Design of broadband high-efficiency superconducting-nanowire single photon detectors
L. Redaelli (CEA Grenoble, Université Grenoble Alpes)
G. Bulgarini (Single Quantum)
S Dobrovolskiy (Single Quantum)
S. N. Dorenbos (Single Quantum)
V.G. Zwiller (KTH Royal Institute of Technology, TU Delft - QN/Zwiller Lab, Université Grenoble Alpes, Kavli institute of nanoscience Delft)
E Monroy (Université Grenoble Alpes, CEA Grenoble)
J. M. Gérard (Université Grenoble Alpes, CEA Grenoble)
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Abstract
In this paper several designs to maximize the absorption efficiency of superconducting-nanowire single-photon detectors are investigated. Using a simple optical cavity consisting of a gold mirror and a SiO2 layer, the absorption efficiency can be boosted to over 97%: this result is confirmed experimentally by the realization of an NbTiN-based detector having an overall system detection efficiency of 85% at 1.31 μm. Calculations show that by sandwiching the nanowire between two dielectric Bragg reflectors, unity absorption (>99.9%) could be reached at the peak wavelength for optimized structures. To achieve broadband high efficiency, a different approach is considered: a waveguide-coupled detector. The calculations performed in this work show that, by correctly dimensioning the waveguide and the nanowire, polarization-insensitive detectors absorbing more than 95% of the injected photons over a wavelength range of several hundred nm can be designed. We propose a detector design making use of GaN/AlN waveguides, since these materials allow lattice-matched epitaxial deposition of Nb(Ti)N films and are transparent on a very wide wavelength range.