1,222 research outputs found
Single photonics at telecom wavelengths using nanowire superconducting detectors
Single photonic applications - such as quantum key distribution - rely on the
transmission of single photons, and require the ultimate sensitivity that an
optical detector can achieve. Single-photon detectors must convert the energy
of an optical pulse containing a single photon into a measurable electrical
signal. We report on fiber-coupled superconducting single-photon detectors
(SSPDs) with specifications that exceed those of avalanche photodiodes (APDs),
operating at telecommunication wavelength, in sensitivity, temporal resolution
and repetition frequency. The improved performance is demonstrated by measuring
the intensity correlation function g(2)(t) of single-photon states at 1300nm
produced by single semiconductor quantum dots (QDs).Comment: 7 pages, 5 figures - submitted 12 OCT 200
Numerical method to optimize the Polar-Azimuthal Orientation of Infrared Superconducting Nanowire Single-Photon Detectors
A novel finite-element method for calculating the illumination-dependence of
absorption in three-dimensional nanostructures is presented based on the RF
module of the COMSOL software package. This method is capable of numerically
determining the optical response and near-field distribution of sub-wavelength
periodic structures as a function of illumination orientations specified by
polar angle, fi, and azimuthal angle, gamma. The method was applied to
determine the illumination-angle-dependent absorptance in cavity-based
superconducting-nanowire single-photon detector (SNSPD) designs.
Niobium-nitride stripes based on dimensions of conventional SNSPDs and
integrated with ~ quarter-wavelength hydrogensilsesquioxane-filled nano-optical
cavities and covered by a thin gold film acting as a reflector were illuminated
from below by p-polarized light in this study. The numerical results were
compared to results from complementary transfer-matrix-method calculations on
composite layers made of analogous film-stacks. This comparison helped to
uncover the optical phenomena contributing to the appearance of extrema in the
optical response. This paper presents an approach to optimizing the absorptance
of different sensing and detecting devices via simultaneous numerical
optimization of the polar and azimuthal illumination angles.Comment: 15 pages, 4 figure
High-detection efficiency and low-timing jitter with amorphous superconducting nanowire single-photon detectors
Recent progress in the development of superconducting nanowire single-photon
detectors (SNSPDs) made of amorphous material has delivered excellent
performances, and has had a great impact on a range of research fields. Despite
showing the highest system detection efficiency (SDE) ever reported with
SNSPDs, amorphous materials typically lead to lower critical currents, which
impacts on their jitter performance. Combining a very low jitter and a high SDE
remains a challenge. Here, we report on highly efficient superconducting
nanowire single-photon detectors based on amorphous MoSi, combining system
jitters as low as 26 ps and a SDE of 80% at 1550 nm. We also report detailed
observations on the jitter behaviour, which hints at intrinsic limitations and
leads to practical implications for SNSPD performance
Measuring thickness in thin NbN films for superconducting devices
We present the use of a commercially available fixed-angle multi-wavelength
ellipsometer for quickly measuring the thickness of NbN thin films for the
fabrication and performance improvement of superconducting nanowire single
photon detectors. The process can determine the optical constants of absorbing
thin films, removing the need for inaccurate approximations. The tool can be
used to observe oxidation growth and allows thickness measurements to be
integrated into the characterization of various fabrication processes
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