells off or the thermic mode of selling off is regulated, with the adjusting of the narrowband reflection light frequency of realizing the described second reaction type Bragg grating.

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