Focused SAW induced sidelobe suppression of integrated acousto-optic tunable wavelength filters

Weighted-coupled integrated acousto-optic tunable filters (IAOTFs) provide significant sidelobe level suppression over conventional uniform-coupling IAOTFs whose sidelobe levels are higher than -9.4 dB. A single-stage low-sidelobe IAOTF in which the weighted-coupling is facilitated by focused surface acoustic waves along an interaction length as short as 6.0 mm is realized on a Y-X LiNbO₃ substrate, 8 mm in length. The measured performance characteristics of this weighted-coupling IAOTF at the optical center wavelength of 1.31 μm include peak mode-conversion at the acoustic center frequency of 214.6 MHz, a wavelength tuning range of 110 nm, -3-dB optical bandwidth of 4.1 nm, and a switching rise time of 0.965 μs. Sidelobe levels below -21.4 dB are achieved with mode-conversion efficiency of 15% and RF drive power of 160 mW