  The optimal orientations are determined for polarized substrate side
illumination of three superconducting nanowire single-photon detector (SNSPD)
designs: (1) periodic niobium-nitride (NbN) stripes standing in air with
dimensions according to conventional SNSPDs, (2) same NbN patterns below
~quarter-wavelength hydrogensilsesquioxane-filled nano-cavity, (3) analogous
NbN patterns in HSQ nano-cavity closed by a thin gold reflector. Numerical
computation results have shown that the optical response and near-field
distribution vary significantly with polar-angle, fi, and these variations are
analogous across all azimuthal-angles, gamma, but are fundamentally different
in various device designs. Larger absorptance is available due to p-polarized
illumination of NbN patterns in P-structure configuration, while s-polarized
illumination results in higher absorptance in S-structure arrangement. As a
result of p-polarized illumination a global maximum appears on absorptance of
bare NbN pattern at polar angle corresponding to NbN-related ATIR; integration
with HSQ nano-cavity results in a global absorptance maximum at polar angle
corresponding to TIR at sapphire-air interface; while the highest absorptance
is observable at perpendicular incidence on P-structures aligned below gold
reflector covered HSQ nano-cavity. S-polarized light illumination results in a
global absorptance maximum at TIR on bare NbN patterns; the highest absorptance
is available below HSQ nano-cavity at polar angle corresponding to ATIR
phenomenon; while the benefit of gold reflector is large and polar angle
independent absorptance.
