Optical Fiber Based Long-pulse Pumped Supercontinuum Laser Source And Its Stability Research

Supercontinuum (SC) radiation generated in optical fibers provides extremely bright light that is both broadband and well collimated enabling many applications in diverse areas of broadband spectroscopy, biophotonics, optical communications and optical frequency metrology, and has recently become a significant scientific and commercial success. The thesis is mainly devoted to the development of long-pulse pumped optical fiber based SC theory, research on SC spectral bandwidth extension and its stability, and techniques for wavefront measurement and beam shaping of high power laser diode array. The main achievements of this thesis are listed as follows.1. A numerical study of interactions between solitons and dispersive waves (DW) for supercontinuum generation in photonic crystal fibers pumped with long-pulses is investigated. We show how the soliton-induced trapping potential evolves along the fiber and affects the dynamics of a soliton-DW pair. Individual frequency components of the DW interact with the soliton yielding stepwise frequency up-shifting in the short wavelength edge of the supercontinuum. The ensemble behavior of all frequency components of the DW exhibits a quasi-continuous frequency up-shift. The step size of the frequency up-conversion and the temporal separation between subsequent soliton-DW interactions are governed by the form of potential well which confines the soliton-DW pair.2. Interactions between SC light pulses result in spectral broadening are investigated. This phenomenon was measured experimentally following our observation in numerical simulations that exhibit so called "temporal aliasing". This occurs in simulations with narrow time grids:as early parts of the SC pulse leave the computational time domain they ’reenter’ at the beginning and so interact with later parts of the evolving SC pulse. We show that this provides an effective model to predict the experimentally observed spectral changes. We show that SC spectrum obtained from500W peak power,5ps pulse duration and20ps separation twin pulses broadens141nm in simulation and143nm in experiment.3. We present an adaptive cut-on filter for analyzing fiber-length dependent properties of optical rogue solitons (RS), which are highly intense and extremely red-shifted solitons that arise during SC generation in photonic crystal fiber. We show that RS arise in different supercontinuum pulses at various positions along the fiber, and exhibit a lifecycle:their intensity peaks over a finite range of fiber length before declining slowly. This has consequences for the design of spectroscopic light sources:SC light generated in longer fibers contains a greater number of mature, declining rogue solitons. These outliers are responsible for significant instabilities near the edges of the emitted SC spectra.4. A new method for the wavefront measurements of high power laser diode array (HPLDA) with large dynamic ranges is presented. The wavefront sensor has a large dynamic range of-π/2to π/2and a high precision on the measured wavefront slopes. According to the measurements of the wavefront slopes and the intensity of high power laser diode arrays, the complex amplitudes can be obtained and the wavefronts can be reconstructed. A low-cost, easy producing beam shaping system for concentration and homogenization of HPLDA beam is demonstrated by experiment and simulation. It consists of silica tapers which are fabricated by using chemical etching technique. By using this device, the beam could be coupled into a200μm silica fiber with uniform intensity and angular distributions.