Polarization Control by Leaky Surface Acoustic Wave in Reverse-Proton-Exchanged LiNbO₃ Optical Waveguide

Polarization control of the optical guided wave in a new configuration using a reverse-proton-exchanged (RPE) LiNbO₃ straight waveguide and a leaky surface acoustic wave (LSAW) which propagates perpendicular to the straight waveguide was proposed. First, the perturbation of the dielectric tensor was estimated by using coupled mode theory. When a Love-type SAW on a proton-exchanged layer/YX-LiNbO₃ was assumed, comparable perturbations to those in conventional Bragg diffraction due to a Rayleigh wave were confirmed. Next, a sample device with an LSAW wavelength Λ of 136 µm was fabricated on YX-LiNbO₃ using an RPE channel waveguide. It was found that the incident linearly polarized wave was rotated by -90° in addition to the inherent rotation due to the perturbation of the LSAW without adding the LSAW wavenumber vector to the propagation constant of the incident optical guided mode. The maximum conversion efficiencies for optical wavelengths of 633, 532, and 473 nm were 87, 43, and 40%, respectively. The measured response time of 280 ns was almost equivalent to the time required for the propagation of the LSAW through the interdigital transducer width.