Thin-film tunable optical filtering using anisotropic and noncollinear acoustooptic interaction in LiNbO3waveguides

Theoretical and experimental studies of optical filtering which utilize anisotropic and noncollinear acoustooptic interaction in a -cut LiNbO3waveguide are reported. A guided-light beam from either an He-Ne laser at 6328 Å or an argon laser at around 5000 Å, propagating at an angle centering around 70° from the axis of the LiNbO3crystal, was Bragg diffracted by the surface acoustic wave with 500 MHz center frequency and propagating at 16° from the axis of the crystal. High optical resolving power, large optical angular aperture, and good spatial separation between the filtered light and the unfiltered light have been simultaneously achieved. An optical passband of 16 Å and an angular aperture of 9° have been measured for the case in which the undiffracted and diffracted light propagate in TE0mode and TM0mode, respectively. Furthermore, by varying the acoustic frequency from 350 to 670 MHz, the filtered optical wavelength may be tuned from 8300 to 5000 Å.