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Design and performance of a low-coherence sensor for industrial applications based on a self-mixing superluminescent diode

In this paper a novel low-coherence sensor based on a self- mixing super-luminescent diode (SM-SLD) is described. A commercial low-cost super-luminescent diodes (SLD) driven at constant current is used as low-coherence source. In the same case of the SLD there is a photodiode generally used to monitor the optical power at the emitting junction back-face. In the SM-SLD technique, this photodiode is exploited to detect the interference signal. Hence, the interference signal is optically amplified by the high-gain active medium. The sensor has been properly designed to work in industrial environments and is suitable for measurement of semitransparent slabs thickness, i.e. glass, Plexiglas, polyethylene, etc. Measurements carried out on glass slabs show a measuring range of 15 mm and a linearity error and stability of 1.3 micrometer and 1.6 micrometer respectively.