CN113777811B - High-bandwidth composite acousto-optic modulation method based on multiple 4F imaging - Google Patents
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- G02F1/11—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on acousto-optical elements, e.g. using variable diffraction by sound or like mechanical waves
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Abstract
The invention belongs to the technical field of laser regulation and control, and particularly relates to a high-bandwidth composite acousto-optic modulation method based on 4F precise imaging. The method comprises the following steps: using 4F lenses for N identical frequenciesThe rate-driven acousto-optic modulator images, so that the single acousto-optic modulation process is split into N coherent processes, high composite diffraction efficiency which cannot be realized by the single acousto-optic modulation is obtained by means of N sound field intensity and phase optimization, and the incident light angle is obtainedWavelength of incident lightFrequency of driving sound waveFault tolerance. The compound diffraction optimizing capability in the invention is gradually improved along with N. Taking N within 5, diffraction regulation and control of nearly 100% efficiency can be realized on incident light which deviates greatly from the Bragg condition. The invention can realize the capacities of high bandwidth polychromatic acousto-optic modulation, large-scale sweep frequency/large-angle beam diffraction and the like which cannot be obtained by the traditional acousto-optic modulation method, and has important application prospects in the scientific and technical fields of realizing quantum regulation and control on atomic molecules by using continuous laser and ultrafast laser.
Description
Technical Field
The invention belongs to the technical field of laser regulation and control, and particularly relates to a high-bandwidth composite acousto-optic modulation method and system based on multiple 4F imaging.
Background
In the technical field of laser regulation and control, an acousto-optic modulation (AOM) technology based on phase matching Bragg diffraction utilizes a radio frequency signal to control the intensity, phase, frequency and direction of an optical field, the modulation speed is far higher than that of mechanical regulation, and the modulation precision and universality are far better than those of electro-optic modulation. In the aspect of regulating continuous light and pulse laser, the acousto-optic modulation has universal and important application in the basic research and technical fields. Important indicators of AOM include acousto-optic diffraction efficiency R, operating frequency range Δf S Applicable wavelength range Deltalambda and modulation bandwidth Deltaf M . Zhongzhuzhuzhuzhuzhu (popular science)It is known that the Gao Shengguang diffraction efficiency R of AOM is difficult and the large operating bandwidth Δf S Large wavelength range Δλ compatible: to obtain the best acousto-optic diffraction efficiency, the optimal incidence angle θ of the modulated laser needs to be close to the frequency f of the acoustic wave S Acoustic wave vector k S ＝2πf S /v S Bragg angle θ commonly determined by wavelength λ of incident light B And operating frequency f s The large change of the incident laser wavelength lambda inevitably leads to the rapid reduction of diffraction efficiency, and limits the application potential of the acousto-optic modulation technology in large-scale frequency shift and multi-color and ultra-short pulse regulation and control. For example, in the well-known ultra-short pulse optical carrier-envelope-relative phase (CEP) lock application (koke 2010), the stability of CEP lock is greatly limited by the range of AOM frequency variation, while dispersion of the ultra-short pulses in AOM diffraction results in "space-time coupling" of the outgoing light, reducing the effective power of the output mode. On the other hand, the AOM's acousto-optic modulation bandwidth δf M I.e. the control bandwidth for the real-time adjustment of the frequency, phase, intensity, direction of the diffracted light-depending on the incident spot size w and the crystal sound velocity v S Can be expressed as δf M ＝v S And/w. Due to the sound velocity v of conventional acousto-optic crystals S In order to obtain a modulation bandwidth of tens of MHz, it is common practice to focus the incident spot beam waist w to below hundred microns. The spread of the incident angle θ corresponding to the focused light may further cause the destruction of the bragg condition, affecting the diffraction efficiency R.
Through investigation and research, no system solution for overcoming high acousto-optic diffraction efficiency and large working frequency range delta f exists in the technical field of acousto-optic modulation at present S Large operating wavelength range Δλ, high modulation bandwidth δf M Contradiction between indexes. In the general processing method, firstly, the diffraction efficiency R is directly sacrificed to replace the broadband working performance, and secondly, the acousto-optic modulation theory is combined, and the working center frequency f is increased S And decreasing the acousto-optic interaction distance L to reduce the severity of the bragg condition, thereby achieving broadband operation. However, the two methods have at least the following disadvantages:
1. the acoustic-optical modulation technology is based on Bragg resonance. In the conventional acousto-optic modulation technology, the optical diffraction efficiency R drops rapidly after deviating from the bragg condition, and the cost of exchanging R for high-bandwidth multi-wavelength operation is often to exchange for a limited operating bandwidth and wavelength range gain by greatly reducing the output power.
2. By increasing f S Is able to obtain sum f by decreasing the interaction distance L S Frequency range Δf of equal scale increase S Wavelength range Deltalambda and modulation bandwidth Deltaf M . However, as crystal dimensions decrease, AOM acoustic wave field designs become increasingly difficult and acousto-optic diffraction is difficult to maintain efficient at high frequencies. The AOM technique currently on the market is at frequency f S The single-device diffraction efficiency R drops rapidly above 250MHz, whereas the diffraction efficiency R for GHz order modulation frequency is very difficult to exceed 50%.
Disclosure of Invention
The invention aims to provide a method for realizing high-bandwidth composite acousto-optic modulation based on multiple 4F imaging, which breaks through the limitation of Bragg conditions in a single acousto-optic modulation device on diffraction efficiency, working frequency range and modulation bandwidth by utilizing multi-parameter control acousto-optic interference, realizes ultra-high bandwidth arbitrary acousto-optic modulation, and can be used in various nonlinear optics and quantum optics experiments.
The invention provides a method for realizing high-bandwidth composite acousto-optic modulation based on multiple 4F imaging, which uses a 4F lens to image N acousto-optic modulators driven by the same frequency, so as to split a single acousto-optic modulation process into N coherent processes, and obtains high composite diffraction efficiency which cannot be realized by single acousto-optic modulation by means of N sound field intensity and phase optimization, and outputs the high composite diffraction efficiency to incident light angle delta theta, incident light wavelength delta lambda and driving sound wave frequency delta F S Fault tolerance, the composite diffraction optimizing capability is gradually improved along with N (N is taken to be within 5), so that diffraction regulation and control of nearly 100% efficiency is realized on incident light which deviates greatly from the Bragg condition. The method comprises the following specific steps:
(1) N identical geometry acousto-optic modulators were imaged with a 4F lens group (fig. 2). The modulator is denoted AOM j J=1, 2,.. j Abbreviated as N-AOM system; specifically, every two lenses with focal length F will AOM j Is imaged onto AOM j+1 Realizing precise imaging of sound field of the acousto-optic modulator under N driving of the same frequency and coherent linking of transmitted/diffracted light. Modulator AOM j (AOM) Acoustic wave Driving frequencies are all f S While the intensity of sound A j Drive phaseThe acousto-optic modulator sequence is recorded as an N-AOM multi-acousto-optic modulation module under the control of a digital radio frequency signal program.
(2) To reference atomic physics and quantum control theory [ wu2005, genov2014], the following mathematical description is made for the N-AOM system under low driving intensity:
for each AOM j For the input and output wavefront, respectively, are noted as |ε j，in >And ∈ j，out >Thus having |epsilon j+1，in >＝|ε j，out >. Note that the initial input wavefront is |ε in >＝|ε 1，in >The wave front of the composite output light field is epsilon out >＝|ε N，out >. AOM recording j Action on wave front by acoustic wave intensity A j Drive phaseThe transmission matrix is controlled to be-> Simultaneously, the transmission matrix under the driving of radio frequency sound waves is recorded as +.>The input-output relationship of the N-AOM system under 4F imaging to the wavefront transformation is:
by decreasing AOM driving strength A j Limiting the higher diffraction (dashed line in FIG. 1), note that the wavefront of the 0 th and 1 st diffraction orders in the transmitted beam is C a ，C b Average wave vector k a ，k b . In response thereto, each of the formulas (1)Composite optical conversion matrixAre all->2 times 2 matrix characterization of parameters, and thus has composite diffraction efficiency
(3) Recording the distribution of output light intensity in transmission and diffraction light paths using a digital camera, and adjusting the N-AOM group in real time by program controlParameters (N amplitudes, N-1 relative phases), optimizing the diffraction efficiency of an N-AOM system under specific requirements based on equation (1)>Obtain the best composite diffraction efficiency->For example:
(3.1) as shown in fig. 1, for monochromatic light collimation incidence at wavelength λ, the bragg condition is first optimized by conventional adjustment of the incidence angle θ: k (k) a -k b ＝±k S Wherein k is a ，k b Wave vectors, k, of the transmitted beam and the diffracted beam respectively S For acoustic wave vectors in acousto-optic modulators, corresponding mismatch wave vectors δk≡k a -k b ±k S Satisfies |delta k| < pi/L (L is crystal sound field length). By driving a single AOM, the acquisition of the optimal single AO is measuredM diffraction efficiency R j Corresponding optimal acousto-optic modulation intensityThen all AOMs are driven simultaneously with intensity reduced to +.>Recording the distribution of the output light intensity in the transmission and diffraction light paths by means of a digital camera and program-controlled real-time adjustment for further optimization +.>The N-AOM coherent diffraction emitter is obtained. Because of->Effectively inhibit high-order diffraction loss, and can obtain high composite diffraction efficiency which is gradually perfect along with the increase of N and cannot be realized by a single AOM
(3.2) on the basis of the monochromatic light collimation incidence of the above (3.1), the wavelength λ (wave vector k) can be changed if the application requires a，b Length) angle of incidence θ (varying wave vector k a，b Direction), acoustic wave driving frequency f S (changing wave vector k) S Length), destroy the Bragg wave vector matching relation k a -k b ＝±k S By properly increasing { A } only in the range of the mismatching wave vector |δk|is less than or equal to pi/L j Digital camera is used for recording the distribution of output light intensity, and further automatic optimization is performed through program controlCan get +.>Toward an optimum diffraction efficiency of 100%, the regulation effect becomes perfect as N increases.
(3.3) for polychromatic light incidence, non-collimated incidence, focused lightIncident etc., wave vector k a ，k b And the mismatch wave vector δk have a large spread. δk spread is denoted as Δk. In order to realize equal and efficient diffraction on incident light with different wavelengths and k components at the same time, fault-tolerant regulation and control technology [ genov2014] aiming at 2-by-2 matrix in formula (1) can be developed by means of Nuclear Magnetic Resonance (NMR) field]Will be optimized for nuclear spin regulationValue applied to N-AOM system by RF signal programming to be +.>Initial value and program control to further optimize +.>The method can obtain +.about.F. again under the condition that Deltak is less than or equal to pi/L and the Bragg condition can not meet different incident light components at the same time>Toward an optimal diffraction efficiency of 100%, the regulation effect also becomes perfect as N increases.
(4) In the scheme, all optical elements are completely shared by diffraction and transmission light paths of the N-AOM multi-acousto-optic modulation system, and the relative displacement of the transmission and diffraction light paths can be controlled to be not more than 1 millimeter by selecting a proper short focal length (for example, F is below 10 cm) aberration eliminating lens, so that the relative optical path change of an interference path is difficult to be caused by environmental disturbance, and the system is ensured to have excellent passive phase stability. While this stability ensures that the N-AOM system goes through the pairing in a particular applicationAutomatic adjustment of parameters achieves a composite diffraction efficiency +.>And the optimization condition is kept for a long time, so that high-bandwidth and high-efficiency diffraction is realized.
The invention also provides a specific implementation system of the high-bandwidth composite acousto-optic modulation method based on multiple 4F imaging, as shown in figures 2 and 3, the system mainly comprises: the system comprises an N-AOM multi-acousto-optic modulation module, a radio frequency signal coding module and a measurement and automatic feedback optimization module.
The N-AOM multi-acousto-optic modulation module is composed of N acousto-optic devices (generally an acousto-optic modulator (AOM) or an acousto-optic deflector (AOD)) which are optically linked through a 4-F imaging system, and can convert radio frequency signals into sound waves (crystal density modulation waves) with corresponding frequencies, intensities and phases, so that multi-angle diffraction is generated on incident laser. Wherein the 4-F imaging system passes the AOM through every two lenses with a focal length F j Is imaged onto AOM j+1 Realizing precise imaging of sound field of the acousto-optic modulator under N driving of the same frequency and coherent linking of transmitted/diffracted light. By selecting a suitable short focal length (F below 10 cm) aberration-eliminating lens, the relative displacement of the transmission and diffraction light paths is controlled to be not more than 1 mm, and the system can be ensured to have excellent passive phase stability. All AOM acoustic wave driving frequencies are f S Acoustic intensity A of N-AOM j And drive phaseIs programmed and controlled by a radio frequency signal.
The N-AOM multi-acousto-optic modulation module correspondingly executes the operation of the step (1) of imaging N acousto-optic modulators with the same geometric dimension by utilizing a 4F lens group;
the radio frequency signal coding module consists of a program-controlled multichannel Direct Digital Synthesis (DDS) signal source and a linear radio frequency amplifier, and provides N paths of independently programmable output intensity A j And relative phaseThe stable radio frequency signal is amplified by radio frequency and used for driving the N-AOM module.
The radio frequency signal coding module correspondingly executes the radio frequency signal coding operation in the step (3);
the measuring and automatic feedback optimizing module is composed of a digital camera and a personal computerThe system comprises a personal computer program control digital camera, an N-AOM system transmission and diffraction output channel light intensity photographing device, a diffraction analysis device and a diffraction analysis device, wherein the personal computer program control digital camera photographs light intensities of the transmission and diffraction output channels of the N-AOM system, and analyzes composite diffraction efficiencyAnd control the RF signal coding module through the communication interface, update RF signal sequence +.>And driving the N-AOM module to form an optimized loop.
The measurement and automatic feedback optimization module correspondingly executes the measurement and automatic feedback optimization operation in the step (3);
the system design and regulation method of the invention is mainly different from the prior art in that the high bandwidth composite acousto-optic modulation system of multiple 4F imaging breaks through the diffraction efficiency R and the working frequency range Deltaf of Bragg conditions in the traditional single AOM method S Wavelength range Deltalambda, modulation bandwidth Deltaf M By precisely imaging a plurality of AOMs through a 4-F lens system, splitting single AOM diffraction into N-AOM coherent diffraction, and realizing nearly 100% diffraction regulation and control on polychromatic and uncollimated incident light under the condition of deviating from Bragg by means of amplitude and phase multiparameter optimization of the multi-acousto-optic modulation. As can be seen from the technical scheme provided by the invention, the invention has the following advantages:
(1) The invention is based on the condition of weak drivingCan be as low as->) Is a sound-light interference effect of (a). Wherein the weak driving condition can greatly inhibit the unavoidable high-order diffraction loss caused by the limited crystal length L in the traditional acousto-optic modulation, and further optimize the acoustic wave driving amplitude A j And drive phase +.>With 2N-1 parameters (N amplitudes and N-1 phases)Phase) to achieve a high composite diffraction efficiency not achievable with a single AOM>
(2) The invention collimates incidence of monochromatic light and satisfies wave vector matching relation k a -k b ≈±k S After that, when the wavelength or the driving frequency is changed to destroy wave vector matching, the mismatch quantity |delta k| < pi/L is not satisfied any more, and under the condition that the conventional acousto-optic diffraction efficiency is drastically reduced, if |delta k| < pi/L exists, the amplitude A can be still driven by automatically adjusting the acoustic wave j And drive phaseSo that the system obtains again +.>Is a diffraction efficiency of (a).
(3) Under the conditions of polychromatic light, non-collimation, focusing incidence and the like, the wave vector mismatch has larger broadening delta k, and under the condition that the conventional acousto-optic diffraction can not realize uniform and efficient diffraction on all incident light, if the broadening delta k is less than or equal to pi/L, the NMR fault tolerance regulation theory can be used as a reference, and the radio frequency programming is used for the diffractionAutomatic optimization, still achieving a near +.>Is uniformly and efficiently diffracted.
(4) All sub-optical paths of the system share the same optical element, the relative displacement of the diffraction and transmission optical paths is short, the relative phase stability of the system has excellent immunity to vibration noise, and the whole system has excellent short-term and long-term phase stability.
The invention can be used for realizing high-bandwidth arbitrary waveform modulation, large-range sweep frequency, large-angle beam deflection and the like for multicolor lasers including ultra-fast pulse lasers. The invention can expand the application of continuous laser and ultrafast laser in the basic and technical fields, and particularly provides support for the technical expansion in the field of atomic molecular quantum regulation and control.
Drawings
FIG. 1 is a schematic diagram of a single acousto-optic diffraction principle, in which the broken lines represent higher order diffraction paths, and the right diagram shows k a -k b ＝±k S The Bragg condition wave vector matching relationship.
Fig. 2 is a schematic diagram of a high bandwidth compound acousto-optic modulation method and system based on multiple 4F imaging.
FIG. 3 is a modular schematic diagram of a high bandwidth compound acousto-optic modulation system based on multiple 4F imaging.
Fig. 4 is a schematic diagram of an n=2 compound acousto-optic modulation system.
FIG. 5 shows the single acousto-optic diffraction efficiency R 1，2 Compound acousto-optic diffraction efficiency with n=2Relationship. Wherein (a) is the acoustic frequency f s Experimental measurements (a, i) and theoretical calculations (a, ii) under 100MHz bragg conditions; at R 1，2 At about 0.5, obtainOptimum value. (b) At the acoustic frequency f S Experimental measurements (b, i) and theoretical calculations (b, ii) at 140MHz offset bragg conditions. At R 1，2 When 0.35 is taken to be the single AOM efficiency limit, +.>Optimum value.
FIG. 6 shows the maximum diffraction efficiency and the acoustic frequency f S Is a relationship of (3). Wherein (a) is Shan Cisheng light diffraction efficiency; (b) is n=2 composite acousto-optic diffraction efficiency.
Detailed Description
The invention is further described by taking the simplest n=2 compound acousto-optic modulation system as an example. In experiments, as in FIG. 4, the acoustic velocity v in the crystal of the acousto-optic modulator s =4260 m/s, set the RF signal frequency f S ＝100MHz, the continuous light (wavelength λ=795 nm, gaussian beam waist radius w≡110 um) is adjusted to be incident on the AOM under bragg conditions 1 The diffracted and transmitted light was imaged precisely to the AOM through a 4-F achromat (f=10 cm) group 2 Then, the second diffraction was performed. Reducing the intensity of individual AOM modulation to suppress higher order coupling, the acousto-optic diffraction effect of each AOM can be determined by a parameterized reflection coefficientAnd transmission coefficient (t) j ) Composed 2 x 2 matrixDescription. Using digital cameras or photodetectors to diffract Shan Cisheng light and transmit R j ＝|r j | 2 、T j ＝|t j | 2 Maximum diffraction efficiency of double AOM system->And measuring, and optimizing the amplitude and the phase of the AOM in real time according to the actual measurement result.
Under the Bragg condition, the maximum acousto-optic diffraction efficiency of a single AOM can reach R 1，2 Approximately 80% (fig. 6 (a)). And as shown in fig. 5 (a, i), by optimizing the radio frequency signalShan Cisheng light diffraction efficiency R in N=2 compound acousto-optic modulation system demonstrated by adjustment experiment 1，2 ＝|r 1，2 | 2 In the optimal case (at the white dashed line in fig. 5 (a, i)), the maximum diffraction efficiency of the compound acousto-optic diffraction system can be up to +.>In fig. 5 (b, i), we also demonstrate the fault tolerance of the composite acousto-optic modulation system when the bragg condition is severely corrupted by δk mismatch. For this purpose we increase the acoustic frequency to f S =140 MHz, regulate->Optimizing and measuring to obtain maximum diffraction efficiency->While the individual AOM diffraction efficiency has been reduced to R 1，2 Approximately 35%. Also in fig. 5 (a, ii) and (b, ii), we give theoretical simulations corresponding to the conditions in fig. 5 (a, i) (b, i), respectively, and give substantially uniform results.
For further explanation, we demonstrate the acoustic frequency f in FIG. 6 S At=80 MHz to 140MHz, a single acousto-optic modulator and the n=2 compound acousto-optic modulation systemIs a variation of (c). At the acoustic frequency f S In the range of =80 MHz to 120MHz, diffraction efficiency +.>The diffraction efficiency of the single acousto-optic modulator is far better than that of the single acousto-optic modulator, and the diffraction efficiency is more than 90%. This result also demonstrates that the system design can still be tuned to the acoustic drive amplitude a in the event of a dramatic drop in conventional acousto-optic diffraction efficiency due to bragg condition mismatch j And drive phase +.>Again to obtain high diffraction efficiency.
Reference is made to:
[koke2010]:S.Koke,C.Grebing,H.Frei,A.Anderson,A.Assion,and G.Steinmeyer,“Direct frequency comb synthesis witharbitrary offset and shot-noise-limited phase noise,”Nat.Photonics4,462–465(2010).
[wu2005]S.Wu,Y.-J.Wang,Q.Diot,and M.Prentiss,“Splitting matter waves using an optimized standing-wave light-pulsesequence,”Phys.Rev.A71,043602(2005).
[genov2014]:G.T.Genov,D.Schraft,T.Halfmann,and N.V.Vitanov,“Correction of Arbitrary Field Errors in PopulationInversion of Quantum Systems by Universal Composite Pulses,”Phys.Rev.Lett.113,043001(2014).
Claims (5)
1. a method for realizing high-bandwidth composite acousto-optic modulation based on multiple 4F imaging is characterized in that N acousto-optic modulators driven by the same frequency are imaged by utilizing a 4F lens, so that a single acousto-optic modulation process is split into N coherent processes, high composite diffraction efficiency which cannot be realized by single acousto-optic modulation is obtained by means of N sound field intensity and phase optimization, and an incident light angle delta theta, an incident light wavelength delta lambda and a driving sound wave frequency delta F are obtained S Fault tolerance is realized, so that the composite diffraction optimization capacity is gradually improved along with N, and diffraction regulation and control of nearly 100% efficiency are realized on incident light which deviates greatly from the Bragg condition; the method comprises the following specific steps:
(1) Imaging the N acousto-optic modulators with the same geometric dimensions by using a 4F lens group; the modulator is denoted AOM j J=1, 2,.. j Abbreviated as N-AOM system; wherein every two lenses with focal length F will AOM j Is imaged onto AOM j+1 Realizing the precise imaging of sound fields of the acousto-optic modulator under the driving of N identical frequencies and the coherent linking of transmitted/diffracted light; modulator AOM j The sound wave driving frequencies are f S While the intensity of sound A j Drive phaseProgrammed by radio frequency signals;
(2) In order to reference the atomic physics and quantum regulation theory, the following mathematical description is made on the N-AOM system under low driving strength:
for each AOM j The wave fronts of the input light wave and the output light wave are respectively recorded as epsilon j，in >And ∈ j，out >Thus there is |ε j+1，in >＝|ε j，out >The method comprises the steps of carrying out a first treatment on the surface of the Note that the initial input wavefront is |ε in >＝|ε 1，in >The wave front of the composite output light field is epsilon out >＝|ε N，out >The method comprises the steps of carrying out a first treatment on the surface of the AOM recording j For wave front derivativeThe radiation is caused by the intensity A of sound wave j Drive phaseThe transmission matrix is controlled to be->Simultaneously, the transmission matrix under the driving of radio frequency sound waves is recorded as +.>The input-output relationship of the N-AOM system under 4F imaging to the wavefront transformation is:
by decreasing AOM driving strength A j Limiting the high-order diffraction, and recording the wave front of the 0 order and 1 order diffraction light in the transmitted light beam as C a ，C b Average wave vector k a ，k b The method comprises the steps of carrying out a first treatment on the surface of the In response thereto, each of the formulas (1)Composite optical conversion matrix> Are all->2 by 2 matrix characterization of parameters, and thus of composite diffraction efficiency +.>
(3) The distribution of the output light intensity in the transmission and diffraction light paths is recorded using a digital camera,adjusting N-AOM groups in real time by program controlParameters: n amplitudes, N-1 relative phases, optimizing the diffraction efficiency of an N-AOM system under specific requirements based on equation (1)>Obtain the best composite diffraction efficiency->
(4) The diffraction and transmission light paths of the N-AOM multi-acousto-optic modulation system completely share all optical elements, and the proper short focal length F is selected to eliminate an aberration lens, so that the relative displacement of the transmission light path and the diffraction light path is controlled to be not more than 1 millimeter, the system is ensured to have excellent passive phase stability, and the N-AOM system is ensured to pass through the lens in specific applicationAutomatic adjustment of parameters achieves a composite diffraction efficiency +.>And the optimization condition is kept for a long time, so that high-bandwidth and high-efficiency diffraction is realized.
2. The method for realizing high bandwidth composite acousto-optic modulation based on multiple 4F imaging according to claim 1, wherein said optimizing diffraction efficiency in step (3)Obtain the best composite diffraction efficiency->The method comprises the following steps:
(3.1) collimated incidence of monochromatic light of wavelength λ, first by incident uponConventional adjustment of the angle θ optimizes the bragg condition: k (k) a -k b ＝±k S Wherein k is a ，k b Wave vectors, k, of the transmitted beam and the diffracted beam respectively S For acoustic wave vectors in acousto-optic modulators, corresponding mismatch wave vectors δk≡k a -k b ±k S Meeting the requirement of delta k pi/L, L is the crystal sound field length; by driving a single AOM, obtaining the optimal single AOM diffraction efficiency R is measured j Corresponding optimal acousto-optic modulation intensityThen all AOMs are driven simultaneously, the intensity is reduced toRecording the distribution of the output light intensity in the transmission and diffraction light paths by means of a digital camera and program-controlled real-time adjustment for further optimization +.>Obtaining the N-AOM coherent diffraction emitter strength; due to->Effectively inhibit high-order diffraction loss, and can obtain high composite diffraction efficiency which can not be realized by a single AOM>
3. The method for implementing high bandwidth compound acousto-optic modulation based on multiple 4F imaging according to claim 2, wherein the optimizing diffraction efficiency in step (3)Obtain the best composite diffraction efficiency->Further, the method comprises the steps of,
(3.2) on the basis of the collimation incidence of the monochromatic light of the above (3.1), the wavelength lambda, the incidence angle theta and the acoustic wave driving frequency f are changed according to the application requirements S Destroying the Bragg wave vector matching relationship delta k ≡k a -k b ±k S By properly increasing { A } only in the range of the mismatching wave vector |δk|is less than or equal to pi/L j Digital camera is used for recording the distribution of output light intensity, and further automatic optimization is performed through program controlObtain +.>Toward an optimum diffraction efficiency of 100%, the regulation effect becomes perfect as N increases.
4. The method for implementing high bandwidth compound acousto-optic modulation based on multiple 4F imaging according to claim 2, wherein the optimizing diffraction efficiency in step (3)Obtain the best composite diffraction efficiency->The method comprises the following steps:
(3.3) wave vector k for polychromatic light incidence, uncollimated incidence or focused light incidence a ，k b And the mismatch wave vector delta k has larger stretching, and the delta k stretching is recorded as delta k; to realize equal and efficient diffraction on incident light with different wavelengths and k components at the same time, the fault-tolerant regulation and control technology of 2-by-2 matrix in the formula (1) is developed by virtue of the nuclear magnetic resonance field, so that nuclear spin regulation and control are optimizedValue applied to N-AOM system by RF signal programming to be +.>Initial value and program control to further optimize +.>Under the condition that Δk is less than or equal to pi/L and the Bragg condition can not meet different incident light components at the same time, obtaining +.>Toward an optimal diffraction efficiency of 100%, the regulation effect also becomes perfect as N increases.
5. Implementing a high bandwidth compound acousto-optic modulation system based on multiple 4F imaging based on the method of one of claims 1-4, comprising: the system comprises an N-AOM multi-acousto-optic modulation module, a radio frequency signal coding module and a measurement and automatic feedback optimization module;
the N-AOM multi-acousto-optic modulation module consists of N acousto-optic modulators (AOMs) which are optically linked through a 4-F imaging system; the method comprises the steps of converting radio frequency signals into sound waves with corresponding frequency, intensity and phase, and generating multi-angle diffraction on incident laser; wherein the 4-F imaging system passes the AOM through every two lenses with a focal length F j Is imaged onto AOM j+1 Realizing the precise imaging of sound fields of the acousto-optic modulator under the driving of N identical frequencies and the coherent linking of transmitted/diffracted light; the short focal length F is selected to be below 10cm, so that the aberration-eliminating lens can control the relative displacement of a transmission optical path and a diffraction optical path to be not more than 1 mm, and the system is ensured to have excellent passive phase stability; all AOM acoustic wave driving frequencies are f S Acoustic intensity A of N-AOM j And drive phaseProgrammed by radio frequency signals;
the radio frequency signal coding module consists of a program-controlled multichannel Direct Digital Synthesis (DDS) signal source and a linear radio frequency amplifierThe constitution provides N paths of independently programmable output intensity A j And relative phaseThe stable radio frequency signal is amplified by radio frequency and used for driving the N-AOM module;
the measuring and automatic feedback optimizing module consists of a digital camera and a personal computer; wherein, the personal computer program controls the digital camera to photograph the light intensity of the transmission and diffraction output channels of the N-AOM system, and analyze the composite diffraction efficiencyAnd control the RF signal coding module through the communication interface, update RF signal sequence +.>And driving the N-AOM module to form an optimized loop.
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