  Fast-responding detector arrays are commonly used for imaging
rapidly-changing scenes. Besides array detectors, a single-pixel detector
combined with a broadband optical spectrum can also be used for rapid imaging
by mapping the spectrum into a spatial coordinate grid and then rapidly
measuring the spectrum. Here, optical frequency combs generated from high-$Q$
silica microresonators are used to implement this method. The microcomb is
dispersed in two spatial dimensions to measure a test target. The
target-encoded spectrum is then measured by multi-heterodyne beating with
another microcomb having a slightly different repetition rate, enabling an
imaging frame rate up to 200 kHz and fillrates as high as 48 MegaPixels/s. The
system is used to monitor the flow of microparticles in a fluid cell.
Microcombs in combination with a monolithic waveguide grating array imager
could greatly magnify these results by combining the spatial parallelism of
detector arrays with spectral parallelism of optics.
