A simple, compact, and highly sensitive gas pressure sensor based on a Fabry–Perot interferometer (FPI) with a silicone rubber (SR) diaphragm is demonstrated. The SR diaphragm is fabricated on the tip of a silica tube using capillary action followed by spin coating. This process ensures uniformity of its inner surface along with reproducibility. A segment of single mode fiber (SMF) inserted into this tube forms the FPI which produces an interference pattern with good contrast. The sensor exhibits a high gas pressure sensitivity of −0.68 nm/kPa along with a low temperature cross-sensitivity of ≈ 1.1 kPa/°C.

We report for the first time the development of a rectangular fiber with two cores consisting of different refractive indices for discrimination of temperature effects during strain or curvature measurements using fiber Bragg gratings written in a single segment of a fiber. Two cores with a diameter of 8 μm and a rectangular cladding with dimensions of 120 μm× 255 μm permit convenient splicing to conventional single mode fiber and support easy identification of the orientation of the fiber. When placed in a desired orientation, each core of the two-core rectangular fiber experiences a different spectral shift in the presence of applied strain or curvature. The sensitivities of the two cores are 0.87 and 1.08 pm/με for strain, 126 and.−128 pm/m−1 for curvature and 10.05 and 10.40 pm/°C for temperature, respectively. In addition, the flat cladding structure of the fiber provides a large physical contact area between the sensing fiber and the substrate than a circular fiber and allows better strain coupling between the object and the fiber.

An optical accelerometer realized with a new side-hole fiber in a Sagnac interferometric scheme, was developed by utilizing the birefringent and stiffness properties of the optical fiber to achieve a high sensitivity, a broad frequency range, a wide acceleration range, and an excellent linearity. The proposed accelerometer exhibits a resonant frequency of 2300 Hz and an average sensitivity of 44.3 (±3.0) pm/g over a broad frequency range from 4 to 900 Hz. The linearity of the signal response exceeds 99.9% and its transverse sensitivity is less than 11% of the main axis. It exhibits a dynamic acceleration range of 62.5 dB which is related to the applied acceleration from 0.03 to 40 g, making the side-hole fiber a good candidate for acceleration/vibration sensing applications. Furthermore, the tradeoff relationship between the sensitivity and the resonant frequency was significantly improved when compared to that of fiber Bragg grating-based accelerometers.

We have fabricated a composite optical fiber with hyperelastic silicone cladding and silica core, and demonstrated a simple and highly sensitive pressure sensor based on the light coupling between two such composite fibers twisted together. The hyperelastic silicone has very low Young's modulus which makes the fiber deformation easier even under small pressure and hence improves the light coupling and pressure sensitivity. Both simulation and experiment show that the light coupling based pressure sensor using the composite fibers is very sensitive to small pressure (e.g. several newtons) compared with those using conventional silica fibers and PMMA polymer fibers, which almost have no response to small pressure. With excellent sensitivity and fast response time (<< 1s), both static and dynamic side pressure have been successfully detected. The sensing configuration is simple without any complicated structures and would be a cost-effective candidate for highly sensitive small pressure monitoring.

This study presents an innovative approach to pressure sensing by utilizing an 8-shaped birefringent optical fiber fabricated through a mechanical milling technique. The proposed sensor employs the Sagnac effect to monitor wavelength shifts in the interference pattern. Experimental results demonstrate that the sensor achieves a high sensitivity of 441 pm/kPa within the pressure range of 0 to 20 kPa, enabling accurate pressure measurements with a resolution of up to 2 Pa. The measurements exhibit good repeatability, and demonstrate a linearity of 99.65%. In addition, by integrating a fiber Bragg grating fabricated using a femtosecond laser into the 8-shaped fiber within the Sagnac loop, the temperature cross-sensitivity was determined to be 20 Pa/°C. The combination of the 8-shaped birefringent fiber and the Sagnac interferometric technique offers a promising solution for achieving precise and reliable pressure sensing in low-pressure environments.

This work presents a compact fiber Bragg grating (FBG)-based sensor that decouples curvature/strain and temperature effects using a configurable rectangular optical fiber design. The sensor structure integrates a side-hole rectangular fiber (SHRF) with dimension of 175 μm × 358 μm with a 97-μm diameter air hole, along with embedded reduced-cladding fibers (RCFs). It features two FBGs, one inscribed in the SHRF, which is sensitive to both curvature/strain and temperature, and another within an RCF embedded in the air hole, which serves as a temperature reference. The design accommodates both reduced-cladding silica optical fiber (RC-SOF) and reduced-cladding polymer optical fiber (RC-POF), with the RC-POF exhibiting significantly enhanced temperature sensitivity (−43.64 pm/°C in the range 20–80 °C), four times greater than that of the SHRF (11.04 pm/°C), enabling precise thermal discrimination. Experimental results demonstrate a curvature sensitivity of −0.26 nm/m⁻¹, an axial strain sensitivity of 0.89 pm/μϵ, and a bending-induced strain sensitivity of 1.09 pm/μϵ for the SHRF. The embedded RCFs show negligible curvature/strain response, with the RC-SOF exhibiting 10.70 pm/°C sensitivity (50–180 °C). The SHRF's flat cladding enables clear orientation identification and enhances strain transfer/bonding. This all-fiber design provides thermal compensation without requiring complex packaging or separate reference elements.