WO2026016325A1 - 一种基于精密衍射叠加的组合声光调制方法 - Google Patents

一种基于精密衍射叠加的组合声光调制方法

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Publication number
WO2026016325A1
WO2026016325A1 PCT/CN2024/127872 CN2024127872W WO2026016325A1 WO 2026016325 A1 WO2026016325 A1 WO 2026016325A1 CN 2024127872 W CN2024127872 W CN 2024127872W WO 2026016325 A1 WO2026016325 A1 WO 2026016325A1
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Prior art keywords
acousto
diffraction
aom
optic
optic modulator
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PCT/CN2024/127872
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English (en)
French (fr)
Inventor
吴赛骏
赵宇翔
胡江勇
刘瑞娟
朱焕峰
李一鸣
邬京谷
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Fudan University
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Fudan University
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Priority claimed from CN202410948241.2A external-priority patent/CN118707762B/zh
Priority claimed from CN202411172141.1A external-priority patent/CN119045222B/zh
Application filed by Fudan University filed Critical Fudan University
Publication of WO2026016325A1 publication Critical patent/WO2026016325A1/zh
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    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—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
    • G02F1/01—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 
    • 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

Definitions

  • This invention belongs to the field of laser control technology, specifically involving a combination of acousto-optic modulation methods using precision diffraction superposition to improve control efficiency and bandwidth, and a combination of acousto-optic modulation methods using retro-reflection interference to improve control efficiency and bandwidth.
  • Acousto-optic modulation [[1] J. Thom et al, “Accurate and agile digital control of optical phase, amplitude and frequency for coherent atomic manipulation of atomic systems,” Opt. Express 21, 18712 (2013)] uses radio frequency signals to control the crystal acoustic field to achieve Bragg diffraction of incident light, thereby achieving precise adjustment of the power, phase, frequency, and propagation direction of the diffracted beam.
  • acousto-optic modulation has significant advantages such as multi-degree-of-freedom controllability, precise modulation phase and amplitude, a wide range of laser wavelength and power selection, and low instrument drive requirements.
  • the purpose of this invention is to provide an ultra-high efficiency combined acousto-optic modulation method based on precision diffraction superposition to suppress higher-order diffraction losses, thereby achieving an ultra-high diffraction efficiency of over 99% and a transmission light single-mode suppression ratio of over 30dB.
  • the present invention provides a combined acousto-optic modulation method based on precise diffraction superposition, which first constructs an encoding module capable of synchronizing radio frequency signals, and a precisely adjustable coherent combined acousto-optic modulation system; wherein:
  • the synchronous radio frequency signal encoding module provides a phase-stable, arbitrarily programmable radio frequency signal, which is amplified by a signal amplifier and input into a coherent combined acousto-optic modulation system to drive the acousto-optic modulator AOM in the system to work.
  • the coherent combined acousto-optic modulation system consists of two identical acousto-optic modulators (AOMs) with similar geometric dimensions and a dual-lens 4-F optical imaging system.
  • the acousto-optic modulator converts the radio frequency signal into sound waves with corresponding frequency, intensity, and phase, generating acousto-optic diffraction on the incident pulsed laser.
  • the dual-lens 4-F optical imaging system consists of two asymmetric lenses with a focal length of F.
  • the crystal sound field of the first acousto-optic modulator (AOM 1 ) and the center of the beam interaction are used as the object plane, and the image is accurately projected onto the center of the second acousto-optic modulator AOM 2 ; the direction of the sound field of the second acousto-optic modulator AOM 2 is the same as the direction of the image of the sound field of the first acousto-optic modulator AOM 1 .
  • n is the oscillation period number
  • n 0, 1, 2, ...
  • ⁇ Loff is the bias, the value of which depends on the sound field length, frequency, and other sound field distribution details of the acousto-optic modulator (AOM).
  • step (5) can be improved .
  • the bias ⁇ L off is reduced to zero, thereby achieving higher-order diffraction suppression and momentum echo optimization, resulting in higher diffraction efficiency ⁇ opt .
  • phase remains constant, precise phase control of the diffracted light can be achieved; at the same time, by changing the driving intensity of the first acousto-optic modulator AOM 1 and the second acousto-optic modulator AOM 2 , the diffraction efficiency ⁇ can be finely adjusted from zero to ⁇ opt , thereby realizing a high-contrast adjustable beam splitter and optical routing function.
  • Pulsed optical routing technology realizes time-division multiplexing (TDM) of pulsed laser [7] and quantum light source [4].
  • Pulse optical path coherent accumulation technology coherently combine multiple laser beams to form a higher power laser [5].
  • the optical frequency can be moved over a wide range of tens of GHz [3].
  • this invention is not limited to the coherent combination of two AOMs; a multi-lens 4-F optical imaging system can be used to achieve the coherent combination of multiple AOMs.
  • N the number of sub-AOMs in the combined acousto-optic modulation system
  • the driving power required for each sub-AOM is reduced to a level typically required for [the latter]. Therefore, this invention can significantly reduce the RF drive power requirements for acousto-optic modulation, thereby expanding the range of acousto-optic modulation crystals.
  • Another objective of this invention is to provide a combined acousto-optic modulation method based on retro-reflection interference, which has high diffraction efficiency, low driving power, and low cost.
  • the combined acousto-optic modulation method based on retro-reflection interference uses an optical imaging system to accurately reflect the primary diffraction output of an acousto-optic modulator (AOM), and then inputs it back into the modulator for secondary diffraction, thereby realizing the multiplexing of the acousto-optic modulator (AOM) and achieving high diffraction efficiency or high contrast using only a single acousto-optic modulator (AOM) to achieve combined acousto-optic modulation.
  • AOM acousto-optic modulator
  • AOM acousto-optic modulator
  • the optical imaging system of this invention can be divided into two configurations: Sagac type and Michelson type (see Figures 6 and 7). Both configurations achieve efficient and low-power composite acousto-optic modulation using CN113777811B, CN113725714B and the aforementioned single acousto-optic modulator.
  • An acousto-optic modulator performs a single-frequency acousto-optic modulation on the laser; let the length of the acousto-optic crystal of the acousto-optic modulator (AOM) be L, and use the acousto-optic modulator (AOM) to modulate a laser beam whose central wave vector is located at...
  • a laser with a transverse wave vector broadening of ⁇ k is subjected to single-frequency acousto-optic modulation to obtain the output wave vector corresponding to the m-order Bragg diffraction. The center of this wave vector is located at...
  • w is the waist of the Gaussian beam
  • k0 is the wave vector of the normally incident beam
  • ks is the wave vector of the modulated sound field
  • the sound wave driving frequency be fS
  • the coefficient ⁇ is related to the sound field distribution profile.
  • the secondary diffraction position is ⁇ L opt , the requirements of the Bragg condition for the combined acousto-optic modulation are reduced due to momentum echo compensation, and the zero-order residual is suppressed.
  • this distance ensures that the higher-order diffraction caused by the two acousto-optic modulations coherently cancels each other out.
  • the bias ⁇ L off is reduced to zero, while optimizing higher-order diffraction suppression and momentum echo compensation, resulting in higher diffraction efficiency ⁇ opt .
  • AOM acousto-optic modulator
  • the combined acousto-optic modulation method specifically involves changing the position of the reflector in the Sanignac type to the back focal point of the collimating lens l1 (see Figure 3), adjusting the reflector angle so that the outputs of each order of the first diffraction can return along the original path, and removing subsequent optical elements.
  • the new reflector be Mm
  • the acousto-optic modulator (AOM) - lens l1 - reflector Mm constitutes the Michelson type combined acousto-optic modulation system.
  • the efficient combined acousto-optic modulation method based on retro-reflection interferometry of this invention reduces the RF signal power of the acousto-optic modulator (AOM) in the constructed coherent combined acousto-optic modulation system to the power required by conventional acousto-optic modulation techniques.
  • This alleviates power consumption pressure and expands the selection and design space for acousto-optic crystals; moreover, by finely adjusting the corresponding ⁇ L displacement of the acousto-optic modulator (AOM) in each imaging system, the diffraction efficiency is further improved.
  • a diffraction efficiency exceeding 99% and a single-mode suppression ratio exceeding 30 dB can be achieved, enabling on-demand laser routing.
  • a single-mode contrast exceeding 30 dB can be achieved, enabling synchronous frequency division of high-repetition-rate pulsed lasers.
  • Figure 1 is a schematic diagram of the dual AOM coherent combined acousto-optic modulation system of the present invention.
  • Figure 2 shows the diffraction results of the dual AOM coherent combination system under different driving conditions.
  • Figure 4 shows the changes in the maximum diffraction efficiency and the corresponding 0th-order suppression ratio of the dual-AOM coherent combination system and the single-AOM system when the driving frequency is changed.
  • Figure 6 is a schematic diagram of the combined acousto-optic modulation system of the present invention in the form of a Saniac.
  • Figure 7 is a schematic diagram of the combined acousto-optic modulation system of the present invention in Michelson type.
  • Figure 8 is a schematic diagram of the transformation from a Saniac-type mirror to a Michelson-type mirror.
  • Figure 9 shows the diffraction effect of the Sagnac interferometer configuration compared to a conventional single AOM.
  • Figure 10 shows the experimental results of frequency division of mode-locked pulsed laser using the Michelson interferometer configuration. Among them, (a) is the time-domain plot of the input pulsed laser, and (b) is the time-domain plot of the pulsed laser after synchronous frequency division using the Michelson interferometer configuration.
  • This invention utilizes a precision diffraction superposition method to achieve ultra-high acousto-optic diffraction efficiency far exceeding that of traditional single AOMs. Its core lies in the process of precision diffraction coherent superposition, where AOM 2 is moved an appropriate distance from the imaging position of AOM 1. This suppresses the diffraction phase shift broadening of the focused beam Bragg diffraction through momentum echo, while simultaneously adjusting higher-order diffraction phase shifts to precisely suppress higher-order diffraction losses through coherent destructive effects. This results in a first-order diffraction efficiency exceeding 99% and a 0th-order single-mode suppression ratio exceeding 30 dB.
  • AOM 2 was finely adjusted back and forth along the optical axis of the 4-F imaging system to minimize the local higher-order diffraction loss.
  • the final diffraction intensity distribution was collected using a CCD camera and fed back to the optimization program to optimize the driving power of AOM 1 and 2 , finally obtaining excellent diffraction effect, as shown in Figure 2(c).
  • Figure 2 shows the output results of the above demonstration experimental setup under three different driving conditions: (a) the state when neither AOM is driven, in which case no diffraction occurs; (b) the state when only one AOM is driven to reach diffraction maxima, at which point the first-order diffraction efficiency is approximately 90%, and higher-order diffraction spots are clearly visible; (c) the state when both AOMs are driven simultaneously under optimal driving conditions, at which point the first-order diffraction efficiency is >99%, and higher-order diffraction spots are almost invisible, while the 0th-order spot is also greatly suppressed.
  • the 0th-order suppression ratio can reach approximately 22 dB in free space, and after single-mode ray mode selection, the 0th-order suppression ratio can be further increased to over 30 dB.
  • Figure 3 shows the trend of first-order diffraction efficiency when the driving intensity of the two AOMs is adjusted simultaneously without changing the phase difference between them.
  • Figure 4 shows the maximum first-order diffraction efficiency (solid line) and the corresponding zero-order suppression ratio (dashed line) in free space for single-AOM diffraction and dual-AOM coherent combination diffraction at other driving frequencies.
  • the driving frequency shifts further away from the optimized frequency (80MHz)
  • both the maximum first-order diffraction efficiency and the zero-order suppression ratio decrease.
  • the dual-AOM coherent combination diffraction consistently outperforms the single-AOM diffraction.
  • Figure 5 illustrates the effect of the fine-tuning distance ⁇ L on different diffraction orders, based on numerical simulation.
  • the horizontal axis represents the fine-tuning distance ⁇ L
  • the vertical axis represents the diffraction efficiency.
  • the large trend in efficiency between the 1st and 0th orders is due to the diffraction phase shift broadening caused by the Bragg diffraction of the focused beam.
  • the optimal distance for momentum echo compensation is achieved when ⁇ L satisfies this requirement.
  • ⁇ 0.2 the first-order diffraction efficiency reaches its peak.
  • the oscillation trend within a small range is influenced by higher-order diffraction.
  • This embodiment utilizes precise retroreflection to achieve efficient combined acousto-optic modulation using only a single acousto-optic modulator (AOM). Its core lies in using an imaging system to precisely retroreflect the primary diffraction output of the AOM, then inputting it back into the same AOM for secondary diffraction, thus achieving multiplexing of the AOM. Based on the characteristics of the retroreflection optical system, it can be divided into two types: the Sanignac configuration and the Michelson configuration.
  • FIG. 6 shows a schematic diagram of a Sagnac-type combined acousto-optic modulation system.
  • a system was built according to the diagram for demonstration experiments.
  • the optimized frequency of the acousto-optic modulator (AOM) was 200MHz, and the speed of sound in the crystal was approximately 4260m/s.
  • AOM Modulator
  • FIG. 7 shows a schematic diagram of a Michelson-type combined acousto-optic modulation system.
  • the reflecting mirror M located at the rear focal plane of lens l1 , is adjusted.
  • the phase of the acousto-optic modulator (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 intensity of the AOM, and further suppress the intensity of adjacent pulses to improve its contrast.
  • AOM acousto-optic modulator
  • FIG 8 is a schematic diagram of the Michelson-type modulation system formed by adjusting the Saignac-type mirror, which is a schematic diagram of the switching method between the two types of combined acousto-optic modulation systems shown in Figures 6 and 7. It illustrates the switching method between the two types of combined acousto-optic modulation systems, combining the Saignac-type combined acousto-optic modulation system shown in Figure 6 and the Michelson-type combined acousto-optic modulation system shown in Figure 7. Specifically, inserting a Michelson-type mirror (M ⁇ sub> m ⁇ /sub> ) into the illustrated system makes the optical path equivalent to that in Figure 7, forming a Michelson-type combined acousto-optic modulation.
  • a Michelson-type mirror M ⁇ sub> m ⁇ /sub>
  • Figure 9 shows a comparison of the diffraction results of the Sagnac-type combined acousto-optic modulation technology and the conventional acousto-optic modulation technology: (a) is the light spot incident on the Sagnac-type 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 of the Sagnac-type combined acousto-optic modulation device, at which time the first-order diffraction efficiency is about 90%; (c) is the optimized diffraction result of the Sagnac-type combined acousto-optic modulation device, where the brightness of the 0th order and higher-order diffractions is significantly weaker, and the first-order diffraction efficiency is about 98% (which can be further optimized), and the 0th order suppression ratio in free space is about 20dB.
  • Figure 10 shows the time-domain plot of the incident light and the outgoing light from one of the channels of the Michelson-type combined acousto-optic modulation device.
  • (a) is the time domain diagram of the incident pulsed mode-locked laser with a repetition frequency of 80 MHz;
  • (b) is the time domain diagram of the pulsed light output from one of the channels, where the repetition frequency of the output laser drops to 40 MHz, and almost no pulse residue is visible between two adjacent pulses.
  • the contrast is about 23 dB (which can be further optimized).

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  • Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)

Abstract

一种基于精密衍射叠加的组合声光调制方法，运用4-F光学系统实现两个声光调制器布拉格衍射振幅相干叠加过程中，将一个声光调制器移出另一个声光调制器的成像位置恰当距离，以动量回波方式抑制聚焦光束布拉格衍射的衍射相移展宽，同时调节高阶衍射相移，以相干相消效应精确抑制高阶衍射损失。还提供了一种基于回射干涉的组合声光调制方法，运用光学成像系统将声光调制器的一次衍射输出精确回射，再次输入该调制器进行二次衍射，实现声光调制器的复用，仅使用单个声光调制器实现组合声光调制的高衍射效率或高反衬度。上述方法可获得99％以上的衍射效率及30dB以上的透射光单模抑制比。

Description

一种基于精密衍射叠加的组合声光调制方法 技术领域
本发明属于激光调控技术领域，具体涉及利用精密衍射叠加的组合声光调制方法来提高控制效率和带宽，以及利用回射干涉的组合声光调制方法，来提高控制效率和带宽。
背景技术
从基础科研到工业控制，激光应用需要对激光输出实现按需调制。声光调制技术(AOM)[[1]J.Thom et al,“Accurate and agile digital control of optical phase,amplitude and frequency for coherent atomic manipulation of atomic systems,”Opt.Express 21,18712(2013)]以射频信号控制晶体声场实现对入射光的布拉格衍射，进而实现衍射光束的功率，相位，频率，及传播方向的精密调节。由于晶体声速vS常在数千米每秒，对宽度w在毫米以下的光束，声光控制带宽ΔωM≈vS/w可高达数十兆赫，调控时间τM＝1/ΔωM可低至十纳秒。相对于速度更快的电光调制[[2]W.Hansel,M.Giunta,M.Fischer,M.Lezius,and R.Holzwarth,Rapid electro-optic control of the carrierenvelope-offset frequency for ultra-low noise frequency combs,2017 Joint Conference of the European Frequency and Time Forum and IEEE International Frequency Control Symposium,EFTF/IFC 2017-Proceedings,128–129(2017)]，声光调制拥有多自由度可控，调制相位和幅度精确，激光波长和功率选择范围大，以及仪器驱动要求低等方面的显著优势。这些优势和高速调制能力的结合使得声光调制器件在基础研究和激光技术发展中拥有几乎无可替代的重要技术地位。然而经调研，常规声光调制技术如[1]&[3]Zhou et al,Laser frequency shift up to 5GHz with a high-efficiency 12-pass 350-MHz acousto-optic modulator,Rev.Sci.Instrum.91,033201(2020)至少存在如下不足：
(1)声光衍射效率不高。以P0功率输入，常规AOM的最大衍射效率η＝P1/P0一般不超过90％。这样的效率限制了AOM在高频迭代[[3]Zhou et al,Laser frequency shift up to 5GHz with a high-efficiency 12-pass 350-MHz acousto-optic modulator,Rev.Sci.Instrum.91,033201(2020)]，激光功率合成[[4]S.Yu,et al,A universal programmable Gaussian boson sampler for drug discovery,Nature Computational Science 3,839,848(2023)],及光学量子信息处理[[5]Arno Klenke et al,Coherent Beam Combination of Ultrafast Fiber Lasers,IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS,VOL.24,NO.5,(2018)]等对效率要求苛刻的领域应用。
(2)和衍射效率低下对应的是AOM打开后零级存在显著的残余。因此，普通AOM无法自由的将入射光相干分束为零级和一级，实现高对比度的光学分束器功能。而高速可控的光学分束器有重要的应用前景，例如可以用来对脉冲激光实现可控路由，或者是构建双路干涉， 以分束比例控制脉冲激光的群速度[2]。
(3)对于普通声光调制来说，获得较高衍射效率η常需要大光斑w入射，从而以牺牲调制带宽δωM为代价：反过来说，为获得数十兆赫调制带宽，通常做法是对入射光斑束腰w聚焦到百微米以下。然而光束聚焦越小对应波矢展宽越宽，这会破坏布拉格条件，降低衍射效率η。
(4)普通声光调制的驱动射频功率偏高，不仅限制了高频调制技术的发展，也限制了声光晶体的选择及声场设计。例如，光学品质卓越，价格低廉的石英晶体常需要提供近十瓦射频驱动功率，较大功耗带来诸多设计方案限制。而声光调制常应用TeO2等晶体[[6]A.Feldman,“Measurement of the Photoelastic Contents of Optical Materials,”Opt.Eng.17,453(1978)]，虽然驱动功率需求稍低，但光插入损耗大，光损伤阈值低，难以用于大功率激光。
(5)在和本发明相关的组合声光调制技术[[7]中国专利号公告号CN113777811B，&[8]中国专利公告号CN113725714B]中，作者提出通过N>1个声光调制器精密成像实现较高的衍射效率和控制带宽。然而对于N＝2的构型，衍射效率η仍很难超过95％。虽然增加AOM个数N可以持续提高衍射效率，但随之而来的问题是资源的消耗和插入损耗的增加。
另外，以N>1个声光调制器件实现N＝1个调制器的基本功能，对应硬件资源的额外消耗，不利于产品的成本控制和系统的小型化设计。
发明内容
本发明的目的在于提供一种基于精密衍射叠加的超高效率组合声光调制方法，以抑制高阶衍射损失，从而获得99％以上的超高衍射效率及30dB以上的透射光单模抑制比。
本发明提供的基于精密衍射叠加的组合声光调制方法，首先构建一个可同步射频信号的编码模块，以及可精密调节的相干组合声光调制系统；其中：
所述可同步射频信号的编码模块，提供相位稳定、可任意编程的射频信号，经信号放大器放大后输入相干组合声光调制系统，驱动该系统中的声光调制器AOM工作；
所述相干组合声光调制系统，由几何尺寸接近的两个同型号声光调制器AOM以及双透镜4-F光学成像系统构成；其中，声光调制器将射频信号转化为相应频率、强度及相位的声波，对入射的脉冲激光产生声光衍射；双透镜4-F光学成像系统由焦距为F的两个消球差透镜构成；将第一(即前一个)声光调制器AOM1的衍射输出以放大率M＝1精确成像到声波同向传播的第二(即后一个)声光调制器AOM2，形成两次衍射的干涉。
在运用双透镜4-F光学成像系统实现两个声光调制器AOM布拉格衍射振幅相干叠加过程中，通过将第二声光调制器AOM2移出第一声光调制器AOM1的成像位置恰当距离，以动量回波的方式抑制聚焦光束布拉格衍射的衍射相移展宽，同时调节高阶衍射相移，以相干相消效 应精确抑制高阶衍射损失，从而获得99％以上的衍射效率及30dB以上的透射光单模抑制比；具体步骤如下：
(1)记AOM声光晶体长度为L；利用第一声光调制器(AOM1)对一束中心波矢位于 横向波矢展宽为Δk的激光进行单频声光调制(其中正入射光束波矢记为k0，调制声场波矢记为ks)得到m级布拉格衍射相应的输出波矢中心位于 有波矢展宽Δk＝π/w，w是高斯光的束腰。
(2)利用双透镜4-F光学成像系统，以第一声光调制器(AOM1)晶体声场与光束作用中心为物面，将其精确成像至第二声光调制器AOM2中心；第二声光调制器AOM2的声场方向与第一声光调制器AOM1声场的像的方向保持相同。
(3)以弱射频信号分别驱动AOM1和AOM2，微调入射光角度，使得AOM1和AOM2的m＝1级衍射效率η<50％并接近等同；对于设计优化在100％射频驱动的商用AOM,此时m≠0,1级的衍射损失总和在1％的级别。
(4)利用AOM2对AOM1出射的所有级别衍射光进行二次衍射，改变AOM2的驱动相位使m＝1级衍射最亮，沿双透镜4-F光学成像系统光轴的方向前后微调AOM2位置δL，发现m＝-1,2级衍射强度具有的空间周期振荡，因此δL在δLn＝nδLh+δLoff处可实现m＝-1,2级衍射损失的局部最小化。其中，n为振荡周期序号，n＝0,1,2…，δLoff为偏置，其值取决于声光调制器(AOM)的声场长度、频率及其他声场分布细节。
(5)通过程序控制联合优化AOM1和AOM2的驱动功率，在处获得全局最优的驱动配置。这里[…]是取整符号，是声光晶体的平均折射率，是忽略高阶衍射损失的二模近似下对Δk衍射相位展宽实现动量回波补偿的最优距离，系数ξ≈0.2和声场分布轮廓相关；当AOM2的位置取δLopt时，由于动量回波补偿，组合声光调制对布拉格条件的要求降低，零级残余被抑制。另一方面，这个距离保证了AOM1和AOM2造成的高阶衍射相干相消。在δLopt距离上可实现m＝+1级衍射效率ηopt>99％，m＝0级单模抑制比大于30dB的目标。
(6)进一步通过精细调节驱动声场频率ωS＝vSkS,可以将上述步骤(5)中 中的偏置δLoff降低到零，同时实现高阶衍射抑制和动量回波的优化，获得更高的衍射效率ηopt。
(7)上述步骤(4)、(5)过程中，输出由稳定的多路干涉形成，具有确定的相位关系；衍射 级m＝1最优输出由第一声光调制器AOM1和第二声光调制器AOM2驱动射频信号对应的相位差及4-F光学成像系统偏移距离δL确定；通过改变第一声光调制器AOM1和第二声光调制器AOM2的共同驱动相位同时保持相位差不变，可以实现对衍射光的精确相位控制；同时，通过改变第一声光调制器AOM1和第二声光调制器AOM2的驱动强度可实现衍射效率η从零到ηopt的精细调节，进而实现高对比度可调分束器及光学路由功能。
本发明方法，具有极高的衍射效率(ηopt>99％)及零级抑制比(单模耦合抑制率α>30dB)，有极高的工作带宽和精确的相位调制能力，可在如下技术领域代替压电，电光，传统声光调制等传统技术，更新组合声光调制技术[6,7],提高激光调制的速度、效率、精度，及光强损伤阈值：
(1)脉冲光路由技术：实现脉冲激光[7]和量子光源[4]的多路时分复用(TDM)。
(2)脉冲光路相干累加技术：将多路激光相干合束，形成更大功率激光[5]。
(3)以干涉仪分束比例调整脉冲激光的群速度，实现大功率光梳的载波-包络相位调节[2]。
(4)通过高效声光调制的迭代运用，实现光学频率的数十GHz级大范围可控移动[3]。
进一步地，本发明不局限于两个AOM的相干组合，利用多透镜4-F光学成像系统可以实现多数量AOM的相干组合。设组合声光调制系统中子AOM数量为N，则每个子AOM所需驱动功率减少到传统需求的因此，本发明可大幅度降低声光调制射频驱动功率需求,从而拓展声光调制晶体的选择范围。例如可以方便利用石英晶体等低声光效率材料发展插入损耗低，损伤阈值高的声光调制系统，以及发展高频调制，深紫外波长激光调制等技术；此外，在N-AOM系统中通过对每个成像系统中声光调制器(AOM)相应的δL位移细调，能够进一步提升衍射效率。
本发明的另一目的在于提供一种衍射效率高、驱动功率低、成本开销少的基于回射干涉的组合声光调制方法。
本发明提供的基于回射干涉的组合声光调制方法，运用光学成像系统将声光调制器(AOM)的一次衍射输出精确回射，再次输入该调制器进行二次衍射，实现声光调制器(AOM)的复用，达到仅使用单个声光调制器(AOM)实现组合声光调制的高衍射效率或高反衬度。根据回射光学系统的光路特征，类比萨尼亚克干涉仪与迈克尔孙光干涉仪[[9]M.Born and E.Wolf,Principles of Optics(Cambridge University Press)(2019)]，本发明光学成像系统可分为两种构型：萨尼亚克型和迈克尔孙型(参见图6、图7所示)。两种构型均以包括CN113777811B,CN113725714B和上述的单个声光调制器件实现高效和低功耗的复合声光调制。
其中，对于萨尼亚克型，组合声光调制的具体步骤如下：
(1)声光调制器(AOM)对激光进行一次单频声光调制；记声光调制器(AOM)声光晶体长度为L，利用声光调制器(AOM)对一束中心波矢位于横向波矢展宽为Δk的激光进行单频声光调制，得到m级布拉格衍射相应的输出波矢，该波矢中心位于 w是高斯光的束腰；k0为正入射光束波矢，ks为调制声场波矢；记声波驱动频率为fS，圆频率为ωS＝2πfS。
(2)通过声光调制器(AOM)形成二次衍射；以焦距为f1的透镜l1对声光调制器(AOM)的多级衍射输出准直，并经约f1+f2传播距离后，由焦距为f2的透镜l2聚焦至反射镜Ms。经反射的所有衍射级逆向依次经过透镜l2,，l1后，再次进入声光调制器(AOM)，形成二次衍射。
(3)调节透镜l1,l2间距，进行衍射效果相干相加；记声光调制器(AOM)出射端和反射镜Ms间距为LD，由步骤(2)可知LD≈2(f1+f2)。通过调节透镜l1,l2间距，使得LD＝πc/ωS。这里c≈3×108米/秒是光速。该LD取值保证第一次和第二次声光调制器(AOM)衍射相位相差实现衍射效果相干相加。
(4)对入射光角度进行微调；以弱射频信号驱动声光调制器(AOM)，微调入射光角度，使得单次衍射的m＝1级衍射效率η<50％，m＝0,1级衍射光斑接近等同；对于设计优化在100％射频驱动的声光调制器(AOM),此时m≠0,1级的衍射损失总和在1％的级别；
(5)通过微调，使衍射损失局部最小化；借助偏振分束器将回射光和入射光分开，运用数字相机观测复合声光调制出射，并实时计算出m＝1级的衍射效率η；改变射频驱动强度(A0)，使m＝1级衍射效率最大；微调声光调制器(AOM)和透镜l1的间距L1＝f1+δL,在m＝-1,2级衍射强度具有的空间周期振荡,因此δL在δLn＝nδLh+δLoff实现m＝-1,2级衍射损失的局部最小化；其中，n为振荡周期序号，n＝0,1,2…，δLoff为偏置；
(6)通过细调，实现高衍射效率、高单模抑制比；具体地，细调声光调制器(AOM)和透镜l1的间距L1＝f1+δL,在处获得全局最优的衍射驱动配置，实现m＝+1级衍射效率ηopt>99％，m＝0级单模抑制比大于30dB的目标。这里[…]是取整符号，是声光晶体的平均折射率，是忽略高阶衍射损失的二模近似下对Δk衍射相位展宽实现动量回波补偿的最优距离，系数ξ和声场分布轮廓相关；当二次衍射位置取δLopt时，由于动量回波补偿，组合声光调制对布拉格条件的要求降低，零级残余被抑制；另一方面，这个距离保证两次声光调制造成的高阶衍射相干相消。
(7)进一步地，通过精调，实现高阶衍射抑制和动量回波补偿的优化；具体地，通过精细调节驱动声场频率ωS＝vSkS，并重复步骤(1)-(5),可将步骤(6)中中的偏置δLoff降低到零，同时实现高阶衍射抑制和动量回波补偿的优化，获得更高的衍射效率ηopt。
(8)进一步地，入射光束经过声光调制器(AOM)的先后两次衍射相对相位稳定。通过改变声光调制器(AOM)的驱动相位可实现组合声光调制下m＝1级衍射光的精确相位控制；同时，通过改变声光调制器(AOM)的驱动强度A0可实现m＝1级衍射效率η从零到ηopt的精细调节，实现高对比度可调分束器及光学路由功能。
进一步地，
对于迈克尔孙型，组合声光调制方法，具体是将萨尼亚克型中反射镜位置改变为准直透镜l1的后焦点处(参见图3)，调整反射镜角度使一次衍射的各级输出能够原路返回，并移除后续光学元件。记新反射镜为Mm，则声光调制器(AOM)-透镜l1-反射镜Mm构成迈克尔孙型组合声光调制系统。该构型的特点在于第二次声光衍射的衍射级别m'和第一次衍射级别m以m'＝1-m关系对应。因此一级衍射相位以驱动射频的二倍频率演化， 从而有周期振荡的衍射效率
根据迈克耳孙组合声光调制构型,通过将驱动射频信号和锁模脉冲激光输出同步，可将重频为frep＝4fS/(2n+1)的锁模脉冲激光实现m＝0级透射和m＝1级衍射之间的高效切换,进而在透射和衍射光路中同时实现入射激光的f'rep＝frep/2重频分频，相邻脉冲单模耦合抑制比可高达30dB以上；n为整数。
本发明的基于回射干涉的高效组合声光调制方法，在构建的相干组合声光调制系统中，声光调制器(AOM)的射频信号功率减少到常规声光调制技术所需功率的缓解功耗压力，拓展声光晶体选择及设计空间；而且通过对每个成像系统中声光调制器(AOM)相应的δL位移细调，进一步提升衍射效率。
对于萨尼亚克型，可实现超99％的衍射效率及超30dB的透射光单模抑制比，可用于激光的按需路由；对于迈克尔孙型，可实现超30dB的单模反衬度，可用于高重频脉冲激光的同步重频分频。本发明组合声光调制技术在高衍射效率及低驱动功率方面的优势，同时降低成本，便于小型化设备开发。本发明在脉冲激光调制、光学和量子信息处理、激光相干分/合束等精密光学操控领域有广泛应用前景。
附图说明
图1本发明的双AOM相干组合声光调制系统示意图。
图2展示了双AOM相干组合系统在不同驱动条件下的衍射结果。
图3展示了双AOM相干组合系统以不同强度的射频驱动时，m＝1级衍射效率的变化，其中横轴是实际的射频驱动强度与优化驱动强度的比值。
图4展示了改变驱动频率时，双AOM相干组合系统和单AOM的最大衍射效率以及相应0级抑制比的变化。
图5是利用数值模拟给出的双AOM相干组合声光调制系统中AOM2的位置偏移δL与m＝-1,0,1,2级衍射效率的关系。高阶衍射(m＝-1,2级)呈现周期性振荡，振荡周期
图6本发明的组合声光调制系统萨尼亚克型示意图。
图7本发明的组合声光调制系统迈克耳孙型示意图。
图8为萨尼亚克型调整反射镜而成迈克耳孙型的示意图。
图9展示了萨尼亚克干涉构型对比常规单个AOM的衍射效果。
图10展示了迈克耳孙干涉构型对锁模脉冲激光重频分频的实验结果。其中，(a)是输入脉冲激光的时域图，(b)是迈克尔孙干涉构型同步降重频后脉冲激光的时域图。
具体实施方式
本发明利用精密衍射叠加的方式实现远超传统单AOM的超高声光衍射效率。其核心是在精密衍射相干叠加的过程中，通过将AOM2移出AOM1成像位置恰当距离，以动量回波的方式抑制聚焦光束布拉格衍射的衍射相移展宽，同时还可以调节高阶衍射相移，以相干相消效应精确抑制高阶衍射损失，从而获得99％以上的1级衍射效率及30dB以上的0级单模抑制比。
实施例1
以图1所示的双AOM相干组合系统为例，进行实验。实验中，两个作为基本单元的AOM型号相同，优化频率为80MHz，声速为4260m/s；将连续光(λ＝780nm)以布拉格条件入射AOM1，出射光经两个消色差透镜(F＝100mm)组成的4-F光学成像系统精确成像到AOM2进行二次衍射，需保证AOM2的声场方向与AOM1声场的像的方向相同；改变AOM2的驱动相位使1级衍射最亮；沿着4-F成像系统的光轴前后微调AOM2的位置，使高阶衍射损失局部最小化；利用CCD相机收集最终衍射强度分布，将其反馈给优化程序优化AOM1,2的驱动功率，最终得到优异的衍射效果，如图2(c)所示。
图2展示是上述演示实验装置在三种不同驱动条件下获得的输出结果：(a)是在两个AOM均未被驱动时的状态,此时没有衍射的产生；(b)是仅有一个AOM被驱动达到衍射极大时的状态，此时1级的衍射效率约为90％，能够明显看到高阶衍射光斑；(c)是双AOM在最优驱动条件下同时驱动的状态，此时一级衍射效率>99％,已经几乎无法看见高阶衍射光斑，同时0级光斑也被极大的抑制。由图4可知，在自由空间中0级抑制比可达约22dB，经过单模光线的模式选择，0级抑制比可以进一步升高到至30dB以上。
图3展示的是不改变两个AOM驱动相位差的情况下，同时调节两个AOM驱动强度时1级衍射效率的变化趋势。该实验结果表明，本发明可以通过改变AOM驱动强度的方式实现精细控制双AOM相干组合系统的1级衍射效率。
图4展示的是单AOM衍射和双AOM相干组合衍射在其他驱动频率下所能达到的1级最大衍射效率(实线)和对应自由空间中的0级抑制比(虚线)。随着驱动频率不断偏移优化频率(80MHz)，两种衍射方式1级的最大衍射效率和0级抑制比都在不断下降，但是在80±40MHz的驱动范围内，双AOM相干组合衍射的效果总是优于单AOM衍射的。该实验结果表明，双AOM相干组合系统不仅拥有优于单AOM的1级衍射效率和0级抑制比，还拥有比单AOM更大的驱动频率带宽。
图5是展示的基于数值模拟给出的微调距离δL对不同衍射级别的影响，横轴是微调距离δL，纵轴是衍射效率。其中1级与0级效率大的趋势变化是受聚焦光束布拉格衍射的衍射相移展宽的影响，当δL能够满足动量回波补偿的最优距离时，其中ξ≈0.2，1级衍射效率达到顶点。小范围内的振荡趋势是受高阶衍射的影响，随着δL不断改变，高阶衍射在二次衍射中的相干条件周期性变化，高阶衍射也周期性振荡，周期为该数值模拟结果表明，双AOM相干系统中第二个AOM的微调距离是动量回波补偿距离和高阶振荡最低点对应位置的共同作用结果。
实施例2
本实施例利用精确回射的方式，仅使用单个声光调制器(AOM)就可以实现高效的组合声光调制。其核心在于利用成像系统将声光调制器(AOM)的一次衍射输出精确回射，再次输入该声光调制器(AOM)进行二次衍射，实现声光调制器(AOM)的复用。按照回射光学系统的特点可分为萨尼亚克构型和迈克尔孙构型两种。
图6所示为萨尼亚克型组合声光调制系统的示意图，依照示意图搭建一套系统用于演示实验。实验中，声光调制器(AOM)的优化频率为200MHz，晶体中声速约为4260m/s；将准直后的连续光(λ＝780nm)经消色差透镜l0(焦距f0＝100mm)汇聚后以布拉格条件入射到声光 调制器(AOM)；一次衍射输出经焦距f1＝100mm的消色差透镜l1准直，并经过约f1+f2的传播距离后，由焦距f2＝250mm的平凸透镜l2聚焦至镜面Ms；调整反射镜角度，使m＝…,-1,0,1,2,…级别的衍射分别按照…,2,1,0,-1,…的路径回射；经反射的所有衍射级逆向依次经过透镜l2,1后，再次进入(AOM)，形成二次衍射；将AOM驱动至m＝0,1级衍射光斑接近等同，优化透镜l2和反射镜Ms整体与透镜l1之间的距离，使最终出射光中的m＝1级衍射光斑最亮；沿系统光轴方向前后微调AOM的位置，使高阶衍射损失局部最小化；利用CCD相机收集最终衍射强度分布，将其反馈给优化程序优化AOM的驱动功率，最终得到优异的衍射效果，如图9(c)所示。
图7展示的是迈克尔孙型组合声光调制系统的示意图，依照示意图搭建一套系统用于演示实验。实验中，入射光为皮秒脉冲锁模激光(λ＝795nm)，脉冲重复频率frep＝80MHz；因此声光调制器(AOM)的驱动频率fs＝100MHz，晶体中声速约为4260m/s；将准直后的脉冲锁模激光经消色差透镜l0(焦距f0＝100mm)汇聚后以布拉格条件入到射声光调制器(AOM)；一次衍射输出经焦距f1＝100mm的消色差透镜l1准直，调整处于透镜l1后焦面处的反射镜Mm使各级别衍射光沿原光路再次入射AOM,形成二次衍射；将声光调制器(AOM)驱动至m＝0,1级衍射光斑接近等同，改变声光调制器(AOM)驱动射频的相位，使其与锁模激光的脉冲输出同步；利用高速光电探测器监测输出中的一个通道，优化AOM的驱动强度，进一步抑制相邻脉冲的强度提高其反衬度。
图8为萨尼亚克型调整反射镜而成迈克耳孙型的示意图，即是图6和图7所示两类组合声光调制系统的切换方法示意图。展示的是两类组合声光调制系统的切换方法，综合了图6展示的萨尼亚克型组合声光调制系统以及图7展示的迈克尔孙型组合声光调制系统。具体来说，在图示系统中插入迈克尔孙构型反射镜(Mm)，该光路即和图7等价，形成迈克尔孙型组合声光调制。而如果去除迈克尔孙构反射镜(Mm),并添加萨尼亚克型反射镜(Ms)，即形成和图6等价的萨尼亚克型组合声光调制。可依照示意图搭建一套系统用于演示实验。
图9为萨尼亚克型组合声光调制技术与常规声光调制技术的衍射结果对比：(a)是入射到萨尼亚克组合声光调制装置与常规声光调制装置的光斑；(b)是常规声光调制装置的最优衍射结果，可在萨尼亚克型组合声光调制装置一次衍射后获得，此时一级衍射效率约为90％；(c)萨尼亚克型组合声光调制装置优化后的衍射结果，0级和高阶衍射的亮度明显更弱，此时一级衍射效率约为98％(可进一步优化)，自由空间的0级抑制比约为20dB，经单模光纤选择后0级抑制比将进一步提升至30dB以上。
图10展示的是迈克尔孙型组合声光调制装置入射光与其中一个通道的出射光的时域图。 (a)是入射的脉冲锁模激光的时域图，其重复频率为80MHz；(b)是其中一个通道输出的脉冲光的时域图，输出激光的重复频率降到了40MHz，相邻两个脉冲之间几乎看不见脉冲残余，此时其反衬度约为23dB(可进一步优化)。
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Claims (10)

  1. 一种基于精密衍射叠加的组合声光调制方法，其特征在于，首先构建一个可同步射频信号的编码模块，以及可精密调节的相干组合声光调制系统；其中：
    所述可同步射频信号的编码模块，提供相位稳定、可任意编程的射频信号，经信号放大器放大后输入相干组合声光调制系统，驱动该系统中的声光调制器(AOM)工作；
    所述相干组合声光调制系统，由几何尺寸接近的两个同型号声光调制器(AOM)以及双透镜4-F光学成像系统构成；其中，声光调制器将射频信号转化为相应频率、强度及相位的声波，对入射的脉冲激光产生声光衍射；双透镜4-F光学成像系统由焦距为F的两个消球差透镜构成；将第一声光调制器(AOM1)的衍射输出以放大率M＝1精确成像到声波同向传播的第二声光调制器(AOM2)，形成两次衍射的干涉；
    在运用双透镜4-F光学成像系统实现两个声光调制器(AOM)布拉格衍射振幅相干叠加过程中，通过将第二声光调制器(AOM2)移出第一声光调制器(AOM1)的成像位置恰当距离，以动量回波的方式抑制聚焦光束布拉格衍射的衍射相移展宽，同时调节高阶衍射相移，以相干相消效应精确抑制高阶衍射损失，从而获得99％以上的衍射效率及30dB以上的透射光单模抑制比；具体步骤如下：
    (1)记声光调制器(AOM)声光晶体长度为L；利用第一声光调制器(AOM1)对一束中心波矢位于横向波矢展宽为Δk的激光进行单频声光调制，得到m级布拉格衍射相应的输出波矢中心位于Δk＝π/w，w是高斯光的束腰；k0为正入射光束波矢，ks为调制声场波矢；
    (2)利用双透镜4-F光学成像系统，以第一声光调制器(AOM1)晶体声场与光束作用中心为物面，将其精确成像至第二声光调制器(AOM2)中心；第二声光调制器(AOM2)的声场方向与第一声光调制器(AOM1)声场的像的方向保持相同；
    (3)以弱射频信号分别驱动第一声光调制器(AOM1)和第二声光调制器(AOM2)，微调入射光角度，使得第一声光调制器(AOM1)和第二声光调制器(AOM2)的m＝1级衍射效率η<50％并接近等同；对于设计优化在100％射频驱动的光调制器(AOM),此时m≠0,1级的衍射损失总和在1％的级别；
    (4)利用第二声光调制器(AOM2)对第一声光调制器(AOM1)出射的所有级别衍射光进行二次衍射，改变第二声光调制器(AOM2)的驱动相位使m＝1级衍射最亮，沿双透镜4-F光学成像系统光轴的方向前后微调第二声光调制器(AOM2)位置δL，在m＝-1,2级衍 射强度具有的空间周期振荡,因此δL在δLn＝nεLh+δLoff实现m＝-1,2级衍射损失的局部最小化；其中，n为振荡周期序号，n＝0,1,2…，δLoff为偏置；
    (5)通过程序控制联合优化第一声光调制器(AOM1)和第二声光调制器(AOM2)的驱动功率，在处获得全局最优的驱动配置，这里[…]是取整符号，是声光晶体的平均折射率，是忽略高阶衍射损失的二模近似下对Δk衍射相位展宽实现动量回波补偿的最优距离，系数ξ和声场分布轮廓相关；当第二声光调制器(AOM2)的位置取δLopt时，由于动量回波补偿，组合声光调制对布拉格条件的要求降低，零级残余被抑制；另一方面，这个距离保证第一声光调制器(AOM1)和第二声光调制器(AOM2)造成的高阶衍射相干相消；在δLopt距离上可实现m＝+1级衍射效率ηopt>99％，m＝0级单模抑制比大于30dB的目标。
  2. 根据权利要求1所述的基于精密衍射叠加的组合声光调制方法，其特征在于，进一步通过精细调节驱动声场频率ωS＝vSkS,将步骤(5)中中的偏置δLoff降低到零，同时实现高阶衍射抑制和动量回波补偿的优化，获得更高的衍射效率ηopt。
  3. 根据权利要求1所述的基于精密衍射叠加的组合声光调制方法，其特征在于，步骤(4)、(5)过程中，输出由稳定的多路干涉形成，具有确定的相位关系；衍射级m＝1最优输出由第一声光调制器(AOM1)和第二声光调制器(AOM2)驱动射频信号对应的相位差及4-F光学成像系统偏移距离δL确定；通过改变第一声光调制器(AOM1)和第二声光调制器(AOM2)的共同驱动相位同时保持相位差不变，可以实现对衍射光的精确相位控制；同时，通过改变第一声光调制器(AOM1)和第二声光调制器(AOM2)的驱动强度可实现衍射效率η从零到ηopt的精细调节，进而实现高对比度可调分束器及光学路由功能。
  4. 根据权利要求1-3之一所述的基于精密衍射叠加的超高效率组合声光调制方法，其特征在于，所构建的相干组合声光调制系统中，声光调制器(AOM)的数量为N，其对应的4-F光学成像系统数量为N，N≥2，则驱动单个声光调制器(AOM)的射频信号功率减少到传统需求的缓解功耗压力，拓展声光晶体选择及设计空间；而且通过对每个成像系统中声光调制器(AOM)相应的δL位移细调，进一步提升衍射效率。
  5. 一种基于回射干涉的组合声光调制方法，其特征在于，运用光学成像系统将声光调制器(AOM)的一次衍射输出精确回射，再次输入该调制器进行二次衍射，实现声光调制器(AOM)的复用，达到仅使用单个声光调制器(AOM)实现组合声光调制的高衍射效率或高反衬度；光 学成像系统分为两种构型：萨尼亚克型和迈克尔孙型；对于萨尼亚克型，组合声光调制的具体步骤如下：
    (1)声光调制器(AOM)对激光进行一次单频声光调制；记声光调制器(AOM)声光晶体长度为L，利用声光调制器(AOM)对一束中心波矢位于横向波矢展宽为Δk的激光进行单频声光调制，得到m级布拉格衍射相应的输出波矢，该波矢中心位于 Δk＝π/w，w是高斯光的束腰；k0为正入射光束波矢，ks为调制声场波矢；记声波驱动频率为fS，圆频率为ωS＝2πfS；
    (2)通过声光调制器(AOM)形成二次衍射；以焦距为f1的透镜l1对声光调制器(AOM)的多级衍射输出准直，并经约f1+f2传播距离后，由焦距为f2的透镜l2聚焦至反射镜Ms；经反射的所有衍射级逆向依次经过透镜l2,，l1后，再次进入声光调制器(AOM)，形成二次衍射；
    (3)调节透镜l1,l2间距，进行衍射效果相干相加；记声光调制器(AOM)出射端和反射镜Ms间距为LD，由步骤(2)知LD≈2(f1+f2)；通过调节透镜l1,l2间距，使得LD＝πc/ωS；这里c≈3×108米/秒是光速，该LD取值保证第一次和第二次声光调制器(AOM)衍射相位相差 实现衍射效果相干相加；
    (4)对入射光角度进行微调；以弱射频信号驱动声光调制器(AOM)，微调入射光角度，使得单次衍射的m＝1级衍射效率η<50％，m＝0,1级衍射光斑接近等同；对于设计优化在100％射频驱动的声光调制器(AOM),此时m≠0,1级的衍射损失总和在1％的级别；
    (5)通过微调，使衍射损失局部最小化；借助偏振分束器将回射光和入射光分开，运用数字相机观测复合声光调制出射，并实时计算出m＝1级的衍射效率η；改变射频驱动强度(A0)，使m＝1级衍射效率最大；微调声光调制器(AOM)和透镜l1的间距L1＝f1+δL,在m＝-1,2级衍射强度具有的空间周期振荡,δL在δLn＝nδLh+δLoff实现m＝-1,2级衍射损失的局部最小化；其中，n为振荡周期序号，n＝0,1,2…，δLoff为偏置；
    (6)通过细调，实现高衍射效率、高单模抑制比；具体地，细调声光调制器(AOM)和透镜l1的间距L1＝f1+δL,在处获得全局最优的衍射驱动配置，实现m＝+1级衍射效率ηopt>99％，m＝0级单模抑制比大于30dB的目标；这里[…]是取整符号，是声光晶体的平均折射率，是忽略高阶衍射损失的二模近似下对Δk衍射相位展宽实现动量回波补偿的最优距离，系数ξ和声场分布轮廓相关；当二次衍射位置取δLopt时，由于动量回波补偿，组合声光调制对布拉格条件的要求降低，零级残余被抑制；另一方面，这个距 离保证两次声光调制造成的高阶衍射相干相消。
  6. 根据权利要求5所述的组合声光调制方法，其特征在于，进一步通过精调，实现高阶衍射抑制和动量回波补偿的优化；具体地，通过精细调节驱动声场频率ωS＝vSkS，并重复步骤(1)-(5),将步骤(6)中中的偏置δLoff降低到零，同时实现高阶衍射抑制和动量回波补偿的优化，获得更高的衍射效率ηopt。
  7. 根据权利要求5所述的组合声光调制方法，其特征在于，入射光束经过声光调制器(AOM)的先后两次衍射相对相位稳定；通过改变声光调制器(AOM)的驱动相位实现组合声光调制下m＝1级衍射光的精确相位控制；同时，通过改变声光调制器(AOM)的驱动强度A0，实现m＝1级衍射效率η从零到ηopt的精细调节，实现高对比度可调分束器及光学路由功能。
  8. 根据权利要求5至7任一项所述的组合声光调制方法，其特征在于，调整回射光学系统中反射镜的摆放位置，成为迈克尔孙型，具体是将反射镜放置于准直透镜l1的后焦点处，调整反射镜角度使一次衍射的各级输出能够原路返回，并移除后续光学元件；记调整后的反射镜为Mm，则声光调制器(AOM)-透镜l1-反射镜Mm构成迈克尔孙型组合声光调制系统；该构型在第二次声光衍射的衍射级别m'和第一次衍射级别m以m'＝1-m关系对应；因此一级衍射相位以驱动射频的二倍频率演化，从而有周期振荡的衍射效率
  9. 根据权利要求8所述的组合声光调制方法，其特征在于，通过将驱动射频信号和锁模脉冲激光输出同步，将重频为frep＝4fS/(2n+1)的锁模脉冲激光实现m＝0级透射和m＝1级衍射之间的高效切换,进而在透射和衍射光路中同时实现入射激光的f'rep＝frep/2重频分频，相邻脉冲单模耦合抑制比高达30dB以上；n为整数。
  10. 根据权利要求8所述的组合声光调制方法，其特征在于，光学成像系统分中萨尼亚克型和迈克尔孙型切换按如下方法：在光学成像系统中插入迈克尔孙构型反射镜Mm，该光路即形成迈克尔孙型组合声光调制；而如果去除迈克尔孙构型反射镜Mm,并添加萨尼亚克型反射镜Ms，即形成萨尼亚克型组合声光调制。
PCT/CN2024/127872 2024-07-16 2024-10-28 一种基于精密衍射叠加的组合声光调制方法 Pending WO2026016325A1 (zh)

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