Suppression of sidelobe levels for guided-wave acousto-optic tunable filters using weighted coupling

An analysis of guided-wave acousto-optic tunable filters (AOTFs) that employ simple acousto-optic (AO) weighted coupling techniques for sidelobe reduction and the calculated and experimental results from a specific example that involves only variation of the width of a surface acoustic wave (SAW) slot waveguide are presented. The calculations on single- and multi-stage AOTFs consisting of an optical channel waveguide and a SAW slot waveguide in LiNbO(3) substrate show that waveguide width weighting using generalized Hamming functions would provide significant improvement in sidelobe suppression. Calculated results together with the design, fabrication, and measured performance characteristics of a single-stage AOTF that utilizes a weighted-aperture SAW slot waveguide in YX-LiNbO(3) substrate at the optical wavelength of 1.55 mum and the acoustic center frequency of 175 MHz are reported. The measured sidelobe level is -13.6 dB and the measured FWHM bandwidth is 26 A, as compared to the theoretical values of -15.0 dB and 15 A, respectively. The RF drive power was measured to be 1.0 W at a mode-conversion efficiency of 100%