Nonideal optical cavity structure of superconducting nanowire single photon detector

TL;DR

This paper investigates how non-ideal, arc-shaped optical cavities in superconducting nanowire single photon detectors affect their optical absorption efficiency and wavelength response, providing insights for improved device design.

Contribution

It analyzes the impact of unexpected arc-shaped cavities caused by fabrication over-etching on SNSPD performance using optical simulations.

Findings

Arc-shaped cavities cause a blue shift in the device’s central wavelength.

The arc-shaped cavity behaves like a flat cavity with reduced height.

Non-ideal cavity structures influence polarization-dependent absorption efficiency.

Abstract

Optical cavity structure has been proven to be a crucial factor for obtaining high detection efficiency in superconducting nanowire single photon detector (SNSPD). Practically, complicated fabrication processes may result in a non-ideal optical cavity structure. The cross-sectional transmission electron microscope (TEM) image of SNSPD fabricated in this study shows unexpected arc-shaped optical cavities which could have originated due to the over-etching of SiO2 layer while defining NbN nanowire. The effects of the arc-shaped optical cavity structure, such as the wavelength dependence of the optical absorption efficiency for different polarization, were analyzed by performing optical simulations using finite-difference time-domain method. The central wavelength of the device is found to exhibit a blue shift owing to the arced cavity structure. This effect is equivalent to the flat cavity with a reduced height. The results may give interesting reference for SNSPD design and fabrication.