Excitation of surface plasmon resonance with sodium-based photonic crystal fiber for sensing applications

Abstract

Surface plasmon resonance (SPR) sensors using precious metal excitation have encountered bottlenecks in performance enhancement. To address this issue, we propose a photonic crystal fiber (PCF) sensor that utilizes a polymer-protected sodium film to excite the SPR effect. The PCF has hexagonally arranged air holes and a polishing plane. The sodium film is deposited on the polished plane and protected with polymethyl methacrylate or polydimethylsiloxane for refractive index sensing or temperature sensing. We analyzed this structure using the finite element method and found that the sodium-based SPR sensor has greater sensitivity, wider detection range, and higher figure of merit (FOM) than the SPR sensor using precious metal excitation. Numerical results showed that the maximum sensitivity was 35,400 nm/RIU, the widest detection range was 1.22–1.42, and the highest FOM was 3550RIU−1 at different sodium film thicknesses. When applied to temperature sensing, its maximum sensitivity is 20.5 nm/°C, and the temperature detection range is 0°C–100°C. In addition, our proposed sodium-based SPR fiber sensor is compatible with a thermo-assisted spin-coating process, so a good guideline scheme is available for the preparation. Therefore, our proposed sensor shows excellent potential in sensing and expands the application range of sodium-based plasma devices.