Study of Laser Feedback Phase under Self-Mixing leading to Improved Phase Unwrapping for Vibration Sensing

International audienceIn this paper, the inherent error as well as the robustness of a previously published displacement retrieval technique called the phase unwrapping method (PUM) is analyzed. This analysis, based on a detailed study of laser feedback phase behavior, results in a new algorithm that removes the PUM inherent error while maintaining its robustness. The said algorithm has been successfully tested on simulated and experimental Self-Mixing (SM) interferometric signals. Simulations in weak and moderate feedback regimes demonstrate that the said algorithm can reach a subnanometric precision compared to approximately 25nm for PUM. For experimental SM signals affected by noise, the mesured rms displacement error and the maximum absolute error is approximately 14nm and 37nm respectively for the proposed algorithm and 34nm and 123nm for the PUM, which indicates a three fold displacement precision improvement over the PUM. Finally, it is explained that the precision can be further improved by a reduction of the noise level of experimental SM signals