Page 218 - Optofluidics Fundamentals, Devices, and Applications

Adaptive Optofluidic Devices 193

membrane’s torsion in some areas, while increasing it in the others.
Angular rotation of the grating by up to 8 degrees was demonstrated
at applied pressure of approximately 2 psi (see Fig. 8-6c).

8-3 Summary
In this chapter we reviewed a number of tunable optofluidic
devices. In these devices gases and liquids are used to manipu-
late and control light in its many forms: planar-guided and free-
space, coherent, and broadband. These devices comprise two
major parts—the microfluidic device used as an actuator and the
optical element that performs the optical tuning function. We pro-
vided a detailed review of adaptive and tunable optical elements
such as lenses, gratings, scanners, and beam shapers. Integration
of these elements with their actuation devices and other optical
components allows construction of miniature multifunctional
optical devices enabling further integration into micro- and mac-
roscale systems.
Additionally, optofluidic switches use liquids and thus can
operate with ultrawide spectral bandwidth and simultaneously be
invariant to the state of polarization of optical beams; these proper-
ties cannot be achieved with other technologies. N × 1 optical switch-
ing based on optofluidic components is made possible and allows
significant simplification of N × N optical switching and interconnec-
tions. Both total internal reflection and diffraction phenomena were
exploited to construct optofluidic switches.
Pneumatically driven compound lens overcomes pitfalls of tradi-
tional liquid-filled tunable lenses. Absence of liquid allows faster
operation and improved performance, which is not compromised by
bubbles under mechanical stresses and vibrations. Moreover, aper-
tures much larger than in liquid-filled lenses are readily available.
These lenses were shown to produce considerable refractive power
under comparatively low applied pressures.
Composite membrane technology presented in this chapter is
based on soft polymer membranes patterned with rigid epoxy
inclusions. These inclusions are designed to obtain the desired
mechanical properties of the membrane and allow good control of
the deformation profile. As the fabrication relies on planar litho-
graphic techniques, the pattern can be easily produced in high vol-
umes with high accuracy. Although composite membranes were
so far exploited for tunable gratings [119], they show much poten-
tial for any adaptive and tunable optics where arbitrary geometry
is desired.
In this early stage of development of optofluidics as a field of
research, every new device opens new perspectives and stimulates
research showing improved performance and new applications. The
significant progress of micro- and nanofabrication techniques is striving