  The advent of the digital age has driven the development of coherent optical
modems -- devices that modulate the amplitude and phase of light in multiple
polarization states. These modems transmit data through fiber optic cables that
are thousands of kilometers in length at data rates exceeding one terabit per
second. This remarkable technology is made possible through near-THz-rate
programmable control and sensing of the full optical wavefield. While coherent
optical modems form the backbone of telecommunications networks around the
world, their extraordinary capabilities also provide unique opportunities for
imaging. Here, we introduce full-wavefield lidar: a new imaging modality that
repurposes off-the-shelf coherent optical modems to simultaneously measure
distance, axial velocity, and polarization. We demonstrate this modality by
combining a 74 GHz-bandwidth coherent optical modem with free-space coupling
optics and scanning mirrors. We develop a time-resolved image formation model
for this system and formulate a maximum-likelihood reconstruction algorithm to
recover depth, velocity, and polarization information at each scene point from
the modem's raw transmitted and received symbols. Compared to existing lidars,
full-wavefield lidar promises improved mm-scale ranging accuracy from brief,
microsecond exposure times, reliable velocimetry, and robustness to intererence
from ambient light or other lidar signals.
