A highly sensitive optofluidics-based refractometer in a Young interferometer design

Abstract

This paper proposes a highly sensitive and compact optofluidics-based refractometer. Our key idea is based on the use of a two-channel microfluidic chip in a free-space Young interferometer structure that provides an inherent advantage in cancelling the unwanted optical phase noise induced from the surrounding environment during optical beam propagation. By using a 655-nm monochromatic light that travels in free space for 57.5 cm and a microfluidic chip designed to have two fluidic channels in parallel with a distance between channels of 900 μm and a channel depth of 100 μm, our simulation indicates that analysis of the movement of the interference fringe offers a sensitivity of better than 1.31×10-4 in measuring the change of the refractive index. A better than thousand-fold improvement can also be accomplished by investigating the amplitude change of the interference fringe via a > 10-bit digitalization. Our experiment in analyzing the change of the refractive index of the sucrose solution will be discussed. Polarization insensitivity and simplicity in design and implementation are also additional key advantages. © 2010 Copyright SPIE - The International Society for Optical Engineering.