A Compact and Broadband Photonic Crystal Fiber Polarization Filter Based on a Plasmonic Resonant Thin Gold Film

A novel high birefringence gold-coated photonic crystal fiber (PCF) polarization filter based on surface plasmon resonance is proposed. The six elliptical holes arranged in a specific mode surrounding the core are utilized to gain high birefringence, and gold is coated inside the air holes to generate surface plasmons. By improving structural parameters, we achieve one state of polarization to propagate through the filter whereas the other state is severely attenuated. Specially, in the 1550 nm communication band, the confinement loss of y-polarized mode can reach 442 dB/cm while the corresponding loss of x-polarized mode is only 0.0316 dB/cm. The distinction between two losses is more than 10 000 times. In addition, when the length of the designed PCF filter is 1 mm, an extinction ratio of 326 dB/cm is obtained. The applicable bandwidth is up to 300 nm while the fiber length is merely 50 μm, which is better than other reported literatures. Owing to above-mentioned characteristics, the proposed polarization filter can be widely applied in compact and broadband filters in the communication band.