Philips Laser Sensors, a business within the Philips Technology Incubator, has developed a new generation of ultra-small position/velocity sensors based on Philips’ twin-eye laser technology. The highly integrated and smart laser sensor can meet the price levels needed for use in consumer products such as computer mice, identification devices, printers or mobile phones. Compared to other optical sensors like LED- and CCD-based devices, this twin-eye laser sensor has high resolution, consumes less power and can detect the movement of virtually any physical surface.

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Featuring fully integrated optics and digital signal processing, these highly innovative system-in-package (SiP) sensors have a footprint of less than half a centimeter square. These low-power sensors have the potential to measure movements of less than 1 µm and velocities of several meters per second. Because the sensor can directly measure velocity, it has no intrinsic acceleration limit.

Philips twin-eye laser technology exploits a phenomenon known as laser self-mixing, in which laser light reflected from the target surface re-enters the illuminating laser where it optically interferes with the emitted laser light. This interference effect, which depends on the frequency difference between the emitted and reflected radiation caused by motion of the target, results in power fluctuations in the laser that are detected by a photo-diode integrated into the sensor. The resolution is similar to that in far more expensive laser Doppler interferometers. By modulating the wavelength of the laser, it is possible to detect the direction in which the target surface is moving as well as its speed, allowing continuous displacement vectors to be calculated. Eye-safety is insured by dynamic control of laser power and independent power-monitoring circuitry integrated into the device.

Philips Laser Sensors’ first implementation of this technology in a commercial product is the company’s PLN2020 twin-eye laser sensor. This dual laser sensor is developed in close collaboration with Logitech for use in the Logitech V400 laser cordless mouse for notebooks. The 11-pin 3.85-mm high twin-eye laser sensor has a printed circuit board footprint of a mere 6.8 mm x 6.8 mm and incorporates lenses for its two lasers in the package assembly. These lenses project two orthogonal laser beams for X-Y position sensing. Working together, they can also simultaneously detect Z-axis movements. The SiP also contains a dedicated ASIC (application-specific integrated circuit) which performs all the necessary digital and analog signal processing for displacement calculation and laser power saving and eye-safety management functions. Mass production of the PLN2020 twin-eye laser sensors is planned for Q4, 2005.

Philips has already established an extensive IP portfolio for the technology, both in terms of patents and invention disclosures.