Embedded in-line fiber etalon/Bragg grating hybrid sensor to measure strain and temperature in a composite beam

An optical fiber sensor for simultaneous measurement of axial strain and te mperature in composite structures is reported. This sensor configuration co nsists of an in-line fiber etalon (ILFE) cascaded with an in-fiber Bragg gr ating (BG) and is demultiplexed using a variation of coherence division mul tiplexing. The strain/temperature sensor is demonstrated by embedding it in to a graphite/epoxy composite cantilever beam. Concentric cylinders microme chanics models are developed that enable the optical signals from the embed ded sensors to be cast in terms of the composite host strain and temperatur e without the need for calibration. The fiber optic strain/temperature sens or with a gage length of similar to 1.0 cm is found to agree with tradition al strain and temperature sensors to within 5 mu epsilon and 0.5 degrees C, respectively.