  Superconducting nanowire single-photon detectors (SNSPDs) have attracted
remarkable interest for visible and near infrared single-photon detection,
owing to their outstanding performance. Conventional SNSPDs are generally used
as binary photon-counting detector. Another important characteristic of light,
i.e., polarization, has not been resolved using standalone SNSPDs. In this
work, we simulated, fabricated, and characterized a linear polarimeter based on
a four-pixel NbN superconducting nanowire array, capable of resolving the
polarization state of linearly polarized light at the single-photon level. The
detector array design is based on a division of focal plane sensor, in which
the orientation of each nanowire division (pixel) is offset by 45 degree. Each
single nanowire pixel operates as a combination of photon detector and almost
linear polarization filter, with an average polarization extinction ratio of
approximately 10. The total system detection efficiency with four pixels is
approximately 1% at a total dark count rate of 680 cps, when the detector array
is free-space coupled and illuminated with 1550 nm photons. The Stokes
parameters are extracted from polarization measurements of the four pixels. The
mean errors of the measured AoP and DoLP were about -3 degree and 0.12,
respectively. Our results indicate that it is possible to develop a scalable
polarization polarimeter or imager based on a superconducting nanowire array.
This detector array may find promising application in single-photon
polarization detection and imaging.
