Abstract

We report an ultrasmall microfiber-probe-based reflective interferometer for highly sensitive liquid refractive index measurement. It has a $3.5\mathrm{\mu m}$ micronotch cavity fabricated by focused ion beam micromachining. A sensitivity of $110\mathrm{nm}/\mathrm{RIU}$ (refractive index unit) in liquid is achieved with over $20\mathrm{dB}$ extinction ratio. Theoretical analysis shows this kind of device is a hybrid of Fabry–Perot and modal interferometers. In comparison with normal fiber interferometers, this probe sensor is very compact, stable, and cheap, offering great potentials for detecting inside sub-wavelength bubbles, droplets, or biocells.

© 2010 Optical Society of America

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