Design and Theoretical Analysis of a Dual-Polarized Quasi D-Shaped Plasmonic PCF Microsensor for Back-to-Back Measurement of Refractive Index and Temperature

We present a new quasi D-shaped plasmonic photonic crystal fiber (PCF) microsensor with dual polarization for back-to-back measurement of refractive index (RI) and temperature. The PCF structure of the microsensor is form birefringent and supports two orthogonal polarizations for independent probing of both RI and temperature variations. Thin layers of tantalum pentoxide (Ta2O5) and gold (Au) are applied to the side-polished plane to form the RI sensing section. Furthermore, four micro air holes in the lower part of its outer cladding ring are gold-coated and selectively infiltrated with a temperature-sensitive liquid. A detailed investigation and numerical analyses of the coupling characteristics and sensing responses are presented using the finite element method (FEM) with a circular perfectly matched layer (PML). The RI metrics show a maximum wavelength sensitivity of 5000 nm/RIU and a maximum amplitude sensitivity of 266.54 RIU−1 from 1.35 to 1.46 RI range in the specified operating wavelength range of 1.25- $1.65~\mu \text{m}$ . The corresponding RI resolution is $2.0\times 10^{-5}$ RIU. For the temperature sensing metrics, a maximum amplitude sensitivity of $4.8\times 10^{-2}\,\,^\circ \text{C}^{-1}$ , a maximum wavelength sensitivity of 3.0 nm/°C, and a maximum resolution of $3.33\times 10^{-2}\,\,^{\circ }\text{C}$ from −50°C to 50°C is achieved. With appropriate instrumentation incorporating a polarization selector, the microsensor can double as a real-time simultaneous multiparameter sensor. Applications for the proposed microsensor can be found in molecular science, medical measurement and analysis, terrestrial environmental engineering and data assessment, aquatic ecosystem investigations, pharmaceutical and alimentary process control and validation, cryogenic studies, and several others.