Ultimate Phase Sensitivity in Surface Plasmon Resonance Sensors by Tuning Critical Coupling with Phase Change Materials

TL;DR

This paper introduces a novel SPR sensor design that uses phase-change materials to achieve ultra-high sensitivity, overcoming fabrication limitations and enabling detection of extremely small refractive index changes for biomedical and environmental applications.

Contribution

It proposes a PCM-assisted SPR sensor that leverages multilevel phase states to reach critical coupling conditions with practical fabrication tolerances.

Findings

Achieves detection limits as low as 10^{-10} RIU.

Demonstrates theoretical ultra-high phase sensitivities.

Provides a robust method for high-sensitivity sensing applications.

Abstract

Plasmonic sensing is an established technology for real-time biomedical diagnostics and air-quality monitoring. While intensity and wavelength tracking are the most commonly used interrogation methods for Surface Plasmon Resonance (SPR), several works indicate the potential superiority of phase interrogation in detection sensitivity. Here, we theoretically and numerically establish the link between ultra-high sensitivities in phase interrogation SPR sensors and the critical coupling condition. However, reaching this condition requires a technically infeasible angstrom-level precision in the metal layer thickness. We propose a robust solution to overcome this limitation by coupling the SPR with a phase-change material (PCM) thin film. By exploiting the multilevel reconfigurable phase states of PCM, we theoretically demonstrate ultra-high phase sensitivities with a limit of detection as low as $10^{-10}$ refractive index unit (RIU). Such a PCM-assisted SPR sensor platform paves the way for unprecedented sensitivity sensors for the detection of trace amounts of low molecular weight species in biomedical sensing and environmental monitoring.