Bragg diffraction of microcavity polaritons by a surface acoustic wave

Bragg scattering of polaritons by a coherent acoustic wave is mediated and strongly enhanced by the exciton states resonant with the acoustic and optic fields in the intraband and interband transitions, respectively. In this case, in contrast with conventional acousto-optics, the resonantly enhanced Bragg spectra reveal the multiple orders of diffracted light. For polaritons in GaAs microcavities driven by a surface acoustic wave of nu(SAW)=1 GHz and I(ac)< or approximately 100 W/cm(2) the main acoustically induced band gap can be as large as Delta(MC)(ac) approximately equal to 0.6 meV and the Bragg replicas up to n=3 can be observed.     

Modeling of Coulomb coupling and acoustic wave propagation in LiNbO3

The angular spectrum propagation technique is applied to modeling of wave propagation through piezoelectric media. The calculations of the angular spectrum propagator are based on the relevant equation for the slowness surface resulting from the solution of the Christoffel equation with piezoelectrically stiffened elastic constants. A two-dimensional FFT algorithm is applied in the final field superposition. We concentrate on the case of Coulomb coupling through local electrical point contacts on both the excitation and detection side. To model that case we superpose solutions for acoustic Green's functions of different propagation modes convoluted with equivalent distributed effective sources. Calculated results are in good agreement with the measured ones.     

ZnO薄膜/金刚石在不同激励条件下声表面波特性的计算与分析

本文首先以刚度矩阵法为基础, 给出了ZnO薄膜/金刚石在四种不同激励条件下的有效介电常数计算公式. 然后以此为工具, 分别计算了多晶ZnO(002) 薄膜/多晶金刚石和单晶ZnO(002) 薄膜/多晶金刚石的声表面波特性, 并根据计算结果及设计制作声表面波器件的要求, 对ZnO膜厚的选择进行了详细地分析. 最后讨论了ZnO/金刚石/Si复合晶片可以忽略Si衬底对声表面特性影响时对金刚石膜厚的要求. 关键词： 声表面波 压电多层结构 有效介电常数 刚度矩阵法     

The characteristics of surface acoustic waves on AlN/LiNbO3 substrates

The characteristics of surface-acoustic-wave (SAW) devices on various substrates were measured by a network analyzer in the temperature range from 0 to 80 °C. Based on the structure of IDT/AlN/LiNbO₃, it was revealed that the magnitude of the temperature coefficient of frequency (TCF) of a SAW on a LiNbO₃ substrate was significantly decreased due to the thickness increase of AlN thin film deposited on the LiNbO₃ substrate. The TCF of a SAW on an AlN/LiNbO₃ device was measured to be about -51 ppm/°C at h/λ=0.1, where h is the thickness of the AlN film and λ is the wavelength of the SAW. This indicates that the deposition of an AlN film on a LiNbO₃ substrate could improve the temperature stability, as compared with that of a SAW on a LiNbO₃ substrate (-73 ppm/°C). The SAW device on the ST-X quartz is shown to have a positive TCF as the AlN thin film is deposited on the surface of the ST-X quartz. In addition, the phase velocity (V_p) of the SAW on an AlN/LiNbO₃ substrate was significantly increased by the increase of AlN thickness (h/λ). Received: 14 October 2002 / Accepted: 15 October 2002 / Published online: 29 January 2003 RID="*" ID="*"Corresponding author. Fax: +886-7/525-4199, E-mail: ycc@ee.nsysu.edu.tw     

X-ray diffraction analysis of the surface acoustic wave propagation in langatate crystal

X-ray diffraction on a langatate crystal (La₃Ga_5.5Ta_0.5O₁₄, LGT) modulated by a Λ=12 μm Rayleigh surface acoustic wave (SAW) was studied in a double axis X-ray diffractometer scheme at the BESSY synchrotron radiation source. SAW propagation in the crystal causes sinusoidal modulation of the crystal lattice and the appearance of diffraction satellites on the rocking curves, with their number, angular positions, and intensities depending on the wavelength and amplitude of acoustic vibrations of the crystal lattice. Strong absorption of X-ray radiation in LGT enables the observation of the diffraction spectra extinction at certain SAW amplitudes. X-ray diffraction spectra analysis makes it possible to determine SAW amplitudes and wavelengths, to measure the power flow angles, and investigate the diffraction divergence in acoustic beam in LGT.     

Surface acoustic wave distribution and acousto-optic interaction in proton exchanged LiNbO3 waveguides

The efficiency of acoustooptic (AO) interaction in YZ-cut proton exchanged (PE) LiNbO₃ waveguides is theoretically analysed by determining the overlap between the optical and acoustic field distributions. The present analysis takes into account the perturbed SAW field distribution due to the presence of the PE layer on the LiNbO₃ substrate determined by the rigorous layered medium approach. The overlap is found to be significant upto very high acoustic frequencies of the order of 5 GHz, whereas in the earlier analysis by vonHelmolt and Schaffer [6] for diffused waveguides, it was shown that the overlap integral rolls down to nearly zero at this high frequency range.     

声表面波介质表面受力条件下的波速变化研究

为了计算力负载直接作用在声表面波传播表面时波速的变化特性,通过有效材料系数将负载引入,并用广义Green函数计算声速,得到了数值计算的结果,并用声表面波谐振器进行了实验.实验结果表明,将力负载直接加载在声表面波的传播表面时,波速变化量和力负载大小近似为线性关系,该加载方式下,实验中声表面波谐振器的谐振频率对外加质量负载有较高的灵敏度,可达1900 Hz/g.     

Anisotropic surface relief diffraction gratings under arbitrary plane wave incidence

A modal method is used for the analysis under oblique incidence of a diffraction grating made of anisotropic material. The problem is studied viewing the structure as the cascade of junctions between periodic arrays of anisotropic slab waveguides with the same period and different heights. This diffraction problem is formulated in terms of an integral equation that enforces the continuity of the transverse magnetic field at the junction. The unknown is the transverse electric field at the junction. It is possible to use also another formulation, where the role of the two fields is exchanged. The kernels of these equations are the relevant Green's functions, which are expressed in terms of eigenfunction expansions. The determination of the modes of the various regions composed of arrays of anisotropic dielectric slabs has been carried out by the method of spectral elements, whereby the field components are represented in a polynomial basis and the original differential eigenvalue problem is converted into an algebraic one. The integral equation is solved numerically by the method of moments and each junction is characterized by its generalized scattering matrix (GSM). Finally, the diffraction efficiencies of the grating are obtained by combining the various GSM's.     

声表面波驱动的转动马达研究

在128°旋转Y切割x方向传播的LiNbO₃基片表面平行地光刻两对工作频率为30MHz的叉指换能器(IDT)作为定子,当高频电压加在IDT1和IDT3(或IDT2和IDT4)时,基片上将产生两列平行但方向相反的瑞利波束,从而使得基片与其上部的转子间存在局部地相对运动,在滑动摩擦力偶的作用下转子经过加速后运动趋于稳定。本文给出了工作频率为30MHz的声表面波转动马达的一些实验测量结果:在120V_p-p的电压驱动下,马达经过400ms的加速后,转动速度达到稳定,约为270rpm,并对其工作机理进行了理论分析及计算。     

Temperature-dependent attenuation of surface acoustic waves in proton-exchanged 128°-rotated Y-cut LiNbO3

3 has been experimentally studied in the frequency range 100 to 460 MHz and in the temperature range 90 to 300 K. At room temperature, the proton exchange leads to the considerable enhancement of acoustic attenuation as compared to the pure samples. Annealing in air, in general, reduces the attenuation. However, an anomalous enhancement of the attenuation at several frequencies for particular conditions of annealing is observed. When the temperature is reduced, the attenuation decreases practically to zero in as-exchanged samples. In the annealed ones, the attenuation attains a minimum in the vicinity of 160 K, and begins to grow at lower temperatures. A sharp peak in the attenuation is observed at 210 K. Several different physical mechanisms including acousto-protonic interaction and structural phase transition seem to be responsible for the observed acoustic attenuation behaviour. Received: 17 July 1996/Accepted: 2 December 1996     

衍射法测量低频液体表面波的衰减系数

提出了一种可用于几百赫兹低频液体表面声波研究的激光衍射法测量新技术。在实验上采用入射光掠入射到表面波上在远场得到了中间亮,两边暗的高反衬度的衍射条纹,实验中发现对频率为几百赫兹的低频衰减液体表面波,当移动振源改变激光入射点与振源间距离时发现零级条纹消失,这意味着此时的衍射效率接近100%。在理论上给出了衍射光强度与表面波振幅的解析关系,并利用所提出的新技术实现了对几百赫兹液体表面波的衰减系数的实时测量。     

Effect of rippled laser beam on excitation of ion acoustic wave

Growth of a radially symmetrical ripple, superimposed on a Gaussian laser beam in collisional unmagnetised plasma is investigated. From numerical computation, it is observed that self-focusing of main beam as well as ripple determine the growth dynamics of ripple with the distance of propagation. The effect of growing ripple on excitation of ion acoustic wave (IAW) has also been studied.     

Effect of melting on the excitation of surface acoustic wave pulses by UV nanosecond laser pulses in silicon

The influence of melting on the excitation of Surface Acoustic Wave (SAW) pulses in silicon is studied both theoretically and experimentally. The developed theory of Rayleigh-type SAW laser-induced thermoelastic excitation in a structure composed of a liquid layer on a solid substrate predicts that the SAW is predominantly generated in the solid phase due to the absence of shear rigidity in a liquid. The characteristic changes in the SAW pulse shape as well as the saturation and even the decrease of the SAW pulse amplitude observed above the melting threshold are explained theoretically to be a result of the decrease of the heat flux into the solid phase as well as due to the decrease of the volume of the solid phase caused by melting. Although the heat flux into the solid phase is decreased both as a consequence of the reflectivity increase and the additional energy losses (latent heat of melting) at the phase transition, it is demonstrated that the influence of reflectivity changes on the SAW pulse is negligible in comparison with the effect of melt-front motion. For laser pulses of 7 ns duration at 355 nm, the threshold value of laser fluence for meltingF _m=0.23±0.04 J/cm² and for the ablationF _a=1.3±0.2 J/cm² were determined experimentally as the points of characteristic changes in the observed SAW pulses.     

基于衍射条纹非对称性的表面波衰减系数的测量

通过采用将入射光掠入射到频率为几百赫兹的衰减低频液体表面波上,观察到了清晰的间距分布具有明显非对称性的衍射条纹。当入射光掠入射到低频液体表面上时,衍射图样非对称分布具有普遍性。理论上得到了考虑表面波衰减影响后观察屏处衍射光强分布的解析表达式。理论结果表明:衍射图样的这种非对称分布与衍射级次、入射光波波长、液体表面波波长及表面波衰减系数有关;正负级次衍射亮条纹距离中央零级亮条纹的间距体现表面波衰减信息;正衍射级次之间以及负衍射级次之间的条纹间距体现表面波波长信息。利用所提出的方法实现了对几百赫兹液体表面波的衰减系数的实时便捷测量。     

Estimation methodology for amplitude of second-order harmonic in nonlinear surface acoustic wave measured by optical diffraction method

An estimation methodology for amplitude from the fundamental to fourth-order harmonic composed of nonlinear surface acoustic waves on a LiNbO₃ substrate with a 128° Y-X propagation axis was demonstrated. First, equations for estimation of amplitudes from diffracted light intensity were shown and then numerical simulations of main factors were carried out. Normalized diffraction light intensities due to components of nonlinear surface acoustic waves were measured and their amplitudes were obtained from measured values. Finally, the amplitude of the second harmonic propagating on a gold thin film of about 50 nm thickness was estimated. It was found that the amplitude of the second harmonic increased continuously from 0.8 to 2.0 Å with propagation distance in the thin film.     

声表面波扩频多符号检测器研究

报道了一种用于差分双相相移键控/双相相移键控调制信号的声表面波扩频多符号检测器;基于声表面波,实现了直接序列扩频信号匹配滤波和多符号延迟差分解调的融合;研制了13位巴克码的4符号DBPSK/BPSK扩频多符号检测器,并对该检测器进行了实验测试和性能分析。     

Surface acoustic wave diffraction in spectral theory of interdigital transducers

A theory of interdigital transducer is presented that accounts for the surface acoustic wave diffraction. It is formulated with help of the Blotekjaer, Ingebrigtsen, and Skeie expansion method used earlier in the plane-wave theory. Now, the electric field is applied to the breaks in the strips making parts of them polarized with different potentials. This way the finite aperture width transducers are modeled residing within an infinite system of periodic strips. Closed expressions are derived for system working below the Bragg condition. The theory is open for further development accounting for elastic strips, pseudo surface, leaky or even surface skimming bulk waves, for any frequency range, including Bragg reflection exploited in surface wave resonators.     

声表面波在压电晶体表面上的聚焦特性

研究了压电晶体表面上圆弧形叉指换能器产生的声表面波的聚焦现象。用作者提出的压电晶体表面激发的严格矢量场理论来计算会聚的表面波声场,取代了比较流行的源于光学的标量角谱理论。理论分析表明介质的各向异性对声束的会聚特性有很大的影响,如焦长和焦点附近声场的对称性。在实验中可以用光学暗场法来观察声表面波场的会聚。尽管各向异性介质或各向异性压电晶体上表面波声场的会聚都非常复杂,实验的结果和理论分析比较一致。     

Peculiarities of the formation of the X-ray diffraction image of a surface acoustic wave in grazing geometry

The x-ray diffraction image of a Bluestein-Gulyaev surface acoustic wave (SAW) at grazing angles of incidence is considered in the noncoplanar symmetric Laue geometry. It is assumed that the SAW propagation direction makes a small angle with the diffraction vector. It is shown that small deviations from the Bragg angle (～0.01″) due to SAWs that do not lead to a change in the reflection coefficient result in the formation of diffraction satellites for both standing and traveling SAWs. The recorded x-ray diffraction image representing the time-averaged intensity distribution has characteristic profiles for even-and odd-order satellites.