Development and analysis of three-dimensional imaging laser radar system using Geiger-mode avalanche photo diode

Abstract

Direct-detection laser radar system using Geiger-mode avalanche photodiode (GAPD) has been inves-tigated in order to acquire three-dimensional images of objects at a long distance (more than 100m). Due to extremely high sensitivity of the GAPD, the characteristics of a laser radar system using GAPD are not only advantageous in terms of ranging a distant object but also in detecting a target screened by a sparse obstacle located in front of it. Both laser radar systems using a single-pixel GAPD and 1x8-pixel GAPD focal plane array as detectors have been built up and analyzed. The theoretical model of the laser radar system using GAPD has been also established with Poisson statistics and demonstrated experimentally. Passively Q-switched microchip laser has been used as a laser source; a compact peripheral compo-nent interconnect system, which includes a time-to-digital converter (TDC), has been set up for fast signal processing. With both the GAPD having short dead-time (45ns) and the TDC functioning multi-stop acquisition, the system operates in a multi-hit mode. The software for the three-dimensional visualization and an algorithm for the removal of noise have been developed. The comparisons between single- and multi-hit modes were carried with the theoretical analysis of target-detection probability and three-dimensional images taken in both modes. It was shown that the single-shot precision of the system is ~ 10cm (σ) and the precision is improved by increasing the number of laser pulses to be averaged so that the precision of ~1cm (σ) was acquired with more than 150 laser pulses scattered from the target. The accuracy of the system has been measured to be 12cm when the energy of the emitted laser pulse varied with a factor of 7; the technique for the reduction of range walk error was proposed and demonstrated experimentally. Three-dimensional images taken by the laser radar systems are shown. For better transverse spatial resolution in the case of using GAP...