Abstract

There is a large demand for the development of portable easy-to-use on-chip biosensors capable of single molecule detection. In this paper, we propose a new ultrasensitive label-free optical refractive index sensor consisting of a Fabry–Perot resonator evanescently coupled to a microring resonator. The coupling between the Fabry–Perot standing wave mode and degenerate whispering gallery modes of the microring leads to a splitting of the resonances proportional to the coupling. Choosing the coupling region to be a microfluidic channel through which the analyte solution is pumped leads to a change in the splitting proportional to the index of refraction of the analyte that is immune to common-mode noise sources in the resonators such as thermal noise. The high sensitivity of the coupling to the analyte index combined with the reduced noise leads to significant improvement in the detection limit down to $\sim {10}^{-9}\mathrm{RIU}$.

© 2017 Optical Society of America