Acousto-optic interaction in proton-exchange 128° rotated Y-cut LiNbO3 optical waveguides

The characteristics of proton-exchanged optical waveguides using a new substrate of 128° rotated Y-cut LiNbO3 were investigated. The variation of refractive index was found to be Δn≂0.07, because the crystallographic c axis was oblique to the surface normal. As a result, the number of guided modes versus the depth of proton exchange was small compared with that in conventional substrates. Acousto-optic interaction between a guided mode and surface acoustic wave exhibited the diffraction efficiency of about 50% for the acoustic power of 18 mW at 130 MHz. This suggested that after the proton-exchange process, an apparent photoelastic coefficient was still maintained with the reduction factor of 1/ 7/8 .