ALL-FIBER ACOUSTOOPTIC FILTER WITH LOW-POLARIZATION SENSITIVITY AND NO FREQUENCY-SHIFT

An acoustooptic tunable filter based on an all-fiber null coupler, exh ibiting low polarization sensitivity and zero net frequency shift, is demonstrated, The polarization dependence has been eliminated by simul taneously applying two acoustic waves that independently satisfy the p hase-matching condition for the two eigenpolarization states, A simple double-pass arrangement is employed to exactly cancel the net frequen cy shift and to provide an enhanced spectral sidelobe suppression of b etter than -17 dB.