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 temperature in composite structures is reported. This sensor configuration consists of an in-line fiber etalon (ILFE) cascaded with an in-fiber Bragg grating (BG) and is demultiplexed using a variation of coherence division multiplexing. The strain/temperature sensor is demonstrated by embedding it into a graphite/epoxy composite cantilever beam. Concentric cylinders micromechanics models are developed that enable the optical signals from the embedded sensors to be cast in terms of the composite host strain and temperature without the need for calibration. The fiber optic strain/temperature sensor with a gage length of-1.0 cm is found to agree with traditional strain and temperature sensors to within 5 με and 0.5 ⁰ C, respectively.