Strain Measurement Using Transmission/Reflection-Type Hybrid A Extrinsic Fabry-Perot Interferometric Optical Fiber Sensors

Conventional interferometric optical fiber sensors have a disadvantage of directional ambiguity generally. In a TRHEFPI optical fiber sensor, the reflection and transmission sensor signals can be obtained simultaneously. The reflection signal contains the information of only measurement quantity. On the other hand, the transmission signal contains the information of both measurement quantity and directions. The interferometric fringes of the linear combination between the transmission and reflection signals have phase shifts from those of the reflection signal. Due to the phase shifts, which show the lead or lag behavior according to measurement directions, the. clear information of measurement directions can be obtained. To control the phase shift magnitude, the coefficient in the linear combination signal must be designed adequately. The precise measurement quantity can be obtained from the reflection sensor signal with high visibility. For strain measurement, the sensor was attached on a surface of an aluminum-alloy tension specimen. In this research, the repeated sinusoidal strain of the fatigue test was measured using TRHEFPI sensors. The health monitoring of the smart structures was possible with the fatigue monitoring.