FMCW laser range-finder with an avalanche photodiode working as an optoelectronic mixer

摘要

A Frequency Modulation Continuous Wave (FMCW) laser range-finder has been designed for distances from 1m to 20m with cooperative or diffusing targets. This range-finder is compared to a phase shift laser range-finder. A heterodyne photoreception method is studied. In order to reduce noise, the non linear current-voltage characteristic of the APD is used to obtain an optoelectronic mixer. The photocurrent gain is modulated by the VCO signal working as a local oscillator (LO). The optical and electrical LO injection methods are studied. The theoretical analysis using the Miller model and thermal effects are compared with the first experimental results. The electrical LO injection gives a better ratio-to-noise than the optical LO injection. For electrical injection, it is shown that the heterodyne conversion gain can reach the maximal theoretical value 0.5.