Page 227 - Optofluidics Fundamentals, Devices, and Applications

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Starting from a simple epithelial cell with photodetection capa-
bilities, animal eyes have evolved into highly compact, efficient, and
diversified vision systems. For the best interest of the species, animal
vision has been specialized either into a telephoto system (e.g., bird’s
eye) or into a wide angle system (e.g., fish eye). In spite of the diversity
of animal vision, images of high resolution and sensitivity have been
obtained in numerous animal eyes. For example, with merely two
lenses, of which one is a tunable lens, human eyes can achieve a reso-
lution as high as one arc minute in the fovea area.
Although the anatomy of animal eyes varies widely, the optics in
most eyes are simple yet highly effective. This is in sharp contrast with
human-made imaging systems, which are far more complicated and
bulkier than animal eyes. The most marked difference in optics between
animal eyes and human-made optics is that the former achieves focusing
by change of lens shape, while the latter achieves focusing by varying the
distances between fixed-shaped lenses. The human ciliary muscles can
achieve an accommodation range of 10 D (corresponding to a focal range
from 10 cm to infinity) with less than 8 g of force and a motion no greater
than 0.1 mm. We are not aware of any existing human-made systems
capable of the same performance with such limited force and travel.
By changing the curvature of the lens, animals can have a wide tun-
ing range in an extremely compact design. For instance, a young person
can achieve a tuning range of up to 14 D, producing a focal range from
around 8 cm to infinity. Some water birds have a tuning range as wide as
50 D. Many evidences in animal vision show that changing lens shape is
an effective and economical way to change the focal length of an optical
system. This offers a particularly attractive tuning mechanism for minia-
ture cameras in laptop computers, cellular phones, and other handheld
devices where both the image quality and the form factor of the cameras
are of primary concerns. Our exploration of fluidic lens optics is moti-
vated by its significant potential in commercial applications as well as
the intrinsic elegance found in animal vision.
This chapter covers the following subjects: fundamentals of fluidic
lenses (Sec. 9-1), fluidic lens imaging systems (Sec. 9-2), fluidic intraocu-
lar lenses (IOLs) for implanted IOL (Sec. 9-3), and two extended areas
from the core technology: fluid-filled tunable molding techniques
(Sec. 9-4) and photonic integrated circuits using fluidic optics (Sec. 9-5).
In Sec. 9-1, we give a detailed discussion on the fabrication pro-
cess and the characteristics of the devices, which provide readers the
fundamentals of fluidic lenses. Similar to the biological lenses in most
animal eyes, which are generally of aspherical shapes, fluidic lenses
can also obtain aspherical shapes to compensate for aberrations and
to be most space efficient. Understanding the actual lens profile and
developing the ability to control the profile are essential for achieving
high-performance fluidic lens systems.
The main focus of this chapter is to demonstrate the unique func-
tionality and superb performance of bio-inspired fluidic lens systems.