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An ultra high-sensitivity temperature and refractive index (RI) sensor based on surface plasmon resonance (SPR) effect in D-shape high birefringence photonic crystal fiber (PCF) is presented and discussed by the finite element method (FEM). The designed PCF is polished to enhance the interaction of the evanescent field with the external medium, ultimately improving the sensing performance. The influence of three different plasma materials, gold, silver and aluminum, on the sensing performance was investigated. Finally, the chemically stable plasma material gold is selected to coat on flat surface of D-shape PCF for SPR sensing, realizing the sensitive real-time monitoring of RI and temperature. The sensing performance was greatly improved, with a wide RI (1.43 to 1.50) and temperature (36 $^{\circ }$ C to 86 $^{\circ }$ C) detection range, and the corresponding maximum sensitivity was 44850 nm/RIU and −16.875 nm/ $^{\circ }$ C, respectively. Furthermore, the sensitivity is not particularly sensitive to the sizes of the designed air holes, which leads to a sensor with high structure tolerance. Numerical results show that the coating thickness not only affects the sensitivity but also the detection range of the sensor, so we can tune the RI and temperature detection range by adjusting the gold film thickness to meet specific detection requirements. The sensor with enhanced sensitivity, tunable detection range, and high fabrication tolerance has a wide application prospect in the field of life science research, chemical production, and environmental monitoring. [ABSTRACT FROM AUTHOR]

A magnetic field sensor based on a Sagnac interferometer using a magnetic fluid-filled birefringent photonic crystal fiber (MF-BPCF) was proposed and studied by finite element method. Two large air holes in the birefringent photonic crystal fiber were designed to fill with magnetic fluid. The MF-BPCF in the proposed Sagnac interferometer acted as the sensing head. As magnetic field perpendicular to the MF-BPCF, magnetic fluid was anisotropic. The characteristics of the output spectrum of the Sagnac interferometer was simulated. The results showed that when the phase difference $\phi$ satisfied integer multiples of $2\pi$ , several dip wavelengths appeared. Not only the intensity but also the direction of the magnetic field was measured. The measuring sensitivity could be further promoted by making the dip wavelength approach $\lambda _{B_g=0}$. [ABSTRACT FROM AUTHOR]