Analysis and applications of acousto-optic interaction in optical fiber using two orthogonal acoustic waves

Acousto-optic mode coupling can be observed in single-mode optical fiber. The flexural acoustic wave couples the core mode to cladding modes, which are eventually absorbed in the fiber protective jacket. In this work we launched two acoustic waves with orthogonal vibration directions onto the fiber. The acoustic wave is generated by a newly designed transducer consisting of two shear mode piezoelectric discs. The two gratings formed on the fiber can couple different polarizations of core mode to different cladding modes, namely TE01, TM01, and HE 21. This coupling is highly polarization dependent and the polarization dependency changes as the polarization of the acoustic wave is changed. The theoretical explanation of polarization dependent coupling is developed, based on the coupled mode theory, and verified by experiments. In order to observe the coupling to TE01, TM01, and HE21 cladding modes, Dispersion Compensating Fiber is used as the medium for acousto-optic coupling. Due to the dispersion properties of this kind of fiber coupling to individual modes is discernable. Three different applications of the coherent coupling are discussed and experimental results are presented for each application.; Utilizing the highly polarization dependent coupling of the device and the fact that the polarization dependency of the mode coupling can be adjusted, a polarimeter is developed. Different acoustic polarizations are generated, which can couple different components of the core mode polarization to the cladding. Measuring the power in the cladding mode or the core mode loss it is possible to calculate the polarization of the core mode.; The ability to couple different polarization of the core mode to a single cladding mode using different acoustic polarizations allows us to build a polarization controller. We show that by choosing the right amplitude and phase for the two acoustic waves, it is possible to change the core mode polarization by partially coupling it to a cladding mode and coupling it back to the core mode with no loss.; Finally, the acousto-optic interaction between acoustic and optical vortices is studied. A new set of orthonormal fiber modes are introduced which are eigen modes of the spin and orbital angular momentum. It is shown that the spin of the optical modes cannot be changed during the coupling process but the orbital angular momentum carried by an acoustic vortex can be transferred to optical modes. This provides a method for creation and detection of optical vortex modes.