Theoretical Study On Hybrid Photonic Crystal Fiber And Experimental Research On Photonic Crystal Fiber Supercontinuum

This paper introduced on the structure design, transmission theory and characteristics of the hybird photonic crystal fiber, as well as the supercontinuum experiments of the nonlinear photonic crystal fiber. Theoretically, the full vector finite element method and the multipole method are applied to simulate the characteristics of the the hybrid photonic crystal fiber. The cluster-multi-core photonic crystal fiber which possesses both the large effective mode area and the high nonlinearity is designed in order to produce high-power supercontinuous spectrum. The fundamemd wave and second harmonic wave are used to generate supercontinuum in the highly nonlinear photonic crystal fiber, providing evidence for the mechanism research of supercontinuum generation in photonic crystal fiber. The relevant research mainly includes the following aspects:1 The transmission characteristics of the hybrid photonic crystal fiber with the change of the core refractive index were studied in theoretics. The light transmission characteristic is also simulated with the increase of the core refractive index. We found:â‘ if the core refractive index is smaller than the effective refractive index of the air holes in the hybrid cladding, the transmission mechanism of the core mode is"double-bandgap mechanism";â‘¡if the core refractive index is between the effective refractive index of the air holes and that of high refractive-index cladding, the transmission mechanism is"single bandgap + total internal reflection mechanism";â‘¢if the core refractive index is larger than the effective refractive index of the high refractive-index cladding, the transmission mechanism is"total internal reflection mechanism".2 We discussed in detail the relationship between the transmission properties and structure parameters of these two kinds of hybrid photonic crystal fiber, i.e. the"total internal reflection + bandgap"and the"two bandgaps: general bandgap structure + antiresonant bandgap". The hybrid photonic crystal fiber is composed with a inner single cladding and a outer cladding. Contrary to the ordinary photonic crystal fiber of single structure, this newly designed photonic crystal fiber possesses two kinds of transmission mechanisms.3 The photonic crystal fiber with high nonlinearity and large mode area was designed in theoretics. Reduction in the core diameter can increase the nonlinearity of the photonic crystal fiber, and meanwhile the pumped light has to be confined into an even smaller core area, thus the power density of the core area rises accordingly, which will easily cause damages to the fiber surface. In order to solve this problem, we designed two kinds of photonic crystal fiber, i.e. the cluster-solid-core photonic crystal fiber and the cluster-multi-core photonic crystal fiber, both of which possess large mode area in the whole and high nonlinearity in parts.4 The experimental research on the supercontinuum of the high-nonlinear photonic crystal fiber was carried out in this paper. The mixture light is pumped to highly nonlinear photonic crystal fiber of different structures. The working mechanism of this double-light-pumping is discussed in this paper. After the process of the tapering technology, two zero-dispersion photonic crystal fibers are obtained; the fundamemd wave and second harmonic wave are pumped into the tapered photonic crystal fiber with different power, producing wide supercontinuum.