Identical FBG-Based Quasi-Distributed Sensing by Monitoring the Microwave Responses

We present a quasi-distributed fiber sensing technique by monitoring the microwave responses through the reflections of the fiber Bragg gratings (FBGs). These FBGs are all identically and specially fabricated with the low reflectivity and the broad reflection bandwidth. The microwave signals are used to resolve the positions and the reflected intensities from FBGs along the optical fiber. The reflected intensity of each FBG can be modulated through the wavelength shift induced by the sensing parameter, since the optical bandpass filter with the matched spectrum is adopted in the detection. The relative amplitude change (RAC) of the microwave responses are determined by the change of reflected intensities from FBGs. We demonstrate a proof-of-concept experiment for the strain sensing using six identical FBGs. The experimental measurements show that a high-strain sensing sensitivity of 0.0452% RAC/mu epsilon is achieved within the measured range of 2000 mu epsilon. The sensing positions also can be accurately located from the demodulation figure through invert-fast Fourier transform algorithm with the locating resolution of similar to 10.2 cm.