  The absorptance of p-polarized light in superconducting-nanowire
single-photon detectors (SNSPDs) was improved by integrating (1)
~quarter-wavelength nano-optical cavity closed by a gold reflector (OC-SNSPD),
(2) nano-cavity-array closed by vertical and horizontal gold segments
(NCAI-SNSPD), and (3) nano-cavity-deflector-array consisting of longer vertical
gold segments (NCDAI-SNSPD) into short- (p-) and long- (3p-) periodic
niobium-nitride (NbN) stripe-patterns. In OC-SNSPDs the highest absorptance is
observable at perpendicular incidence onto NbN stripes in P-orientation due to
E-field concentration at the bottom of nano- cavities. In short-periodic
NCAI-SNSPDs off-axis illumination results in almost polar-angle-independent
perfect absorptance due to collective resonances on plasmonic MIM
nano-cavity-arrays in S-orientation. In long-periodic NCAI-SNSPDs the surface
wave-excitation phenomena promote EM-field transportation to the NbN stripes in
S-orientation and results in local absorptance maxima. In NCDAI-SNSPDs with
proper periodicity large absorptance maxima appear due to synchronous E-field
enhancement via deflected SPPs below NbN stripes in S-orientation, which make
possible fill-factor-related loss compensation.
