Design of an asymmetric gold-coated photonic crystal fiber (PCF) polarization filter based on surface plasmon resonance (SPR)

To obtain better filtering characteristics and transmission performance, an asymmetric gold-coated photonic crystal fiber (PCF) polarization filter based on surface plasmon resonance (SPR) was designed and investigated. The surface plasmon mode is generated by coating gold film to the inner walls of two liquid-filled holes along the y polarization direction. Three air holes with different diameters are introduced near the core which break the symmetry of the primary fiber structure and make the resonance wavelengths of the x polarization and y polarization of the core mode well separated. The filtering performances are evaluated with the finite element method (FEM) based software. The numerical simulation shows that the confinement loss of y polarization is as high as 1375.94 dB/cm at 1.55 mu m, while the x polarization loss is only 10.45 dB/cm. Furthermore, the crosstalk (CT) has a maximum of 1186.06 dB in the communication bands when the length of the fiber is 1000 mu m. In the range from 1.1 mu m to 2 mu m, the bandwidth of the filter is approximately 900 nm. The asymmetry of the structure and liquid filling of gold-coated holes enhance the coupling strength of the filter. Meanwhile, the higher confinement loss, crosstalk and wider bandwidth may have useful applications for polarization filters with significance for the design of other filters.