Abstract
Since the first demonstration of noise-like-pulse (NLP) operation in the ring cavity of an Er: doped fiber oscillator, there has been tremendous interests in this special regime of pulsed lasers. In this dissertation, we describe our work on generation and amplification of medium- and high-energy noise-like pulses with Yb-doped fibers. We also demonstrate supercontinuum (SC) generation techniques where NLPs serve as the pump. Theoretical aspects as well as discussions about physical mechanisms which make NLPs distinguishable from regular mode-locked pulses are also discussed. SC pumped by NLPs has been employed successfully in optical coherence tomography (OCT) systems. The advantages of such approach as well as the promising features of NLPs for such applications are presented. Beginning with a brief description of the cavity configurations that are typically used in fiber laser oscillators, we then focus our attention on ring-type cavities where nonlinear polarization evolution (NPE) is involved in pulsed operation. We show that both regular Gaussian pulses and noise-like pulses can be achieved in the same cavity by choosing proper cavity components and adjustment. We analyze and compare two popular cavity configurations: dispersion mapped cavity and all-normal-dispersion (ANDi) one. Simulation results based on coupled nonlinear Schrodinger equations are supported by experimental measurements. Second part of the dissertation is about supercontinuum (SC) generation. Here we analyze the possibilities of efficient SC generation by using standard silica fibers. It is shown that unique features of NLPs make them very useful for such purpose. That is, the central wavelength of the pump and zero-dispersion wavelength (ZDW) of SC generation media is not critical. We show that even if the pump wavelength is deep in the normal dispersion regime (for example, ~1 μm where ZDW=1.33 μm), SC can be efficiently generated. Simulations and experimental results of SC generation by NLPs using different single-mode fibers are presented. We discuss the optimal selection of fiber types and other characteristics to generate flat SC in spectral region above 1 μm. The pros and cons of using specialty fibers such as photonic crystal fibers pumped by NLPs will also be elaborated. In the third part of the dissertation we consider the application of noise-like pulses for selected applications. The SC spectrum scheme is flat with a bandwidth of 365 nm centered at 1320 nm. The light source is successfully employed in a time-domain OCT, achieving an axial resolution of 2.3 μm. High resolution fiber-based spectral-domain OCT imaging of bio-tissue (onion skin), comparable to that obtained using a commercial swept source, is also demonstrated.