Extrinsic sensors, fiber optic properties

Both extrinsic- and intrinsic-type sensors incorporate a transducer element making it an active device. Extrinsic sensors have an external transducer, and the optical fiber just serves the purpose of a light carrier to and from the external transducer whereas, intrinsic sensors have the structure of the optical fiber modified to incorporate the transducer element. In both cases, the transduction mechanisms change the light properties based on interaction with chemical species. 

Fiber-optic chemical sensors can be divided into two categories based on their structure (a) Intrinsic sensors are based on the analyte s intrinsic optical properties, and (b) extrinsic sensors are based on sensing materials (chemical or biological) immobilized to the fiber surface, with... 

Due to their high sensitivity to strain, temperature variation, vibration, and acoustic waves, embedded extrinsic Fabry-Perot interferometric optical fiber sensors have been developed to detect delamination, based on changes in the acoustic properties of the materials before and after delamination [41]. Impact events and corrosion cracking generate ultrasonic waves, which can be characterized using elliptical core fiber sensors [40]. The in-line Fabry-Perot interferometer seems well suited for the local detection of shear waves and the characterization of impact-induced damage. 

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