Optical Mode Converter Using Lamb Wave

A Lamb wave propagating through a crystal induces refractive-index variations in the crystal due to its photo-elastic effect; this crystal forms a phase cyclic structure. Therefore, if an incident light is transmitted into this crystal, light diffraction and mode transformation occur. In this study, we theoretically and experimentally examined light-wave propagation in a crystal in which Lamb waves had caused cyclic variations in the refractive index. In the experiment, it was verified that the Lamb wave power required for 100% mode conversion is 4 mW/mm in a LiTaO3 substrate with a Lamb wave wavelength of 132 µm and a substrate thickness of 50 µm.