Single-shot 3D imaging matrix offers stealth capabilities

Researchers have demonstrated a single-pulse active 3D imaging matrix operating in the infrared. The imaging matrix can produce a three-dimensional image of a distant object with only a single laser pulse, said the investigators, who work with the Laboratory for Electronics & Information Technology (CEA-Léti), a public research and technology organization.

Development of the imaging matrix was initially driven by military applications, said Gérard Destéfanis of CEA-Léti – specifically, the need to identify a distant object with good stealth, with a single shot. But the device also could contribute to a range of civilian applications, including aerial surveying and mapping the Earth from planes. It offers a spatial resolution of 30 cm.

A view, visible to the eye, of the scene used to demonstrate laser detection and ranging imagery (left). Intensity image expressed in number of photoelectrons per pixel (middle) and relative range color-coded image after nonuniformity correction and intensity correction (right). Because the integration time for 2D was longer (~1 μs) than the duration of the voltage ramp (200 ns), the depth of field is wider in the 2D image than in the 3D. Courtesy of CEA-Léti.

Currently, for eye safety reasons, the 320 x 256 imaging matrix operates at a wavelength of 1.55 µm. It can also operate with infrared lasers at wavelengths up to 5 µm.

CEA-Léti reports that the 3D imaging matrix is the result of two major technical innovations by its researchers. The first of these is the manufacture of an avalanche photodiode matrix created in the HgCdTe semiconductor. Operating in the nanosecond range, the matrix imitates the characteristics of a perfect amplifier, the organization said. It can obtain very high gains (more than 100) at low polarization voltages (less than 10 V), without any excess noise.

The second innovation is the design and manufacture of a readout circuit combining a time-of-flight measurement with a three-dimensional radiometric acquisition.

CEA-Léti performed the work in conjunction with the French company Sofradir. The researchers reported some details of the technical innovations at the SPIE Defense, Security and Sensing meeting in Orlando last April, and at the SPIE Security and Defense meeting in Toulouse last September.