Optimized polar-azimuthal orientations for polarized light illumination of different Superconducting Nanowire Single-Photon Detector designs

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.