Characterizing and controlling extreme optical nonlinearities in photonic crystal fibers

The development of the photonic crystal fibers (PCFs or microstructured fibers) has been one of the most intellectually exciting events in the optics community within the past few years. The introduction of air-hole structures in PCFs allows for new degrees of freedom to manipulate both the dispersion and optical nonlinearities of the fibers. Not only the zero group-velocity-dispersion of a PCF can be engineered from 500 nm to beyond 1500 nm, but the extremely high optical nonlinearities of PCFs also lead to ultrabroadband supercontinuum generation (>1000 nm) when pumped by nanoJoules femtosecond Ti: Sapphire laser pulses. Therefore, PCF is an ideal system for investigating nonlinear optics.; In this dissertation, we present results of controlling nonlinear optical processes in PCFs by adjusting the input pulse properties and the fiber dispersion. We focus on supercontinuum, resulting from the extreme nonlinear processes. A simulation tool based on the extended nonlinear Schrodinger equation is developed to model our experiments and predict output spectra.; To investigate the impact of input pulse properties on the supercontinuum generation, we perform open- and closed-loop control experiments. Femtosecond pulse shaping is used to change the input pulse properties. In the open-loop (intuitively designed) control experiments, we investigate the effects of input pulse spectral phase on the bandwidth of supercontinuum generation. Furthermore, we use phase-sculpted temporal ramp pulses to suppress the self-steepening nonlinear effect and generate more symmetric supercontinuum spectrum. Using the genetic algorithm in closed-loops (adaptive) control experiment to synthesize the appropriate temporal pulse shape, we enhance the supercontinuum generation bandwidth and perform control of soliton self-frequency shift. For both the open- and closed-loop control, simulation results show good agreement compared with the experiment optimized spectra. To our knowledge, this is the first time that femtosecond pulse shaping has been used to control the pulse nonlinear propagations in PCFs.; We also develop a pulse compression model to study how the microstructured fiber dispersion characteristics can affect the supercontinuum temporal compressions. Using numerically simulated dispersion-flattened microstructured fibers at different wavelengths, simulation results show that it is possible to compensate the stable supercontinuum spectral phase and compress the pulse to the few-cycle regime.