Cuiting Sun

In this work, we present a compact twin-core-fiber (TCF) Mach–Zehnder interferometer for strain, bending and torsion sensing. The sensor consists of a single-mode fiber (SMF)-multimode fiber (MMF)-TCF-MMF-SMF structure fabricated by electric-arc fusion splicing. Periodic V-shaped grooves are fabricated on the TCF cladding using CO ₂ laser polishing, followed by oxyhydrogen flame treatment to enhance mode coupling. The sensor achieves sensitivities of −30.571 nm m ⁻¹ for bending and −100 pm µ ϵ ⁻¹ for strain. Directional torsion sensitivities of 0.703 and 0.310 nm (rad m ⁻¹ ) ⁻¹ are obtained for clockwise and counterclockwise twisting, respectively. Characterized by a total length of merely 3.5 mm, along with the benefits of high sensitivity and ease of fabrication control, the proposed sensor shows potential for multi-parameter sensing in confined environments.

In this paper, a high-sensitivity sub-zero temperature sensor based on the Mach–Zehnder interferometer coated with organic silicone film is proposed. The sensor is fabricated by polishing four orthogonal sides in the multimode fiber (MMF) of the single-mode–multimode–single-mode (SMS) structure with a CO₂ laser and then coating the structure with a mixed film of hydroxyl-terminated siloxane and methyl MQ silicone resin to form a sub-zero-sensitive layer. The sub-zero temperature sensitivity of the coated sensors is experimentally compared for samples with different numbers of polished facets. The experimental results show that the sub-zero temperature sensitivity of the sensors with one to four polished facets increased from 0.73 nm/K to 2.15 nm/K in the temperature range of 223 K to 273 K. The fiber sub-zero sensor has the advantages of compact structure, high sensitivity and low cost, which lead to the potential for application in fields such as biomedicine, aerospace and energy.

In this work, we propose a bamboo-shaped Mach-Zehnder interferometer coated with chitosan for relative humidity (RH) and temperature measurement. The sensor is fabricated by fusing no-core fiber and multimode fiber segments through arc discharge, followed by tapering with a hydrogen–oxygen flame to form a unique bamboo-shaped configuration. To functionalize the structure for humidity sensing, chitosan is coated onto the fiber surface. The refractive index of chitosan varies with water molecule adsorption, which enhances the spectral response of the sensor to RH. Therefore, the sensitivity response is enhanced after the film coating is applied. Experimental results demonstrate that the proposed sensor achieves the maximum sensitivities to RH and temperature determined at −0.9261 nm/%RH and 0.0952 nm/°C, respectively. The sensor features a compact structure, high sensitivity and the ability to achieve dual-parameter sensing, which supports applications in biomedical, agricultural and electronic manufacturing fields.

A high-resolution asymmetric sensor is designed for simultaneously measuring temperature and micro-displacement. The sensor is based on a bent single-mode-multimode-single-mode (SMS) fiber structure, forming a balloon-like shape that incorporates two tapers of distinct diameters. This novel structure not only facilitates Mach-Zehnder interference but also strengthens the evanescent field exposure, resulting in two distinct dips that exhibit unique responses to micro-displacement and temperature. Therefore, the interferometer can measure both micro-displacement and temperature simultaneously. Experimental results demonstrate that the sensitivities of the micro-displacement and temperature for the two spectral dips are 807.7 pm/µm, 35.9 pm/ ℃ and 341.0 pm/µm, 52.4 pm/ ℃ , respectively. Meanwhile, the resolutions for micro-displacement and temperature are 0.011 µm and 0.310 °C, respectively. It is demonstrated that the micro-displacement sensitivity and resolution of the sensor in this work are significantly higher than those of previously reported designs. The sensor is a relatively simple structure to fabricate, is cost-effective and has both high sensitivity and resolution. It is, therefore, a promising candidate for various industrial applications, including aerospace, marine engineering and precision spatial positioning.

In this article, we propose a novel method to fabricate a torsion sensor. A series of asymmetric offsets were introduced at the splicing points of a single-multi-single mode fiber (SMS) structure and a helical-offset ultra-long-period fiber grating (HO-ULPFG) structure is finally formed. The torsion and temperature sensing characteristics of the HO-ULPFG were examined experimentally. The HO-ULPFG exhibits high sensitivities of 2.33 nm/(rad/m) in the clockwise direction and 1.97 nm/(rad/m) in the counterclockwise direction. Further, the structure exhibits a minimal temperature-induced crosstalk of 0.0142 (rad/m)/°C, which is considerably lower than that of comparable sensors. The results demonstrate that the HO-ULPFG has potential applications in torsion measurement under harsh conditions.