Absorption engineering of NbN nanowires deposited on silicon nitride nanophotonic circuits

Abstract

Abstract:We investigate the absorption properties of U-shaped niobium nitride (NbN) nanowires atop nanophotonic circuits. Nanowires as narrow as 20nm are realized in direct contact with Si3N4 waveguides and their absorption properties are extracted through balanced measurements. We perform a full characterization of the absorption coefficient in dependence of length, width and separation of the fabricated nanowires, as well as for waveguides with different cross-section and etch depth. Our results show excellent agreement with finite-element analysis simulations for all considered parameters. The experimental data thus allows for optimizing absorption properties of emerging single-photon detectors co-integrated with telecom wavelength optical circuits. Harris, "High quality mechanical and optical properties of commercial silicon nitride membranes," Appl.

Waveguide integrated superconducting single-photon detectors with high internal quantum efficiency at telecom wavelengths

“…half the wire length for two-striped, single-loop wires, is varied from 40-90 μm in 10 μm increments, thus allowing us to investigate the detection efficiency in dependence of the wire length. Because the absorption efficiency increases exponentially with increasing wire length 33 , the overall detection efficiency improves accordingly. In the following we restrict our analysis to the longest wires where the absorption efficiency reaches its maximum value.…”

“…In our travelling wave geometry, the AE of the SNSPD can be maximized by increasing the nanowire-covered area of the waveguide, i.e. by adjusting the width and the length of the detector 33 39 . The QE on the other hand inherently depends on the kinetics of the breakdown of the superconductivity upon the absorption of a photon 18 47 .…”

“…This behavior in QE allows us to operate our detectors in a region where the internal QE is high while remaining sufficiently far from I C to avoid the accumulation of false counts, which is attractive compared to alternative single-photon detectors at 1550 nm wavelength. The absolute OCDE values can then be further improved by extending the nanowire length to increase the AE 33 . Alternatively the waveguide cross-section could be reduced to achieve stronger coupling of propagating light to the nanowire.…”

“…In this design, photons are no longer absorbed under normal incidence, but rather by evanescent coupling to the superconducting nanowire which is situated directly atop an optical waveguide. The available coupling length over which photons are absorbed can in principle be increased arbitrarily to achieve near-unity absorption efficiency 33 . More importantly, however, such a design is directly compatible with integrated optical circuits and thus ideally suited to complement integrated quantum optical platforms 34 35 36 37 38 .…”

Superconducting single-photon detectors integrated with diamond nanophotonic circuits

“…For detectors with longer wires the on-chip detection efficiency improves due to the increase in absorption efficiency. 51 In the case of an 80 µm long single meander detector the measured on-chip detection efficiency is 40% when biased at 96% of the critical current. As expected from the absorption measurements, detectors with the same device length but different meander conformation show different efficiencies (Fig.…”