Doubled Optical Path Length for Photonic Bandgap Fiber Gas Cell Using Micromirror

In this paper, we presented the double optical path length of a photonic bandgap fiber (PBGF) gas cell. The gas sensor sensitivity can be improved by a two fold lengthening of the optical length without changing the gas fluid. Furthermore, a high-reflection micromirror was included in the proposed double optical path length gas cell. A Cr/Au sputtering process was applied to fabricate the vertical micromirror using a single-mode fiber (SMF). A measurement system for low gas concentrations based on the micromirror has been implemented, and sensitivity was improved without increasing the response time.