We report a new method to measure the refractive index change in optical fiber core induced by femtosecond (fs)laser exposure. An in-line Fabry-Perot interferometer, serving as the measurement platform, is constructed on a commercial single-mode optical fiber by one-step femtosecond (fs) laser fabrication. A positive refractive index change is observed and measured accurately as the laser pulse energy surpasses the ablation threshold.
This paper summarizes our recent research progresses in developing optical fiber harsh
environment sensors for various high temperature harsh environment sensing applications
such as monitoring of the operating conditions in a coal-fired power plant and in-situ
detection of key gas components in coal-derived syngas. The sensors described in this paper
include a miniaturized inline fiber Fabry-Perot interferometer (FPI) fabricated by one-step fs
laser micromachining, a long period fiber grating (LPFG) and a fiber inline core-cladding
mode interferometer (CMMI) fabricated by controlled CO<sub>2</sub> laser irradiations. Their operating
principles, fabrication methods, and applications for measurement of various physical and
chemical parameters in a high temperature and high pressure coexisting harsh environment
This paper demonstrates the chemical sensing capability of a miniaturized fiber inline Fabry-Pérot sensor fabricated by
femtosecond laser. Its accessible cavity enables the device to measure the refractive index within the cavity. The
refractive index change introduced by changing the acetone solution concentration was experimentally detected with an
error less than 4.2×10<sup>-5</sup>.