CO<sub>2</sub>Laser Tapering of Intrinsic Fabry–Perot Interferometers for Sensing
Xinruo Yi, Yuqi Li, Kehao Zhao, Zekun Wu, Qirui Wang, Bo Liu, Michael Buric, Ruishu Wright, Kevin P. Chen
Abstract
We present a highly reproducible method of fabricating a tapered intrinsic Fabry–Perot interferometer (IFPI) device with 5–6 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> diameter at the taper waist. A femtosecond laser was applied to inscribe an IFPI with 3-cm cavity length in a single-mode fiber. A CO2 laser-heated tapering process enabled by digitally controlled mirrors and a precision motorized fiber feed system was used to create a stable heating zone with the desired temperature profile for tapering the fiber IFPI cavity. The well-engineered tapering process produced tapered IFPI devices with insertion loss less than 0.3 dB at 1550 nm. A strong evanescent field exposed by the taper Section was explored for refractive index (RI) sensing. Using swept optical frequency domination reflectometry (OFDR), the tapered IFPI fiber sensor achieved a minimal RI sensing resolution of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\times 10^{-{5}}$ </tex-math></inline-formula> . This article demonstrates an integrated laser fabrication technique to produce tapered fiber optic devices for sensing applications.