Design guidelines for optical resonator biochemical sensors

We propose a design tool for dielectric optical resonator-based biochemical refractometry sensors. Analogous to the widely accepted photodetector figure of merit, the detectivity $D^{*}$, we introduce a new sensor system figure of merit, the time-normalized sensitivity $S^{*}$, to permit quantitative, cross-technology-platform comparison between resonator sensors with distinctive device designs and interrogation configurations. The functional dependence of $S^{*}$ on device parameters, such as resonant cavity quality factor (Q), extinction ratio, system noise, and light source spectral bandwidth, is evaluated by using a Lorentzian peak fitting algorithm and Monte Carlo simulations to provide theoretical insights and useful design guidelines for optical resonator sensors. Importantly, we find that $S^{*}$ critically depends on the cavity Q factor, and we develop a method of optimizing sensor resolution and sensitivity to noise as a function of cavity Q factor. Finally, we compare the simulation predictions of sensor wavelength resolution with experimental results obtained in ${\mathrm{Ge}}_{17}{\mathrm{Sb}}_{12}{\mathrm{S}}_{71}$ resonators, and good agreement is confirmed.