Source of sidelobe asymmetry in integrated acousto-optic filters

The often-observed extreme asymmetry in the sidelobe spectra of integrated acousto-optic filters exacerbates cross talk between wavelength-multiplexed optical channels. We explain the source of this asymmetry in terms of a systematic even-order variation of the effective waveguide birefringence as a function of distance from the device center. Calculations show what degree of nonuniformity in Ti-stripe thickness, width, or diffusion temperature are required to account for typical asymmetries. We describe two experiments in which temperature gradients were applied to low-power acousto-optic filters in order to induce sidelobe suppression on either side of the optical transmission function, while greatly enhancing sidelobes on the opposite side.