In this paper, a dual hollow-core negative curvature fiber is proposed for the polarization beam splitter. The effects of the structure parameters of the dual hollow-core negative curvature fiber on the coupling length and coupling length ratio of the x -polarized and y -polarized core modes and the higher-order mode extinction ratio are analyzed by the finite element method. Moreover, the normalized output powers of the x -polarized and y -polarized modes in the cores A and B and the corresponding extinction ratio are also investigated by the mode coupling theory. The simulation results show that a dual hollow-core negative curvature fiber polarization beam splitter with the length of 6.45 cm can achieve a broad bandwidth of 400 nm (1.23–1.63 µm), covering the O + E + S + C + L communication band. In addition, the higher-order mode extinction ratio is greater than 100 in the considered wavelength range, which means that it has good single-mode characteristics. It is believed that the proposed dual hollow-core negative curvature fiber polarization beam splitter will have significant applications in the optical communication system.

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An ethanol and gold wires-filled single-polarization hollow-core negative curvature fiber is proposed for temperature sensing. The average sensitivity and R2 can reach 3.03 nm/ and 0.999 in the temperature range of 20 to 70, respectively.

.A hollow-core negative curvature fiber (HC-NCF) with high birefringence for temperature sensing based on surface plasmon resonance effect is proposed. For the HC-NCF, the cladding layer is composed of six silica tubes, and the thickness and radius of the two silica tubes in the y-axis direction are different from those of other ones. Moreover, the two silica tubes in the y-axis direction are filled with the gold wires, and the ethanol to be tested is filled in other silica tubes and air area. As the temperature changes, the coupling state between the x-pol core mode and surface plasmon polarization mode will change. The temperature sensitivity can be up to 3.1  nm  /    °  C in the range of 20°C to 40°C. Moreover, the proposed HC-NCF temperature sensor simultaneously achieves the maximum R of 3.333  ×  10  −  2  °  C and maximum FOM of 269  °  C  −  1, which indicates that it has high sensitivity, good linearity, high R, and large FOM. The proposed HC-NCF temperature sensor is expected to be useful in the field of the environmental monitoring.

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