Microwave Photonics Filtering Technique for Interrogating a Very-Weak Fiber Bragg Grating Cascade Sensor

A system to interrogate photonic sensors based on a very weak fiber Bragg grating cascade fiber is presented and experimentally validated and dedicated to detecting the presence and location of a spot event. The distributed sensor proposed consists of a 5-m-long fiber, containing 500 9-mm-long Bragg gratings with a grating separation of 10.21 mm. The principle of operation is based on a technique used to analyze microwave photonics filters. The detection of spot events along the sensor is demonstrated with remarkable accuracy under 1 mm, using a photodetector and a modulator with a bandwidth of only 500 MHz. The simple proposed scheme is intrinsically robust against environmental changes and is easy to reconfigure.