High Aspect-Ratio Open Grating Fabry-Perot Resonator for High-Sensitivity Refractive Index Sensing

Abstract

This paper presents a high aspect-ratio open grating Fabry-Perot resonator theoretically and experimentally for aqueous refractive index sensing with high figure of merit. Transmission line modelling and associated Smith charts are utilized to give a better intuitive understanding of the physical sensing mechanism. The analysis aids understanding of the relative contribution to refractive index changes both within the grating fingers and external to them. Measurements of refractive index are carried out with Kretschmann coupling configuration for both transverse magnetic (TM) and transverse electric (TE) polarization. The results show an improvement of 10- and 44-fold in figure of merit over conventional SPR for TM and TE, respectively. When the designed system is analyzed for sensitivity, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${{1}.{874}\times }{{{10}}}^{-{8}}{\textit {RIU}}$ </tex-math></inline-formula> is achieved with a single frame even without a reference channel for noise cancellation. With 794 frames averaging (approximately 1-second acquisition time), the sensitivity of the system can be further improved to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${{1}.{609}\times }{{{10}}}^{{-{9}}}{\textit {RIU}}$ </tex-math></inline-formula> . The simulations and experimental results demonstrate strong potential for biosensing applications, e.g., kinetic molecular binding, ultrasensitive refractive index sensing and photoacoustic detection.