Ultrabroadband polarization filter based on gold-coated PCF with high birefringence

Ultrabroadband polarization filter based on gold-coated photonic crystal fiber with high birefringence is proposed and analyzed by using the finite-element method. An elliptical central air hole is designed for high birefringence and shifting the wavelength of the loss peak. The gold layers are selectively coated on the inner surface of two elliptical air holes to support the surface plasmon resonance, which contributes to the filtering characteristics. By optimizing the structural parameters, a high extinction ra2tio is obtained of about 290.56 dB at a communication wavelength of 1310 nm when the length of L = 400 µm, and its bandwidth is ∼530 nm. In addition, the birefringence can reach near 0.004 at 1310 nm.