A proton-exchanged layer with an elastically soft property can be buried into a substrate by a reverse proton exchange (RPE) process. It is expected that the RPE layer with a property similar to that of bulk LiNbO 3 (LN) will prevent the degradation of the coupling factor and that the buried PE layer will reduce the leaky SAW (LSAW) attenuation. In this study, first, a layered structure of air/bulk LN/softened LN was assumed for the rotated Y-X LN and the LSAW attenuation was calculated. The rotation angle from the Y-axis giving zero attenuation shifted from 64˚ toward 5˚ for a metallized surface. The range of rotation angles at which the LSAW phase velocity exceeds that of a fast shear bulk wave was markedly expanded for a free surface, and the attenuation vanished at these boundaries. Next, the LSAW propagation loss PL was measured on 41˚ Y-X LN. The PL for the metallized surface was decreased by carrying out the RPE process from 0.036 dB/λ of a virgin sample to 0.015 dB/λ. The decrease of the PL for the free surface was also observed.
It was found for the first time that a diffraction grating was formed by perturbation in film thickness and refractive index with period of half the wavelength of surface acoustic waves, when thin film was deposited on substrate in which standing surface wave was excited. No such phenomenon has been reported so far, and its application to optical elements is hoped to be a new applications of surface acoustic waves.
SUMMARYPlate wave (Lamb wave) propagation in an extremely thin quartz substrate is analyzed. A cut angle is sought that exhibits an ultrastable temperature dependence of the frequency characteristics so that the frequency changes little with temperature. Highly stable temperature characteristics of the frequency indicating second-and third-order curves are obtained. Theoretical and experimental investigations of the temperature characteristics of the frequency of Lamb waves propagating in an AT-cut quartz substrate indicate excellent agreement between the two, confirming that the reliability of the results of the present analysis is high.
By depositing a thin film on a substrate in which a standing surface wave is excited, we fabricated a phase grating in which variations in the film thickness as well as the refractive index occurred at half the wavelength of the surface acoustic waves. As no such phenomenon has been reported until now, its application for optical elements is expected.
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