Design Of Highly Nonlinear Dispersion-Flattened Photonic Crystal Fibers And The Applications

Nonlinear effects in optical fiber can be used in optical communication and medical applications and so on. Photonic crystal fiber (PCF) is a new class of optical waveguide that enable light to be controlled in the ways not possible or even imaginable in conventional optical fibers. PCF possesses a series of unique properties which is impossible to achieve in conventional optical fibers, especially overall controllable dispersion properties, and high nonlinearity. Here, highly nonlinear PCFs with near-zero flattened dispersion which can be used in both optical communications and medical applications were proposed.The main works are as the followings:1) The fundamental of photonic crystal fiber was studied. Several different numerical methods were compared, then the finite difference method (FDM) with anisotropic perfectly matched layers was used to analyze the various properties of PCF.2) Highly nonlinear coefficient was realized by decreasing effective area. By controlling air hole diameter and pitch, a simple hexagonal PCF with only one kind of diameter was proposed, then the effects of changing inner different-ring diameter on properties of PCF were analyzed. According to this principle, a simple PCF was proposed, it has a high nonlinear coefficient of36.5W-1km-1at1.55μm, flattened near-zero dispersion of-0.3ps/(km.nm)-0ps/(km.nm) in1470nm-1570nm wavebands, and confinement loss of10-2dB/m. The proposed HN-HPCF can be used in Raman amplifier, and the switch gain was simulated.3) Highly nonlinear coefficient was obtained by adding germanium (Ge)-doped silica core in the center, two octagonal PCF (just the diameter of sixth ring was different) was proposed, the effect of changing the outer ring diameter was analyzed. And a flattened dispersion of less than-1.0ps/(nm.km) in75nm waveband (1265-1340nm), nonlinear coefficient of56.3W-1km-1at1.31μm was obtained. This HN-OPCF can be used in dental optical coherence tomography (OCT), and spatial resolution of penetration depth of the OCT was found to be around6.0μm.