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All-Fiber Acousto-Optic Tunable Bandpass Filter Based on a Lateral Offset Fiber Splicing Structure

An all-fiber acousto-optic tunable bandpass filter has been proposed and experimentally demonstrated by fabricating a lateral offset fiber splicing structure between the lead-in single-mode fiber and acoustic fiber grating. In the presence of acoustic fiber grating that enables the coupling between the antisymmetric cladding modes and symmetric fundamental core mode, the proposed bandpass filter shows a broadband tunable wavelength range up to 152.9 nm with a wavelength tuning sensitivity of -206.07 nm/MHz through adjusting the acoustic frequency. Further experimental results indicate that by using HF acid to etch part of the fiber cladding, the largest tunable bandpass wavelength range could be expanded to 210.2 nm with an improved wavelength tuning sensitivity of -256.89 nm/MHz. Moreover, by adjusting the applied RF signal voltage, a dynamic peak transmission range in a magnitude of ~10 dB have been experimentally achieved.