Investigation of a Bragg Grating-Based Fabry-Perot Structure Inscribed Using Femtosecond Laser Micromachining in an Adiabatic Fiber Taper

This paper presents the fabrication of a fiber Bragg grating (FBG)-based Fabry-Perot (FP) structure (7 mm total length) in an adiabatic fiber taper, investigates its strain and temperature characteristics, and compares the sensing characteristics with a standard polyimide coated FBG sensor. Firstly, a simulation of the said structure is presented, followed by the fabrication of an adiabatic fiber taper having the outer diameter reduced to 70 mu m (core diameter to 4.7 mu m). Next, the sensing structure, composed of two identical uniform FBG spaced apart by a small gap, is directly inscribed point-by-point using infrared femtosecond laser (fs-laser) micromachining. Lastly, the strain and temperature behavior for a range up to 3400 mu epsilon and 225 degrees C, respectively, are investigated for the fabricated sensor and the FBG, and compared. The fabricated sensor attains a higher strain sensitivity (2.32 pm/mu epsilon) than the FBG (0.73 pm/mu epsilon), while both the sensors experience similar sensitivity to temperature (8.85 pm/degrees C). The potential applications of such sensors include continuous health monitoring where precise strain detection is required.