Characteristics On The Supercontinuum Generated In Photonic Crystal Fibers

Photonic crystal fibers (PCF) have permitted significant progress in various domains such as nonlinear optics, medical science and telecommunication for its great flexibility in design and unique optical properties. Small core photonic crystal fibers have proven to be the most important way for the generation of supercontinuum (SC). The principle for supercontinuum generation is the interaction among many nonlinear effects in fiber which can lead to an unltra-broad bandwidth spanning more than two octave. Supercontinuum source has widely applied in many fields such as optical communication, optical coherence tomography (OCT), optical metrology, biology and pulse compression. This thesis is mainly focused on the experimental analysis on the supercontinuum generated in different photonic crystal fibers and the coherence and properties of it. The second harmonic of supercontinuum is also attained in experiment. The main contents can be summarized as following:1. A detailed content is used to introduce the principles, characteristics, preparations and applications of photonic crystal fiber. Theories about the nonlinear effects and propagation of ultra-short pulses in fiber are also introduced briefly.2. Experiments on the supercontinuum generation using different pump sources and photonic crystal fibers are carried out and abundant experimental results are attained. Supercontinuum with bandwidths of 850nm and 400nm are generated from the polarization-maintaining (PM) and high nonlinear photonic crystal fibers which are pumped by Ti: sapphire femtosecond (fs) laser. The lengths of the fibers used above are 0.5m and 1.5m respectively. The maximum power of SC is 110mW by using the PM-PCF. Supercontinuum with bandwidths of about 700nm and 750nm are generated in photonic crystal fibers with zero-dispersion wavelengths at 1550nm and 800nm which are pumped by microchip solid-laser. The lengths of the PCF are 100m and 30m, respectively. Mode-locked Er³⁺ fiber laser which generated 60fs pulses at 1550nm is used as source to pump PCF with zero dispersion wavelength at 1550nm to generated supercontinuum. The bandwidth of the SC is more than 450nm.3. Based on the theory of partial coherence, the temporal and spatial coherence properties of SC generated from PM-PCF are experimentally analyzed by using Michelson interferometer with different experimental schemes. The coherence lengths of SC and Ti: sapphire fs laser are calculated to be 6.5μtm and 59.14μm, respectively. The degree of coherence of SC at zero point is measured to be 0.77 which is an indication of good spatial coherence property. The evolution of temporal coherence property of SC with different spectral bandwidth is also investigated.4. The second harmonic of supercontinuum generated from PM-PCF pumped by Ti: sapphire laser is experimental investigated by using a BBO crystal with a thickness of 0.05mm. Various second harmonic lights are observed in experiment. The second harmonic of laser from Ti: sapphire laser is also investigated by two BBO crystals. The thicknesses of BBO crystals used here are 3mm and 0.05 mm, respectively. The frequency doubled phenomena are both very salience.