LOW-LOSS ALL-FIBER ACOUSTOOPTIC TUNABLE FILTER

We report significant advances in the development of simple all-fiber, tunable acousto-optic spectral filters based on null couplers. The pe rformance agrees well with theoretical predictions and is attributed t o improved control of the coupler uniformity. Furthermore, using a dou ble-pass arrangement, we demonstrate filter bandwidth reduction and Im proved sidelobe suppression of -20 dB. The double-pass configuration i s also shown to double the frequency shifts that are obtainable from s uch devices. (C) 1997 Optical Society of America