WO2023030050A1 - 基于多重4f成像的高带宽复合声光调制方法 - Google Patents
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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
- G02F1/113—Circuit or control arrangements
Definitions
- the invention belongs to the technical field of laser regulation, and in particular relates to a high-bandwidth composite acousto-optic modulation method and system based on multiple 4F imaging.
- AOM acousto-optic modulation technology
- R operating frequency range ⁇ f S
- applicable wavelength range ⁇ applicable wavelength range ⁇
- modulation bandwidth ⁇ f M modulation bandwidth
- the frequency range of AOM greatly limits the stability of CEP locking, and the ultrashort pulse in AOM Dispersion in diffraction leads to "space-time coupling" of the outgoing light, reducing the effective power of the output mode.
- the basis of acousto-optic modulation technology is Bragg resonance.
- the light diffraction efficiency R drops rapidly after departing from the Bragg condition, and the price of sacrificing R in exchange for high-bandwidth multi-wavelength work is often a large reduction in output power in exchange for limited working bandwidth and wavelength range gain.
- the frequency range ⁇ f S , wavelength range ⁇ , and modulation bandwidth ⁇ f M that increase in the same proportion as f S can indeed be obtained.
- the design of the AOM acoustic wave field becomes more and more difficult, and it is difficult to maintain high efficiency of acousto-optic diffraction at high frequencies.
- the current AOM technology on the market drops rapidly when the frequency f S >250MHz is higher than the single-device diffraction efficiency R, while the diffraction efficiency R of GHz-level modulation frequency is difficult to exceed 50%.
- the purpose of the present invention is to propose a method based on multiple 4F imaging to realize high-bandwidth composite acousto-optic modulation, using multi-parameter-controlled acousto-optic interference to break through the Bragg conditions in a single acousto-optic modulation device on diffraction efficiency, operating frequency range, and modulation bandwidth. limit, to achieve arbitrary acousto-optic modulation with ultra-high bandwidth, and can be used in various nonlinear optics and quantum optics experiments.
- the method for realizing high-bandwidth composite acousto-optic modulation based on multiple 4F imaging uses a 4F lens to image N acousto-optic modulators driven by the same frequency, thereby splitting the single acousto-optic modulation process into N coherent processes.
- the sound field intensity and phase are optimized to obtain high composite diffraction efficiency that cannot be achieved by single acousto-optic modulation, and it is fault-tolerant to the incident light angle ⁇ , incident light wavelength ⁇ , and driving acoustic wave frequency ⁇ f S , so that the composite diffraction optimization ability gradually improves with N, (take N is within 5) so as to achieve nearly 100% efficient diffraction regulation for incident light that deviates greatly from Bragg conditions.
- Specific steps are as follows:
- N AOM j Use a 4F lens group to image N AOMs with the same geometric size (Fig. 2).
- Modulator AOM j (AOM) sound wave driving frequency is f S
- sound wave intensity A j driving phase Controlled by a digital radio frequency signal program
- the sequence of acousto-optic modulators is recorded as N-AOM multi-acousto-optic modulation module.
- each of the formula (1) and compound optical conversion matrix by is characterized by a 2 by 2 matrix of parameters, and then has a composite diffraction efficiency
- the optimal acousto-optic modulation intensity corresponding to the optimal single AOM diffraction efficiency R j is measured All AOMs are then driven simultaneously, with the intensity reduced to The distribution of the output light intensity in the transmission and diffraction light paths is recorded by a digital camera, and the program controls the real-time adjustment for further optimization
- the coherent diffraction of N-AOM is extremely strong. because The weak drive effectively suppresses the loss of high-order diffraction, and can obtain a high composite diffraction efficiency that is gradually perfected with the increase of N, which cannot be achieved by a single AOM
- the wave vectors ka , k b and the mismatched wave vector ⁇ k all have a large broadening.
- the ⁇ k broadening is denoted as ⁇ k.
- the fault-tolerant control technology for the 2 ⁇ 2 matrix in formula (1) developed in the field of nuclear magnetic resonance (NMR) can be used [genov2014] to control the nuclear spin optimized Value, programmed by radio frequency signal and applied to N-AOM system becomes Initial value, and program control for further automatic optimization It can be obtained again when ⁇ k ⁇ /L and the Bragg condition cannot satisfy different incident light components at the same time Tends to the best diffraction efficiency of 100%, and the control effect also becomes perfect with the increase of N.
- the diffraction and transmission optical paths of the N-AOM multi-acousto-optic modulation system completely share all optical components, and by selecting an appropriate short focal length (for example, F below 10 cm) aberration-elimination lens, the transmission and diffraction optical paths are opposite to each other.
- the displacement can be controlled to no more than 1 mm, and it is difficult for environmental disturbance to cause the relative optical path change of the interference path, thus ensuring that the system has excellent passive phase stability. And this stability ensures that the N-AOM system can pass through the
- the automatic adjustment of parameters realizes the effect on compound diffraction efficiency
- the optimized conditions are maintained for a long time to achieve high-bandwidth and efficient diffraction.
- the present invention also provides a specific implementation system of a high-bandwidth composite acousto-optic modulation method based on multiple 4F imaging, as shown in Figures 2 and 3, the system mainly includes: N-AOM multi-acousto-optic modulation module, radio frequency signal encoding module, 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)) through an optical link through a 4-F imaging system, and they can be
- N acousto-optic devices generally an acousto-optic modulator (AOM) or an acousto-optic deflector (AOD)
- AOM acousto-optic modulator
- AOD acousto-optic deflector
- the 4-F imaging system images the diffraction and transmission output surfaces of AOM j to the corresponding output surfaces of AOM j+1 through every two lenses with a focal length of F, realizing the precision of the sound field of N AOMs driven by the same frequency.
- Coherent linking of imaging and transmitted/diffraction light By selecting a suitable short focal length (F below 10 cm) aberration lens and controlling the relative displacement of the transmitted and diffracted optical paths to no more than 1 mm, the system can be guaranteed to have excellent passive phase stability.
- the acoustic driving frequency of all AOMs is f S , the acoustic intensity Aj and driving phase of N-AOM Programmable control by radio frequency signal.
- the N-AOM multi-acousto-optic modulation module corresponds to the operation of performing step (1) using a 4F lens group to image N acousto-optic modulators with the same geometric size;
- the radio frequency signal encoding module is composed of a program-controlled multi-channel direct digital synthesis (DDS) signal source and a linear radio frequency amplifier, providing N paths that can independently program the output intensity A j and the relative phase
- the stable radio frequency signal is amplified by radio frequency to drive the N-AOM module.
- DDS direct digital synthesis
- the radio frequency signal encoding module corresponds to the radio frequency signal encoding operation in step (3);
- the measurement and automatic feedback optimization module is composed of a digital camera and a personal computer, wherein the personal computer program controls the digital camera to take pictures of the light intensity of the N-AOM system transmission and diffraction output channels, and analyzes the composite diffraction efficiency And control the RF signal encoding module through the communication interface to update the RF signal sequence Drive the N-AOM module to form an optimized loop.
- the measurement and automatic feedback optimization module corresponds to the measurement and automatic feedback optimization operation in step (3);
- the high-bandwidth composite acousto-optic modulation system of multiple 4F imaging breaks through the Bragg condition in the traditional single AOM method on the diffraction efficiency R, the working frequency range ⁇ f S , and the wavelength range ⁇ , the modulation bandwidth ⁇ f M is limited, multiple AOMs are accurately imaged through a 4-F lens system, and the single AOM diffraction is split into N-AOM coherent diffraction.
- Polychromatic, non-collimated incident light under certain conditions achieves nearly 100% diffraction control.
- the present invention is based on weak driving conditions can be as low as acousto-optic interference effect.
- the weak driving condition can greatly suppress the unavoidable high-order diffraction loss due to the limited crystal length L in traditional acousto-optic modulation, and then optimize the acoustic driving amplitude A j and driving phase Adjust with 2N-1 parameters (N amplitudes and N-1 relative phases) to obtain high composite diffraction efficiency that cannot be achieved by a single AOM
- the invention can be used to realize high-bandwidth arbitrary waveform modulation, wide-range frequency sweep and large-angle beam deflection for multi-color lasers including ultrafast pulse lasers.
- This invention can expand the application of CW laser and ultrafast laser in fundamental and technical fields, especially provide support for the technological expansion in the field of molecular molecular regulation.
- Figure 1 is a schematic diagram of the principle of single-shot acousto-optic diffraction.
- Fig. 2 is a schematic diagram of a high-bandwidth composite acousto-optic modulation method and system based on multiple 4F imaging.
- Fig. 3 is a modular schematic diagram of a high-bandwidth composite acousto-optic modulation system based on multiple 4F imaging.
- Figure 6 shows the relationship between the maximum diffraction efficiency and the acoustic frequency f S.
- (a) is single acousto-optic diffraction efficiency
- the present invention is further introduced.
- the maximum acousto-optic diffraction efficiency of a single AOM can reach R 1,2 ⁇ 80% (Fig. 6(a)).
- 2 in the N 2 compound acousto-optic modulation system demonstrated by the tuning experiment, in the optimal case (the white dotted line in Fig. 5(a,i) ), the maximum diffraction efficiency of the compound acousto-optic diffraction system can reach In Fig.
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Abstract
本发明属于激光调控技术领域，具体为一种基于4F精密成像的高带宽复合声光调制方法。本发明方法包括：利用4F透镜对N个相同频率驱动的声光调制器成像，从而将单声光调制过程分裂为N个相干过程，借助N声场强度和相位优化，获得单声光调制无法实现的高复合衍射效率，并对入射光角度Δθ、入射光波长Δλ、驱动声波频率Δf S容错。本发明中的复合衍射优化能力随N逐步提高。取N在5以内，即可对大幅度偏离布拉格条件下的入射光实现近100％效率的衍射调控。本发明可实现传统声光调制方法无法获得的高带宽多色声光调制、大范围扫频/大角度光束衍射等能力，在运用连续激光和超快激光对原子分子实现量子调控等科研和技术领域有重要应用前景。
Description
本发明属于激光调控技术领域，具体涉及一种基于多次4F成像的高带宽复合声光调制方法和系统。
在激光调控技术领域，基于相位匹配布拉格衍射的声光调制技术(AOM)利用射频信号实现对光场的强度，相位，频率和方向的控制，其调制速度远高于机械类调节，而调制精度和普适性又远优于电光类调制。在对连续光和脉冲激光的调控方面，在基础研究和技术领域，声光调制都有普遍和重要的应用。AOM的重要指标包括声光衍射效率R，工作频率范围Δf
S，适用波长范围Δλ，及调制带宽δf
M。众所周知，AOM的高声光衍射效率R难以和大工作带宽Δf
S，大波长范围Δλ兼容：为获得最佳声光衍射效率，被调制激光的最优入射角θ需要接近由声波频率f
S，声波波矢k
S＝2πf
S/v
S，入射光波长λ共同决定的布拉格角θ
B，而工作频率f
S、入射激光波长λ的大幅度改变必然导致衍射效率的急剧下降，限制了声光调制技术在大范围移频和多色、超短脉冲调控中的应用潜力。举例来说，在著名的超短脉冲光载波-包络面-相对相位(CEP)锁定应用中(koke2010)，AOM频率变化范围极大的限制了CEP锁定的稳定性，而超短脉冲在AOM衍射中的色散导致出射光的“时空耦合”，降低了输出模式的有效功率。另一方面，AOM的声光调制带宽δf
M–即对衍射光的频率，相位，强度，方向实时调节的控制带宽–取决于入射光斑大小w及晶体声波速度v
S，可表达为δf
M＝v
S/w。由于常规声光晶体的声速v
S为数千米每秒，为获得数十MHz的调制带宽，通常做法是对入射光斑束腰w聚焦到百微米以下。而聚焦光对应的入射角θ展宽会进一步导致布拉格条件的破坏，影响衍射效率R。
经调查研究，目前在声光调制技术领域尚没有系统解决方案来克服高声光衍射效率R和大工作频率范围Δf
S，大工作波长范围Δλ,高调制带宽δf
M指标之间的矛盾。在一般处理方法上，一是直接通过牺牲衍射效率R来换取宽带工作性能，二是结合声光调制理论，通过提高工作中心频率f
S和减小声光相互作用距离L来降低布拉格条件的严格性，进而实现宽带工作。然而上述两种方法至少存在如下缺点：
1、声光调制技术基础是布拉格共振。常规声光调制技术中，偏离布拉格条件后光衍射效率R下降很快，通过牺牲R换取高带宽多波长工作的代价常常是以大幅度降低输出功率来换取有限的工作带宽和波长范围增益。
2、通过增大f
S的同时降低相互作用距离L，确实可以获得和f
S同比例增长的频率范围Δf
S，波长范围Δλ，及调制带宽δf
M。然而随着晶体尺度减小，AOM声波场设计愈发困难，声光衍射在高频很难维持高效。目前市场上的AOM技术在频率f
S>250MHz以上单器件衍射效率R迅速下降，而GHz级调制频率的衍射效率R很难超过50％。
发明内容
本发明的目的在于提出一种基于多重4F成像实现高带宽复合声光调制的方法，运用多参数控制的声光干涉突破单个声光调制器件中布拉格条件对衍射效率、工作频率范围，调制带宽的限制，实现超高带宽任意声光调制，可用于各类非线性光学、量子光学实验中。
本发明提出的基于多重4F成像实现高带宽复合声光调制的方法，利用4F透镜对N个相同频率驱动的声光调制器成像，从而将单声光调制过程分裂为N个相干过程，借助N声场强度和相位优化，获得单声光调制无法实现的高复合衍射效率，并对入射光角度Δθ、入射光波长Δλ、驱动声波频率Δf
S容错，使复合衍射优化能力随N逐步提高，(取N在5以内)从而对大幅度偏离布拉格条件下的入射光实现近100％效率的衍射调控。具体步骤如下：
(1)利用4F透镜组对N个几何尺寸相同的声光调制器成像(图2)。调制器记为AOM
j,j＝1,2,…,N，N个AOM
j简记为N-AOM系统；具体来说，每两个焦距为F的透镜将AOM
j的衍射和透射输出面成像到AOM
j+1的相应输出面，实现N个相同频率驱动下的声光调制器声场的精密成像及透射/衍射光的相干链接。调制器AOM
j(AOM)声波驱动频率均为f
S，而声波强度A
j,驱动相位
由数字射频信号程序控制，该声光调制器序列记为N-AOM多声光调制模块。
(2)为借鉴原子物理和量子调控理论[wu2005,genov2014]，对低驱动强度下的N-AOM系统做如下数学描述：
对于每个AOM
j来说，分别记其输入和输出光波前为|ε
j,in>和|ε
j,out>，从而 有|ε
j+1,in>＝|ε
j,out>。另记初始输入光波前为|ε
in>＝|ε
1,in>,复合输出光场波前为|ε
out>＝|ε
N,out>。记AOM
j对波前衍射作用由声波强度A
j,驱动相位
控制的透射矩阵为
同时记无射频声波驱动下的透射矩阵为
则4F成像下的N-AOM系统对波前变换的输入输出关系为：
通过降低AOM驱动强度A
j限制高阶衍射(图1虚线)，记透射光束中0级及1级衍射光波前为C
a,C
b，平均波矢为k
a，k
b。与此对应，式(1)中的每个
以及复合光学转换矩阵
均由以
为参数的2乘2矩阵刻画,进而有复合衍射效率
(3)运用数字相机记录输出光强度在透射和衍射光路中的分布，通过程序控制实时调节N-AOM组的
参数(N个振幅，N-1个相对相位)，基于式(1)优化N-AOM系统在特定需求下的衍射效率
获得最佳复合衍射效率
举例来说：
(3.1)如图1所示，对于波长λ的单色光准直入射，首先通过对入射角度θ的常规调节优化布拉格条件：k
a-k
b＝±k
S，其中k
a，k
b分别为透射光束与衍射光束波矢，k
S为声光调制器中声波波矢，对应失配波矢δk≡k
a-k
b±k
S满足|δk|＜＜π/L(L是晶体声场长度)。通过驱动单个AOM，测出获取最优单AOM衍射效率R
j对应的最优声光调制强度
然后同时驱动所有AOM，强度降为
通过数字相机记录输出光强度在透射和衍射光路中的分布，并程序控制实时调节进一步优化
获得N-AOM相干衍射极强。因
的弱驱动有效抑制了高阶衍射损失，可获得随N增大逐渐完美，单个AOM无法实现的高复合衍射效率
(3.2)在上述(3.1)的单色光准直入射基础上，如果应用需求，可改变波长λ(波矢k
a,b长度)入射角度θ(改变波矢k
a,b方向),声波驱动频率f
S(改变波矢k
S长度)，破坏布拉格波矢匹配关系k
a-k
b＝±k
S，只需在失配波 矢|δk|≤π/L的范围内，通过适当增大{A
j},并利用数字相机记录输出光强度的分布，通过程序控制进一步自动优化
可再次获得
趋于100％的最佳衍射效率，该调控效果随N增大变得完美。
(3.3)对于多色光入射，非准直入射，聚焦光入射等情况，波矢k
a，k
b及失配波矢δk均有较大展宽。δk展宽记为Δk。为同时对不同波长和k分量入射光实现同等高效衍射，可借助核磁共振(NMR)领域发展的，针对式(1)中2乘2矩阵的容错调控技术[genov2014]，将对核自旋调控优化的
值，通过射频信号编程运用于N-AOM系统成为
初值，并程控进一步自动优化
可在Δk≤π/L，布拉格条件无法同时满足不同入射光分量的情况下,再次获得
趋于100％的最佳衍射效率，该调控效果亦随N增大变得完美。
(4)本方案中N-AOM多声光调制系统的衍射和透射光路完全共享所有光学元件，且通过选择合适的短焦距(例如F在10厘米以下)消像差透镜，透射和衍射光路相对位移可以控制到不超过1毫米，环境扰动难以导致干涉路径的相对光程变化，从而保证系统拥有优异的被动相位稳定性。而该稳定性确保N-AOM系统在特定应用中通过对
参数的自动调节实现对复合衍射效率
的优化，并长时间保持该优化条件，实现高带宽高效衍射。
本发明还提供基于多重4F成像的高带宽复合声光调制方法的具体实现系统，如图2,3所示，系统主要包括：N-AOM多声光调制模块，射频信号编码模块，测量及自动反馈优化模块。
所述N-AOM多声光调制模块，其中由N个声光器件(一般为声光调制器(AOM)或声光偏转器(AOD))通过4-F成像系统经光学链接组成，它们可将射频信号转化为相应频率、强度及相位的声波(晶体密度调制波)，对入射激光产生多角度衍射。其中4-F成像系统通过每两个焦距为F的透镜将AOM
j的衍射和透射输出面成像到AOM
j+1的相应输出面，实现N个相同频率驱动下的声光调制器声场的精密成像及透射/衍射光的相干链接。通过选择合适的短焦距(F在10厘米以下)消像差透镜，控制透射和衍射光路相对位移不超过1毫米，可保证系统拥有优异的被动相位稳定性。所有AOM声波驱动频率均为f
S，N-AOM的声 波强度A
j和驱动相位
由射频信号编程控制。
该N-AOM多声光调制模块，对应执行步骤(1)利用4F透镜组对N个几何尺寸相同的声光调制器成像的操作；
所述射频信号编码模块，由程控多通道直接数字合成(DDS)信号源及线性射频放大器构成，提供N路可以独立编程输出强度A
j和相对相位
稳定的射频信号，经过射频放大，用于驱动N-AOM模块。
该射频信号编码模块，对应对应执行步骤(3)中射频信号编码操作；
所述测量及自动反馈优化模块，由数字相机及个人电脑构成，其中，个人电脑程序控制数字相机对N-AOM系统透射和衍射输出通道光强拍照，分析复合衍射效率
并通过通信接口控制射频信号编码模块，更新射频信号序列
驱动N-AOM模块，形成优化回路。
该测量及自动反馈优化模块，对应对应执行步骤(3)中的测量及自动反馈优化操作；
本发明的系统设计与调控方法与现有技术的主要区别在于多重4F成像的高带宽复合声光调制系统突破了传统单AOM方法中布拉格条件对衍射效率R、工作频率范围Δf
S，波长范围Δλ,调制带宽Δf
M的限制，通过4-F透镜系统对多个AOM精确成像，将单AOM衍射分裂为N-AOM相干衍射，借助多声光调制的振幅和相位多参数优化，实现对偏离布拉格条件下的多色、非准直入射光实现近100％的衍射调控。由上述本发明提供的技术方案可以看出，本发明具有以下的优越性：
(1)本发明基于弱驱动条件下
可低至
的声光干涉效应。其中弱驱动条件可大幅度抑制传统声光调制中因晶体长度L有限而无法避免的高阶衍射损失，进而通过优化声波驱动振幅A
j和驱动相位
以2N-1个参数(N个振幅及N-1个相对相位)调节来获得单个AOM无法实现的高复合衍射效率
(2)本发明在单色光准直入射并满足波矢匹配关系k
a-k
b≈±k
S后，在波长或驱动频率发生改变破坏波矢匹配，失配量|δk|＜＜π/L不再满足，常规声光衍射效率急剧下降的情形下，如果有|δk|≤π/L,仍然可以通过自动调节声波 驱动振幅A
j和驱动相位
使得系统在偏离布拉格条件下再次获得
的衍射效率。
(3)在多色光、非准直，聚焦入射等情况下，波矢失配存在较大展宽Δk，常规声光衍射无法对全部入射光实现均匀高效衍射的情形下，如果有展宽|Δk|≤π/L,可借鉴NMR容错调控理论，通过射频编程对
自动优化，仍可实现接近
的均匀、高效衍射。
(4)本发明系统所有子光路共享完全相同的光学元件，衍射和透射光路相对位移短，其相对相位稳定性对振动噪音有优越的免疫力，整个系统拥有卓越的短期和长期相位稳定性。
本发明可用于实现对包括超快脉冲激光在内的多色激光实现高带宽任意波形调制，大范围扫频及大角度光束偏折等。这一发明可拓展连续激光和超快激光在基础和技术领域的应用，特别是对原子分子量子调控领域的技术拓展提供支持。
图1为单次声光衍射原理示意图,图中虚线代表高阶衍射路径，右图显示了k
a-k
b＝±k
S的布拉格条件波矢匹配关系。
图2为基于多次4F成像的高带宽复合声光调制方法和系统示意图。
图3为基于多次4F成像的高带宽复合声光调制系统的模块化示意图。
图4为N＝2复合声光调制系统示意图。
图5为单次声光衍射效率R
1,2与N＝2复合声光衍射效率
关系。其中，(a)为声波频率f
s＝100MHz布拉格条件下的实验测量(a,i)和理论计算(a,ii)；在R
1,2≈0.5时，获得
最优值。(b)为声波频率f
s＝140MHz偏离布拉格条件下的实验测量(b，i)和理论计算(b,ii)。在R
1,2≈0.35取单AOM效率极限时，获得
最优值。
图6为最大衍射效率和声波频率f
S的关系。其中(a)为单次声光衍射效率；(b)为N＝2复合声光衍射效率。
以最简单的N＝2复合声光调制系统为例，进一步介绍本发明。如图4，实 验中，声光调制器的晶体中声速v
s＝4260m/s，设置射频信号频率f
S＝100MHz时，调节连续光(波长λ＝795nm，高斯束腰半径w≈110um)以布拉格条件入射AOM
1，衍射光和透射光经4-F消色差透镜(F＝10cm)组精确成像到AOM
2后进行二次衍射。降低单个AOM调制强度来抑制高阶耦合，每个AOM的声光衍射效果都可由参数化的反射系数
和透射系数(t
j)组成的2×2矩阵
描述。利用数字相机或光电探测器对单次声光衍射效率及透射效率R
j＝|r
j|
2、T
j＝|t
j|
2、双AOM系统最大衍射效率
进行测量，并根据实际测量结果对AOM的振幅和相位进行实时优化。
在上述布拉格条件下，单个AOM的声光衍射效率最大可达到R
1,2≈80％(图6(a))。而如图5(a,i)中所示，通过优化射频信号
调节实验所演示的N＝2复合声光调制系统中的单次声光衍射效率R
1,2＝|r
1,2|
2，在最优情况下(图5(a,i)中白色虚线处)，该复合声光衍射系统的最大衍射效率可达到
图5(b,i)中，我们还演示了当布拉格条件因δk失配而严重破坏时，复合声光调制系统的容错性。为此，我们将声波频率增大至f
S＝140MHz，调节
进行优化，并测量得到最大衍射效率
而此时单个AOM衍射效率已经降低到R
1,2≈35％。同时在图5(a,ii)和(b,ii)中，我们给出了分别对应图5(a,i)(b,i)中条件的理论模拟，并得出了基本一致的结果。
为进一步说明，在图6中我们演示了声波频率f
S＝80MHz至140MHz下，单个声光调制器与该N＝2复合声光调制系统
的变化。在声波频率f
S＝80MHz至120MHz范围内，衍射效率
均达到了90％以上，远优于单一声光调制器的衍射效率。这一结果，也证实了因布拉格条件失配，而导致的常规声光衍射效率急剧下降的情形下，本系统设计仍然可以通过调节声波驱动振幅A
j和驱动相位
来再次获得高衍射效率。
参考文献：
[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)
- 一种基于多重4F成像实现高带宽复合声光调制方法，其特征在于，利用4F透镜对N个相同频率驱动的声光调制器成像，从而将单声光调制过程分裂为N个相干过程，借助N声场强度和相位优化，获得单声光调制无法实现的高复合衍射效率，并对入射光角度Δθ、入射光波长Δλ、驱动声波频率Δf S容错，使复合衍射优化能力随N逐步提高，从而对大幅度偏离布拉格条件下的入射光实现近100％效率的衍射调控；具体步骤如下：(1)利用4F透镜组对N个几何尺寸相同的声光调制器成像；调制器记为AOM j,j＝1,2,…,N，N个AOM j简记为N-AOM系统；其中，每两个焦距为F的透镜将AOM j的衍射和透射输出面成像到AOM j+1的相应输出面，实现N个相同频率驱动下的声光调制器声场的精密成像及透射/衍射光的相干链接；调制器AOM j声波驱动频率均为f S，而声波强度A j、驱动相位由射频信号编程控制；
(2)为借鉴原子物理和量子调控理论，对低驱动强度下的N-AOM系统做如下数学描述：对于每个AOM j，分别记其输入和输出光波前为|ε j,in>和|ε j,out>，于是有|ε j+1,in>＝|ε j,out>；另记初始输入光波前为|ε in>＝|ε 1,in>,复合输出光场波前为|ε out>＝|ε N,out>；记AOM j对波前衍射作用由声波强度A j,驱动相位控制的透射矩阵为
同时记无射频声波驱动下的透射矩阵为
则4F成像下的N-AOM系统对波前变换的输入输出关系为：
通过降低AOM驱动强度A j限制高阶衍射，记透射光束中0级及1级衍射光波前为C a,C b，平均波矢为k a，k b；与此对应，式(1)中的每个以及复 合光学转换矩阵
均由以
为参数的2乘2矩阵刻画,进而有复合衍射效率
(3)运用数字相机记录输出光强度在透射和衍射光路中的分布，通过程序控制实时调节N-AOM组的参数：N个振幅，N-1个相对相位，基于式(1)优化N-AOM系统在特定需求下的衍射效率
获得最佳复合衍射效率
(4)N-AOM多声光调制系统的衍射和透射光路完全共享所有光学元件，通过选择合适的短焦距F，以消像差透镜，控制透射和衍射光路相对位移不超过1毫米，保证系统拥有优异的被动相位稳定性，从而确保N-AOM系统在特定应用中通过对参数的自动调节实现对复合衍射效率
的优化，并长时间保持该优化条件，实现高带宽高效衍射。
- 根据权利要求1所述的基于多重4F成像实现高带宽复合声光调制方法，其特征在于，步骤(3)中所述优化衍射效率获得最佳复合衍射效率
具体为：
(3.1)对于波长λ的单色光准直入射，首先通过对入射角度θ的常规调节优化布拉格条件：k a-k b＝±k S，其中k a，k b分别为透射光束与衍射光束波矢，k S为声光调制器中声波波矢，对应失配波矢δk≡k a-k b±k S满足|δk|＜＜π/L，L是晶体声场长度；通过驱动单个AOM，测出获取最优单AOM衍射效率R j对应的最优声光调制强度然后同时驱动所有AOM，强度降为
通过数字相机记录输出光强度在透射和衍射光路中的分布，并程序控制实时调节进一步优化
获得N-AOM相干衍射极强；由于
的弱驱动有效抑制了高阶衍射损失，可获得随N增大逐渐完美，单个AOM无法实现 的高复合衍射效率
- 根据权利要求2所述的基于多重4F成像实现高带宽复合声光调制方法，其特征在于，步骤(3)中所述优化衍射效率获得最佳复合衍射效率
进一步地，
(3.2)在上述(3.1)的单色光准直入射基础上，根据应用需求，改变波长λ、入射角度θ、声波驱动频率f S，破坏布拉格波矢匹配关系k a-k b＝±k S，只需在失配波矢|δk|≤π/L的范围内，通过适当增大{A j},并利用数字相机记录输出光强度的分布，通过程序控制进一步自动优化再次获得
趋于100％的最佳衍射效率，该调控效果随N增大变得完美。
- 根据权利要求2所述的基于多重4F成像实现高带宽复合声光调制方法，其特征在于，步骤(3)中所述优化衍射效率获得最佳复合衍射效率
具体为：
(3.3)对于多色光入射、非准直入射或聚焦光入射情况，波矢k a，k b及失配波矢δk均有较大展宽，δk展宽记为Δk；为同时对不同波长和k分量入射光实现同等高效衍射，借助核磁共振领域发展的，针对式(1)中2乘2矩阵的容错调控技术，将对核自旋调控优化的值，通过射频信号编程运用于N-AOM系统成为
初值，并程控进一步自动优化
在Δk≤π/L，布拉格条件无法同时满足不同入射光分量的情况下,再次获得
趋于100％的最佳衍射效率，该调控效果亦随N增大变得完美。
- 基于权利要求1-4之一所述方法的基于多重4F成像实现高带宽复合声光调制系统，其特征在于，包括：N-AOM多声光调制模块，射频信号编码模块，测量及自动反馈优化模块；所述N-AOM多声光调制模块，由N个声光调制器(AOM)通过4-F成像系统经光学链接组成；它们将射频信号转化为相应频率、强度及相位的声波，对入射激光产生多角度衍射；其中4-F成像系统通过每两个焦距为F的透镜将AOM j的衍射和透射输出面成像到AOM j+1的相应输出面，实现N个相同频率驱动下的声光调制器声场的精密成像及透射/衍射光的相干链接；通过选择短焦距F在10厘米以下，以消像差透镜，控制透射和衍射光路相对位移不超过1毫米，保证系统拥有优异的被动相位稳定性；所有AOM声波驱动频率均为f S，N-AOM的声波强度A j和驱动相位由射频信号编程控制；
所述射频信号编码模块，由程控多通道直接数字合成(DDS)信号源及线性射频放大器构成，提供N路可以独立编程输出强度A j和相对相位稳定的射频信号，经过射频放大，用于驱动N-AOM模块；
所述测量及自动反馈优化模块，由数字相机及个人电脑构成；其中，个人电脑程序控制数字相机对N-AOM系统透射和衍射输出通道光强拍照，分析复合衍射效率并通过通信接口控制射频信号编码模块，更新射频信号序列
驱动N-AOM模块，形成优化回路。
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN113777811A (zh) * | 2021-08-29 | 2021-12-10 | 复旦大学 | 基于多重4f成像的高带宽复合声光调制方法 |
| CN113777811B (zh) * | 2021-08-29 | 2024-03-29 | 复旦大学 | 基于多重4f成像的高带宽复合声光调制方法 |
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| CN113777811A (zh) | 2021-12-10 |
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