Diffraction of guided optical waves by surface acoustic waves in GaN

We report on acousto-optical diffraction of the guided optical modes (λ=633 nm) in GaN layers grown on (0001) sapphire substrates. The diffraction of both transverse electric (TE) and transverse magnetic (TM) modes has been observed. The dependence of the diffraction efficiency on the surface acoustic wave (SAW) power is in good agreement with Raman-Nath theory. The values of acousto-optic figure of merit, M2, and effective photoelastic constants p have been determined. For the SAW propagating in [11̄00] direction, the extracted values are M2=1.54×10−15 s3/kg, p=0.061 (TE modes) and M2=1.95×10−15 s3/kg, p=0.066 (TM modes). These values of M2 correspond to 1 and 1.3 of the acousto-optic figure for fused quartz. The obtained results demonstrate the potential of GaN-based structures for the development of blue–ultraviolet acousto-optical devices.