Hot Cavity Optical Fiber Fabry–Perot Interferometer as a Flow Sensor With Temperature Self-Calibrated

An optical fiber flow sensor is developed based on a hot cavity fiber Fabry-Perot (F-P) interferometer formed by a pair of fiber Bragg gratings (FBG). Part of the F-P cavity is made up by a short (2 mm) cobalt-doped fiber (CDF). The CDF can be heated up by a heating laser so that the effective optical path length of the cavity increases. The fluid flow can take some heat away depending on the flow rate and also changes the resonant wavelength of the F-P cavity. The FBG spectrum is recovered by fitting the envelope of the F-P spectrum. The generated heat is centralized inside the cavity and could hardly influence the FBG. As the F-P and FBG are with the same sensitivity to the environment temperature, the recovered Bragg wavelength can be used as a perfect reference for the self-calibration of the temperature.