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

• Published in: Applied sciences 2020-02, Vol.10 (3), p.1069
• Main Authors: Madan, Aayush, Yap, Stephanie Hui Kit, Paulose, Varghese, Chang, Wonkeun, Shum, Perry Ping, Hao, Jianzhong
• Format: Article
• Language: English
• Subjects: Adiabatic; Adiabatic flow; Bragg gratings; direct writing; Fabrication; fabry–perot; femtosecond laser micromachining; harsh environment fiber sensor; Infrared lasers; Investigations; Laser machining; Lasers; microfiber sensor structure; Micromachining; point-by-point fabrication; Sensitivity; sensor for structural health monitoring; Sensors; Simulation; Strain analysis; Tapering; Temperature; Temperature effects; Writing
• ISSN: 2076-3417; 2076-3417
• DOI: 10.3390/app10031069

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 μ m (core diameter to 4.7 μ 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 μ ε and 225 ° C, respectively, are investigated for the fabricated sensor and the FBG, and compared. The fabricated sensor attains a higher strain sensitivity (2.32 pm/ μ ε ) than the FBG (0.73 pm/ μ ε ), while both the sensors experience similar sensitivity to temperature (8.85 pm/ ° C). The potential applications of such sensors include continuous health monitoring where precise strain detection is required.