Efficient diaphragm-based Fiber Bragg grating vacuum sensor

An efficient diaphragm-based fiber Bragg grating (FBG) vacuum sensor was designed, developed and experimentally demonstrated. The devised sensor was independently interrogated by spectral and intensity demodulation techniques. In spectral demodulation, a linear red-shift was observed in the Bragg spectrum with enhancement in the vacuum level with sensitivity and resolution of 18.5 p.m./mbar and 6.644 mbar, respectively. In intensity demodulation, a chirped fiber Bragg grating (CFBG) was used as an optical filter for the Bragg spectrum of the FBG which linearly varied reflected light intensity from the FBG with enhancement in vacuum level inside the chamber. The intensity demodulation was able to detect the pressure difference in the chamber from 67 mbar to 0.2 mu bar with sensitivity and resolution of 1.40 nW/mbar and 6.41 mbar, respectively. The sensor offered 2000 times faster response time than the reference commercial vacuum gauge for intensity demodulations.