Optical Properties of Superconducting Nanowire Single-Photon Detectors

TL;DR

This study measures and models the optical absorptance of superconducting nanowire single-photon detectors, revealing polarization-dependent sensitivities and the impact of optical cavities on detection efficiency.

Contribution

It provides the first detailed measurements and a numerical model of absorptance in superconducting nanowire detectors, including polarization effects and cavity enhancements.

Findings

Absorptance is 21% for parallel polarization at 1.55 μm.

Devices are five times more sensitive to parallel-polarized photons.

Optical cavities significantly enhance detection efficiency.

Abstract

We measured the optical absorptance of superconducting nanowire single photon detectors. We found that 200-nm-pitch, 50%-fill-factor devices had an average absorptance of 21% for normally-incident front-illumination of 1.55-um-wavelength light polarized parallel to the nanowires, and only 10% for perpendicularly-polarized light. We also measured devices with lower fill-factors and narrower wires that were five times more sensitive to parallel-polarized photons than perpendicular-polarized photons. We developed a numerical model that predicts the absorptance of our structures. We also used our measurements, coupled with measurements of device detection efficiencies, to determine the probability of photon detection after an absorption event. We found that, remarkably, absorbed parallel-polarized photons were more likely to result in detection events than perpendicular-polarized photons, and we present a hypothesis that qualitatively explains this result. Finally, we also determined the enhancement of device detection efficiency and absorptance due to the inclusion of an integrated optical cavity over a range of wavelengths (700-1700 nm) on a number of devices, and found good agreement with our numerical model.