Compact resonant integrated microfluidic refractometer

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Abstract
We introduce a class of highly compact refractometers integrated onto a planar microfluidic geometry that demonstrates high resolution refractive index measurements in 50 μ m fluid channels utilizing a Fabry–Perot cavity formed between resonant Bragg grating reflectors. This cavity forms a resonant peak in the transmission spectrum which is dependent upon the refractive index of the fluid in the microfluidic channel. We demonstrate this class of refractometer using optical fiberBragg gratings; to provide high resolution, intracavity losses are minimized using integrated collimating optics. The refractometer can resolve refractive index changes of 0.2% and is simulated using coupled mode theory.