A low-cost medium-resolution rangefinder based on the self-mixing effect in a VCSEL

This paper focuses on a compact self-aligned noncontact laser rangefinder using a vertical-cavity surface-emitting laser (VCSEL) exposed to optical feedback. By directly modulating the injection current, a number of mode hops occur due to the optical power reinjected in the laser cavity by reflections from the target located in front of the sensor. These reflections are detected by a simple signal processing of the current produced by the monitoring photodiode placed in the same package as the laser. The distance between the target and the laser is proportional to the number of mode hops. Distance measurement can be achieved simply by counting the number of mode hops during a period of the current modulation. The advantage of using a VCSEL over other laser sources is its very low price compared to expensive distributed Bragg reflector (DBR) laser diodes. The resolution obtainable, even if lower than with a DBR source, may, however, be sufficient for most purposes. To our knowledge, it is the first time a VCSEL is used in such a sensor.