Propagation loss characterization in metal-coated microstructured fiber for multiparameter sensing

Abstract In this paper, we propose and theoretically analyze an ultra-compact microstructured fiber (MSF) sensor for multiparameter sensing. The MSF is based on a photonic crystal fiber (PCF) with four air holes, two of which are polished to form open semicircular holes. Silver film can be easily coated on the surface of these semicircular holes to excite surface plasmon resonance (SPR). Polydimethylsiloxane (PDMS) is deposited in one semicircular hole, while the other semicircular hole directly interacts with the surrounding environment. Owing to the flexible fiber structure, the effective refractive index (RI) of core mode can be readily tuned to match RIs of the plasmonic modes around the metal films. Phase matching induces two hybrid plasmonic modes that distribute both in the MSF core region and the two semicircular holes. The hybrid mode in PDMS region exclusively responds to temperature variations, exhibiting a sensitivity of −3.2 nm/°C over the range of 30 °C to 60 °C. In contrast, the hybrid mode in the other semicircular hole only responds to RI change, with a sensitivity of 2312 nm RIU −1 in the RI range of 1.30 to 1.33. Furthermore, by polishing a third air hole into open semicircular hole and coating it with magnetic fluid (MF), three environmental parameters—temperature, RI and magnetic field (with a sensitivity of 0.78 nm mT −1 over 10 mT to 40 mT)—can be measured simultaneously.