Page 203 - Optofluidics Fundamentals, Devices, and Applications

178 Cha pte r Ei g h t

methods used in microfluidics to build new optical elements and
attain new functionalities. In this chapter we focus on those optical
elements and devices that are based on integrated optofluidic compo-
nents. Throughout this chapter we use the term fluid in its broad
sense, meaning liquid or gaseous phases of the substances and pure
or mixed liquids including solutions and colloids.
The diverse field of optofluidics has been steadily penetrating
application areas of optical communications, data storage, display
technologies, bioengineering, medical devices, imaging, metrology,
computing, and many others. Ever-growing field of microfluidics
enabled fast and easy fabrication, versatile and modular design, simu-
lation tools, and robust integration of fluids into optoelectronic compo-
nents. In the following sections we discuss areas in optofluidics, which
have been under our thorough investigation. Specifically, we cover flu-
idic lenses, optofluidic switches, and integrated tunable devices.

8-1 Switching and Beam Deflection
Optical switching technologies were advanced by the fast-developing
field of telecommunication. Various physical phenomena were employed
for optical switching applications including electro-optic [3–6], acousto-
optic [7,8], magneto-optic [9], and thermo-optic [10,11] effects and micro-
mechanical components [12,13].
One of the first fluid-based switches was magneto-optic fluidic
switch. When a magnetic fluid thin film is subjected to an external
magnetic field parallel to the plane of the film, the particles in the film
agglomerate and form chains. As the strength of the field increases,
the chains evolve from a disordered phase to structured patterns,
exhibiting optical anisotropy. These magneto-optic fluids were exten-
sively exploited in magneto-optic fluidic switches [14–19].
All-optical switching based on changing the physical properties of
black oils was suggested in 1986 [20]. The surface of a liquid film is
deformed using an optical beam. These modifications alter the phase
and intensity distribution of the reflected and transmitted laser beams.
Surface deformation of a laser-heated liquid film and time evolution of
the geometry of the surface were theoretically studied [21].
Despite numerous works on optofluidic switches, these devices are
still in their embryonic stage. Ever-growing field of communications
requires fast multiport switching with short delays, wide bandwidth,
and low insertion losses. Very compelling optofluidic technology set a
few records trying to address these requirements during the last
decade. Broad scope of effects was employed to perform optical switch-
ing using fluids. These include total internal reflection on solid-fluid
interfaces, diffraction from tunable gratings, and reconfigurable liquid-
core waveguides.
Since the timescales on which fluids can be displaced (replaced)
are commonly on the order of milliseconds, these components