Abstract
We report a microfluidic fiber-optic refractive index (RI) sensor based on an in-line Fabry-Perot (FP) interferometer, which is formed by a silica tube sandwiched by two microstructured fibers (MFs). The sensor reported here can be fabricated at low cost, possess a robust structure, and has microfluidic capability. The micro-sized holes in the MFs naturally function as microfluidic channels through which liquid samples can be efficiently and conveniently delivered into and out of the FP cavity by a pressure/vacuum pump system for high-performance RI measurement. Due to the microfluidic capability enabled by the MFs, only sub microliter sample is required. We also experimentally study and demonstrate the superior performances of the sensor in terms of high RI sensitivity, good measurement repeatability, and low temperature cross-sensitivity.
Highlights
Fiber-optic refractive index (RI) sensors have received a great deal of attention due to their important applications in biosensing and chemical sensing and their many advantages such as immunity to electromagnetic interference, remote sensing capability, small size and high sensitivity
We report a microfluidic fiber-optic refractive index (RI) sensor based on an in-line Fabry-Perot (FP) interferometer, which is formed by a silica tube sandwiched by two microstructured fibers (MFs)
The sensor reported here can be fabricated at low cost, possess a robust structure, and has microfluidic capability
Summary
Fiber-optic refractive index (RI) sensors have received a great deal of attention due to their important applications in biosensing and chemical sensing and their many advantages such as immunity to electromagnetic interference, remote sensing capability, small size and high sensitivity. As most of the light energy is contained in the fiber glass material, evanescent-field based sensors suffer from low RI sensitivity, nonlinear RI response, and large temperature crosssensitivity These drawbacks can be overcome by a Fabry-Perot (FP) interferometer (FPI)based RI sensor whose cavity can be filled with the liquid being measured, resulting in a complete overlap between the optical field and the medium being measured. The small thermal expansion coefficient of the silica material renders the sensor’s insensitivity to temperature variations Such a sensor has been fabricated by machining a micro-notch into the core of a single-mode fiber (SMF) to form a fiber in-line FPI using a femtosecond (fs) laser [6]. The smooth cleaved fiber end faces lead to high fringe visibility
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