Optofluidic refractometer using resonant optical tunneling effect

This paper presents the design and analysis of a liquid refractive index sensor that utilizes a unique physical mechanism of resonant optical tunneling effect (ROTE). The sensor consists of two hemicylindrical prisms, two air gaps, and a microfluidic channel. All parts can be microfabricated using an optical resin NOA81. Theoretical study shows that this ROTE sensor has extremely sharp transmission peak and achieves a sensitivity of 760 nm/refractive index unit (RIU) and a detectivity of 85 000 RIU⁻¹. Although the sensitivity is smaller than that of a typical surface plasmon resonance (SPR) sensor (3200 nm/RIU) and is comparable to a 95% reflectivity Fabry–Pérot (FP) etalon (440 nm/RIU), the detectivity is 17000 times larger than that of the SPR sensor and 85 times larger than that of the FP etalon. Such ROTE sensor could potentially achieve an ultrahigh sensitivity of 10⁻⁹ RIU, two orders higher than the best results of current methods.