ITEE Innovation Expo 2008 : Project Details

Electronically controlled optical system for a ultra-compact laser rangefinder

Self-mixing interferometry is an alternative process for sensing information about an object using lasers. Unlike standard sensing methods, which rely on a separate laser source and returning light photo detector, self-mixing infers information about a target by measuring a change in laser response due to light reflected back into the lasing cavity.

Research in this area is being expanded to include different methods of sensing, such as using an array of multiple lasers to further improve quality, leading to more accurate vibration, velocity, and flow sensors, as well as rangefinders. Vertical Cavity Surface Emitting Lasers (VCSEL) are used for their ability to be manufactured in arrays on a single chip. Experimentation involving self-mixing requires individual laser drivers and signal recovery circuits exhibiting low noise and a high degree of precision. Additionally, accurate alignment and collimation of each laser is essential.

The aim of this thesis was to redesign an existing instrument used to measure self-mixing signals generated by a 12 channel monolithic VCSEL array. The redesign focused on miniaturising the circuit by reducing the amount of redundant components and adding computer control of the lasers. The miniaturisation should decrease the noise floor caused by long connections. A separate mount, which directly connects to a rigid cage, was designed to allow for accurate laser alignment. Finally the design was made modular to allow future expansion.

The new design is flexible and will help further self-mixing research.