  A coherent receiver that can demodulate high-speed in-phase and quadrature
signals of light is an essential component for optical communication,
interconnects, imaging, and computing. Conventional waveguide-based coherent
receivers, however, exhibit large footprints, difficulty in coupling a large
number of spatial channels efficiently, and limited operating bandwidth imposed
by the waveguide-based optical hybrid. Here, we present a surface-normal
coherent receiver with nanometallic-grating-based polarizers integrated
directly on top of photodetectors without the need for an optical hybrid
circuit. Using a fabricated device with the active section occupying a
70-{\mu}m-square footprint, we demonstrate demodulation of high-speed (up to 64
Gbaud) coherent signals in various formats. Moreover, ultra-broadband operation
from 1260 nm to 1630 nm is demonstrated, thanks to the wavelength-insensitive
nanometallic polarizers. To our knowledge, this is the first demonstration of a
surface-normal homodyne optical receiver, which can easily be scaled to a
compact two-dimensional arrayed device to receive highly parallelized coherent
signals.
