Impact of Polar-Azimuthal Illumination Angles on Efficiency of Nano-Cavity-array Integrated Single-Photon Detectors

The absorptance of superconducting nanowire single-photon detectors consisting of subwavelength NbN stripes arrayed in 200 nm and 600 nm periodic patterns and integrated with nano-cavity-array and closing gold segments is maximized at the wavelength of 1550 nm via numerical computations. It is shown that the optimum azimuthal angles are gamma = 90 degrees (S-orientation) in case of p-polarized illumination, and gamma = 0 degrees (P-orientation) during s-polarized illumination. The p-polarized illumination of 200-nm-pitch design in S-orientation results in polar angle independent similar to 95% NbN absorptance due to collective resonances on the nano-cavity-array. In 600-nm-pitch design a local absorptance maximum (37.2%) appears as a result of near-field concentration promoted by Brewster-wave excitation during p-polarized illumination in S-orientation. For practical applications s-polarized illumination of 600-nm-pitch design in P-orientation is proposed, as similar to 52% absorptance larger than in case of perpendicular incidence is attainable due to total internal reflection. (C) 2012 Optical Society of America