Beyond Q: The Importance of the Resonance Amplitude for Photonic Sensors

Resonant photonic sensors are enjoying much attention basedon the worldwide drive toward personalized healthcare diagnostics and theneed to better monitor the environment. Recent developments exploitingnovel concepts such as metasurfaces, bound states in the continuum, andtopological sensing have added to the interest in this topic. The drive towardincreasingly higher quality (Q)-factors, combined with the requirement forlow costs, makes it critical to understand the impact of realistic limitationssuch as losses on photonic sensors. Traditionally, it is assumed that thereduction in theQ-factor sufficiently accounts for the presence of loss. Here,we highlight that this assumption is overly simplistic, and we show that losseshave a stronger impact on the resonance amplitude than on theQ-factor. Wenote that the effect of the resonance amplitude has been largely ignored in theliterature, and there is no physical model clearly describing the relationship between the limit of detection (LOD),Q-factor, andresonance amplitude. We have, therefore, developed a novel, ab initio analytical model, where we derive the completefigure of meritfor resonant photonic sensors and determine their LOD. In addition to highlighting the importance of the optical losses and theresonance amplitude, we show that, counter-intuitively, optimization of the LOD is not achieved by maximization of theQ-factor butby counterbalancing theQ-factor and amplitude. We validate the model experimentally, put it into context, and show that it isessential for applying novel sensing concepts in realistic scenarios.

Automated summary

Resonant photonic sensors have significant applications in personalized healthcare diagnostics and environmental monitoring. However, there is currently a lack of comprehensive theoretical models for understanding the impact of practical limitations such as losses. In this study, a new model is proposed, which reveals that losses have a stronger impact on the resonance amplitude than on the Q-factor. Furthermore, it is shown that optimizing the detection limit is achieved by balancing the Q-factor and amplitude, rather than maximizing the Q-factor.