SH-mode SAW and its acousto-optic interaction in KNbO3

The pure SH (shear horizontal) mode surface acoustic wave on rotated Y-cuts about the Z-axis of potassium niobate (KNbO₃) is theoretically analyzed. The results show that there exists a pure SH-mode surface wave, which has a velocity lower than the piezoelectrically inactive Rayleigh wave for most of the rotated cuts. The particle displacement of the SH-mode surface wave on Y-cut KNbO₃ has a depth profile different from that in 6 mm crystals. The electromechanical coupling factor K² ranges from a very large value of 0.53 to a relatively small value of 0.026, depending on substrate orientation. The collinear interaction between the SH-mode surface wave and optical waves in KNbO, is also theoretically analyzed. It is shown that both the photoelastic and electro-optic effects contribute constructively to the acousto-optic interaction and that the optical TE-to-TM mode conversion produced by the SH-mode surface wave is very efficient compared with that produced by the Rayleigh wave in Y-X LiNbO₃