Abstract
We discuss the detection limit for refractometric sensors relying on high-Q optical cavities and show that the ultimate classical detection limit is given by min {Δn} ≳ η, with n + iη being the complex refractive index of the material under refractometric investigation. Taking finite Q factors and filling fractions into account, the detection limit declines. As an example we discuss the fundamental limits of silicon-based high-Q resonators, such as photonic crystal resonators, for sensing in a bio-liquid environment, such as a water buffer. In the transparency window (λ ≳ 1100 nm) of silicon the detection limit becomes almost independent on the filling fraction, while in the visible, the detection limit depends strongly on the filling fraction because the silicon absorbs strongly.
Highlights
Refractometry is one of the classical workhorses among a variety of optical techniques in analytical chemistry
With the aid of perturbation theory, we have explored the fundamental limitations on the detection limit due to material absorption
The main assumption behind this quite intuitive result is that the smallest detectable frequency shift is limited by the resonance linewidth
Summary
Refractometry is one of the classical workhorses among a variety of optical techniques in analytical chemistry. For silicon based sensors operating in an aqueous environment, we find that for λ & 1100 nm, the ultimate detection limit is given by min {∆n} ∼ η with η being the strongly wavelength-dependent imaginary index of water, i.e., the extinction coefficient. We discuss our results in the context of various resonator examples and as a particular example we consider the ultimate detection limit for silicon-based sensors in an aqueous environment.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
