Material limitations on the detection limit in refractometry

Peder Skafte-Pedersen, Pedro Nunes, Sanshui Xiao, Asger Mortensen

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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.
Original languageEnglish
Issue number11
Pages (from-to)8382-8390
Publication statusPublished - 2009

Bibliographical note

This article is an open-access article distributed under the terms and conditions of the Creative Commons Attribution license


  • resonators
  • optofluidics
  • refractometry
  • photonic crystals


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