  In-line polarimeters perform non-destructive polarization measurements of
optical signals, and play a critical role in monitoring and controlling the
polarization environment in for example optical networks. While current in-line
polarimeters are constructed with multiple optical components, either
fabricated into an optical fiber or using free-space optics, we present here a
novel architecture conducive to monolithic on-chip integration. This enables
the scalable fabrication of high-performance polarization sensors with
exceptional stability, compactness and speed. The method relies on the
detection of the highly polarization-dependent scattered field of a
sub-wavelength antenna array known as metasurface, and is shown here to provide
polarization state measurements matching those of a state-of-the-art commercial
polarimeter.
