M. Csete, A. Szenes, D. Maráczi, B. Bánhelyi, T. Csendes, G. Szabó
University of Szeged, Hungary
pp. 259 - 263
Keywords: single-photon, detector, plasmonics, grating, absorptance, polarization contrast
Superconducting nanowire single photon detectors (SNSPDs) are important for single-photon detection at 1550 nm infrared wavelength in quantum information processing (QIP), telecommunication and astronomy [1, 2]. Absorptance of single photons with a specific polarization has to be maximized to read-out encoded information with good fidelity in QIP. A-SNSPD configurations capable of maximizing p-polarized light absorptance, and P-SNSPDs with potential to maximize p-to-s absorptance ratio, referred as polarization contrast, were determined for four different plasmonic structure integrated detectors. The studied device types are nano-cavity-array (NCAI-), nano-cavity-deflector-array (NCDAI-), nano-cavity-double-deflector-array (NCDDAI-) and nano-cavity-trench-array (NCTAI-) integrated SNSPDs. The inspected devices consisted of integrated periodic patterns with half- and one-wavelength periodicity, which results in Bragg scattering and Rayleigh phenomenon, respectively. An in-house developed GLOBAL optimization methodology was implemented using LiveLink for MATLAB in RF module of COMSOL to determine the optimal A- and P-SNSPD configurations. In case of C-SNSPDs optimization has been performed for polarization contrast by setting a condition regarding the p-polarized absorptance that have to be parallel met. The criterion regarding the p-polarized absorptance was varied with 0.25% steps in 3% interval of the maximal absorptance. According to our previous studies the optimal tilting of linear plasmonic structure integrated SNSPDs is device structure dependent in S-orientation (90° azimuthal angle) [3-5]. In NCAI- / NCDAI- / NCDDAI-A-SNSPD half-wavelength-scaled patterns are optimal, and results in 94.2% - 94.7% - 94.6% p-polarized absorptance at tilting corresponding to the plasmonic Brewster angle (PBA, 76.4°) / inside a wide plasmonic pass band (0.04°) / and inside crossing bands of cavity and propagating modes (60.9°). The highest 95.1% p-polarized absorptance is achieved via wavelength-scaled NCTAI-A-SNSPD inside an inverted minigap (0.0°), due to the Rayleigh phenomenon on the integrated pattern and promoted by minimized competitive gold absorptance. These p-polarized absorptance maxima are accompanied by moderate 2.4 10^2 / 1.5 10^3 / 2.7 10^3 / 1.2 10^2 polarization contrast. In NCAI- / NCDAI- / NCDDAI- and NCTAI-P-SNSPDs the highest 6.4 10^2 / 6.9 10^11 / 1.8 10^13 / 1.9 10^3 polarization contrasts are achieved uniformly in wavelength-scaled integrated patterns at 85° tilting close to the second Brillouin zone boundary. However, these contrast maxima are accompanied by significantly lower 65.6% - 64.5% - 70.4% - 31.4% p-polarized absorptances. The enhanced and the extremely large polarization contrasts in NCDAI- and NCDDAI-P-SNSPDs indicate the polarization selection role of deflectors. In C-SNSPD devices 3.2 10^2 / 3.0 10^7 / 2.2 10^9 / 2.6 10^2 polarization contrasts are reachable at the expense of 3.0% absorptance decrease. The polarization contrast exhibits correlation with the (extended) cavity length/width, (extended) cavity length in quarter wavelength units and NbN/Au volume fraction ratio. All A-SNSPD devices consist of quarter wavelength cavities capable of squeezing the MIM modes, while in C-SNSPD devices p-polarization specific coupling phenomena become to be at play. Accordingly, in P-SNSPD devices the extended cavities are quarter- / half- / three-quarter- / half-wavelength scaled, which cause decrease in p-polarized absorptance. C-SNSPD devices make possible to achieve the optimal trade-off between absorptance and polarization contrast maximization.