Numerical method to optimize the polar-azimuthal orientation of infrared superconducting-nanowire single-photon detectors

Abstract

A finite-element method for calculating the illumination-dependence of absorption in three-dimensional nanostructures is presented based on the radio frequency module of the Comsol Multiphysics software package (Comsol AB). This method is capable of numerically determining the optical response and near-field distribution of subwavelength periodic structures as a function of illumination orientations specified by polar angle, φ, and azimuthal angle, γ. The method was applied to determine the illuminationangle-dependent absorptance in cavity-based superconducting-nanowire single-photon detector (SNSPD) designs. Niobium-nitride stripes based on dimensions of conventional SNSPDs and integrated with ∼ quarter-wavelength hydrogen-silsesquioxane-filled nano-optical cavity and covered by a thin gold film acting as a reflector were illuminated from below by p-polarized light in this study. The numerical results were compared to results from complementary transfer-matrix-method calculations on composite layers made of analogous film-stacks. This comparison helped to uncover the optical phenomena contributing to the appearance of extrema in the optical response. This paper presents an approach to optimizing the absorptance of different sensing and detecting devices via simultaneous numerical optimization of the polar and azimuthal illumination angles.

Plasmon enhanced single-photon detection

“…The preference to E-field oscillation direction parallel to the pattern is in accordance with the literature and is attributed to the larger penetration into the lossy nanowires 17,18 .…”

“…To determine the optimal configuration of each design type, the numerical method developed in our previous work was applied, which is based on the RF module of COMSOL software package 17 . The optimal illumination direction was determined by varying the ϕ polar and γ azimuthal angles, than the spectral response was studied around the NbN absorptance maxima observed in polar angle, finally higher resolution computations were performed at the optimal orientations to determine the bandwidth, where significant absorptance enhancement is attainable.…”

“…In our previous studies we have inspected versatile plasmonic structure integrated devices, such as (i) optical cavity integrated OC-SNSPD 17,18 , where the meandered NbN pattern is embedded into single continuous quarter-wavelength dielectric layer closed by a gold reflector, (ii) nano-cavity-array-integrated NCAI-SNSPD 19,20 comprising array of quarter-plasmonic-wavelength nano-cavities closed by vertical and horizontal segments, as well as (iii) nano-cavitydeflector-array integrated NCDAI-SNSPD 20 , consisting of longer vertical gold segments.…”

“…Two periodicity intervals were inspected, the usual sub-wavelength ~200 nm pitch capable of maximizing absorptance [17][18][19][20] , and an approximately three-times larger periodicity commensurate with the plasmon wavelength, having potential to promote interaction with propagating surface modes 19,20 .…”

Improvement of infrared single-photon detectors absorptance by integrated plasmonic structures

“…Novel approaches based on plasmonic structures' integration into SNSPDs open novel avenues in secure communication and in quantum-key computing as well44454647484950. The most simple noble metal structure integrated into SNSPDs was a thin gold reflector aligned onto the top of quarter-wavelength dielectric cavity, which made possible to reach ~50% absorptance454647.…”