An investigation of nonlinear core fiber structures for optical limiting applications.

摘要

This thesis presents a detailed study of optical limiting in a nonlinear core optical fiber array for picosecond and nanosecond laser pulses. The nonlinear optical effects are introduced, explained and discussed as they relate to the limiting characteristics of the fiber array. A theoretical model is presented to simulate the limiting mechanisms within the fiber array due to the photonic processes of linear absorption, intermediate state absorption, two-photon absorption, excited state absorption and reverse saturable absorption. This model requires knowledge of the nonlinear coefficients from the core material being used in the fiber array to make it accurate, therefore a method of measuring these nonlinear coefficients is presented and the measurements are carried out on the nonlinear core materials. The results of this simulation, combined with the measured nonlinear coefficients, are compared to the actual experimental results to demonstrate the veracity of the model and explain the limiting process in the picosecond time regime. This model is also compared to experimental results from the nanosecond time regime and is shown to not work. This failure to accurately model the nanosecond limiting response verifies the argument that the thermal/density nonlinear effects, which are not included in the model, contribute significantly to the limiting at this time scale. The temporal response of the transmission through the nonlinear fiber array is measured and demonstrates how the fiber array may provide protection into the millisecond regime.; The nonlinear core fiber array faceplate is designed to be used in an imaging system to protect delicate sensors or the human eye. To this end the imaging capabilities of the fiber array are demonstrated.