Multiplexed fiber Fabry-Perot temperature sensor system using white light interferometry

The object of this research is to develop a new technique for monitoring the optical path difference (OPD) in an optical fiber interferometer that provides both high accuracy and high dynamic range. The technique is applied in the sensing of temperature and to the multiplexing of sensors deployed along the length of a single mode fiber.; A fiber Fabry-Perot interferometer (FFPI) is used as the sensing head and a bulk Michelson interferometer as the optical processing interferometer, with a superluminescent diode (SLD) as the light source and a motor-driven translation stage for mirror scanning. A second interferometer with a distributed feedback laser (DFB) as the light source is used to monitor and correct for mechanical irregularities in the stage motion. Fringes from the DFB interferometer serve as a precise metric for determining the difference in OPD of the sensing interferometer vs. that of a reference FFPI that is held at ambient temperature.; The measured temperature resolution of 0.0135°C for a FFPI sensor of 10 mm cavity length corresponds to an OPD resolution of 0.0025 fringes. The system has been characterized over a temperature range from room temperature to 810°C. Coherence multiplexing of three sensors of different optical length has also been demonstrated. The OPD monitoring technique and multiplexing technique introduced here can be used for other measurands (e.g., strain, pressure) and for other interferometric fiber sensor configurations.