Page 232 - Optofluidics Fundamentals, Devices, and Applications

Bio-Inspir ed Fluidic Lenses for Imaging and Integrated Optics 207

Aluminum ring Optically clear elastic membrane
Blackened
support material
Fluidic
inlet/outlet

Supporting glass Chamber filled with optical fluid

FIGURE 9-4 Membraned fl uidic lens. The main components are (1) optically
clear elastomer membrane and (2) lens chamber fi lled with optical fl uid.
Optical fl uids having an index of refraction from 1.40 and 1.67 can be chosen
for different applications and design requirements. Fluid can be moved into or
out of the chamber by an actuator, producing a concave or convex lens. Fluidic
lens with this structure provides superior mechanical stability, scalability,
thermal stability, and tuning range unmatched by other liquid lenses.

fluidic lenses. As long as the fluid does not interact with the elasto-
mer membrane, one has the freedom to select the optical fluid of
desired index and dispersion properties for optimal system per-
formance. Another merit of the design is that the lens profile is
determined solely by the mechanical properties of the membrane,
independent of the lens fluid. Hence, one can engineer the lens profile
by adjusting the processing and material structure of the membrane.
Different lens configurations, including plano-convex, biconvex,
plano-concave, biconcave, positive meniscus, negative meniscus, and
the like, have been demonstrated [27]. Various lens actuation mecha-
nisms have been investigated, including piezoelectric actuator,
thermal actuator [28], pneumatic actuator [29], aperture size actuator
[30,31], electromagnetic actuator [32], fibrous actuator [33], pH-
responsive hydrogel actuator [34], and so on.
To assess the pros and cons of various liquid lens technologies, we
consider the following figures of merit: tuning range, scalability, and
mechanical and thermal stability. Tuning range determines the func-
tionality and performance. A small tuning range yields a limited focal
range for auto-focusing system, but creates great difficulties for com-
pact optical zoom systems. Scalability refers to the range of optical
clear aperture (or lens diameter) a technology can produce. High image
quality is often achieved with a larger clear aperture of the lens. Finally,
to live up to the expectation of being a paradigm-shifting solution in
the field of optics, fluidic lens needs to be mechanically robust, ther-
mally stable, and low cost to manufacture. We have found that fluid-
filled, elastomer-membrane lenses perform well in all the above areas.
Such fluidic lenses can produce a record high tuning range of 200 D,
can change the lens type between convex and concave structures, can
scale to a relatively large clear aperture of over 10 mm, and have superb
mechanical robustness and reliability. Therefore, we will focus on this
fluidic lens technology in the remaining part of this chapter.