A sensor compares frames of pixels representing a speckle pattern caused by interference of light through an optical fiber to detect magnitudes of deflection of the fiber. A coherent light source illuminates the optical fiber. An image sensor captures the speckle pattern and frames of pixels produced by the image sensor are processed to determine deflection. A baseline frame is generated from frames previously received. Each frame is compared to the baseline frame to determine the cumulative amount of deflection on the fiber. To compensate for drift and large-scale movements of the optical fiber, the baseline frame is updated as frames are received. The processed output from comparing to the baseline frame has larger amplitude signals than from comparing to adjacent frames due to larger deflections over time since the baseline frame. Signal-to-Noise ratio is improved, and the processed output better matches a plot of the actual total deflection.
