Ultra-high birefringence and nonlinearity photonic crystal fiber with a nanoscale core shaped by an air slot and silicon strips

A novel polarization-maintaining photonic crystal fiber (PCF) with high birefringence and nonlinearity was designed and numerically optimized. By embedding high-index silicon strips and a low-index nanoscale air slot at the core region, X- polarization mode could be well confined in the low-index slot region due to the discontinuity of its electric displacement field vector at the silicon-air interface, whereas Y-polarization mode was dominated by total internal reflection (TIR) induced by elliptical air holes of the inner cladding, which resulted in a birefringence up to 10−1 order. Moreover, according to the antiresonant reflecting guidance mechanism, when the width of silicon strips was adjusted to 0.12 μm, an ultrahigh birefringence of ~0.94 at 1.55 μm could be obtained. In addition, benefiting from the tight field confinement and highly nonlinear silicon, an ultrahigh nonlinear coefficient of up to 2.4 × 106 W−1 km−1 can be achieved at the wavelength of 1.55 μm. Furthermore, the low confinement loss can also be yielded in our proposed PCF. With these advantages, the proposed PCF will offer important potential applications in optical communications, supercontinuum generation and other fields.