Abstract:
This Thesis presents a series of experimental and numerical investigations of nonlinear frequency conversion processes in both optical fibers and microresonators. In the context of optical fibers, we consider the cascaded four-wave mixing dynamics that underlie the interaction between solitons and linear waves, while in microresonators we look in detail at the formation of optical frequency combs and their properties. We first consider the interactions between solitons and weak linear waves co-propagating in an optical fiber. Through comprehensive experiments and simulations, we demonstrate the equivalence between soliton-linear wave interactions and cascaded Bragg scattering. The observed dynamics are also interpreted in terms of fiber-optic analogues of event horizons. We also investigate cascaded four-wave mixing processes in optical fibers in the absence of weak input linear waves. Specifically, we examine the excitation of a higher-order sideband that is phasematched through the cascade, and study how the efficiency of this excitation depends on the frequency detuning between the two continuous-wave pumps that initiate the four-wave mixing process. We find that the pump separation has a significant effect on the conversion efficiency to the phasematched sideband, which we explain by treating the individual cycles of the pump beat note as independent higher-order solitons. In the study of microresonators, we quantify the coherence properties of different microres-onator frequency combs. By passing the resonator output through a delayed interferometer, the modulus of the complex degree of first order coherence can be extracted from the spectral fringes. In addition to allowing for the quantitative assessment of comb coherence across the full bandwidth, we demonstrate how this method can be used to experimentally determine the comb operating regime. Finally, we demonstrate for the first time the formation of temporal cavity solitons in silica microspheres, and experimentally verify the high coherence of the resulting frequency combs. Further experiments and numerical simulations are carried out to investigate the influence of perturbations on the generation of microresonator cavity solitons.