Self-referenced intensity-based fiber optic sensor system using fiber Bragg gratings

We present a method for measuring the intensity variation regarding the measured physical attributes of intensity-based fiber Bragg grating sensors. These sensors can be configured for multiplexing, thermal insensitivity, and immunity to noise from the light source and/or the lead-in/out fibers caused by the external load. To achieve these goals, the intensity-based optical fiber sensor is implemented between a pair of fiber Bragg gratings. Based on the ratio or dBm difference from the two reflecting intensities of the reference and the sensing fiber Bragg gratings, the appropriate measurable parameters associated with the intensity variations can be detected. Different from transmission type intensity-based sensors, a reflective type based on a pair of fiber Bragg gratings is introduced. To validate the proposed method, a transducer made by using an etched-cladding fiber is deposited onto the metal thin film for sensing metal corrosion. Based on the evanescent field of a fiber and a pair of fiber Bragg gratings, multiple embedded corrosion sensors could be designed for civil structural health monitoring. Also, the proposed method could be applied to a biosensing design on a transducer.