Design Of Highly Nonlinear Photonic Crystal Fibers And Study On Transport Properties Of Ultrashort Laser Pulses

Highly nonlinear photonic crystal fiber has important applications in various areas such as ultrashort laser pulse frequency conversion, spectrum widening, pulse compression, wave breaking and so on. The effect of high nonlinearity can be achieved by minishing the area of core, increasing the air filling fraction or using the background material with large nonlinear refractive index. In this dissertation, the fundamental properties of nano-structured photonic crystal fibers and chalcogenide glass photonic crystal fibers which are transparency in the wavelength region from visiable to mid-infrared are studied. And the propagating properties of femtosecond pulse in nanostructured photonic crystal fibers are stimulated. Particular emphasis is on the wave breaking phenomenon.Firstly, the fundamental properties of nanostructured photonic crystal fibers are studied by using the electromagnetic scattering theory of multi-pole. It is found that the high nonlinearity, high birefringence and flexblity dispersion can achieved in the wavelength region of blue-green. For the design of photonic apparatus that apply to the wavelength region of blue-green devide a mean.Secondly, the fundamental properties of chalcogenide glass photonic crystal fibers which are transparency in the wavelength region from visiable to mid-infrared are studied. Finding that it can keep high birefringence, high nonlinearity, low confinement loss and flexibility dispersion in the region of from visible to mid-infrared. For the design of photonic apparatus that apply to the wavelength region of mid-infrared devide a method.Finally, the delivery of femtosecond laser pulses in the normal dispersio regime of nanostructured photonic crystal fibers are numerically studied by using the split-step Fourier method. The wave breaking phenomenon is studied. The appearance of oscillatory structures at the pulse edges and sidelobes at the edges of pulse spectrum are signs of wave breaking. Wave breaking distance, intense of the oscillatory structures and the broad of flat spectrum are associated with the dispersion parameter and nonlinear coefficient. Choosing the pulse with optimal parameters propagate in nanostructured photonic crystal fibers can achieve a broadband superflatten spectrum in a short length.