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.