Highly Nonlinear Chalcogenide Core Nanofiber and Photonic Crystal Fiber Showing Zero Dispersion at 1.55 μm

摘要

We present the design of the chalcogenide (As_2S_3) glass nanofibers with the nonlinear tellurite glass as the cladding material. Both of these glasses have high nonlinearity. We show that the simple step index structure with tellurite cladding has the normal dispersion in the telecommunication window for any value of the core diameter, ranging from the sub-wavelength size to a few micro-meters. The dispersion achieved is flat so as to be applicable to dispersion compensating devices. However, the dispersion can not be tailored to zero. So we propose the photonic crystal fiber (PCF) structure, which has six circular identical air holes introduced in the tellurite cladding around the chalcogenide core. The air holes introduced cause the decrease in the effective cladding index. This structure shows anomalous dispersion in the telecommunication band with two zero dispersion wavelengths. With further optimization the structure can show zero flattened dispersion. We study the effect of the various design parameters - the chalcogenide core diameter, the air hole diameter, and the pitch, that is the distance between the centers of two neighbouring air holes, which is same as the distance between the center of the core and any of the air holes. We optimize the design to achieve zero slope (flattened) at the zero dispersion wavelength, 1.55 μm. The thermal characteristics of tellurite glass match with the chalcogenide making the fabrication of the chalcogenide core PCF with the tellurite glass as a cladding material feasible. We also present the calculation of the nonlinearity of the PCF.