CN102545028B - Cascaded optical parameter-based high-power red, green and blue optical maser - Google Patents

Abstract

The invention discloses a cascaded optical parameter-based high-power red, green and blue optical maser. The cascaded optical parameter-based high-power red, green and blue optical maser comprises a resonant cavity, a temperature control furnace, a piece of optical superlattice and a filtration system, wherein the resonant cavity consists of a pump light source, a calibration system, a focusing system, a front cavity mirror and a rear cavity mirror; the optical superlattice is formed by cascading different structures; the light emitted by the pump light source enters the resonant cavity through the calibration system and the focusing system; after the light passes through the optical superlattice with a cascading structure, red light and blue light are emitted from the rear cavity mirror;and the red light, the blue light and the residual pump green light form the red, green and blue optical maser. The damage resistant threshold of crystals is greatly improved, and the maximal pump light power born by the crystal is also correspondingly improved, so the red light and the blue light with higher power can be obtained. The thickness of the optical superlattice is increased, so that the incidence area of pump beams is increased and then the pump power which can be born by the crystal is improved. If the red light and the blue light with narrow bandwidth are obtained, an element, such as an FP standard device or a raster, is added into the cavity.

Description

High power red turquoise laser based on the cascade optical parameter process

Technical field

The present invention relates to a kind of cascade structure optical superlattice that utilizes and realize optical parametric oscillation cascade and frequency process, obtaining the device of high power visible light wave range multiwavelength laser output, particularly is the full-solid-state red turquoise laser of frequency-changer crystal with superlattice such as lithium niobate, lithium tantalates.

Background technology

White and black displays, colored demonstration, this several stages of numeral demonstration have been experienced in the development of Display Technique.In the colored epoch, change into colour by black and white, represented the bright and colourful world.In digital Age, turn to high definition by SD, promoting from simulation signal generator is derived digital signal, therefrom small-size screen is brought up to large-screen.Laser display is " the 4th generation " Display Technique (LDT) after first three is for Display Technique, and laser display is to be the Display Technique of light source with red, green, blue (RGB) tricolor laser, can reproduce abundant, the gorgeous color in objective world the most truly.Compare with the natural daylight colour gamut, conventional display apparatus can only reproduce human eye finding color 30% and at present laser display mode just under development can cover 90%, this great potential let us is to being full of expectation the future of laser display technology, so laser display is called as " revolution on the human vision history ".Along with all solid state laser technology obtains the development of advancing by leaps and bounds, above RGB DPL (the diode pump laser) all solid state laser of watt level that volume is little, power is high is developed in succession, and this just lays a good foundation for the development laser video shows.

Laser projection display technology has obtained fast development.Laser projection display technology has been compared following advantage with traditional Display Technique: brightness height, saturation height, high color purity height, colour gamut are big, simultaneously can also be on curved surface projection etc., therefore will become the mainstream technology of the big panchromatic demonstration of colour gamut of future generation.Laser display most possible field of using in the recent period comprises laser film projector, laser projection, laser television and the little throwing of laser etc.Red, green, blue is natural three basic colors, and any visible color can be formed by regulating a certain proportion of red, green, blue.Usually the method that produces the redgreenblue lasing light emitter has following several: a kind of be utilize a plurality of first-harmonics source and a plurality of non-linear frequency conversion crystal realize frequency multiplication or and frequently; Another kind is to utilize a plurality of first-harmonics source and a non-linear frequency conversion crystal to realize that frequency multiplication reaches and the frequency process; The third is to utilize a first-harmonic source and a nonlinear frequency transformation crystal to realize parameter and and frequency process.Preceding two kinds of schemes have increased complexity and the cost of structure greatly, for the acquisition compact conformation, and flexible design, all solid state laser system that volume is little, cost is low, simple, the third scheme is more succinct.

Summary of the invention

Purpose of the present invention is exactly to provide a kind of high power red turquoise laser based on the cascade optical parameter process in order to address the above problem, and it has solved existing RGB laser structure complexity, be unfavorable for integrated, and cost problem of higher.

To achieve these goals, the present invention adopts following technical scheme:

A kind of high power red turquoise laser based on the cascade optical parameter process, it comprises the first-harmonic light source, and the first-harmonic light source focuses on after colimated light system and focusing system through attenuator and aperture, focuses on the laggard optics resonant cavity of going into, and optical resonator matches with speculum.

Described first-harmonic light source is pulse or quasi-continuous light source, is sent by pump light source, and pump light source is the 532nm green glow, and repetition rate is tuning from 1Hz to 150KHz.

Described focusing system is the post lens, and focal length is 300mm.

Described light beam resonant cavity comprises front cavity mirror, cascade structure optical superlattice and Effect of Back-Cavity Mirror, and optical superlattice places temperature control furnace; The control precision of described temperature control furnace is 0.1 ℃, and front cavity mirror is coated with multilayer film, and front cavity mirror is circular concave mirror, and Effect of Back-Cavity Mirror is coated with multilayer film, and Effect of Back-Cavity Mirror is the cylindrical concave mirror.

Described cascade structure optical superlattice comprises paracycle, aperiodic, binary cycle and cascade cycle; The host material of cascade structure optical superlattice comprises congruent LiTaO3, congruent LiNbO3, stoichiometric proportion LiTaO3, stoichiometric proportion LiNbO3, the lithium niobate of mixing MgO, the lithium tantalate of mixing MgO, potassium titanyl oxygenic phosphate(KTP) crystal KTP and phosphoric acid titanyl rubidium crystal RTP.

The preferred commensurability of described cascade structure optical superlattice to improve the optical superlattice polarization quality, realizes the redgreenblue laser output of high-efficiency high power than bi-period structure optical superlattice.

Described bi-period structure is to be superimposed upon on the cycle of another one by the one-period structure, and two cycles are denoted as l and L, l＜L, and corresponding modulation sequence is respectively f ₁(x) and f ₂(x), f ₁(X) and f ₂(x) only get+1 and-1, representing two opposite polarised directions, bi-period structure is as follows:

$f\left(x\right)=f_1\left(x\right)f_2\left(x\right)=\underset{m,n=-\∞}{\overset{\∞}{\mathrm{\Σ}}}{g}_m{g}_n{e}^{-i(G_m+G_n)x}=\underset{m,n=-\∞}{\overset{\∞}{\mathrm{\Σ}}}{g}_{m,n}{e}^{{-\mathrm{iG}}_{m,n}x}$

Wherein double-periodic reciprocal lattice vector is by G _{M, n}=G _m+ G _n=mG _l+ nG _LDecide, Fourier coefficient is by g _{M, n}=g _mg _nDecide; G _l=2 π/l and G _L=2 π/L is the single order reciprocal lattice vector of two modulation periods, and integer m, n are the exponent numbers of reciprocal lattice vector;

Two reciprocal lattice vectors that bi-period structure provides are mated two position phase mismatches in the additive mixing process simultaneously: conversion reaches and frequency under the parameter; Conversion is that 532nm green glow and 3604nm infrared light are converted to 463.4nm blue light, the reciprocal lattice vector G that the phase mismatch of two processes is provided by bi-period structure with frequency by being converted to the infrared idle light of 624nm ruddiness and 3604nm and frequency process under the 532nm green glow under the parameter _{M, n}And G _{M ', n '}Compensation:

Δk ₁＝k _p-k _r-k _i-G _m，n＝0

Δk ₂＝k _b-k _p-k _i-G _m′，n′＝0

Here k _p, k _r, k _i, k _bBe respectively pump green light, ruddiness, the wave vector of infrared light and blue light.

Beneficial effect of the present invention:

1, the present invention utilizes the higher SLT of anti-damage threshold, SLN, MgO:LiNbO ₃, MgO:LiTaO ₃In crystal, because the anti-damage threshold of crystal improves greatly, therefore also corresponding raising of the maximum pumping light power that crystal bears can obtain more high-power ruddiness and blue light.

2, increase the thickness of optical superlattice, with the incident area of increase pump beam, thereby improve the pump power that crystal can bear.

3, if obtain ruddiness and the blue light of narrow linewidth, then in the chamber, add elements such as FP etalon or grating.

Description of drawings

Fig. 1 is structural representation of the present invention;

The commensurability that Fig. 2 takes for embodiment of the invention microscopically is than binary cycle LiTaO ₃Optical superlattice structure+C face farmland shape appearance figure;

Fig. 3 is that embodiment of the invention ruddiness and blue power are with the change curve of pumping light power;

Fig. 4 is that embodiment of the invention blue power is with the change curve of crystal temperature effect;

Fig. 5 is that embodiment of the invention ruddiness and blue light wavelength are with the variation tendency of crystal temperature effect;

Fig. 6 for the embodiment of the invention through the redgreenblue laser after the prism light splitting.

Embodiment

The invention will be further described below in conjunction with accompanying drawing and embodiment.

High power red turquoise laser based on the cascade optical parameter process, the optical superlattice and the filtering system that comprise resonant cavity, temperature control furnace and the cascade of a slice different structure that pump light source, colimated light system, focusing system, front cavity mirror and Effect of Back-Cavity Mirror constitute, pump light source is the 532nm green (light) laser, the optical superlattice of cascade structure is as the additive mixing crystal, place temperature control furnace, the optical superlattice of cascade structure and temperature control furnace all are positioned at resonant cavity.The cascade structure optical superlattice is as the additive mixing crystal, is converted to ruddiness and infrared light and infrared light and 532nm green glow under the 532nm laser frequency and produces blue light frequently in order to realizing; The light that pump light source is sent incides resonant cavity through colimated light system, focusing system, by Effect of Back-Cavity Mirror end output ruddiness and blue light, forms redgreenblue laser with remaining pump green light behind the optical superlattice of cascade structure.

The cascade structure optical superlattice comprises paracycle, aperiodic, binary cycle and cascade cycle.The host material of optical superlattice comprises congruent LiTaO ₃, congruent LiNbO ₃, stoichiometric proportion LiTaO ₃, stoichiometric proportion LiNbO ₃, mix the lithium niobate of MgO, the lithium tantalate of mixing MgO, potassium titanyl oxygenic phosphate(KTP) crystal KTP and phosphoric acid titanyl rubidium crystal RTP.

Further, the cascade structure optical superlattice can be designed as commensurability than bi-period structure to improve the optical superlattice polarization quality, realize the redgreenblue laser output of high-efficiency high power.

532nm green (light) laser repetition rate is tuning from 1Hz to 150KHz, and the first-harmonic light source is pulse or quasi-continuous; The control precision of temperature control furnace is 0.1 ℃; Pump light source is provided with attenuator, aperture and passing through a collimating system successively on the light path of resonant cavity, focusing system, and the output light path of resonant cavity is provided with 532nm laser part speculum, and this speculum has high permeability to ruddiness and blue light.

In order to improve the incident pumping light power that crystal can bear, between colimated light system and optical superlattice, add focusing system, focusing system adopts the post lens, the pump beam after the collimation is focused on the back through the post lens incide crystal with ellipse light spot.The front cavity mirror of optical resonator adopts the circular concave mirror of long-focus, and Effect of Back-Cavity Mirror adopts the cylindrical concave mirror, to improve the mode volume of resonant cavity, realizes the resonant cavity steady running simultaneously.Need parameteric light when output of narrow linewidth in resonant cavity, to add spectro-grating or extender lens group.

The cavity structure of the idle light single resonance that uses among the present invention is in order to obtain ruddiness and blue light output more efficiently.Idle light so do not participate in the proportioning of accurate white light, resonates idle light owing to be infrared light in resonant cavity, can more effectively export ruddiness and blue light.

The present invention proposes a kind of scheme based on conversion cascade under the parameter and the redgreenblue of process generation frequently laser, has design flexible on this scenario-frame, not only can use the cascade periodic structure, can also use paracycle, aperiodic, binary cycle, particularly commensurability to realize simultaneously that than bi-period structure the position of two non-linear process is complementary, and a plurality of structures can be integrated on the wafer, make structure compacter, improved the integration of system.The incident pump spot adopts the post lens to focus on optical superlattice to improve the pump power that crystal bears, resonant cavity adopts cylindrical mirror to increase the mode volume of resonant cavity, be conducive to obtain the RGB laser output of high-power high-efficiency, resonant cavity adopts idle light single resonance, thereby make resonant cavity be operated in the state of stable high Q value, obtain ruddiness and blue light output more efficiently.

The pump light source that the present invention adopts is the 532nm green glow, repetition rate can be tuning from 1Hz to 150KHz, therefore, the first-harmonic light source can be pulse, also can be quasi-continuous, after the collimated system of fundamental wave expands through entering after the focusing system in the resonance cavity system, resonance cavity system comprises front cavity mirror, additive mixing crystal and Effect of Back-Cavity Mirror, crystal places temperature control furnace, and front cavity mirror and Effect of Back-Cavity Mirror are high permeability to pump light, and parameteric light (idle light) wherein is high reflectance.The cascade structure optical superlattice is as the additive mixing crystal, is converted to ruddiness and infrared light and infrared light and green glow under the 532nm laser frequency and produces blue light frequently in order to realizing.Realize control to crystal temperature effect by the temperature of regulating temperature control furnace, thereby realize the blue light output of maximum power in specific temperature.

The present invention is applicable to that pump light source is the laser of 532nm, and pumping laser can be continuous, pulse, low-repetition-frequency or high repetition frequency.Satisfy different application requirements by different resonant cavitys is set, comprise average chamber, flat-concave cavity, concave-concave chamber etc.In order to improve the incident pumping light power that crystal can bear, pump light can adopt the post lens to focus on, with ellipse light spot incident, the front cavity mirror of optical resonator can adopt the circular concave mirror of long-focus, Effect of Back-Cavity Mirror adopts the cylindrical concave mirror, to improve the resonator mode volume, realizes stable resonator simultaneously.Need parameteric light when output of narrow linewidth in resonant cavity, to add spectro-grating or extender lens group.

The present invention uses the host material of optical super lattice material, comprises congruent LiTaO ₃(CLT), congruent LiNbO ₃(CLN), stoichiometric proportion LiTaO ₃(SLT), stoichiometric proportion LiNbO ₃(SLN), mix the lithium niobate of MgO, the lithium tantalate of mixing MgO, nonlinear optical crystals such as KTP, RTP.Wherein, SLT, the relative CLT of SLN crystal, CLN crystal have higher optic damage threshold value; Mix the lithium niobate of MgO, the lithium tantalate of mixing MgO can be worked at room temperature, and the unglazed effect of selling off.Can calculate the structural parameters of particular optical superlattice according to the dispersion of refractive index relation of different crystal material, thereby realize the output of efficient stable redgreenblue laser.

The optical superlattice of cascade structure involved in the present invention can use different structures, comprises paracycle, binary cycle, aperiodic, the cascade cycle etc.Bi-period structure can be designed as commensurability than binary cycle, to improve the polarization quality of superlattice, obtains red, blue light output efficiently.

To be pump light source with high repetition frequency 532nm laser below, be the additive mixing crystal with commensurability than binary cycle optical superlattice, illustrates the redgreenblue laser output that how to realize stability and high efficiency.

Introduce commensurability below than the structural design of binary cycle optical superlattice.So-called superlattice are exactly the periodic modulation of passing through in ferroelectric crystal non linear coefficient, thereby provide reciprocal lattice vector to come the wave vector mismatch of bringing because of chromatic dispersion in the compensating non-linear interaction, obtain effective enhancing of nonlinear optical effect.The common structure of optical superlattice has cycle, paracycle, binary cycle, aperiodic etc.

Simple periodic structure can only provide an independently reciprocal lattice vector, realizes that the position of single optical parameter process is complementary, as frequency multiplication and frequency, difference frequency etc.The reciprocal lattice vector of periodic structure can be expressed as follows:

Wherein Λ is the cycle, and m is integer, represents the exponent number that the position is complementary.

For a plurality of parametric processes, such as conversion under the parameter then and frequently, must provide two above reciprocal lattice vectors compensate respectively conversion under the parameter and and the mismatch mutually of the position in the process frequently, namely multiple accurate is complementary, we use commensurability to realize than bi-period structure here.

Bi-period structure is to be superimposed upon another one on the less cycle by the one-period structure, and two cycles are denoted as l and L, and (l＜L), corresponding modulation sequence is respectively f ₁(x) and f ₂(x), f ₁(x) and f ₂(x) only get+1 and-1, represent two opposite polarised directions, for distribution and the size of analyzing reciprocal space reciprocal lattice vector, with f ₁(x) and f ₂(x) carrying out Fourier expansion is

$f_1\left(x\right)=\underset{m=-\∞}{\overset{\∞}{\mathrm{\Σ}}}{g}_m{e}^{-i{G}_{m}x}$

(1)

$f_2\left(x\right)=\underset{n=-\∞}{\overset{\∞}{\mathrm{\Σ}}}{g}_n{e}^{{-\mathrm{iG}}_{n}x}$

Ignore the interaction between the reciprocal lattice vector, bi-period structure can be reduced to

$f\left(x\right)=f_1\left(x\right)f_2\left(x\right)=\underset{m,n=-\∞}{\overset{\∞}{\mathrm{\Σ}}}{g}_m{g}_n{e}^{-i(G_m+G_n)x}=\underset{m,n=-\∞}{\overset{\∞}{\mathrm{\Σ}}}{g}_{m,n}{e}^{{-\mathrm{iG}}_{m,n}x}---\left(2\right)$

Wherein double-periodic reciprocal lattice vector is by G _{M, n}=G _m+ G _n=mG _l+ nG _LDecide, Fourier coefficient is by g _{M, n}=g _mg _nDecide.G _l=2 π/l and G _L=2 π/L is the single order reciprocal lattice vector of two modulation periods, and integer m, n are the exponent numbers of reciprocal lattice vector.

Two reciprocal lattice vectors that bi-period structure provides are mated two position phase mismatches in the additive mixing process simultaneously: conversion and and frequency under the parameter.Conversion is that 532nm green glow and 3604nm infrared light are converted to the 463.4nm blue light with frequency by being converted to the infrared idle light of 624nm ruddiness and 3604nm and frequency process under the 532nm green glow under the parameter.The reciprocal lattice vector G that the phase mismatch of two processes is provided by bi-period structure _{M, n}And G _{M ', n '}Compensation.

Δk ₁＝k _p-k _r-k _i-G _m，n＝0

(3)

Δk ₂＝k _b-k _p-k _i-G _m′n′＝0

Here k _p, k _r, k _i, k _bBe respectively pump green light, ruddiness, the wave vector of infrared light and blue light.

We select LiTaO ₃As the additive mixing crystal.In theoretical the calculating, when temperature is made as 200 ℃, when red light wavelength was 624.1nm, corresponding infrared light and blue light wavelength were 3604.7nm and 463.6nm, obtain G according to equation (3) _{M, n}And G _{M ', n '}Be respectively 0.536 μ m ^-1And 0.714 μ m ^-1, make m=1, n=-1, m '=1, we obtain l=10.053 μ m n '=1, L=70.371 μ m, L/l 7 has just determined the bi-period structure of commensurability than modulation here.

Laser as shown in Figure 1, first-harmonic light source 1 is sent by pump light source, pump light source is the adjustable 532nm pulse laser of repetition rate 1Hz～150KHz, laser pulse width is nanosecond order.The first-harmonic light source is through attenuator 2 and aperture 3, after colimated light system 4 and focusing system 5, focus on, focusing system is cylindrical mirror, focal length is 300mm, light beam focuses on the laggard optics resonant cavity of going into, resonant cavity comprises front cavity mirror, commensurability is than binary cycle optical superlattice and Effect of Back-Cavity Mirror, optical superlattice 8 places temperature control furnace 9, and the control precision of temperature control furnace 9 is 0.1 ℃, and front cavity mirror 6 is coated with multilayer film, 532nm had high permeability, 3604nm is had high reflectance, and front cavity mirror 6 is circular concave mirror, radius of curvature 600mm, Effect of Back-Cavity Mirror 7 is coated with multilayer film, 532nm is had high permeability, 3604nm is had high reflectance, 624.1nm and 463.6nm are had high permeability, Effect of Back-Cavity Mirror 7 is the cylindrical concave mirror, radius of curvature 100mm, the resonant cavity that front cavity mirror 6 and Effect of Back-Cavity Mirror 7 are formed idle light 3604nm wavelength resonances, the long 60mm in chamber, 10 pairs of speculums are by changing the 532nm laser that reflection angle can obtain different percent of pass, 10 pairs of ruddiness of speculum, blue light has high-transmission rate.By a certain proportion of mixing, obtain the redgreenblue laser output of high-efficiency high power.

Optical superlattice is by the preparation of room temperature Polarization technique, and crystal is of a size of 40mm * 3mm * 0.5mm (long * wide * thick).After the polarization, crystal is placed in the HF acid and soaks a few hours demonstrating domain structure, and Fig. 2 provided+shape appearance figure on C face farmland, wherein the farmland distributes very evenly, and duty ratio is near 50%.

The result is shown in Fig. 3-5.Figure 3 shows that ruddiness and blue power are with the change curve of pumping light power, crystal temperature effect is set to 182.6 ℃, pump light starting of oscillation threshold value is greatly about 2.65W, ruddiness power and blue power increase with pumping light power, and when pumping light power reached 4.2W, ruddiness power reached 980mW, its conversion efficiency is 23.3%, tiltedly efficient is 47%, and the blue light peak power output is 200mW, and ruddiness and blue light gross power are 28.1% with respect to the conversion efficiency of pumping light power.

Fig. 4 is that blue power is with the variation tendency of crystal temperature effect.Reach optimum Match with the frequency process 182.6 ℃ the time, the power output of blue light is the highest under this temperature, and the temperature bandwidth that match obtains is about 3 ℃, and this moment, the live width of ruddiness and blue light was respectively 0.19nm and 0.20nm.

Fig. 5 is that ruddiness and blue light wavelength are with the variation of temperature curve.When crystal temperature effect changed to 186 ℃ by 180 ℃, the centre wavelength of ruddiness was reduced to 624.4nm by 624.9nm, and blue light wavelength is increased to 463.8nm by 463.3nm, and rate of change is 0.08nm/ ℃.

Fig. 6 is through the redgreenblue laser after the prism light splitting.By proportioning 980mW ruddiness, 820mW remains green glow, the 200mW blue light, and we obtain 2W redgreenblue laser (accurate white light), and accurate white light is 48% with respect to the conversion efficiency of pump light, and brightness is 770lm.This shows, based on the optical superlattice of cascade structure, utilize the post lens to assemble pump beam can obtain high-efficiency high power in conjunction with the system configuration of idle optical parameter resonance ruddiness and blue light output.

Though above-mentionedly by reference to the accompanying drawings the specific embodiment of the present invention is described; but be not limiting the scope of the invention; one of ordinary skill in the art should be understood that; on the basis of technical scheme of the present invention, those skilled in the art do not need to pay various modifications that creative work can make or distortion still in protection scope of the present invention.

Claims (1)

1. high power red turquoise laser based on the cascade optical parameter process, it is characterized in that, it comprises the first-harmonic light source, the first-harmonic light source is through attenuator (2) and aperture (3), after colimated light system (4) and focusing system (5), focus on, focus on the laggard optics resonant cavity of going into, optical resonator matches with speculum (10);

Described first-harmonic light source (1) is pulse or quasi-continuous light source, is sent by pump light source, and pump light source is the 532nm green glow, and repetition rate is tuning from 1Hz to 150KHz;

Described focusing system (5) is the post lens;

Described optical resonator comprises front cavity mirror (6), cascade structure optical superlattice (8) and Effect of Back-Cavity Mirror (7), and optical superlattice places temperature control furnace (9); The control precision of described temperature control furnace (9) is 0.1 ℃, front cavity mirror (6) is coated with multilayer film, and 532nm is had high permeability, and 3604nm is had high reflectance, and front cavity mirror (6) is circular concave mirror, radius of curvature 600mm, Effect of Back-Cavity Mirror (7) is coated with multilayer film, and 624.1nm and 463.6nm are had high permeability, and Effect of Back-Cavity Mirror (7) is the cylindrical concave mirror, radius of curvature 100mm, front cavity mirror and Effect of Back-Cavity Mirror are formed the resonant cavity to idle light 3604nm wavelength resonances, the long 60mm in chamber; Described cascade structure optical superlattice (8) comprises paracycle, aperiodic, binary cycle and cascade cycle; The host material of cascade structure optical superlattice (8) comprises congruent LiTaO ₃, congruent LiNbO ₃, stoichiometric proportion LiTaO ₃, stoichiometric proportion LiNbO ₃, mix the lithium niobate of MgO, the lithium tantalate of mixing MgO, potassium titanyl oxygenic phosphate(KTP) crystal KTP and phosphoric acid titanyl rubidium crystal RTP; Described resonant cavity adopts the cavity structure of idle light single resonance;

The preferred commensurability of described cascade structure optical superlattice to improve the optical superlattice polarization quality, realizes the redgreenblue laser output of high-efficiency high power than bi-period structure optical superlattice;

Described bi-period structure is to be superimposed upon on the cycle of another one by the one-period structure, and two cycles are denoted as l and L, l＜L, and corresponding modulation sequence is respectively f ₁(x) and f ₂(x), f ₁(x) and f ₂(x) only get+1 and-1, representing two opposite polarised directions, bi-period structure is as follows:

$f\left(x\right)=f_1\left(x\right)f_2\left(x\right)=\underset{m,n=-\∞}{\overset{\∞}{\mathrm{\Σ}}}{g}_m{g}_n{e}^{-i(G_m+G_n)x}=\underset{m,n=-\∞}{\overset{\∞}{\mathrm{\Σ}}}{g}_{m,n}{e}^{-i{G}_{m,n}x}$

Wherein double-periodic reciprocal lattice vector is by G _{M, n}=G _m+ G _n=mG _l+ nG _LDecide, wherein G _mAnd G _nBe respectively any rank reciprocal lattice vector that provides for two modulation periods, Fourier coefficient is by g _{M, n}=g _mg _nDecide; G _l=2 π/l and G _L=2 π/L is the single order reciprocal lattice vector of two modulation periods, and m, n are the exponent numbers of reciprocal lattice vector, and span is arbitrary integer;

Two reciprocal lattice vectors that bi-period structure provides are mated two position phase mismatches in the additive mixing process simultaneously: conversion reaches and frequency under the parameter; Conversion is that 532nm green glow and 3604nm infrared light are converted to 463.4nm blue light, the different reciprocal lattice vector G that the phase mismatch of two processes is provided by bi-period structure with frequency by being converted to the infrared idle light of 624nm ruddiness and 3604nm and frequency process under the 532nm green glow under the parameter _{M, n}And G _{M ', n '}Compensation:

Δk ₁＝k _p-k _r-k _i-G _m,n＝0

Δk ₂＝k _b-k _p-k _i-G _m′,n′＝0

Here k _p, k _r, k _i, k _bBe respectively pump green light, ruddiness, the wave vector of infrared light and blue light.

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