Technology

Introduction

The principle of operation is based on the use of laser self-mixing to detect displacements of an external object. This can provide both displacement resolution down to sub-micron resolution and allow detection of very high object speeds (>> 1m/sec).

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Optimal power management is obtained by the use of various power save modes such that power is consumed only when motion is detected.

 

High sensitivity of the device is obtained by use of coherent mixing of light (as in an interferometer) and further enhanced by the fact that an active detector is used that is matched to the wavelength being detected.

 

Principles of the laser self-mixing technology

The sensor contains a laser which spot is imaged on an external surface. This surface reflects light back into the sensor and depending on the phase difference between the reflected light and the light in the cavity, interferes constructively or destructively. Here the laser acts as a tuned receiver that is sensitive only to the emission wavelength. Due to the interaction between emitted beam and reflected beam the laser establishes a new equilibrium wherein more or less power is emitted from front and rear mirror (opposite response at the rear mirror).

1. 3D proximity sensor based on laser self-mixing in the sensor.

 

The laser self-mixing technology is based on:

  • interference
  • doppler effect
Self mixing laser principle

2. Light created in cavity mixes with light reflected back into the sensor from a surface in front of laser.

Constructive & destructive interference

3. The resulting mixed signal is called the undulation signal. This enables the implementation of direction detection

Implementation of direction detection

Protected by a strong patent portfolio

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