Large-Capacity WDM FBG Array Interrogated by OFDR for Large Strain Measurement

Abstract We propose a wavelength-division multiplexing (WDM) fiber Bragg grating (FBG) array designed to mitigate the spectral shadow effect, thereby enhancing multiplexing capacity. The array comprises 7560 FBGs, which are periodically arranged across 21 distinct wavelength channels. Each FBG has an average reflectivity of 5.5‰ and a bandwidth of 0.113 nm. We employ an optical frequency-domain reflectometry (OFDR) system for interrogation, which enables high-density array demodulation and large-strain measurement. A convolutional localization algorithm is proposed to achieve fast and accurate addressing of each FBG. The sensing system achieves a maximum sensing-fiber length of 120 m and spatial resolution of 16 mm, along with a demonstrated strain range of 10000 με and wavelength accuracy of 1.2 pm. Furthermore, a 21-fold enhancement in spectral demodulation speed is realized over identical FBG arrays. Consequently, the average demodulation time per FBG is substantially reduced from 11.25 ms to 0.53 ms. These results affirm the exceptional suitability of our system for applications demanding high precision, an extensive strain range, and substantial sensor capacity.