Applications of fiber acousto-optic tunable filters in optical communications and sensors

The vision of "all-in-the fiber communication" that incorporates tunable fiber lasers, fiber modulators, and dynamic wavelength add-drop fiber grating modules represents the ideal physical platform for optical networks. All-fiber acousto-optic tunable filters (AOTFs) are one of the promising devices applied in the wavelength divisions multiplexing systems. Currently it has been commonly used in tunable spectral filter, optical switch, tunable attenuator and dynamic gain equalizer of EDFAs.; In this dissertation, we begin by first explaining the acousto-optic mode coupling between core and cladding modes in single-mode optical fibers induced by a single acoustic flexural wave. The flexural wave (microbending) induced mode-coupling is analyzed and method of bending measurement is proposed. The "acousto-optic interaction" phenomenon is then extended to coherent coupling between optical wave and two acoustic waves vibrating in orthogonal directions. Coherent acousto-optic coupling provides both amplitudes and the phase control of individual acoustic waves, which results in novel mode coupling processes that open up many new applications.; We applied coherent acousto-optic mode coupling to dynamic compensation of the polarization-dependent loss in both x and y axes over a widely tunable wavelength band. The process is analyzed theoretically and demonstrated on a Polarization Maintaining Fiber (PMF). We also implemented a novel tunable bandpass filter by transforming the notch-filter response of an AOTF using the coherent couplings inside a Sagnac interferometer. This novel bandpass filter is used to demonstrate a tunable single-wavelength laser and for the first time, a wavelength-selectable dual-wavelength fiber laser. The dynamic response of this tunable laser is also investigated.