Integrated optical components utilizing acoustooptic and electrooptic diffraction in micro-waveguides

The diffraction efficiency of integrated optics using microwaveguides with electrooptic and acoustooptic effects is calculated from truncated equations for coupled modes describing steady-state interaction of an incident wave and the wave diffracted by a surface acoustic wave, considering, specifically, Bragg diffraction of light. The resulting wave equation is solved either in the Wentzel-Kramers-Brillouin approximation or by piecewise-linear approximation. The result yields the dependence of diffraction efficiency on the voltage applied to the electrooptic phase grating. Theoretical data are correlated with experimental data on waveguides in Y-cut LiNbO3 crystals with 35 nm to 50 nm thick titanium films. Phase gratings were formed by interdigital capacitor arrays, for operation as modulator. Measurements were made in the Raman-Nath diffraction mode as well as in the Bragg diffraction mode.