A Technique for Improving the Noise-Equivalent-Displacement of SM-SLD Interferometers for Industrial Processes

Non-contact absolute distance measurements are desirable in several industrial processes. For this purpose, the interferometric Self-Mixing Super Luminescent Diode technique represents a unique approach for simplicity and robustness. Thanks to optical feedback, large interference fringes, even with diffusive targets and without utilizing high-sensitivity detectors, can be obtained rejecting any stray-light. To establish the absolute target position, the most common approach is to process the interference fringes envelope by the zero-crossing technique. In this paper, we propose to process the photogenerated signal by a custom modified envelope detector to reduce the measurement uncertainty.