Proposal of hydrostatic pressure sensor integrated in a dual-core hollow optical fiber

Abstract

In this paper, a novel dual-core hollow optical fiber (DHOF) based Mach-Zehnder interferometer (MZI) is proposed for hydrostatic pressure sensing. For the proposed fiber, two cores of the dual-core fiber are separated by a large air hole, and a D-type platform is fabricated adjacent one core. The existence of the central large air hole enhances the pressure-induced refractive index change of the dual-core fiber and ensures the independent transmission of the guiding light in the two fiber cores. Meanwhile, the D-type platform ensures that the dual-core fiber is subjected to asymmetric hydrostatic pressure, which results in the pressure-induced guiding mode phase change. For the dual-core hollow optical fiber, Mach-Zehnder interferometer (MZI) can be integrated in the fiber. One core is to measure the external environment as a sensing arm, and the other core is used as a reference arm. Furthermore, a dual-platform dual-core hollow optical fiber (DDHOF) is proposed, which further improves the asymmetry of the hydrostatic pressure on the dual-core fiber to continuously increase the sensing sensitivity. The mode field distribution and light guiding properties of DHOF and DDHOF under different hydrostatic pressures are analyzed by the finite element method and beam propagation method. The results show that the DHOF has a sensitivity of 2.4125 nm/MPa for the measurement range from 0 MPa to 100 MPa and the temperature cross-sensitivity is − 0.0886 nm/ ℃, the DDHOF has a sensitivity of 9.23 nm/MPa for the measurement range from 5 MPa to 10 MPa. The proposed DHOF and DDHOF can achieve different ranges of hydrostatic pressure sensing and possess extremely low temperature cross-sensitivity, which is suitable for the field of deep-sea exploration. Furthermore, the sensors possess a flexible structure, low temperature cross-sensitivity, can be integrated in the fiber, is easy to manufacture, and have other advantages.