An investigation of spectral broadening by nonlinear optical effects in photonic crystal fibers

Abstract

When a pulse of light with sufficient power moves through optical fiber its spectrum broadens as a result of nonlinear optical effects such as self-phase modulation, self-steepening, and stimulated Raman scattering. This spectral broadening is of great interest because it can be used to construct a simple wavelength tunable laser source for nonlinear optical microscopy. Nonlinear optical microscopy is a form of microscopy which utilizes nonlinear optical effects within a sample as a contrast mechanism. This includes effects such as second-harmonic generation, third-harmonic generation, and coherent anti-Stokes Raman Scattering. These forms of microscopy have been shown to have applications in medical imaging, including as possible tools for accurately diagnosing certain cancers. <br />This thesis explores the use of nonlinear optical effects to broaden the spectrum of ultrashort pulses of light. This is done through experimental work in which the effects of pulse energy, pulse duration, and fiber length on spectral broadening are explored. Numerical simulations of the equations of optical pulse propagation are also used in order to evaluate which effects dominate the spectrum of an ultrashort optical pulse, and to investigate the effect of pulse shape on the resulting spectrum. These results will be helpful in evaluating the usefulness of spectral broadening in optical fiber in the construction of a wavelength tunable laser source for nonlinear optical microscopy.