Proximity Sensor using Self-mixing Effect

This paper is about the utilisation of the well-known self-mixing effect as base for the development of a novel proximity detector. The common used setup for this kind of a sensor is based on two elements: a laser as an emitter and a position-sensitive sensor as a detector. The sensor developed detects the optical power reflected by the object within the laser cavity itself, with no need of any additional detectors. One of the main feature is the ability to measure diffusive target accessible only from one side. A continuous range of measurement starting from 10 mm up to 80 mm is obtained by means of two different physical phenomena: from 0 up to 5mm the detection is only dependent by the level of the optical power returned into the laser cavity, whereas from 5 mm up to 80 mm reading the frequency of the modulation of the interferometric signal. The main advantage of the novel sensor is the elimination of the external detector. In addition, multiple devices configurations can be utilized and there is no need of any optical filters, cause the laser cavity itself works as an optical filter. Background rejection is intrinsically obtained because self-mixing effect shows a sharp cut-off after the focus.