Modified D-type surface plasmon resonance (SPR)-based photonic crystal fiber (PCF) for application as a polarization filter and refractive index sensor

Abstract A surface-modified D-type photonic crystal fiber (PCF) based on surface plasmon resonance (SPR) is reported for application as a polarization filter and refractive index sensor. The gold film is deposited on the surface of the designed fiber structure to stimulate the SPR effect. Through etching, the upper surface of the designed structure forms an angle of 170°. The etching angle changes the distance between the fiber core and the surface of gold film to enhance the local field SPR effect. The designed optical device is numerically simulated using the finite element method (FEM), the mode distribution is studied, and the coupling phenomenon is analyzed. At a wavelength of 1.31 µm, the y-polarization loss is 1307.90 dB/cm, while the loss of x-polarization is 1.13 dB/cm; at 1.55 µm, the y-polarization loss is 1755.19 dB/cm, while the x-polarization loss is only 1.24 dB/cm. In the case of the same structure parameters as the proposed polarization filter, of which communication window is 1.55 µm, the designed structure also serves as a refractive index sensor from 1.330 to 1.365. The average sensitivity of the refractive index sensor is up to 4857 nm/RIU, and the highest sensitivity is 7588 nm/RIU when the refractive index is 1.365. The results show that the reported SPR-based PCF simultaneously implements dual communication window polarization filtering and refractive index sensing. Hence, the designed device has promising applications with good filtering and sensing performance.