FBG laser sensor with PS

Owing to unstable multi-wavelength lasing, robust measurement is difficult with a fibre Bragg grating (FBG) laser sensor system that uses FBGs as laser cavity mirrors as well as sensors. A stabilising technique is essential for proper data acquisition. Here, it is demonstrated that polarisation scrambling (PS) stabilises the output of laser sensor system in combination with a spectrometer demodulation. The state of polarisation (SOP) of a fibre-optic laser cavity is changed by a 1 MHz PS. A 5 kHz spectrometer traces the distribution of output laser wavelengths. The rapid changes in SOP make all the FBG wavelengths lase as long as necessary to determine the Bragg wavelength shifts in the sampling windows of a photo-diode array. A laser sensor system with eight FBG sensors is used to demonstrate robust measurement and data collection under environmental perturbations.