A vector curvature sensor based on a single fiber Bragg grating (FBG) is proposed and experimentally demonstrated. The sensor is easily fabricated by encapsulating an FBG on a thin steel plate with ultraviolet glue. When the FBG deviates from the neutral plane, its effective refractive index and grating constant are changed by bending, therefore, the sensor can realize curvature measurement. Due to the opposite stress direction on the two sides of the neutral plane during bending, the sensor can realize vector measurement of curvature. The curvature sensitivity of the sensor in convex and concave bending is 558.42 pm/m<sup>-1</sup> and -818.09 pm/m<sup>-1</sup>, respectively. This sensor has the advantage of simple structure, low cost, and easy industrial production. It has potential applications in engineering health monitoring and deformation measurement.
A simple composite cavity fiber tip (CCFT) Fabry-Perot interferometer (FPI) is proposed and experimentally demonstrated. The composite cavity is composed of an air cavity and a silica cavity. The air cavity is an elliptical air hole embedded in the SMF. The silica cavity is a short section of SMF cascaded to the air cavity. The CCFT FPIs were applied for temperature sensing. To take advantage of the FP’s resonant property, a laser whose wavelength is tuned to the steep slope of one of the FP resonances is used to interrogate the CCFT FPI system. With a laser interrogation, a small wavelength shift caused by a small temperature change will then be translated into a large change in output power, which can be easily detected. Therefore, the temperature sensitivity can be enhanced significantly, and the CCFT FPI can routinely resolve much smaller temperature changes.
A miniature fiber-optic sensor fabricated by fuse splicing a section of hollow silica tube between two sections of single-mode fiber is proposed and experimentally demonstrated for simultaneous measurement of the liquid refractive index (RI) and temperature. The sensitivities of RI and temperature are measured by linear fitting, respectively, and corresponding detecting resolutions are obtained by the sensitivity matrix. The different response sensitivities of two dips to RI and temperature manifest that the structure proposed can be used for simultaneous measurement. The experimental evidence indicates that the miniature fiber sensor with advantages of easy fabrication, ultracompactness, and robustness is insensitive to axial strain.