Ultimate phase sensitivity in surface plasmon resonance sensors by tuning critical coupling with phase change materials

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