Laser-frequency locking techniques for high-sensitivity strain measurements byhigh-birefringence fiber Bragg gratings and resonators

摘要

A new approach to simultaneously interrogate orthogonal axes of single Fiber-Bragg-Gratings (FBGs) and FBG-FabryPerot resonator sensors fabricated inlinearly highly birefringent (HiBi) fibre is presented. Novel interrogationtechniquesof single Fiber-Bragg-Gratings (FBGs) and FBG-resonator sensors arepresented. For a single FBG, we combined alaser-modulation technique to anelectronic feedback loop that keeps the source always frequency locked to onepeak ofthe sensor's reflected spectrum. Two different lasers, with orthogonally-polarized states, were adopted to monitorsimultaneously both the "fast" and"slow" FBG peaks. The corresponding correction signals from the servo-loopoutputscan be interpreted as strain or temperature induced on the FBG. Detectionlimits ranging from 1 nε/√Hz to 100 nε/√Hz,for axial dynamic and staticdeformations, respectively, and of 0.025 °C/√Hz for temperature variations, areexpected. Asimilar approach was developed for sub-pϵ resolution interrogation ofan optical resonator made of a high-reflectivityFBG-pair, using the Pound-Drever-Hall (PDH) stabilizati