A three-dimensional laser range scanner based on the self-mixing effect in a laser diode.

Abstract

In the last few decades, the field of artificial vision has witnessed an overwhelming growth through academic research and increasing industry demands. One of the more exciting and promising developments in the field has taken form in the 3D vision paradigm. With the advent of 3D vision, the possibility to directly map in three dimensions the shape of an object has opened a wealth of new possibilities. The purpose of this work is to present the theory and design of a low-cost, portable and accurate 3D laser range scanning system. The system allows direct acquisition of 3D images from a scene. The proposed 3D imaging method uses a laser beam for measuring the distance to a target in a fixed point and computing its (X, Y, Z) coordinate in space. Through deflection of this beam using small motorized mirrors, a distant surface may be scanned into a full 3D range image. Unlike conventional ranging systems, the present design uses a single semiconductor laser diode serving as both a laser source and detector. Laser ranging is achieved through frequency modulation of the laser with time-of-flight coherent detection, based on the self-mixing effect in a laser diode. This allows for unambiguous range measurement capabilities over several meters. The benefits of this sensing approach over existing laser-based systems are numerous, and include: (1) Very low cost solution to the ranging problem. (2) No need for external optical sensing elements. (3) Coaxial source and detector configuration eliminates shadowing problems. (4) Coherent detection yields constant ranging error over useful workspace. (5) Velocity and range information available from a single measurement. (6) Interferometric scale measurements possible in fixed-frequency regime.