100% Efficient narrow-band acousto-optic tunable reflector using fibre Bragg grating

We report a 100% efficient Bragg-grating-based acoustooptic superlattice modulator in a fibre whose diameter is reduced by HF etching. The acoustically-induced reflections, which appear on both sides of the Bragg stop-band, are tunable by altering the acoustic frequency, and have bandwidths corresponding to weak versions of the permanent Bragg grating. These unique properties may lead to important applications in, e.g., reconfigurable wavelength-division-multiplexing, Q-switching, amplitude modulation and frequency shifting. We also show that the acoustooptic superlattice effect is a sensitive diagnostic tool for assessing the uniformity of long, strong Bragg grating