Novel infrared superconducting nanowire single-photon detectors (SNSPD) were designed, which comprise a meandered pattern of niobium-nitride (NbN) stripes and different integrated plasmonic structures on silica substrate. To enhance absorptance of 1550 nm wavelength p-polarized light, patterns with p=264 nm periodicity were investigated, while to enhance detection efficiency, patterns with P=792.5 nm periodicity commensurate with the wavelength of surface plasmon polaritons at silica-gold interface were also designed. In OC-SNSPDs integrated with ~quarter-photonicwavelength nano-optical cavity closed by a gold reflector, the highest 63/27 % absorptance was attained in p/P-pitch design at perpendicular incidence onto NbN patterns in P-orientation corresponding to incidence plane parallel to the stripes, due to the E-field antinode at the NbN-silica interface. In NCAI-SNSPDs, where each NbN stripe is located at the entrance of a quarter-plasmon-wavelength MIM nano-cavity, enhanced 85.1/34 % absorptance is attainable in p/Ppitch design at perpendicular incidence in S-orientation, when the incidence plane is perpendicular to the integrated pattern, due to collective resonances. The maximal 95.3/70.3 % absorptances are attained at large tilting corresponding to plasmonic Brewster angles via ultra-broadband tunneling. In NCDAI-SNSPDs the longer vertical gold segments with P-pitch, which can be embedded into the silica substrate via two-step lithography, enable to attain large absorptance at small polar angles in S-orientation, due to efficient grating-coupling phenomenon. The highest 92.7/75 % absorptances are attained at 19.85°/19.35°polar angles in p/P-pitch design. P-pitch NCDAI-SNSPD supporting coupled surface waves capable of ensuring synchronous E-field enhancement below the NbN stripes is proposed for detection efficiency maximization in specific spectral-bands.