Dual‐Function SPR‐PCF for High‐Sensitivity RI Sensing and Tunable Ultrabroadband Polarization Filtering

A dual‐function surface plasmon resonance‐photonic crystal fiber (SPR‐PCF) with a double‐sided polished structure is proposed and numerically investigated. This PCF exhibits excellent performance in refractive index (RI) sensing and tunable ultrabroadband polarization filtering. For sensing, it demonstrates a high maximum wavelength sensitivity of 19 800 nm/RIU and the resolution of 5.05 × 10 −6 RIU in the RI range of 1.23–1.385. For filtering, by simply adjusting the thickness of the dielectric layer zinc oxide (ZnO) and the RI of analyte n a , a tunable ultrabroadband filter can be achieved. Notably, for a 100‐nm thick ZnO layer and n a of 1.51, the extinction ratio (ER) over a 700‐μm fiber length is 238.43 dB. The operating bandwidth with an ER above 20 dB is 610 nm, corresponding to an effective filtering range from 1.21 to 1.82 μm. In comparison, for a 10 nm thick ZnO layer and n a of 1.36, the ER reaches 302.10 dB over the same fiber length, with the bandwidth of 660 nm. The filtering range shifts to longer wavelengths, spanning from 1.34 to 2.00 µm. Owing to its simple structure and exceptional dual‐function performance, the proposed PCF presents a significant step forward in the integration and multifunctionalization of compact photonic devices.