Abstract

The piezoelectrically induced strain-optic (PESO) effect can significantly influence the optical response of linear electrooptic crystals to electric driving fields. By utilizing this effect, low voltage modulators operating at the piezoelectric resonance can be developed.¹,² We have achieved high efficiency modulation of a laser beam using standing acoustic waves generated at piezoelectric resonance in bulk electrooptic crystal with the PESO effect. An 8 × 8-mm aperture, 25-mm long LiNbO₃ crystal was chosen in the experiment. The sample was driven by an rf signal from a frequency synthesizer and an rf amplifier. High efficiency modulation on the refractive index by shear acoustic waves was observed in the 10-100-MHz range by using a He-Ne laser. The resonance width (FWHM) is under 10 kHz, confirming the high acoustic Q of the piezoelectric resonant vibrations. For the assembly investigated, the strongest modulation occurred at rf frequency around 50 MHz. A 100% light intensity modulation was achieved at a peak-to-peak driving voltage of 20 V. When the rf frequency was above 100 MHz, the modulation efficiency decreased quickly. However, we can still observe diffraction spots at resonance frequencies as high as 400 MHz. The light modulator based on the PESO effect differs from the conventional acoustooptic modulator. It combines the transducer and the resonance body into one. Thus, construction of the modulator is greatly simplified. With improvements of electric coupling, temperature compensation, and selection of better materials, we expect better performance of the PESO modulators.

© 1989 Optical Society of America