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

Abstract

Resonant photonic sensors are enjoying much attention based on the worldwide drive toward personalized healthcare diagnostics and the need to better monitor the environment. Recent developments exploiting novel concepts such as metasurfaces, bound states in the continuum, and topological sensing have added to the interest in this topic. The drive toward increasingly higher quality (Q)-factors, combined with the requirement for low costs, makes it critical to understand the impact of realistic limitations such as losses on photonic sensors. Traditionally, it is assumed that the reduction in the Q-factor sufficiently accounts for the presence of loss. Here, we highlight that this assumption is overly simplistic, and we show that losses have a stronger impact on the resonance amplitude than on the Q-factor. We note that the effect of the resonance amplitude has been largely ignored in the literature, and there is no physical model clearly describing the relationship between the limit of detection (LOD), Q-factor, and resonance amplitude. We have, therefore, developed a novel, ab initio analytical model, where we derive the complete figure of merit for resonant photonic sensors and determine their LOD. In addition to highlighting the importance of the optical losses and the resonance amplitude, we show that, counter-intuitively, optimization of the LOD is not achieved by maximization of the Q-factor but by counterbalancing the Q-factor and amplitude. We validate the model experimentally, put it into context, and show that it is essential for applying novel sensing concepts in realistic scenarios.

Multiplexed Near-Field Optical Trapping Exploiting Anapole States

“…However, for excitation with a focused beam, which is required for the trapping application to achieve reasonable intensities, the coupled anapole state clearly dominates over the distributed mode (Figure 2c and Supporting Information 4). 27,28 Numerical Simulations of the Trapping System. The trapping strength can be enhanced by the self-induced backaction (SIBA) effect 29−31 via red-detuning the input laser by approximately 1 nm from the resonance.…”

Metasurface-enhanced mid-infrared spectroscopy in the liquid phase

“…Such angle-induced mode splitting is a well-understood phenomenon that has previously been reported. 20 The thickness of the Si slab was chosen to maximise performance in terms of the amplitude and quality factor 14 while ensuring ease of fabrication (see Fig. S2 in the ESI † ).…”

“…4,6,13 In contrast, photonic structures such as dielectric metasurfaces involve low losses, support resonances of higher quality and amplitude, and provide eld enhancement at the microscale, which makes them much more suitable for investigating liquid samples, as are commonly found in biological analytes. Such metasurfaces have been demonstrated for SEIRA in physisorbed monolayers, 4,13,14 but demonstrations in dilute liquid samples are yet to be reported.…”

Exfoliated Flexible Photonic Crystal Slabs for Refractive Index and Biomolecular Sensing

“…E.g., plasmonic resonator show a Q-factor around 10, while microsphere resonators may have a high Q-factor of 10 8 to 10 9 [29,30] . Conteduca et al have argued that for labelfree sensing an interplay of amplitude and Q-factor is the limiting factor [31]. We target intermediate Q factors of around 100 to 200 to achieve a good amplitude signal.…”