Optimized polar-azimuthal orientations for polarized light illumination of different superconducting nanowire single-photon detector designs

Abstract

The optimum orientations were determined for polarized light illumination of three superconducting nanowire single-photon detector (SNSPD) designs consisting of niobium-nitride (NbN) stripes with dimensions according to conventional devices in 200 nm periodic pattern: (1) standing in air (bare-SNSPD), (2) below ∼quarter-wavelength hydrogen-silsesquioxane (HSQ) filled nano-cavity (DC-SNSPD), and (3) below HSQ-filled nano-cavity closed by a thin gold reflector (OC-SNSPD). Computations showed that the optical response and near-field distribution vary significantly with polar angle φ, and these variations are analogous across all azimuthal angles γ, but are fundamentally different in different device designs. Larger absorptance is attainable due to p-polarized illumination of NbN patterns in P-orientation, while s-polarized illumination results in higher absorptance in S-orientation. As a result of p-polarized illumination, a global NbN absorptance maximum appears in bare-SNSPD at polar angle corresponding to attenuated total internal reflection (ATIR); in DC-SNSPD exactly at total internal reflection (TIR); and at perpendicular incidence in OC-SNSPD. S-polarized illumination results in a global NbN absorptance maximum in bare-SNSPD at TIR; in DC-SNSPD at polar angle corresponding to ATIR phenomenon; while large and almost polar angle independent absorptance is attainable in OC-SNSPD at small tilting.