Optical proximity sensor based on self-mixing interferometry

A proximity detector based on self-mixing technique, well suited for different industrial applications, is demonstrated. Instead of using a light-source plus a detector, the proposed sensor is realized by a single laser source. Two different physical effects in the laser diode allow for a continuous detecting range, from 10 mm up to 80 mm. The main advantages of the sensor are target detection from just one point of view; multiple sensors configuration does not need optical filters; separation of source and detector is eliminated; and background rejection is intrinsically given by the self-mixing effect, which shows a sharp cut-off after the focus.