Harry Yeates, 15 September 2005, Philips has announced low-cost, compact laser sensors for measuring position and velocity that use a self-mixing effect to give sub-µm resolution similar to that available from laser Doppler interferometers. The firm calls the technology “twin-eye”.
In the effect, laser light is reflected from the target surface and re-enters the illuminating laser, where it interferes with the emitted beam.
Motion of the target results in a frequency difference between the two beams, which causes power fluctuations in the laser that are detected by a photo-diode integrated into the sensor.
By modulating the wavelength of the laser it is possible to detect the direction and speed of travel of the target surface, allowing continuous displacement vectors to be calculated. Because the illuminating and reflected light uses the same optical pathways, the optical components can be simplified.
“As well as improving the performance of conventional position-sensing devices such as computer mice, this technology opens up a new range of applications where high resolution, small size and design-in simplicity are essential design requirements,” said Ralph Gudde, director of marketing and sales at Philips Laser Sensors.
The devices include the necessary optics and DSP functions in one system-in-package, which helps keep costs at a level suitable for consumer applications. The first product to use one is a cordless mouse for notebooks made by Logitech.
