1.1. Previous work and aim of this research

Pulsed time-of-flight (TOF) laser rangefinding is one of the main areas of research at the Electronics Laboratory of the University of Oulu. Work began over twenty years ago (Ahola 1979), and 5 doctoral theses have been produced to date (Ahola 1987, Kostamovaara 1986, Määttä 1995, Ruotsalainen 1999a, Räisänen-Ruotsalainen 1998) together with numerous Licenciate theses and M.Sc. dissertations. The research has been concentrated in three subareas: receiver channel electronics, time interval measurement and generation of optical pulses, which together cover the main functions of a pulsed time-of-flight laser rangefinder. The ensuing co-operation has helped companies in the Oulu area to create and develop commercial products in the field of laser rangefinding.

The focus in the research at the Electronics Laboratory has moved from large, discrete component realisations into smaller realisations utilising full-custom application-specific integrated circuits (ASIC). The laser radars constructed using discrete components, shown in Fig. 1a, are already commercial products and achieve cm-level measurement accuracy with a power consumption of about 20 W (Määttä 1995). A prototype of a hand-held laser radar device, shown in Fig. 1b, that achieves mm-level accuracy with a power consumption 4 W (paper VI) utilises AISCs in the receiver channel and time interval measurement functions and is coupled to a portable PC for displaying and storing the results. The next phase in the research, which is already under way, is aimed at further increasing the level of integration and constructing a ”component-like” miniaturised laser radar which also includes a laser pulse transmitter. An example of the research is the receiver hybrid for a laser radar, comprising a photodetector, amplifier channel and timing discriminator, shown in Fig. 1c.

The aim of this work was to develop pulsed TOF laser rangefinding technologies for a laser radar module usable in industrial measurement applications where mm or cm-level accuracy is needed. The goal of this development effort was to reduce the size of the laser radar and to increase the level of integration. The smaller size would open up new applications such as positioning of tools and vehicles, anti-collision radars and proximity sensors.