G. Griffel

Linear electro‐optic effect in sputtered polycrystalline LiNbO3 films

Light guiding and modulation was demonstrated in sputtered LiNbO3 films deposited on glass substrates. We report on films’ exceptionally low attenuation (<2 dB/cm) and the highest electro‐optical coefficient reported so far for this kind of film (1.34×10−12 m/V).

Unified approach for calculating the number of confined modes in multilayered waveguiding structures

A general formalism is developed in order to find the number of modes and mode cutoff conditions in multilayer waveguiding structures. An explicit expression is presented for the number of confined modes that allows the modes to be counted without having to analyze the specific eigenvalue equation of the structure. The method is illustrated by its application to several structures: the buried layer, the directional coupler, and the three-guide symmetrical arrangement. By a suitable extension of the formalism, the number of well-confined modes is found for a four-layer structure.

Characterization of sputtered LiNbO3 films for integrated optics applications

Abstract LiNbO3 films were deposited onto Corning glass substrates by r.f. sputtering in a reactive Ar-10% O2 atmosphere. A systematic study of the influence of sputtering parameters such as substrate temperature, r.f. sputtering power and partial oxygen pressure was carried out. The sample composition was analysed using electron diffraction, electron microscopy and Auger electron spectroscopy. It was found that the films are amorphous at a given critical temperature and r.f. power. Beyond this critical temperature the films are polycrystalline and the grain size depends strongly on the substrate temperature. The scattered light along the surface of the deposited LiNbO3 film guides was detected using optical fibre scanning and the attenuation was determined as a function of sputtering parameters. Loss figures of about 3–6 dB cm-1 were obtained.

Modal analysis and cut-off conditions of multichannel surface-acoustic-waveguide structures

Multichannel guides for surface acoustic waves can improve the efficiency of SAW (surface acoustic-wave) devices significantly. Focusing, steering, and modulating the propagating acoustical modes can be achieved similarly to optical waveguided devices. A general formulation is presented for the analysis of the lateral waveguiding properties of Rayleigh modes in surfaces loaded with deposited strips of different materials. General expressions are obtained for the number of modes and cutoff conditions in these structures. As examples of applications, a simple directional coupler and an electrically controlled coupler are proposed.<<ETX>>

Distributed feedback guided surface acoustic wave microresonator

Surface acoustic wave resonators have been used in a number of applications: high‐Q frequency filtering, very accurate frequency sources, etc. A major disadvantage of conventional resonators is their large dimensions, which makes them inadequate for integrated acoustics applications. In order to overcome these size limitations a new type of microresonator was designed, developed, and tested. In this paper, theoretical calculations and measurements on two kinds of such devices (a corrugated waveguide filter and a microresonator structure) are presented and their possible applications are discussed.

Expression for the Number of Acoustic Love Modes and Their Cutoff Conditions in Stratified Structures

Absfraet-A formulation that yields the cutoff conditions of acoustic Love modes in a stratified isotropic structure is presented. The formulation also enables the counting of the number of guided modes in any structure without the need to solve the specific eigenvalue equation. The cases of a two-layered structure and a buried layer are analyzed; the plotting of a mode map for the number of modes as a function of the structure parameters are included.

Novel types of surface acoustic wave microreflectors: Performance analysis and simulations

Surface acoustic waves for micrograting reflectors have been characterized. Based on the perturbation theory, eight different types of structures on an acoustic waveguide were analyzed. Results of simulations of all eight types of corrugation structures were evaluated in order to find the least leaky waveguide, the most efficient reflector (with minimum necessary perturbations), and the optimal mode shape for improved performances. General design curves are presented in order to illustrate the behavior of the incident and reflected waves under a variety of structural conditions. Analytic expressions for the calculations of the mode amplitude and mode shape, and for general acoustic corrugations are derived and then the simulations results are presented.

Thermal effects in scanning acoustic microscopy for fine resolution applications

A novel scanning acoustic microscopy technique for achieving high resolution acoustic images by employing thermal effects and image subtraction has been studied and demonstrated. Experiments were performed on a perspex block patterned with a machined grid on the reverse surface, and on a buried channel in similar material. If was found that using the image subtraction technique, short periods of sample heating can lead to a stronger pattern selectivity, because of the strong temperature dependency of the elastic parameters of the polymer. In previous SAM techniques improvement in signal has been achieved through the use of special liquids as acoustic coupling media between the acoustic lens and the sample. The reported technique retains water as the coupling medium and the acoustic impedance matching is performed by varying the elastic parameters of the sample itself through direct heating. The temperature increase in the sample decreases the velocity of propagation of acoustic waves in the solid, and brings the acoustic impedance close to that of water. A theoretical model, including expressions for the acoustic aberrations, depth dependence and acoustic impedance matching has been derived. Examples of the results obtained are presented.<<ETX>>

Linear Electrooptic Effect In Sputtered Polycrystalline LiNbO3 Films

Light guiding and modulation was demonstrated in sputtered LiNbO3 films deposited on glass substrates. The films exhibit exceptionally low attenuation (< 2dB/cm) and the highest electrooptical coefficient reported so far for this kind of films (1.34 x 10-12 m/V).

General approach to calculating the number of confined modes in graded-index waveguides

A method presented previously [ J. Opt. Soc. Am. A3, 116 ( 1984)] for the determination of the number of guided modes in layered structures is extended to the case of graded-index waveguides. It is shown that the recursion relation that connected the phase of the wave function in adjacent layers is transformed into a form of nonlinear, first-order differential equation for this phase. Mathematical properties of this equation are discussed, and examples of applications are presented.