Design of broadband high-efficiency superconducting-nanowire single photon detectors

TL;DR

This paper explores various designs to enhance the absorption efficiency of superconducting nanowire single-photon detectors, achieving over 97% efficiency with optical cavities and proposing broadband, polarization-insensitive waveguide-coupled detectors using GaN/AlN materials.

Contribution

It introduces novel cavity and waveguide-based designs for superconducting nanowire single-photon detectors with significantly improved efficiency and broadband capabilities.

Findings

Absorption efficiency over 97% with simple optical cavity.

Potential for >99.9% absorption with dielectric Bragg reflectors.

Design of polarization-insensitive detectors with >95% efficiency over broad wavelength range.

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 micrometers. 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.