Compensation of Scanning Speed Instability in a Wavelength-Swept Laser for Dynamic Fiber Optic Sensors

The scanning speed stability of a wavelength-swept laser (WSL) with a polygon-scanner-based wavelength filter (PSWF) is affected by the speed of the brushless direct current (BLDC) motor driving a polygonal scanner mirror (PSM). In particular, the PSM running at low speeds experiences fluctuations in rotational speed, causing the output of the WSL to fluctuate in the temporal domain. The speed variation of the WSL causes critical measurement errors in the fiber Bragg grating (FBG) interrogator sensors. In this study, we successfully corrected the output error of the FBG array sensor caused by the PSM rotational speed fluctuations in a WSL running at a low scanning rate. The FBG array used five FBGs, and the time intervals of the FBGs were corrected according to the PSM rotation speed variation based on the periodic interval of the array signal. A WSL with a scanning rate of 1.0 kHz suggested a 97% improvement after compensating for rotational speed variations of the PSM.