Page 202 - Optofluidics Fundamentals, Devices, and Applications

CHAPTER 8

Adaptive Optofluidic

Devices

Steve Zamek and Yeshaiahu Fainman
Department of Electrical Engineering, University of California, San Diego, California

he primary advantages of fluids are their ability to easily change
their shape, to mix and dissolve, and to form very smooth solid-
Tfluid and fluid-fluid interfaces. Moreover, various fluids provide
very wide range of refractive indices, and by mixing fluids with large
refractive index difference, we can create tunable index fluids with
wide dynamic range, high resolution, and ease in control. Superiority
of fluids over solids in this regard is obvious. First, geometry variations
are very limited with solids, for which the stresses inherent in deforma-
tions result in undesired birefringence and aging. Second, controllable
real-time mixing of liquids allows tuning of the refractive index of the
mixture by ±0.1. This tuning range is several orders of magnitude
wider than the one obtained in solids with electro-optic, magneto-
optic, thermo-optic, photorefractive, and other effects. In fact, even
wider tuning range is obtained by introduction and displacement of
fluids with very different optical properties into and out of the region
of interest. These unique features enabled by fluids gave rise to two
primary approaches in optofluidics: varying the geometry and tuning
the refractive index of the optical medium.
In the beginning of the 1980s, an intersection of physics, chemis-
try, and nanotechnologies laid the foundations for microfluidics.
Microfluidics allowed manipulation of very small volumes of fluid in
a fast controllable fashion, and these capabilities opened new avenues
in optics. Integration of fluidics with optoelectronic components
became known as optofluidics [1,2]. This integration throve twofold.
First, it allowed integration of optical components into lab-on-a-chip
devices, giving a clear path for miniaturization of biomedical devices,
known also as micro total analysis systems (μTAS). Second, it inherited

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