Research Of Supercontinuum Modes Output From Photonic Crystal Fiber

Supercontinuum is widely used in optical frequency measurement, WDM communication systems and optical coherence tomography for its excellent properties. So it has a rapid development since it was discovered last century. This article focus on supercontinuum generation in photonic crystal fiber(PCF) in theory, and have got supercontinuum source in subsequent experiments. Firstly, a brief introduction of the development? application and history of ultra-fast laser technology?photonic crystal fiber and supercontinuum source are included in this article. Then, formula derivation of Maxwell equations to receive nonlinear Schrodinger equation that can show the pluses evolution in optical fiber. And then introduce self-phase modulation and cross-phase modulation, which are the main cause of the most nonlinear broadening, that caused by changes of the optical fiber refractive index brought by the intensity of incident light, and describe other nonlinear effects cause spectrum broadening, such as stimulated Raman scattering caused by Raman effect and four-wave mixing when phase matching. Finally, theoretical studies and obtained a supercontinuum Bessel beams in experiment, and mode shaped from seven core PCFs by Kagome fiber. The main contents include:1. Theoretical study of the principles and characteristics of Bessel beams, numerical simulation of Bessel beams generation from photonic crystal fiber with a negative axicon on fiber end and studied its caractristics of self-healing and diffraction free. Broadband spectrum Bessel Beams directly output from a nonlinear photonic crystal fiber are designed. A femtosecond laser beam from a nonlinear polarization evolution laser system is directly coupled into a nonlinear photonic crystal fiber that collapsed 1 mm by a fiber fusion splicer to enable the direct generation of broadband spectrum Bessel Beams due to the modes coupling and coherent superposition at the collapsed district. The system operation can achieve full fiber without any other discrete devices. The broadband spectrum Bessel Beams directly output from photonic crystal fiber have diffraction-free propagation in meter-scaled free space and are proved to have the characteristics of diffraction free and selfheal in all spectrum.2. Theoretical studies mode feature of seven core PCFs and characteristic of Kagome fiber. Femtosecond pulse coupled into a seven core PCFs to generate supercontinuum beams containing lots of supermodels. Reply on characteristics of Kagome fiber, broad band transmission spectrum and support one mode in fiber core, to shape modes from seven core PCFs. When adjusting the continuous light grazing in Kagome fiber, we can got a well base mode output.