1f:T524,A photonic crystal fiber (PCF) made of silicon is proposed and numerically optimized with both ultrahigh birefringence and nonlinearity. By introducing an elliptical low-index slot in the core region, one of the orthogonally polarized fundamental modes can be confined in the low-index region due to the discontinuity of its electric field at the interface of the slot and the surrounding material, while the other fundamental mode is dominated by the modified total internal reflection (MTIR) induced by air holes of the cladding, leading to a birefringence as high as 10 ^-1 order. On the other hand, benefiting from the tight field confinement and highly nonlinear material, nonlinear coefficients up to 1068 W ^-1 · m ^-1 and 162 W ^-1 · m ^-1 can be achieved for the slot mode and the MTIR mode, respectively.20:T463,A novel (to our knowledge) type of photonic crystal fiber (PCF) with high nonlinearity and flattened dispersion is proposed. The propagation characteristics of chromatic dispersion, effective area, and nonlinearity are studied numerically by using the full-vector finite element method. Several PCF designs with high nonlinearity and nearly zero flattened dispersion or broadband flattened, and even ultraflattened, dispersion over different wavelength bands are obtained by optimizing the structural parameters. One optimized PCF has a nearly zero ultraflattened dispersion of 2.3 ps/(nm·km) with a dispersion variation of 0.2 ps/(nm·km) over the C+L+U wavelength bands. In addition, the dispersion slope and nonlinear coefficient at 1.55 μm can be up to 2.2×10−3 ps/nm2·km and 33.2 W−1·km−1, respectively. The designs proposed in this paper have bright prospects for applications in all-optical format conversion, supercontinuum generation, optical wavelength conversion, and many other fields.

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