Improvement of coupling efficiency for an acoustooptic tunable filter and its prospects in sensing applications

In this paper, through structural parameter optimization, a highly efficient single-mode-fiber-based acoustooptic tunable filter is experimentally demonstrated. The mode coupling characteristics of the tunable filter consisting of an aluminum horn and a piezoelectric transducer with different geometrical settings have been compared, and experimental results show that the acoustic horn with a diameter of 8 mm and height of 8 mm yields a best coupling efficiency, corresponding to a transmission peak loss up to 9.3 dB, for mode coupling from LP01 core mode to LP12 cladding mode. To further increase its mode coupling efficiency, the fiber cladding is decreased to ∼50 μm by HF acid etching. In this way, an acoustooptic tunable filter with nearly 300 nm operation bandwidth has been achieved and its maximum transmission peak loss reaches about 12.5 dB. Moreover, the potential sensing applications of the proposed acoustooptic tunable filter has also been discussed.