Optimization of Plasmonic Structure Integrated Single-Photon Detector Designs

Mária Csete Department of Optics and Quantum Electronics, University of Szeged, Szeged, Hungary Gábor Szekeres Department of Optics and Quantum Electronics, University of Szeged, Szeged, Hungary Balázs Bánhelyi Department of Computational Optimization, University of Szeged, Szeged, Hungary András Szenes Department of Optics and Quantum Electronics, University of Szeged, Szeged, Hungary Tibor Csendes Department of Computational Optimization, University of Szeged, Szeged, Hungary Gábor Szabó Department of Optics and Quantum Electronics, University of Szeged, Szeged, Hungary

Superconducting nanowire single photon detectors (SNSPD) are devices to detect infrared light up to single-photon resolution with high speed. Plasmonic structures integrated into SNSPDs are capable of enhancing absorptance along with the reduction of kinetic inductance. Nano-cavity-array (NCAI), nanocavity-deflector-array (NCDAI) and nano-cavity-double-deflector-array (NCDDAI) were integrated around meandered pattern of 4 nm thick niobium-nitride (NbN) superconducting stripes [1, 2]. To find the optimal plasmonic structure integrated SNSPD configurations resulting in maximal NbN absorptance for p-polarized 1550 nm light illumination the built in algorithms of COMSOL were used, and all geometrical parameters as well as the illumination direction were varied.

The highest p-polarized absorptance was achieved in S-orientation (γ=90° azimuthal angle) of all integrated SNSPDs. The highest 94.2% absorptance was attained in half-wavelength-scaled periodic NCAI-SNSPD at 76.4° tilting corresponding to the plasmonic Brewster angle. In half-wavelength-scaled NCDAI-SNSPD plasmonic pass bands appeared, and the highest 94.6% absorptance was attained at 50.7° tilting due to refIectance suppression. In NCDDAI-SNSPD three-quarter-wavelength-scaled pattern results in the largest 92.9% absorptance at 18.9° tilting due to first-order grating coupling.

In the optimized configurations the spectral sensitivity and dispersion characteristics were investigated of all integrated SNSPD devices. The optical response for s-polarized light illumination was also inspected, and the achievable polarization contrast was determined. Finally the illumination direction and spectral sensitivity of the polarization contrast was examined, which is a crucial property of SNSPDs in quantum communication and cryptography. In conclusion: half-wavelength-scaled deflector arrays promote to reach larger absorptance, while three-quarter-wavelength-scaled double deflectors make possible to enhance polarization contrast considerably.

Fig. 1

(a) NbN absorptance and polarization contrast as a function of φ polar angle in integrated SNSPDs optimized by COMSOL. Dispersion relation of the optimized (b) NCAI-, (c) NCDAI- and (d) NCDDAI-SNSPD. Time-averaged E-field with power-flow arrows at maxima are depicted as insets.

[1] M. Csete, A. Szalai, Á. Sipos, G. Szabó: Optics Express 20/15, 17065-17081 (2012)

[2] M. Csete, Á. Sipos, A. Szalai, F. Najafi, G. Szabó. K.K. Berggren: Scientific Reports 3:2406 (2012)

mcsete@physx.u-szeged.hu









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