Optical signal processing in transverse acousto-optic waveguide-type functional devices with SAW

Among several optical devices, fundamental characteristics and processing systems of collinear optical switching device have been studied about optical dielectric waveguides on LiNbO3crystal substrates. Conventional waveguide-type A-O devices use collinear interaction with mode coupling based on Bragg condition between optical waves and SAW both propagating in same directions. Collinear A-O devices of waveguide-type show sufficient performance for wavelength selective switching with narrow bandwidths in case of low switch speed. However, in these collinear A-O devices, since SAW propagation speed is very slow, interaction time is several micro seconds for 10mm waveguide device length.In A-O devices of optical waveguides using transverse A-O interaction, where SAW propagates transversely and at right angles to optical wave propagation direction, SAW propagation lengths needed for complete A-O interaction may become 10μm and interaction time may be several nano seconds, with ultra high speed switching. Transverse A-O waveguides with SAW have high efficient and high speed switching characteristics of a few giga Hertz frequency bands. In this paper, fundamental characteristics of transverse A-O interaction are studied as electromagnetic boundary value problem. Field characteristics are discussed by Mathieu function expansion method and perturbation method for core and clad regions with acousto-optic effects due to SAW. Propagation constants and eigen mode fields of A-O waveguides are derived by perturbation method to solutions of Mathieu equations with A-O effects based on field expansions by normal eigen modes in slab waveguides satisfying boundary condition without A-O effects. Based on the optical characteristics in transverse A-O waveguides with SAW of high efficient and high speed switching characteristics, transverse A-O wave coupler and wave separator are concretely discussed. Mode couplings and switchings in transverse A-O waveguide devices consisting of coupled several optical waveguides controlled by SAW are shown.