Self-Mixing Laser Distance-Sensor Enhanced by Multiple Modulation Waveforms

Optical rangefinders based on Self-Mixing Interferometry are widely described in literature, but not yet on the market as commercial instruments. The main reason is that it is relatively easy to propose new elaboration techniques and get results in controlled conditions, while it is very difficult to develop a reliable instrument. In this paper, we propose a laser distance sensor with improved reliability, realized through a wavelength modulation at a different frequency, able to decorrelate single measurement errors and obtain improvement by averages. A dedicated software is implemented to automatically calculate the modulation pre-emphasis, needed to linearize the wavelength modulation. Finally, data selection algorithms allow to overcome signal fading problems due to the speckle effect. A prototype demonstrates the approach with about 0.1 mm accuracy up to 2 m of distance at 200 measurements per second

Short-Range Contactless Laser Sensor

In this paper is shown all the process is needed to build a laser sensor, developed specifically for very short distance with a very compact size. Only the laser chip, a red VCSEL laser without any lens, makes the sensor. Features of this contactless sensor is a dynamic of measurement of 3 mm starting at 2 mm up to 5 mm with a resolution of 10 µm measuring continuously at 6.6 kHz. This sensor can be exploited in applications in harsh environments where the size of the sensor is challenging