Elliptical-hole PCF structure with selective Y-axis gold coating for tunable single-polarization band-stop filtering

Abstract

An elliptical-hole photonic crystal fiber (PCF) based on surface plasmon resonance (SPR) is proposed, which can work as a tunable single-polarization band-stop filter (BSF). Theoretical results show that the proposed structure is very sensitive to the polarization of the guided modes, due to its high birefringence coefficient and strong SPR effect. It can achieve single-polarization single-mode (SPSM) filtering without liquid filled in the gold coated air holes. At resonant wavelength, the loss of the y polarization fundamental mode reaches 792.16 dB cm−1, but the loss of the x polarization fundamental mode is only 0.52 dB cm−1, causing that the extinction ratio is as high as 688 dB and the bandwidth is larger than 520 nm with the PCF length of 1 mm. When liquids with the refractive index (RI) ranging from 1.44 to 1.48 are filled in the gold coated air holes, the PCF could be used as a BSF to filter the x polarization fundamental mode selectively on the premise of SPSM filtering. And the center wavelength of the BSF is extremely sensitive to the liquid RI with a high sensitivity of 16 820 nm/RIU, which indicates a potential application in RI sensing. The proposed PCF realizing the integration of SPSM filter and BSF is available for compact optical communication systems.