  Recently, there has been growing interest and effort in developing high-speed
high-precision 3D imaging technologies for a wide range of industrial,
automotive and biomedical applications. Optical frequency-modulated continuous
wave (FMCW) light detection and ranging (LiDAR), which shares the same working
principle as swept-source optical coherence tomography (SSOCT), is an emerging
3D surface imaging technology that offers higher sensitivity and resolution
than conventional time-of-flight (ToF) ranging. Recently, with the development
of high-performance swept sources with meter-scale instantaneous coherence
lengths, the imaging range of both OCT and FMCW has been significantly
improved. However, due to the limited bandwidth of current generation
digitizers and the speed limitations of beam steering using mechanical
scanners, long range OCT and FMCW typically suffer from a low 3D frame rate
(<1Hz), which greatly restricts their applications in imaging dynamic or moving
objects. In this work, we report a high-speed FMCW based 3D surface imaging
system, combining a grating for beam steering with a compressed time-frequency
analysis approach for depth retrieval. We thoroughly investigate the
localization accuracy and precision of our system both theoretically and
experimentally. Finally, we demonstrate 3D surface imaging results of multiple
static and moving objects, including a flexing human hand. The demonstrated
technique performs 3D surface imaging with submillimeter localization accuracy
over a tens-of-centimeter imaging range with an overall depth voxel acquisition
rate of 7.6 MHz, enabling densely sampled 3D surface imaging at video rate.
