A large-scale coherent 4D imaging sensor

Detailed and accurate three-dimensional (3D) mapping of dynamic
environments is essential for machines to interface with their
surroundings, and for human-machine interaction. Although considerable
effort has been spent to create the equivalent of the CMOS image sensor
for the 3D world, scalable, high-performance, reliable solutions have
proven elusive. Focal plane array (FPA) sensors using frequency modulated
continuous wave (FMCW) light detection and ranging (LiDAR) have shown
potential to meet all the requirements and also provide direct measurement
of radial velocity as a fourth dimension (4D). Prior demonstrations, while
promising, have not achieved the simultaneous scale and performance
required by commercial applications. In this paper, we present a
large-scale, coherent LiDAR FPA enabled by comprehensive chip-scale
optoelectronic integration. A 4D imaging camera is built around the FPA
and used to acquire point clouds. At the core is a 352x176 pixel
two-dimensional FMCW LiDAR FPA comprising over 0.6 million photonic
components, all integrated on-chip together with their associated
electronics. This represents a five times increase in pixel count with
respect to previous demonstrations. The pixel architecture combines the
outbound and inbound optical path within the pixel in a monostatic
configuration, together with coherent detectors and electronics. Frequency
modulated light is directed sequentially to groups of pixels by in-plane
thermo-optic switches with integrated electronics for driving and
calibration. An integrated serial digital interface controls both optical
switching and readout synchronously. Point clouds of objects ranging from
4 to 65 meters with per-pixel integration time compatible with frame rates
from 3 to 15 fps are shown. This result demonstrates the capabilities of
FMCW LiDAR FPA sensors as enablers of ubiquitous, low cost, compact
coherent 4D imaging cameras.