Photonic crystal fiber devices based on acousto-optic effect

Abstract

This thesis investigates photonic crystal fiber devices based on acousto-optic effect. Firstly, We report an all-fiber acousto-optic tunable filter based on a two-mode photonic crystal fiber. The properties of photonic crystal fiber allow us to demonstrate a single notch-filter tunable from below 700 to 1700 nm with a single acoustic transducer. The dynamic tuning range is over 5 times larger than conventional fiber. In addition, the 3-dB bandwidth of the resonant notch changed from 5 to 6 nm for whole optical wavelength. The extreme dynamic range coupled with small insertion loss and fast response time $(~100 \mu s)$ makes this device promising for ultra-wideband optical systems. Furthermore, band-pass filter using chirped and appodized static long period grating after acousto-optic region is proposed. Secondly, we theoretically and experimentally analyze the structural irregularities in the highly birefringent photonic crystal fiber. Numerical simulation shows that small deviation in the symmetry of air-hole structure can cause non-negligible birefringence non-uniformity in the highly photonic crystal fiber. Form birefringence change caused by small structural irregularities are measured by acousto-optic coupling between two orthogonal polarization modes propagating along the fiber using torsional acoustic wave. Because the torsional acoustic wave has no dispersion in the fiber whose diameter is much smaller than acoustic wavelengths, the birefringence non-uniformity measured via the acousto optic coupling is purely originated from the structural irregularities in the air-hole structure. Finally, We proposed and simulated the broad-band and narrow-band directional coupler using finite element method(FEM). The calculation is based on the ``normal mode theory`` and we analysis the energy transference as a function of wavelength using the coupling length deviation. Broad-directional coupler can be achieved using material dispersion between effective index...