  In this paper, the design of superconducting-nanowire single-photon detectors
which are insensitive to the polarization of the incident light is
investigated. By using high-refractive-index dielectrics, the index mismatch
between the nanowire and the surrounding media is reduced. This enhances the
absorption of light with electric field vector perpendicular to the nanowire
segments, which is generally hindered in this kind of detectors. Building on
this principle and focusing on NbTiN nanowire devices, we present several
easy-to-realize cavity architectures which allow high absorption efficiency (in
excess of 90%) and polarization insensitivity simultaneously. Designs based on
ultranarrow nanowires, for which the polarization sensitivity is much more
marked, are also presented. Finally, we briefly discuss the specific advantages
of this approach in the case of WSi or MoSi nanowires.
