Optical distance meter using a short pulse width laser diode and a fast avalanche photodiode

Abstract

An accurate optical distance meter that features a pulsed laser diode as a light source and two avalanche photodiodes as detectors, is reported. A cascade connection of avalanche transistors drives the laser diode to emit a periodic output pulse of 0.8 ns rise time. The photodiode rise time was found to increase whenever the incident intensity decreased below a certain threshold. Measurement errors caused by this effect were corrected by numerical processing. The optical distance meter yielded a calibration error of 0.5 mm for a white paper target placed 1 m from the laser source. The distance meter was also utilized to profile the bottom of a plastic waterpipe.