A tunable filter with collinear acoustooptical TE-TM modeconversion in a GaAs-AlAs multiquantum-well waveguide

We investigate theoretically an acoustooptic tunable filter (AOTF) based on TE-TM mode conversion by collinear acoustooptic interaction, using the high form birefringence that occurs in a GaAs-AlAs multiquantum-well (MQW) rib waveguide. Mode conversion is achieved using a transverse piezoelectric surface acoustic wave. We propose to use a piezoelectric layer (ZnO or AlN) of 6-mm symmetry, which can be deposited by plasma-enhanced chemical vapor deposition. The c axis is then parallel to the plane of the layer. Under this condition, a transverse piezoelectric surface acoustic wave excited by inderdigital electrodes can propagate within the GaAs-AlAs MQW optical waveguide. TE-TM conversion is then possible with a relatively low acoustic frequency (some tens of megahertz), yielding a high diffraction efficiency and a figure of merit 14 times higher than that of conventional LiNbO₃ filters based on AOTFs     

Certain features of the effect of diffraction on the acoustooptic interaction in an elastically anisotropic medium

With the use of the distribution of the ultrasonic-beam intensity calculated with allowance for elastic anisotropy, it is shown that the transverse divergence of acoustic waves affects the diffraction efficiency of an acoustooptic cell. The calculations are in agreement with measurements of the acoustic-field distribution in the acoustic lines of crystalline- and fused-quartz acoustooptic devices. The distribution is measured in the plane perpendicular to the diffraction plane.     

Acoustooptic interactions in AlGaAs-GaAs planar multilayerwaveguide structures

The acoustooptic interaction of guided optical waves and surface acoustic waves (SAW's) is studied in multilayered structures of dimensions of the order of those seen in multiple-quantum-well (MQW) structures. The guided mode profiles and SAW-induced electric field and strain profiles are used to calculate the diffraction efficiency, using an expression derived from coupled mode theory. Diffraction efficiency is plotted as a function of SAW frequency, and the effects of acoustic power, acoustic aperture, and material structure are considered. For a specific structure, the diffraction efficiency is seen to increase with increasing aluminum content for low concentrations and the opposite is seen for higher concentrations. This is explained in terms of the opposing effects of guided optical mode parameters and material properties. Possibilities for optimization of the diffraction efficiency through tailoring of the refractive index profile of the material structure are suggested     

复杂流场的激光—超声测试方法及原理性实验研究

本文从复杂流场-旋涡场参量的激光-超声测试方法的需要出发,论述了超声波产生的声位相光栅对激光产生的衍射及偏转特性。在水中进行了声光偏转等试验,测出了产生声光偏转时折射率的变化及声压变化,从而估算出空气复杂流场激光——超声方法所需的超声频率及能量,为实现空气流场激光——超声无接触测试的研究提供了依据。     

基于Bragg衍射的多频声光衍射效应研究

文章首先介绍多频声光衍射的原理,然后推导Bragg声光介质的声光衍射耦合波方程,并结合该声光波矢量的分析,定量和定性地讨论了衍射效率、波矢量失配和三阶互调等多频衍射效应.实验表明,各种效应都能很好地与Bragg理论极限相吻合.     

Features of the dependence of the diffraction efficiency of an acousto-optic Bragg cell with multielement traveling wave transformer on its geometric parameters

An equation for calculation of the diffraction efficiency of an acousto-optic Bragg cell with multielement traveling wave transformer taking into account the exponential distribution of the acoustic field along of the transformer is obtained. The results of theoretical and experimental studies of the dependence of the diffraction efficiency of the Bragg cell on the number of radiating elements in the piezoelectric traveling wave transformer are given. Nonlinear behavior of the dependence of the diffraction efficiency on the number of radiators in the considered transformer is analyzed.     

A wide-band acoustooptic TE-TM mode converter using a doubly confined structure

Bandwidth limitations of collinear acoustooptic TE-TM mode converters have been overcome by a method in which the optical and surface acoustic waves have been interacted in a doubly confined waveguide structure. A 5 percent bandwidth centered at 550 MHz and a conversion efficiency of 50 percent at a total acoustic input power of less than 1 mW have been obtained withY-cut LiNbO3. It is found that the power transfer efficiency does not degrade significantly when the phase mismatch increases.     

Conditions for observation of the nonreciprocal effect in a collinear acoustooptic filter at various wavelenghts of light radiation

The features of the nonreciprocal effect observed during collinear acoustooptic interaction in a lithium niobate crystal are investigated theoretically and experimentally. It is shown that one of the main reasons that restrict the possibility of observation of the nonreciprocal effect in the crystal is damping of an acoustic wave. It is proved that, when an acoustooptic cell is illuminated with monochromatic light, the ultrasound damping increases the frequency band of the collinear acoustooptic interaction, a circumstance that affects the possibility of observation of the nonreciprocal effect in an acoustooptic experiment. The conclusion that the creation of acoustooptic filters having a high spectral resolution and operating at acoustic microwaves necessitates taking into account the nonreciprocal effect is drawn.     

Modeling of noncollinear multifrequency acoustooptic interaction inguided-wave Bragg cells

We present an original detailed theoretical modeling of guided-wave noncollinear acoustooptic (AO) interaction produced by a multifrequency surface acoustic wave (SAW) in planar guided-wave structures. The modeling of the multifrequency AO interaction is based on a modified version of the coupled-mode theory. The first- and third-order diffraction efficiency and optimum dynamic range of the Bragg cell have been calculated as a function of acoustic power, acoustic radiofrequency, and optical waveguide parameters in Y-cut Ti:LiNbO₃ planar waveguides. Polynomial approximations, describing the first and third order diffraction efficiency versus normalized acoustic power in the cases of two- and three-frequency interactions, are derived and presented for the first time for arbitrarily large RF signals     

Wide-band guided-wave acoustooptic Bragg cells in GaAs-GaAlAs waveguide

One of the key components in future GaAs-based monolithic integrated acoustooptic modules or circuits is an efficient and wide-band acoustooptic Bragg cell. In this paper, design, fabrication, and performance characteristics of compact miniaturized GaAs-GaAlAs waveguide acoustooptic Bragg cells that operate at the acoustic frequency from 190 to 625 MHz are reported. A 201 MHz bandwidth has been obtained with the Bragg cell that employs a single tilted-finger chirp transducer centering at 360 MHz. The acoustic propagation losses in the GaAs-GaAlAs waveguides that were measured using acoustooptic Bragg diffraction as a probe are also presented.     

Acoustooptic modulators for single-mode fibers

The design of in-line acoustooptic modulators for single-mode fibers is discussed. The basic configuration consists of a cylindrically symmetric piezoelectric transducer fabricated on the fiber surface, so that the fiber itself acts as a cylindrical acoustic resonator. Depending on the fiber design, the acoustic wave can induce phase, birefringence, or polarization modulation of the light in the fiber. Pairs of the polarization modulators in series can be used to shift the optical frequency. Factors affecting the performance of all of these devices are discussed.     

基于声学黑洞的压电俘能结构系统仿真与优化

薄板结构中的声学黑洞(ABH)可降低弯曲波的相速度,同时增大振幅,在声学黑洞区域产生高能量密度和能量聚集效应,与压电俘能结构相结合,可提升能量转化效率。该文首先建立了基于声学黑洞的压电俘能结构的有限元模型,对比分析了均匀板及声学黑洞结构的动能密度及电压输出特性;基于有限元法推导了压电振子等效电路模型,并通过Multisim软件建立压电俘能全系统等效电路耦合模型,确定了负载电路最优电阻,提高系统俘能效率。     

Acoustooptic modulator using the Stark effect and stress-inducedbandgap changes

An analysis of the semiconductor multiple-quantum-well (MQW) acoustooptic modulator is performed. The strain and electric-field components generated by surface acoustic waves (SAW's) in a multilayered semiconductor piezoelectric structure are presented. The effects of a SAW propagation on the modulator optical parameters are studied. Two kinds of SAW effects in the modulator structure are taken into account: the variation of the excitonic energies of the MQW due to strain and the companion electric field generated by the SAW is determined. The hole's effective mass change induced by the SAW is analyzed and included in the Schrodinger equation. The optical absorption coefficient spectra of the modulator as a function of the SAW power is presented. Experimental results concerning optical absorption variations of quantum-well structures produced by various SAW powers are shown     

Diffraction loss of the signal in microwave acoustic delay lines with multielement piezoelectric transducers

On the basis of the Green??s function, a method for calculation of diffraction fields in multielement piezoelectric transducers used in anisotropic crystal acoustic ducts is developed. The results of the numerical analysis of diffraction fields, which are created by multielement piezoelectric transducers on the face of the acoustic duct, are given together with the results of calculation of the diffraction loss of the main signal and the triple and quintuple transit echoes in an acoustic delay line of the microwave signal, which operates in the direct mode. The dependences of the diffraction loss on the angle between the crystallographic axis and the geometrical axis of the acoustic duct are studied.     

基于1-3压电复合材料宽带超声换能器研究

电声转换效率与换能器带宽是评价聚焦超声换能器性能的重要指标。传统压电陶瓷制备的聚焦超声换能器,其电声转换效率与换能器带宽偏低。该文采用实验结合仿真模拟的方式,通过研究1-3压电复合材料中压电相的体积比、环氧相改性、调控匹配层阻抗与匹配层厚度对换能器性能的影响,开发了一种基于1-3压电复合材料的聚焦超声换能器,实现了82.3%的电声转换效率与140 kHz的换能器带宽。结果表明,与同等规格的传统压电陶瓷聚焦超声换能器相比,该超声换能器的两项指标分别提升了105%与250%,这为大功率聚焦超声换能器的设计开发提供了参考与指导。     

压电三迭片式高阶声压梯度水听器研究

该文从数学上计算了不同阶声压梯度组合对空间声场的估计误差,分析了差分通道幅度和相位不一致性对有限差分近似误差的影响,研究了水听器自噪声及模数转换量化误差对高阶水听器工作频率下限的制约关系,提出了一种由4片压电三迭片构成的高阶声压梯度水听器,尺寸为?100 mm×50 mm,能够测量声场一阶声压梯度和二阶混合声压梯度。利用有限元法计算获得平面波自由声场中水听器各通道的输出电压。计算结果表明,二阶混合声压梯度通道的输出电压响应每倍频程升高12 dB,指向性与纵向四极子声源指向性一致。     

Design of high-frequency ZnO-coated optical fiber acoustoopticphase modulators

In this paper, we present a theory of an optical fiber acoustooptic phase modulator using piezoelectric zinc oxide (ZnO) coating. The effects of changing device parameters in the acoustooptic resonator are investigated for transducer design. These results are entirely different from those of the well-known; planar device structure since every part plays an important role in the resonator structure. Optical phase modulation in the frequency region up to 1 GHz is also demonstrated. Multiple sharp resonance peaks with a maximum phase shift of 0.7 radians are observed     

用衍射光脉冲回波技术测量声光介质的体波声衰减系数

扼要介绍用衍射光脉冲回波技术测量声光介质体波声衰减系数的基本原理、实验装置和样品制备等，并分别测量了声光介质为石英玻璃、声光玻璃和ＬｉＮｂＯ３，ＰｂＭｏＯ４单晶的体波声衰减系数，给出了实验结果。     

基于1-3压电复合材料的相控聚焦系统

针对相控聚焦超声系统控制电路复杂、移相精度低, 锆钛酸铅(PZT)材料制备的换能器转换效率较低的问题。控制电路采用Verilog HDL语言将通信、倍频锁相、信号发生及信号移相功能集成在现场可编程门阵列(FPGA)中。换能器采用1-3型压电复合材料制作。实验结果显示,该相控聚焦系统提高了电路集成度与移相精度及换能器的电声转换效率。     

Acoustooptic properties of a weakly multimode solid core photonic crystal fiber

The acoustic and acoustooptic properties of a weakly multimode solid core photonic crystal fiber (PCF) are studied. The phase velocity of the lowest order flexural acoustic mode is measured as a function of frequency and compared with the results for a hollow core PCF and a standard optical fiber. Acoustooptic interaction is used to couple light from the lowest order to the first higher order optical modes of the solid core PCF. The experimental results are compared with theoretical predictions.