Characteristics Of Photonic Crystal Fibers,Waveguides And Their Applications

We investigate the dispersive properties of photonic crystal fibers (PCFs), the unidirectional transmission of slab waveguides containing photonic crystal defects, and their application in the design of optical devices by theoretical analysis and numerical simulation.Firstly, the dispersion properties of PCFs with hybrid core are systematically investigated by using the plane-wave expansion method. It shows that an ultraflattened dispersion range of more than 800 nm in which the variation of dispersion is less than ±0.6 ps·km^-1·nm^-1 can be achieved at ～1.55μm by optimizing the structure configuration. Also, the coupling characteristics of the dual-core PCFs with elliptical air holes are utilized to realize the polarization splitters. By using the full-vector beam propagation method, we find that a polarization splitter with an extinction ratio better than -20 dB at 1.55 μm and a total length of only 1.651 mm can be developed. The length of the splitters can be further reduced by properly doping the core region of the PCFs.Secondly, we investigate the unidirectional transmission behavior of slab waveguides containing photonic crystal defects with nonlinearity by using the coupled mode theory, focusing on how to enhance the transmission contrast. Although the unidirectional transmission originates from the asymmetric configuration and nonlinear property of the structure, it is revealed that the maximum transmission contrast depends mainly on two linear factors. For two coupled defects, they are the highest order of the frequency detuning appearing in the transmission formula and the frequency splitting due to the coupling. Our analyses are supported by the numerical simulations based on the finite-difference time-domain technique. An enhancement of the maximum transmission contrast by an order of magnitude is achieved in the structure consisting of two coupled defects.