Investigation of Optical Coupling in Microwave Kinetic Inductance Detectors using Superconducting Reflective Plates

TL;DR

This paper explores enhancing optical coupling in MKIDs by integrating a superconducting reflective plate beneath the absorber, aiming to increase photon absorption efficiency.

Contribution

It introduces a novel design with a reflective bilayer and dielectric spacer to improve optical coupling in MKIDs, validated through fabrication and characterization.

Findings

High-Q TiN-based MKIDs achieved on sapphire

Reflective bilayer enhances photon absorption

Design effectively recovers undetected photons

Abstract

To improve the optical coupling in Microwave Kinetic Inductance Detectors (MKIDs), we investigate the use of a reflective plate beneath the meandered absorber. We designed, fabricated and characterized high-Q factors TiN-based MKIDs on sapphire operating at optical wavelengths with a Au/Nb reflective thin bilayer below the meander. The reflector is set at a quarter-wave distance from the meander using a transparent Al$_2$O$_3$ dielectric layer to reach the peak photon absorption. We expect the plate to recover undetected photons by reflecting them back onto the absorber.