Laser-micromachined Fabry-Perot optical fiber tip sensor for high-resolution temperatureindependent measurement of refractive index

We propose and demonstrate a Fabry-Perot (F-P) optical fiber tip sensor for high-resolution refractive-index measurement fabricated by using 157-nm laser micromachining, for the first time to our knowledge. The sensor head consists of a short air F-P cavity near the tip of a single-mode fiber and the fiber tip. The external refractive index is determined according to the maximum fringe contrast of the interference fringes in the reflective spectrum of the sensor. Such a sensor can provide temperature-independent measurement of practically any refractive index larger than that of air and offers a refractive-index resolution of ∼4×10^-5 in its linear operating range. The experimental data agree well with the theoretical results. © 2008 Optical Society of American.