Three-dimensional imaging with arrays of Geiger-mode avalanche photodiodes

Lincoln Laboratory has developed 32×32-pixel ladar focal planes comprising silicon Geiger-mode avalanche photodiodes and high-speed all-digital CMOS timing circuitry in each pixel. In Geiger-mode operation, the APD can detect as little as a single photon, producing a digital CMOS-compatible voltage pulse. This pulse is used to stop a high-speed counter in the pixel circuit, thus digitizing the time of arrival of the optical pulse. This "photon-to-digital conversion" simultaneously achieves single-photon sensitivity and 0.25-ns timing precision. We discuss the development of these focal planes and present imagery from ladar systems that use them.