Improvement of infrared single-photon detectors absorptance by   integrated plasmonic structures
  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. 
M. Csete, A. Sipos, A. Szalai, F. Najafi and K. K. Berggren
physics.optics