声光波导衍射

本文报导在Ti扩散LiNbO_3波导中,由光学导波和声表面波实现的声光衍射实验。实验中,我们测量了两种TE(TE_0,TE_1)模的主要衍射级光强相对声功率的分布,同时给出实用的计算声功率公式:Pa=(4△n~2/n~6P_(3J)~2K)/LP_R。并在声光品质因数Q=2.5条件下,近似选取了Raman-Nath衍射0级光束相消的位相条件,进行了参数处理。计算了声功率、位移和应变。利用光学导波和声表面波衍射作用的集成光学声光器件,可用于光调制,偏转和开关。过去,这方面有代表性的研究工作是Kuhn等人在玻璃膜波导上的声光工作和Schmidt等人在LiNbO_3(LN)扩散波导上的声光工作。     

星形光波导耦合器的耦合特性分析

根据TE0模光波导的本征场分布、瑞利索末菲标量衍射积分公式和激励源与光波导耦合的匹配效率公式,给出光波导端面衍射和耦合的归一化发射系数和接收系数计算公式,推导出光波导端面非接触耦合的耦合效率计算公式。光波导模场分布采用高斯函数近似表达,给出简洁的计算光波导端面非接触耦合的耦合效率函数表达式。最后,基于星形光波导耦合器结构参量的特点,将累加运算采用积分运算近似表达,给出星形光波导耦合器接收光波导总的接收效率与耦合器基本参量的关系,阐明了星形光波导耦合器的耦合特性。     

基于布拉格声光衍射场的光强非均匀空间分布研究

为了保证合成孔径激光雷达测试中信号光的光束质量,从波动方程出发,推导出传统的衍射光源布拉格声光作用的耦合波方程。根据测试对光束质量的不同要求,借助有限差分方法分析衍射场光强的空间三维分布,发现声场振幅的不均匀分布会影响声光衍射场的光强分布,光强分布不均造成实验中信息光源的探测难度。通过光强空间分布研究增大有效通光孔径到3 mm,解决了声光调制器光束衍射质量问题,改进后的光束质量达到实验要求。该研究方法适用于改进声光器件工作参数。     

聚合物脊形光波导的变分有效折射率法分析

聚合物脊形光波导是聚合物集成光电子器件的重要构成单元.利用有效折射率法计算聚合物脊形光波导的横向折射率分布及有效折射率,将各区域中的光场分布近似用分段函数表达.基于导模满足的标量波动方程,利用变分法确定变分参量,以求得准确的横向光场分布.对聚合物脊形多模光波导基模和高阶模的色散特性与横向场分布进行分析,研究了波导结构参数对色散特性的影响,计算出TM基模和高阶模的光场分布,得出了聚合物脊形光波导的单模传输条件.研究表明,该方法计算量小、精度高,对聚合物光电子器件中脊形光波导的理论分析与设计优化提供了简单高效的方法.     

平板宽波导光场分布及极化模

平板宽波导CO₂激光器波导内光场分布满足亥姆霍兹方程。在给定条件下,对光场分布方程进行求解,获得了极化模 EH_nm^x和EH_nm^y 的表达式。通过计算机计算,得出了在3×8 mm²波导放电区中所存在的EH_1.16极化模归一化理论分布曲线,其曲线与实验观测结果符合得很好。     

准共线集成声光模式转换器的性能分析与设计

报道了一种SiO2薄膜声波导和Ti∶LiNbO3光波导之间存在一个角度的准共线的模式转换器结构, 利用波导模式分析导出薄膜声波导的宽度限制; 利用模式耦合理论得出了声光模式转换特性和耦合系数的加权形式. 实现了对耦合系数的加权, 较好地抑制了旁瓣. 在综合考虑旁瓣和线宽的条件下, 设计了这种TE/TM声光模式转换器, 其旁瓣为－16.8 dB, －3 dB线宽和－10 dB线宽分别为1.37 nm和2.31 nm.     

利用TeO2减少多模光纤出射场散斑干扰的研究

 为了减少多模光纤出射光场的散斑干扰,提出了把声光布拉格衍射效应所形成的不同衍射级耦合到多模光纤中,由于衍射级具有不同的偏振态,消弱了光场相干条件,进而在出射光场中消弱了散斑场的对比度,并通过对改变声场频率后得到的散斑场对比度的分析,证实了利用各向异性晶体TeO2能够控制散斑场对比度,改善出射场的高斯分布,得出了可以利用布拉格衍射效应减少散斑场干扰的可能性。     

铌酸锂波导电光重叠积分因子的波长依赖特性分析

通过测量铌酸锂(LN)单模波导在不同波长下的半波电压,结合半波电压与电光重叠积分因子的依赖关系,实验发现了LN单模波导电光重叠积分因子随波长增大而迅速减小.另一方面,通过数值求解法分别得出了LN单模波导在不同波长的导模场分布和调制电场分布以及二者的重叠积分因子,在理论上获得了与实验数据十分近似的结果.进一步的仿真分析指出LN单模波导电光重叠积分因子随波长增大而减小的规律主要来自于导模的光场中心随波长增大逐渐远离波导表面,向低电场强度区域靠近.这种电光重叠积分因子的波长依赖特性是导致LN波导半波电压随波长增大而非线性上升的原因之一,它将为基于LN波导的器件的设计和优化提供重要参考.     

利用 CCD 图像分析法测定激光横向光场分布

运用Matlab的数字图像处理功能,编写程序分析了CCD相机所拍摄的基模TEM00和TEM10模在靶上的反射光斑,得出光场分布的曲线,并与理论曲线进行对比,验证了由基尔霍夫衍射积分方程推导得到的光场分布函数的正确性。     

表面波布拉格声光互作用耦合波方程的研究

定义了压电晶体的增劲声光系数，它反映压电晶体中声光、电光和压电效应共同作用的结果。从参量互作用基本理论出发，同时考虑声光效应、电光效应和压电效应三个因素，用一个压电增劲声光系数来表示三种因素的共同作用，导出表面波声光布拉格互作用的耦合波方程。并求解得出相应衍射效率的计算公式。该式说明在弱声光互作用条件下，衍射导光波强度与超声功率成正比。表面波声光器件具有体积小、工作稳定、能耗小、易于集成等优点。可以用作光偏转器、光调制器、滤光器。在光通信以及各类实时信号处理，如相关、卷积、频谱分析、矩阵光计算等领域具有广泛的应用前景。     

Surface acoustic wave distribution and acoustooptic interactions in silica waveguide Bragg devices

The efficiency of acoustooptic interaction in single-mode strip silica waveguide is analyzed theoretically for the first time by determining the overlap integral between the optical and acoustic field distributions. The results show that there is a good overlap of the optical and SAW fields in the low SAW frequency range. At high acoustic frequencies, the overlap integral decreases with increasing acoustic frequency. At 216 MHz, the maximum of 0.8544 for the overlap integral is obtained provided that the H/Λ equals 0.02.     

二维多通道声光相互作用的理论与实验研究

研究二维多通道并行超声波与光波相互作用的机理,导并求解了二维多通道声光相互作用的耦合波方程.分析了二维多通道声光相互作用中各通道的主衍射和二维多通道声光互调制的线性和非线性效应.研制了二维多通道声光器件,测试了器件的各种特性,实验结果与理论分析相符.并且用二维多通道布拉格声光调制器实现了光学矩阵-矢量运算.     

Influence of viscosity on the diffraction of sound by a circular aperture in a plane screen

The linearized equations of viscous fluid flow are used to analyze the diffraction of a time-harmonic acoustic plane wave by a circular aperture in a rigid plane screen. Arbitrary aperture size and arbitrary angle of incidence are considered. Sets of dual integral equations are derived for the diffracted velocity and pressure fields, and are solved by analytic reduction to sets of linear algebraic equations. In the case of normal incidence, numerical results are presented for the fluid velocity in the aperture and the power absorption due to viscous dissipation. The theoretical results for power absorption are compared to previously obtained results from high amplitude acoustic experiments in air. The conditions under which the dissipation predicted by linear theory becomes significantare quantified in terms of the fluid viscosity and sound speed, the acoustic frequency, and the aperture radius.     

Acousto-optic interaction in a non-homogeneous acoustic field excited by a wedge-shaped transducer

The article is devoted to theoretical analysis of light diffraction in a non-homogeneous acoustic field created by a wedge-shaped piezoelectric transducer. Relationships describing electrical, acoustic and acousto-optic properties of the acousto-optic cell are derived in the approximation of a small thickness of the piezoelectric plate. Principal characteristics of acousto-optic interaction are examined such as dependences of the light diffraction efficiency on the phase mismatch and the acoustic wave amplitude. It is shown that the acoustic field has a complicated amplitude-phase structure changing with the acoustic frequency. It is demonstrated that the diffraction efficiency in the Bragg regime can approach 100% in spite of a noticeable phase mismatch. The appropriate optimal values of ultrasound power and incidence angles of light are found.     

基于绝缘体上硅的一种改进的Mach-Zehnder声光调制器

传统的基于绝缘体上硅的Mach-Zehnder(MZ)声光调制器中,叉指换能器位于两臂的同一侧.为实现高的调制效率,声表面波的波峰和波谷分别调制MZ干涉仪的两臂,这要求控制MZ干涉仪两臂之间的距离为奇数倍声波半波长.但实际上由于传播过程中衬底材料的变化,声波波长会变大,这会导致两臂的间距难以准确设置.另一方面,声波在传播过程中经过MZ干涉仪的一臂后会发生衰减,降低了对另一臂的调制效果,影响了整体的调制效率.本文针对这些问题给出了一种解决方案,把叉指换能器放在MZ波导两臂之间,确保MZ干涉仪两臂到叉指电极中心距离相等.采用有限元法,首先对新提出的结构进行分析,然后通过声光互作用原理得到了材料的折射率变化;进而研究了波导类型、波导宽度、氧化锌厚度及叉指对数等因素对声光调制效率的影响,并对声光调制器的结构参数进行了优化以提高其性能.基于COMSOL Multiphysics的仿真结果表明,当条波导宽度为6μm,氧化锌只覆盖有叉指电极的部分且厚度为2.2μm,控制叉指电极数目为50对时,波导有效折射率变化在驱动电压为1 V时可以达到4.08×10~(-4),比传统结构提高了12%.     

Angular and power characteristics of noncollinear acousto-optic tunable filters

The angular and the power characteristics of noncollinear acousto-optic tunable filters are investigated both experimentally and theoretically. The dependencies of the acoustic wave frequency, the bandpass width and the diffraction efficiency of the filter are studied as functions of the angle of incidence of the optical wave and of the acoustic signal power density. These dependencies are illustrated and tested on the basis of a realized such a filter based on tellurium dioxide (TeO₂). A good agreement of theory and experiment is demonstrated, which indicates that the approach used can be effective in designing such devices.     

Spectral characteristics of non-collinear acousto-optic tunable filters

The bandpass width and the diffraction efficiency of a non-collinear acousto-optic tunable filter are considered as functions of the optical wavelength for fixed values of the direction of propagation of the optic wave, the length of the acousto-optic interaction and the power density of the controlling RF-signal. A comparison between the calculated and the experimentally measured spectral dependencies is discussed and illustrated from the viewpoint of practical application for a TeO₂ filter. It is shown that in the approximation used, satisfactory agreement can be achieved between the experimental and calculated dependencies.     

基于声光效应的光束偏转控制理论研究

基于参量互作用观点及声光互作用原理,构建了入射光为高斯光并且存在声波吸收情况下的声光偏转器模型.基于此模型研究了超声波频率、声波功率和光束入射角对衍射光的影响.对比了有声波吸收和无声波吸收两种情况下上述三个参量对衍射光产生的不同影响.计算结果表明,同无声光吸收时相比,当存在声波吸收时,偏转器的衍射效率将减小,导致衍射波形畸变,光强峰值位置发生偏移.     

Design of the bandpass width, the spectral resolution and the diffraction efficiency of a non-collinear acousto-optic tunable filter of TeO2

The spectral dependencies of the bandpass width, the spectral resolution and the diffraction efficiency of a non-collinear acousto-optic tunable filter of TeO₂ are designed by the method proposed by Chang. The effect of four parameters (the directions of propagation of the acoustic and optic waves, the length of acousto-optic interaction and the power density of the controlling RF-signal) on the filter spectral characteristics is discussed and illustrated from the point of view of practical application. An example of filter design using these dependencies is presented.