Efficient conversion of surface acoustic waves in shallow gratings to bulk plate modes

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Abstract
Nearly 100% conversion of surface acoustic waves to bulk plate modes via gratings has been observed and characterized. The gratings constructed on YZ LiNbO3 had 200 grooves of 20‐μm period and 0.47‐μm depth. Surface acoustic waves with wavelengths near 20 μm were normally incident on the gratings. At selected frequencies, determined by a phase velocity matching condition, nearly the entire surface wave signal was converted to bulk plate modes. In an identical grating on the opposite crystal face the signal was converted back to a surface wave. This transmission of signal from front to back of a crystal occurred at selected narrow (∼0.1%) bandwidths and with a loss of less than 0.5 dB in some cases. A theory has been developed which can predict the resonant frequencies and the transmission coefficient. Possible low‐loss narrow band filter structures are considered.

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