Obtaining High Fringe Precision in Self-Mixing Interference Using a Simple External Reflecting Mirror

Based on the study of laser diode self-mixing interference effects, a simple and effective method that can improve fringe precision is presented. By employing an external reflecting mirror, theoretical and experimental results show an assured increase about two or three times in the resolution of the displacement measurement, which means a fringe shift is corresponding to a near 1/6 wavelength displacement of the target. At a small angle range, when the fringe precision is not fixed, this method can still have a relative high precision and a large measurement range. The maximum measurable displacement and error of precision are also discussed.