Online proceedings - EDA Publishing Association

11-13
May 2011, Aix-en-Provence, France
Large Area Adaptative Fluidic Lens
Solon Mias [1,2], Aurélien Bancaud [1,2], Henri Camon [1,2]
1 CNRS-LAAS, 7 avenue du colonel Roche, F-31077 Toulouse
2 University of Toulouse; UPS; INSA; INP; ISAE; LAAS; F-31077 Toulouse, France
Abstract- We have developed a large area (30mm diameter)
adaptive fluid-lens using simple fabrication procedures that do
not require elaborate micro-fabrication techniques. The lens
structure consists of a 2mm thick liquid reservoir which is
sandwiched between a solid borosilicate glass substrate, a thick
PDMS-elastomer side-wall spacer and a more flexible PDMScoated
PET membrane. The reservoir is connected via a 0.3
mm tube to a commercially available micro-pump used to alter
the pressure within the reservoir, thus altering the surfacecurvature
of the PET membrane and at the same time the
optical power of the lens. The lens focal length can be changed
from infinity to 0.5m.
I. INTRODUCTION
Ophthalmic glasses are one of the oldest portable devices.
Even so, they have remained mostly the same over hundreds
of years consisting of a rigid structure with fixed focal
length. Recently, lenses with variable focal distances
(bifocal and progressive lenses) have been developed
particularly for people suffering from presbyopia [1].
Presbyopia is a condition mostly occurring due to aging of
the human eye and where the eye’s ability to accommodate
is reduced [2]. Other recent developments include the
creation of microstructures on a lens in order to produce a
customized lens [3]. Even so, the above structures are rigid
and their focal length and wavefront correction abilities are
determined by the fabrication.
Adaptive lenses on the other hand have the ability to tune
their focal length according to the needs of the user. Many
such devices have been developed using a variety of
technologies such as liquid crystal devices [4-11],
electrowetting devices [12, 13] and micro-fluidic devices
[14-17]. Liquid crystal adaptive lenses rely on the
birefringence of the liquid crystal mixtures used in order to
create a refractive index modulation within the lens which
then translates into a phase change of the propagating light.
These lenses are limited by the birefringence and the
thickness of the liquid crystal layer. In addition, they exhibit
diffraction effects due to the electrodes used to spatially
address the liquid crystal layer. Different electrode shapes
[18] and variable resistivities [6] have been developed in
order to reduce the diffraction effects but in the expense of
greater fabrication complexity. Finally, the greatest problem
with liquid crystal lenses is their polarization sensitivity.
Therefore two liquid crystal layers are required in order to
modulate all light-polarizations and this increases
fabrication complexity even further, particularly due to the
need of fine alignment between corresponding pixels on
each layer.
Electrowetting devices on the other hand do not suffer
from polarization sensitivity. Two companies have been
recently involved in the fabrication of electrowetting lenses,
namely Varioptic [13] and Philips [12]. Both companies use
two non miscible liquids; an aqueous conducting solution
along with insulating oil of the same density. The liquids
are inserted within a closed cell with appropriately placed
electrodes. The use of two liquids instead of one (e.g. water
in air) is necessary for suppressing any optical distortion of
the gravity on the liquid-liquid interface. The angle of the
conducting fluid with the cell wall changes when an electric
field is applied to the cell. Hence, as the voltage changes,
the curvature of the interface between the two liquids is also
changed. Hence a lens is formed which can be tuned from
convex to concave using appropriate voltage levels.
Unfortunately, devices produced are limited to small active
areas due to distortions on the interface between the two
liquids. Therefore both Varioptic and Philips lenses are
mostly destined for the mobile phone industry rather than
ophthalmic optics.
Fluid-lens devices are also polarisation insensitive. The
tuning of their focal length is achieved by altering the
pressure within a liquid reservoir which has at least one wall
made out of a flexible membrane (usually PDMS). When
the pressure inside the cell is below the atmospheric
pressure, the device turns into a concave lens. As the
pressure increases above the atmospheric pressure then the
lens turns into a convex lens. The change of the pressure
within the lens can be tuned using a micro-pump, a syringe
or a volume changing material [15]. The diameter of the
lenses produced are relatively small (200µm [19] to 20mm
[17]). The uniformity of the devices can be a problem. For
example, PDMS non-uniformity during the membrane
fabrication can cause defects of up to 4µm [19]. Also if the
membrane of the lens is too flexible then the weight of the
liquid can distort the normally-spherical shape of the
membrane when the lens is used in a non-horizontal
position.
In this publication we describe the fabrication of a large
area adaptive fluid-lens using simple fabrication procedures
that do not require elaborate micro-fabrication techniques.
The membrane of the lens is made out of PDMS-coated
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