  Artificial intelligence empowered autonomous vehicles and robotics have to
sense the fast-changing three-dimensional environment with high precision and
speed. However, it is challenging for the state-of-the-art ambiguity-free light
detection and ranging (LiDAR) techniques to achieve absolute distance
measurement with simultaneous high precision and high acquisition rate. Here we
demonstrate an electro-optic frequency comb-enabled precise absolute distance
measurement method, repetition rate modulated frequency comb (RRMFC), with
megahertz-level acquisition rate. To achieve RRMFC, we designed and fabricated
an integrated lithium niobate phase modulator with a modulation length of 5 cm
and a half-wave voltage of 1.52 V, leading to over 50 sidebands and a
continuously tunable repetition rate. Leveraging these unique features, RRMFC
can directly resolve distance in time domain, leading to an acquisition rate as
high as 25 MHz and an Allan deviation down to 13.77 {\mu}m at an averaging time
of 724 {\mu}s. Based on RRMFC, we achieved high-speed 3D imaging at
millimeter-level precision with a single laser. RRMFC-based LiDAR allows the
autonomous vehicles and robotics to sense the fine details of fast-changing
environment with high precision.
