Integrated-optic acoustically tunable reflection filter

We demonstrate a two-stage, integrated-optic, acoustically tunable filter formed by reflecting the output of a single stage acousto-optic filter back through the filter by means of an integral mirror. Relative to a single-stage device, this double-pass configuration provides greatly improved sidelobe suppression (to approximately -20 dB) and a 72% reduction in filter bandwidth (to less than 0.9 nm at a wavelength of 1.52 microm). The performance of this device is shown to be equal to the far more difficult to fabricate cascaded pair of strictly matched acousto-optic filters.