A combined acousto-optic modulation method based on retro-reflection interference

Abstract

The present application belongs to the technical field of laser regulation, and particularly relates to a combined acousto-optic modulation method based on retro-reflection interference. The present application uses an optical imaging system to accurately retro-reflect the first diffraction output of an acousto-optic modulator, and then input the modulator again for secondary diffraction, thereby realizing multiplexing of the acousto-optic modulator, achieving high diffraction efficiency or high contrast of combined acousto-optic modulation using only a single acousto-optic modulator; for a Sagnac type, diffraction efficiency of more than 99% and single-mode suppression ratio of transmitted light of more than 30 dB can be realized, which can be used for on-demand routing of laser; for a Michelson type, single-mode contrast of more than 30 dB can be realized, which can be used for synchronous frequency division of high-repetition-rate pulsed laser. The present application has significant advantages in high diffraction efficiency and low driving power, and simultaneously reduces cost. The present application has wide application prospects in the fields of pulsed laser modulation, optical and quantum information processing, laser coherent beam splitting / combining and other precise optical manipulation.

Description

Technical Field

[0001] The present invention belongs to the technical field of laser control, and in particular relates to a combined acousto-optic modulation method utilizing retroreflection interference to improve control efficiency and bandwidth. Background Art

[0002] From basic scientific research to industrial control, laser applications require on-demand modulation of laser output. Acousto-optic modulation (AOM) [4] uses radio frequency signals to control the crystal acoustic field to achieve Bragg diffraction of the incident light, thereby achieving precise adjustment of the power, phase, frequency, and propagation direction of the diffracted beam. S Often in the thousands of meters per second, for beams with width w below millimeters, the acousto-optic control bandwidth Δω M ≈v S / w can be as high as tens of MHz, and the control time τ M =1 / Δω M It can be as low as ten nanoseconds. Compared with the faster electro-optical modulation (EOM) [5], acousto-optic modulation has significant advantages in terms of multi-degree-of-freedom control, more precise modulation of the laser phase and intensity, a wide range of laser wavelength and power selection, and low instrument drive requirements. The combination of these advantages and high-speed modulation capabilities makes acousto-optic modulation devices have an almost irreplaceable important technical position in basic research and laser technology development. However, after investigation, conventional acousto-optic modulation technology [4,6] has at least the following shortcomings:

[0003] (1) The acousto-optic diffraction efficiency is low. With a power input of P0, the maximum diffraction efficiency of a conventional AOM, η = P1 / P0, generally does not exceed 90%. This efficiency limits the application of AOM in fields with stringent efficiency requirements, such as high-frequency iteration [6], laser power synthesis [7], and optical quantum information processing [8].

[0004] (2) Corresponding to the low diffraction efficiency is the significant residual zero-order after the AOM is turned on. Therefore, ordinary AOMs cannot freely coherently split the incident light into the zero-order and the first-order, realizing the high-contrast optical beam splitter function. High-speed controllable optical beam splitters have important application prospects. For example, they can be used to achieve controllable routing of pulsed lasers or to construct two-way interferometry to control the group velocity of pulsed lasers by the beam splitting ratio [5].

[0005] (3) For ordinary acousto-optic modulation, obtaining a higher diffraction efficiency η often requires a large incident light spot w, thereby sacrificing the modulation bandwidth δω M Conversely, to achieve a modulation bandwidth of tens of megahertz, the usual approach is to focus the incident beam waist w to less than 100 microns. However, the smaller the beam focus, the wider the wave vector, which destroys the Bragg condition and reduces the diffraction efficiency η.

[0006] (4) Conventional acousto-optic modulation requires a relatively high driving RF power, which not only limits the development of high-frequency modulation technology, but also restricts the selection of acousto-optic crystals and the design of acoustic fields. For example, a quartz crystal with excellent optical quality and low price often needs to provide nearly ten watts of RF driving power. The high power consumption brings many design restrictions. Acousto-optic modulation often uses crystals such as TeO2[9]. Although the driving power requirement is slightly lower, the optical insertion loss is large and the optical damage threshold is low, making it difficult to use in high-power lasers.

[0007] (5) In the combined acousto-optic modulation technology [1, 2, 3] related to the present invention, the authors proposed achieving high diffraction efficiency and control bandwidth through precise imaging using N>1 acousto-optic modulators. However, using N>1 acousto-optic modulation devices to achieve the basic functions of N=1 modulators requires additional hardware resources, which is not conducive to product cost control and system miniaturization. Summary of the Invention

[0008] The object of the present invention is to provide a combined acousto-optic modulation method based on retroreflection interference with high diffraction efficiency, low driving power and low cost.

[0009] The combined acousto-optic modulation method based on retroreflection interference provided by the present invention uses an optical imaging system to accurately reflect the primary diffraction output of the acousto-optic modulator (AOM) and input it into the modulator again for secondary diffraction, thereby realizing the multiplexing of the acousto-optic modulator (AOM) and achieving high diffraction efficiency or high contrast of combined acousto-optic modulation using only a single acousto-optic modulator (AOM). According to the optical path characteristics of the retroreflection optical system, by analogy with the Sagnac interferometer and the Michelson optical interferometer

[10] , the optical imaging system of the present invention can be divided into two configurations: Sagnac type and Michelson type (see Figure 1 、 Figure 2 Both configurations achieve high-efficiency and low-power composite acousto-optic modulation with a single acousto-optic modulation device [1,2,3]. For the Sagnac type, the specific steps of combined acousto-optic modulation are as follows:

[0010] (1) The acousto-optic modulator (AOM) performs a single-frequency acousto-optic modulation on the laser. The length of the acousto-optic crystal of the acousto-optic modulator (AOM) is L. The acousto-optic modulator (AOM) is used to modulate a beam with a central wave vector at The laser with the transverse wave vector broadened to Δk is subjected to single-frequency acousto-optic modulation to obtain the output wave vector corresponding to the m-order Bragg diffraction. The center of the wave vector is located at m=…,-1,0,1,2,…;Δk=π / w,w is the beam waist of Gaussian light;k0 is the wave vector of the normal incident beam, k s is the modulated sound field wave vector; the sound wave driving frequency is f S , the circular frequency is ω S =2πf S .

[0011] (2) Secondary diffraction is formed by the acousto-optic modulator (AOM); the multi-order diffraction output of the acousto-optic modulator (AOM) is collimated by the lens l1 with a focal length of f1, and after a propagation distance of about f1+f2, it is focused by the lens l2 with a focal length of f2 to the reflector M s All the diffraction orders reflected in the reverse direction pass through the lens l in turn. 2, , l1, and then enters the acousto-optic modulator (AOM) again to form secondary diffraction.

[0012] (3) Adjust the distance between lenses l1 and l2 to perform coherent addition of diffraction effects; note the output end of the acousto-optic modulator (AOM) and the reflector M s The spacing is L D , from step (2) we can know that L D ≈2(f1+f2). By adjusting the distance between lenses l1 and l2, L D =πc / ω S Here c≈3×10 8 Meters per second is the speed of light. D The value is chosen to ensure that the first and second diffraction phases of the AOM are different. Achieve coherent addition of diffraction effects.

[0013] (4) Fine-tune the incident light angle; use a weak RF signal to drive the acousto-optic modulator (AOM) and fine-tune the incident light angle so that the m=1 order diffraction efficiency η of a single diffraction is less than 50%, and the m=0 and 1 order diffraction spots are nearly identical; for the AOM designed and optimized at 100% RF drive, the total diffraction loss of m≠0 and 1 orders is at the level of 1%;

[0014] (5) By fine-tuning, the diffraction loss is minimized locally; the reflected light and the incident light are separated by a polarization beam splitter, the composite acousto-optic modulated output is observed by a digital camera, and the diffraction efficiency η of the m=1 level is calculated in real time; the RF driving intensity (A0) is changed to maximize the diffraction efficiency of the m=1 level; the spacing L1=f1+δL between the acousto-optic modulator (AOM) and the lens l1 is fine-tuned, and the diffraction intensity of the m=-1 and 2 levels has The spatial period oscillation of δL is n =nδL h +δL off Achieve local minimization of m = -1,2 order diffraction loss; where n is the oscillation period number, n = 0, 1, 2…, δL off is bias;

[0015] (6) Through fine adjustment, high diffraction efficiency and high single-mode suppression ratio are achieved; specifically, the distance L1 = f1 + δL between the acousto-optic modulator (AOM) and the lens l1 is fine-tuned. The global optimal diffraction drive configuration is obtained at , achieving m=+1 order diffraction efficiency η opt >99%, m=0-level single-mode suppression ratio greater than 30dB. Here [...] is the rounding symbol, is the average refractive index of the acousto-optic crystal, It is the optimal distance for compensating the momentum echo for the Δk diffraction phase broadening under the two-mode approximation ignoring the high-order diffraction loss. The coefficient ξ is related to the sound field distribution profile. When the secondary diffraction position is δL opt When the distance is 1 / 4, the requirement of the combined acousto-optic modulation on the Bragg condition is reduced due to the momentum echo compensation, and the zero-order residual is suppressed; on the other hand, this distance ensures the coherent cancellation of the high-order diffraction caused by the two acousto-optic modulations.

[0016] (7) Further, by fine-tuning, the optimization of high-order diffraction suppression and momentum echo compensation is achieved; specifically, by fine-tuning the driving sound field frequency ω S =v S k S , and repeat steps (1)-(5), and the step (6) The bias δL in off Reduce to zero, and optimize high-order diffraction suppression and momentum echo compensation to obtain higher diffraction efficiency η opt .

[0017] (8) Furthermore, the relative phase of the incident light beam after two diffractions by the acousto-optic modulator (AOM) is Stable. By changing the driving phase of the acousto-optic modulator (AOM) The precise phase control of the m=1 order diffracted light under combined acousto-optic modulation can be achieved; at the same time, the m=1 order diffraction efficiency η can be increased from zero to η by changing the driving intensity A0 of the acousto-optic modulator (AOM). opt Fine adjustment of the optical beam splitter and optical routing functions can be achieved.

[0018] Further,

[0019] For the Michelson type, the combined acousto-optic modulation method is to change the position of the reflector in the Sagnac type to the back focus of the collimating lens l1 (see Figure 3 ), adjust the angle of the reflector so that the output of each level of the first diffraction can return to the original path, and remove the subsequent optical elements. The new reflector is called M m , then the acousto-optic modulator (AOM)-lens l1-reflector M m The Michelson type combined acousto-optic modulation system is formed. The characteristic of this configuration is that the diffraction level m of the second acousto-optic diffraction ′ and the first diffraction order m with m ′=1-m. Therefore, the first-order diffraction phase evolves at twice the frequency of the driving radio frequency. Thus, the diffraction efficiency has a periodic oscillation

[0020] According to the Michelson combination acousto-optic modulation configuration, by synchronizing the driving RF signal and the mode-locked pulse laser output, the repetition frequency f rep =4f S / (2n+1) mode-locked pulse laser realizes efficient switching between m=0 order transmission and m=1 order diffraction, thereby simultaneously realizing f′ of the incident laser in the transmission and diffraction optical paths. rep =f rep / 2 frequency division, the adjacent pulse single-mode coupling suppression ratio can be as high as 30dB or more; n is an integer.

[0021] The invention provides a high-efficiency combined acousto-optic modulation method based on retroreflection interference. In the coherent combined acousto-optic modulation system, the radio frequency signal power of the acousto-optic modulator (AOM) is reduced to 1 / 2 of the power required by conventional acousto-optic modulation technology. It alleviates power consumption pressure and expands the selection and design space of acousto-optic crystals. Moreover, by fine-tuning the corresponding δL shift of the acousto-optic modulator (AOM) in each imaging system, the diffraction efficiency is further improved.

[0022] The Sagnac type can achieve diffraction efficiencies exceeding 99% and transmitted light single-mode suppression ratios exceeding 30dB, enabling on-demand laser routing. The Michelson type can achieve single-mode contrast exceeding 30dB, enabling synchronous repetition rate division of high-repetition-rate pulsed lasers. This invention combines the advantages of acousto-optic modulation technology in terms of high diffraction efficiency and low drive power, while reducing costs and facilitating the development of miniaturized devices. This invention has broad application prospects in precision optical manipulation fields such as pulsed laser modulation, optical and quantum information processing, and laser coherent beam splitting and combining. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the Sagnac-type combined acousto-optic modulation system of the present invention.

[0024] Figure 2 Michelson-type schematic diagram of the combined acousto-optic modulation system of the present invention.

[0025] Figure 3 Schematic diagram of a Michelson type telescope obtained by adjusting the reflectors for the Sagnac type telescope.

[0026] Figure 4 The diffraction effect of the Sagnac interferometer configuration compared to a conventional single AOM is demonstrated.

[0027] Figure 5The experimental results of the Michelson interferometer configuration on the repetition rate division of a mode-locked pulse laser are shown. (a) is the time domain diagram of the input pulse laser, and (b) is the time domain diagram of the pulse laser after the Michelson interferometer configuration synchronizes the repetition rate division. DETAILED DESCRIPTION

[0028] This invention utilizes precise retroreflection to achieve efficient combined acousto-optic modulation using only a single acousto-optic modulator (AOM). The key is to use an imaging system to precisely retroreflect the primary diffracted output of the AOM, which is then re-input into the AOM for secondary diffraction, thus achieving AOM multiplexing. Retroreflective optical systems can be categorized into two types: Sagnac and Michelson configurations, depending on their characteristics.

[0029] Figure 1 The figure shows a schematic diagram of a Sagnac-type combined acousto-optic modulation system. A system was constructed according to the schematic diagram for a demonstration experiment. In the experiment, the optimized frequency of the acousto-optic modulator (AOM) was 200 MHz, and the speed of sound in the crystal was approximately 4260 m / s. Collimated continuous light (λ = 780 nm) was converged by an achromatic lens l0 (focal length f0 = 100 mm) and incident on the acousto-optic modulator (AOM) under Bragg conditions. The primary diffraction output was collimated by an achromatic lens l1 with a focal length f1 = 100 mm and, after propagating a distance of approximately f1 + f2, was focused onto the mirror M by a plano-convex lens l2 with a focal length f2 = 250 mm. s Adjust the angle of the reflector so that the diffraction levels m = ..., -1, 0, 1, 2, ... are reflected back along the paths of ..., 2, 1, 0, -1, ...; all the diffraction levels reflected are reversed and passed through the lens l in turn. 2,1 After that, it enters AOM again to form secondary diffraction; drive AOM to m=0, the first-order diffraction spot is almost the same, optimize lens l2 and reflector M s The distance between the whole and lens l1 is such that the m=1 order diffraction spot in the final output light is the brightest; the position of the AOM is fine-tuned forward and backward along the system optical axis to locally minimize the high-order diffraction loss; the final diffraction intensity distribution is collected using a CCD camera and fed back to the optimization program to optimize the driving power of the AOM, ultimately achieving excellent diffraction effect.

[0030] Figure 2 The diagram shows a Michelson-type combined acousto-optic modulation system. A system was built according to the diagram for demonstration experiments. In the experiment, the incident light was a picosecond pulse mode-locked laser (λ = 795nm) with a pulse repetition frequency of f rep =80MHz; therefore, the driving frequency of the acousto-optic modulator (AOM) is f s=100MHz, the speed of sound in the crystal is about 4260m / s; the collimated pulsed mode-locked laser is focused by an achromatic lens l0 (focal length f0 = 100mm) and then enters the acousto-optic modulator (AOM) under Bragg conditions; the primary diffraction output is collimated by an achromatic lens l1 with a focal length f1 = 100mm, and the reflector M at the rear focal plane of lens l1 is adjusted. m The diffracted light of each level is made to re-enter the AOM along the original optical path to form secondary diffraction; the acousto-optic modulator (AOM) is driven to m=0, and the first-order diffraction spot is almost identical. The phase of the AOM driving radio frequency is changed to synchronize it with the pulse output of the mode-locked laser; a high-speed photodetector is used to monitor one channel in the output, optimize the driving strength of the AOM, further suppress the intensity of adjacent pulses and improve their contrast.

[0031] Figure 4 Figure 3. Comparison of diffraction results of Sagnac-type combined acousto-optic modulation technology and conventional acousto-optic modulation technology: (a) is the light spot incident on the Sagnac combined acousto-optic modulation device and the conventional acousto-optic modulation device; (b) is the optimal diffraction result of the conventional acousto-optic modulation device, which can be obtained after one diffraction by the Sagnac-type combined acousto-optic modulation device, at which point the first-order diffraction efficiency is approximately 90%; (c) is the diffraction result of the optimized Sagnac-type combined acousto-optic modulation device, in which the brightness of the 0th and higher-order diffractions is significantly weaker, and the first-order diffraction efficiency is approximately 98% (which can be further optimized). The 0th-order suppression ratio in free space is approximately 20dB, which will be further increased to over 30dB after selecting a single-mode fiber.

[0032] Figure 5 Shown are time-domain plots of the incident light and the output light from one channel of a Michelson-type combined acousto-optic modulation device. (a) is a time-domain plot of the incident pulsed mode-locked laser light with a repetition rate of 80 MHz; (b) is a time-domain plot of the output pulsed light from one channel. The repetition rate of the output laser light has been reduced to 40 MHz, with almost no pulse remnants between adjacent pulses. The contrast at this point is approximately 23 dB (which can be further optimized).

[0033] References:

[0034] [1] Wu Saijun, Ma Yudi, Liu Ruijuan, Qiu Liyang, invention patent: High-bandwidth composite acousto-optic modulation method based on multiple 4F imaging, patent number: CN113777811B.

[0035] [2] Wu Saijun, Liu Ruijuan, Ma Yudi, Qiu Liyang, invention patent: Ultra-high-speed frequency division method of laser pulse repetition rate based on dual-path acousto-optic interference, patent number: CN113725714B.

[0036] [3] Wu Saijun, Zhao Yuxiang, Hu Jiangyong, Liu Ruijuan, Zhu Huanfeng, Li Yiming, Wu Jinggu, invention patent: A combined acousto-optic modulation method based on precision diffraction superposition, application number: 202410948241.2.

[0037] [4] J.Thom et al, "Accurate and agiledigital control of optical phase, amplitude and frequency for coherent atomic manipulation of atomic systems," Opt.Express 21, 18712 (2013).

[0038] [5]W.Hansel, M.Giunta, M.Fischer, M.Lezius, and R.Holzwarth, Rapidelectro-optic control of the carrier envelope-offset frequency for ultra-lownoise frequency combs, 2017Joint Conference of the European Frequency and TimeForum and IEEE International Frequency Control Symposium,EFTF / IFC 2017-Proceedings,128–129(2017).

[0039] [6]Zhou et al,Laser frequency shift up to 5GHz with a high-efficiency12-pass350-MHz acousto-optic modulator,Rev.Sci.Instrum.91,033201(2020).

[0040] [7]S.Yu,et al,A universal programmable Gaussian boson sampler fordrug discovery,Nature Computational Science 3,839,848(2023).

[0041] [8] Arno Klenke et al, Coherent Beam Combination of Ultrafast Fiber Lasers, IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 24, NO. 5, (2018).

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[0043]

[10] M. Born and E. Wolf, Principles of Optics (Cambridge University Press) (2019).

Claims

1. A combined acousto-optic modulation method based on retroreflection interference, characterized in that: An optical imaging system is used to precisely reflect the primary diffraction output of an acousto-optic modulator (AOM) and re-input it into the modulator for secondary diffraction, enabling multiplexing of the AOMs. This allows for high diffraction efficiency or high contrast in combined AOM, achieved using only a single AOM. Optical imaging systems are available in two configurations: Sagnac and Michelson. For the Sagnac type, the specific steps for combined AOM are as follows: (1) The acousto-optic modulator (AOM) performs a single-frequency acousto-optic modulation on the laser. The length of the acousto-optic crystal of the acousto-optic modulator (AOM) is L. The acousto-optic modulator (AOM) is used to modulate a beam with a central wave vector at The laser with the transverse wave vector broadened to Δk is subjected to single-frequency acousto-optic modulation to obtain the output wave vector corresponding to the m-order Bragg diffraction. The center of the wave vector is located at Δk=π / w, w is the beam waist of Gaussian light; k0 is the wave vector of the normal incident beam, k s is the modulated sound field wave vector; the sound wave driving frequency is f S , the circular frequency is ω S =2πf S ; (2) Secondary diffraction is formed by the acousto-optic modulator (AOM); the multi-order diffraction output of the acousto-optic modulator (AOM) is collimated by the lens l1 with a focal length of f1, and after a propagation distance of about f1+f2, it is focused by the lens l2 with a focal length of f2 to the reflector M s All the diffraction orders after reflection pass through lenses l2 and l1 in reverse order and then enter the acousto-optic modulator (AOM) again to form secondary diffraction; (3) Adjust the distance between lenses l1 and l2 to perform coherent addition of diffraction effects; note the output end of the acousto-optic modulator (AOM) and the reflector M s The spacing is L D , from step (2) we know L D ≈2(f1+f2); by adjusting the distance between lenses l1 and l2, L D =πc / ω S ; Here c≈3×10 8 Meters per second is the speed of light, the L D The value is chosen to ensure that the first and second diffraction phases of the AOM are different. Achieve coherent addition of diffraction effects; (4) Fine-tune the incident light angle; use a weak RF signal to drive the acousto-optic modulator (AOM) and fine-tune the incident light angle so that the m=1 order diffraction efficiency η of a single diffraction is less than 50%, and the m=0 and 1 order diffraction spots are nearly identical; for the AOM designed and optimized at 100% RF drive, the total diffraction loss of m≠0 and 1 orders is at the level of 1%; (5) By fine-tuning, the diffraction loss is minimized locally; the reflected light and the incident light are separated by a polarization beam splitter, the composite acousto-optic modulated output is observed by a digital camera, and the diffraction efficiency η of the m=1 level is calculated in real time; the RF driving intensity (A0) is changed to maximize the diffraction efficiency of the m=1 level; the spacing L1=f1+δL between the acousto-optic modulator (AOM) and the lens l1 is fine-tuned, and the diffraction intensity of the m=-1 and 2 levels has The spatial periodic oscillation of δL in δL n =nδL h +δL off Achieve local minimization of m = -1,2 order diffraction loss; where n is the oscillation period number, n = 0, 1, 2…, δL off is bias; (6) Through fine adjustment, high diffraction efficiency and high single-mode suppression ratio are achieved; specifically, the distance L1 = f1 + δL between the acousto-optic modulator (AOM) and the lens l1 is fine-tuned. The global optimal diffraction drive configuration is obtained at , achieving m=+1 order diffraction efficiency η opt >99%, m=0-level single-mode suppression ratio greater than 30dB; here [...] is the rounding symbol, is the average refractive index of the acousto-optic crystal, It is the optimal distance for compensating the momentum echo for the Δk diffraction phase broadening under the two-mode approximation ignoring the high-order diffraction loss. The coefficient ξ is related to the sound field distribution profile. When the secondary diffraction position is δL opt When the distance is 1 / 4, the requirement of the combined acousto-optic modulation on the Bragg condition is reduced due to the momentum echo compensation, and the zero-order residual is suppressed; on the other hand, this distance ensures the coherent cancellation of the high-order diffraction caused by the two acousto-optic modulations.

2. The combined acousto-optic modulation method according to claim 1, characterized in that: Further fine-tuning is performed to optimize high-order diffraction suppression and momentum echo compensation; specifically, by fine-tuning the driving sound field frequency ω S =v S k S , and repeat steps (1)-(5), and change the The bias δL in off Reduce to zero, and optimize high-order diffraction suppression and momentum echo compensation to obtain higher diffraction efficiency η opt .

3. The combined acousto-optic modulation method according to claim 2, characterized in that: The relative phase of the incident light beam after two diffractions by the acousto-optic modulator (AOM) Stable; by changing the driving phase of the acousto-optic modulator (AOM) The precise phase control of the m=1 order diffracted light under combined acousto-optic modulation is achieved; at the same time, by changing the driving intensity A0 of the acousto-optic modulator (AOM), the m=1 order diffraction efficiency η is achieved from zero to η opt Fine adjustment of the optical beam splitter and optical routing functions can be achieved.

4. The combined acousto-optic modulation method according to claim 3, characterized in that: Adjust the placement of the reflector in the retroreflective optical system to become a Michelson type. Specifically, place the reflector at the back focus of the collimating lens l1, adjust the reflector angle so that the output of each level of the primary diffraction can return to the original path, and remove the subsequent optical elements; the adjusted reflector is recorded as M m , then the acousto-optic modulator (AOM)-lens l1-reflector M m The Michelson type combined acousto-optic modulation system is formed; the diffraction level m of the second acousto-optic diffraction is ′ and the first diffraction order m with m ′ =1-m; therefore, the first-order diffraction phase evolves at twice the frequency of the driving radio frequency, Thus, the diffraction efficiency has periodic oscillations 5. The combined acousto-optic modulation method according to claim 4, characterized in that: By synchronizing the driving RF signal and the mode-locked pulse laser output, the repetition frequency f rep =4f S / (2n+1) mode-locked pulse laser realizes efficient switching between m=0 order transmission and m=1 order diffraction, thereby simultaneously realizing the f′ of the incident laser in the transmission and diffraction optical paths. rep =f rep / 2 frequency division, the adjacent pulse single-mode coupling suppression ratio is as high as over 30dB; n is an integer.

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