Discrimination of strain and temperature using Bragg gratings in side-hole rectangular fiber and embedded reduced-cladding fibers

This work introduces a novel fiber Bragg grating (FBG) sensor design for discriminating strain and temperature effects using a side-hole rectangular fiber (SHRF) and embedded reduced-cladding fibers. An FBG in a single-mode fiber with a 75-μm cladding diameter, embedded within the SHRF air-hole, allows independent temperature measurements, while the SHRF FBG senses both strain and temperature. By embedding a polymer fiber with a 76-μm cladding diameter, the sensor achieved temperature sensitivity up to four times greater than that of the SHRF with SMF, enabling precise thermal discrimination. This compact, thermally-stable all-fiber sensor design effectively decouples strain and temperature without the need of complex packaging or a separate reference.