Compact All-Fiber Interrogation Unit for FBG sensors

A two-mode photonic crystal fiber interferometer (PCF) is proposed as a low-cost interrogation unit for FBG-based sensors. The interferometer consists of a piece of index-guiding PCF fusion spliced between two standard single-mode fibers. At the splices the voids of the PCF are sealed allowing the excitation of only two modes. The interferometer exhibits ripples from 800 to 1600 nm with high fringe contrast and behaves as a variable filter in that range. The Bragg wavelength shift is converted into intensity changes which can be measured accurately and in realtime. Detection of wavelength shifts of 2 pm is feasible with the proposed unit which is comparable to state-of-the-art FBG interrofgators.