Directional coupler using acoustic surface waves

The properties of interdigital transducers have been used to construct a directional coupler. The coupler consists basically of an array of eight transducers etched from an aluminium film deposited on a lithium-niobate substrate. Experimentally, a directivity of 17 dB was obtained at 75 MHz.     

Image processing using acoustic surface waves

An application of acoustic surface waves for image processing is reported. The information compression of videophone signals takes advantage of the so-called Hadamard transformation. Acoustic-surface-wave tapped delay lines are efficient for the achievement of such a transform in a low-cost real-time device. The results of initial experiments are reported.     

Realisation of microwave-circuit functions using acoustic surface waves

In realising microwave-circuit functions using surface technology, the physical size of passive components using e.m. waves imposes a limitation. This letter investigates the application of acoustic waves to this case. The feasibility of constructing waveguides and directional couplers is demonstrated experimentally, and some theoretical considerations referring to waveguides are presented.     

Programmable correlation using parametric interactions in acoustic surface waves

Real-time correlation of 31 chip binary p.s.k. waveforms has been obtained using nonlinear interactions of acoustic surface waves, with a signal bandwidth of 8 MHz. A dynamic range of 20 dB was obtained. Calculations indicate that a dynamic range of 50 dB should be obtainable quite readily, making the device attractive for adaptive signal processing.     

Generation of surface acoustic waves using the electrostrictive effect

Surface acoustic waves have been generated and detected on a biased electrostrictive substrate. A delay line with an insertion loss of 26 dB at 77 K has been constructed on strontium titanate. The temperature and electric-field dependence of the insertion loss are given.     

Visualisation of surface acoustic waves

A simple method for acoustic-surface-wave visualisation is described which is applicable to both piezoelectric and non-piezoelectric surfaces. Briefly, a uniform layer of small particles, comparable to the wavelength, is distributed over the acoustic surface. The acoustic-beam pattern of an incident surface wave is then traced out by scattering the particles out of the propagation path. Experiments at 100 MHz on lithium-niobate surfaces are described.     

Generation and correlation of quadriphase-coded signals using acoustic surface waves

The use of acoustic surface waves to generate and correlate a 4-phase 15-bit generalized Barker sequence is described. Experimental results using quartz and LiNbO3as substrates are reported.     

Low-sidelobe weighted-coupled integrated acoustooptic tunablefilter using focused surface acoustic waves

A single-stage low-sidelobe weighted-coupled integrated acoustooptic tunable filter (IAOTF) operating at the optical wavelength of 1.31 μm has been realized on a Y-cut X-propagating LiNbO₃ substrate for the first time. The weighted-coupling, which enabled the achievement of low-sidelobe levels, was facilitated by focused surface acoustic waves generated by a curved interdigital transducer. First sidelobe levels as low as -17.6 dB have been obtained. Optical bandwidth of 4 nm and tuning range of 170 nm for an interaction length of 6 mm were also accomplished     

On a new type of surface acoustoelectric waves in hexagonal crystals

It is shown that, in the basal plane of crystals with hexagonal symmetry, purely longitudinal surface acoustoelectric waves can propagate. In contrast to well-known Gulyaev-Blustein transverse waves, these longitudinal waves are localized in the surface layer, whose thickness is on the order of the wavelength. The field of mechanical displacements and the potential field of the wave are phase shifted by ??/2. The electricfield vector of the wave is circularly polarized in the sagittal plane.     

Variable delay for acoustic surface waves by electro-acousto-optic interaction

Continuosly variable analogue delay is demonstrated by using reflections from a laser-light-induced impedence discontinuity on a photoconductive layer evaporated on an LiNbO3 delay line at 75 MHz. ?30dB reflection loss is obtained with a delay range of 20 ?s.     

Theoretical computations on ridge acoustic surface waves using the finite-element method

Theoretical computations have been carried out on ridge acoustic surface waves using the finite-element method. The results obtained agree substantially with experiments performed previously.     

Optical probing of surface acoustic waves

Light diffraction by surface acoustic waves is used in studying the propagation characteristics of Rayleigh waves on y-cut z-oriented LiNbO3. In reflection, only the surface deformation contributes to the diffracted light. In transmission, the photoelastic effect, which is incident beam polarization dependent, must also be considered. Such optical probing has been used to study the Fresnel diffraction radiation pattern of an interdigital transducer, to measure beam steering effects related to transducer misalignment on an anisotropic substrate, and to measure reflection and transmission coefficients of an electrically loaded transducer. Attenuation measurements have been made over frequencies as high as 3.5 GHz. The power dependence of attenuation and harmonic generation is also examined.     

Wavefront visualisation of acoustic surface waves

Acoustic surface waves (a.s.w.) propagating on yz-cut lithium niobate have been visualised by two imaging techniques. The wavefronts of straight-crested and convergent a.s.w. have been rendered visible on the screen of a storage oscilloscope.     

Ridge guides for acoustic surface waves

A low-velocity flexural mode has been excited on acoustic-surface-wave topographic guides. With structures offering some hope of realisation at high frequencies, very strong confinement of the guided wave is obtained. Q factors in excess of 1000 have been observed on a ring resonator only ten wave lengths in diameter.     

SEM中用表面电子束激励势法研究半导体特性

本文考虑用一种新的非接触法来研究和测量半导体晶体微区特性的方法,这种方法是基于扫描电镜中控测半导体的表面电子束激励电势(SEBIV)法来研究半导体的电物现特性和测量半导体电物现参数。本文讨论了一种测量半导体晶体的非平衡载流子的扩散长度L和寿命τ的方法。本文还讨论了用本方法可观测到的表面电子束激励电势图像衬度的形成和它与扫描方向、半导体材料的物理特性和表面激励电势极性的关系。SEBIV法是一种非接触而且非常有效的观测和研究半导体晶体中活性非平衡载流子电特性的方法,这种方法有下列特点:1测量时不需要与样品直接接…     

Frequency-controlled beam steering of surface acoustic waves using a stepped transducer array

Using stepped arrays of transducers, the direction of propagation of surface acoustic waves can be controlled by varying the input frequency. This effect has applications in maintaining the optimum Bragg angle in acousto-optic devices for integrated optics. The measured beam-steering angle for a given frequency change follows the theory of Pinnow, where anisotropy effects are taken into account.     

Application of the transverse acoustoelectric effect to studying silicon surface charging upon water adsorption

Water adsorption on a silicon surface in a layered Si-LiNbO₃ structure with an air gap is studied using the transverse acoustoelectric effect on surface acoustic waves. A generalized analysis of measurements of the transverse acoustoelectric effect makes it possible to determine the initial band bending of the Si surface, its changes during gas cycles, hence, the sign and charging kinetics of Si upon H₂O adsorption. Depending on the properties of the semiconductor surface defects, both the donor and acceptor nature of the interaction of H₂O with Si are observed. For samples with a thermal oxide, the donor-type interaction occurs; for samples with a natural oxide, both interaction types take place. Based on the used physical model of oxide charging upon exposure to an adsorbate, a comprehensive methodical approach is proposed, which allows the targeted development of acoustoelectronic structures for sensor applications.     

Modified equations of coupled surface acoustic waves

Modified equations for coupled surface acoustic waves (SAWs) are derived on the basis of the complex Umov-Poynting theorem and the Green’s function of a piezoelectric half-space. The equations can be used to calculate the frequency characteristics of various SAW devices. Relationships for frequency-dependent parameters of the equations describing SAW excitation are derived. The efficiency of the computation of frequency characteristics of devices that is based on the obtained relationships is demonstrated by the calculation for a ladder SAW-resonator 64°YX-LiNbO₃ filter. The results of computations and measurements are in good agreement.     

Wavelength-switchable fiber laser using acoustic waves

We report a wavelength-switchable fiber ring laser that includes a Bragg grating-based acoustooptic superlattice modulator. Wavelength switching of the laser emission is achieved by controlling the peak reflectivity of the different reflection bands that appear on both sides of the Bragg wavelength when a longitudinal acoustic wave propagates along the grating.