CONTENTS

Page no.

1. Introduction…………………..................2-4

2. What is liquid Lens? ……………...........5-7

3. Working principle. ……………...............8-10

4. Electrowetting. ……………................... 11-14

5. Working difference…………………………15

6. Characteristics. ……………..................16-18

7. Application……..……………................. 18-20

8. Lens for camera…………………………….21-23

9. Conclusion. ……………........................ 24-25

10. Reference. ……………............................26

INTRODUCTION

The theory behind liquid lens is based on the properties of one or

more fluids to create magnifications within a small amount of

space. Liquid lens can be considered as "infinitely variables" lens

with variable focus, and the focus is controlled without using any

moving parts. The focus of a liquid lens is controlled by the

surface of the liquid. Water forms naturally a bubble shape when

adhered to materials such as glass or plastics. This desirable

property makes water a very suitable candidate for the production

of a liquid lens. To generate a liquid lens, a mixture of two liquids

is sandwiched between two pieces of clear plastics or glass. The

second liquid needs to encapsulate the water drop and to fill any

free space or void. It is well known that water and oil do not mix,

and oil is also inexpensive and safe to use. Therefore, oil is

chosen to be used as the other liquid mixture for the liquid lens

system. The surface profiles of the liquids determine the focal

length of the liquid lens system, and ultimately, how the liquid

lens focuses light. In other words, by altering the surface profile of

the liquids, the focal length can be adjusted. This is done by

changing the shape and size of the drop of water within the liquid

lens.

2

IMRE has made a breakthrough in lens technology. The lens is

cheaper to make has optical zooming abilities and uses only a

fraction of the space of most conventional lenses are called as

fluidlens or liquidlens. In the past 2-3 decades, the need for

miniaturization of optical systems has increased dramatically,

especially incoherent light handling, for various applications

including communications, data storage, security or personal

identification. More recently this trend has extended to imaging

systems. Nowadays camera modules, integrating a digital sensor

and an optical system altogether, have entered into mobile

phones and slim digital cameras, bringing the need for develop in

miniature optical systems.

The camera module were developed first with

low count pixels and ultra small format

sensors (CIF resolution, single element lens),

but the need for better image quality leads

now to the development of mega pixels

sensors, 1/4” or less. These sensors are now

commercially available, but the need for auto focus and zoom

compound lenses remains open: no commercial solution exists

up to now at reasonable prices for this very large scale market.

The liquid lens technology that we present here could be the

solution to this demanding application.

3

A new principle of variable lenses with tunable focal length will be

demonstrated : two iso-density non-miscible liquids are trapped

inside a transparent cell. The liquid-liquid interface forms a drop

shape. The natural interfacial tension between liquids produces a

smooth optical interface, which curvature is actuated by

electrowetting. In addition, in order to have a usable lens, it is

necessary to incorporate a centering mechanism, such that

optical axis remains stable. Intrinsic physical limitations will be

presented as well as actual performances of the technology.

Several applications will be discussed in the

autofocus/macro/zoom optics for CMOS and CCD miniature

imagers. But, because the technique relies on the surface tension

of the liquids inside the lens, it cannot be used to make lenses

larger than a centimetre in diameter. This would place a limit on

the resolution of images.

Nonetheless, Kuiper believes that FluidFocus lenses could be

especially useful for reading from Blu-Ray DVD disks, which store

information more densely than ordinary DVDs. Blu-Ray players

require highly accurate optical systems capable of adjusting for

distortions that naturally occur during dual layer disc reading and

writing.

The FluidFocus lens will be demonstrated at the technology fair

CeBit, in Hannover, Germany, next week. Kuiper says the first

devices that incorporate fluid lenses be available by 2005.

4

What is a liquid lens?

To generate a liquid lens, a

mixture of two liquids is

sandwiched between two pieces

of clear plastics or glass. The

second liquid needs to

encapsulate the water drop and

to fill any free space or void. It is

well known that water and oil do

not mix, and oil is also

inexpensive and safe to use. Therefore, oil is chosen to be used

as the other liquid mixture for the liquid lens system.

A liquid lens uses one or more fluids to create an infinitely-

variable lens without any moving parts by controlling the

meniscus (the surface of the liquid.) There are two primary types

Transmissive and Reflective. These are not to be confused with

liquid-formed lenses that are created by placing a drop of plastic

or epoxy on a surface, which is then allowed to harden into a lens

shape.

Reflective liquid lenses are actually variable mirrors, and are

used in reflector telescopes in place of traditional glass mirrors.

When a container of fluid (in this case, mercury) is rotated,

centripetal force creates a smooth reflective concavity that is

5

ideally suited for telescope applications. Normally, such a smooth

curved surface has to be meticulously ground and polished into

glass in an extremely expensive and tricky process (remember

the Hubble Space Telescope mirror fiasco). A reflective liquid

lens would never suffer from that problem, as a simple change in

rotation speed would change the curve of the meniscus to the

proper shape. Scientists at the University of British Columbia

(UBC) have built a 236-inch (6-meter) Liquid Mirror Telescope

(LMT). The world's 13th largest telescope, its reflective surface is

made of a flat container of mercury spinning at about 5 RPM. The

telescope costs only about $1 million, a significant reduction from

the roughly $100 million cost of what a conventional telescope

with a regular solid glass mirror of the same size would require.

Transmissive liquid lenses use two immiscible fluids, each with a

different refractive index, to create variable-focus lenses of high

optical quality as small as 10 µm (microns). The two fluids, one

an electrically conducting aqueous solution and one a

nonconducting oil, are contained in a short tube with transparent

end caps. The interior of the tube and one of the caps is coated

with a hydrophobic material, which causes the aqueous solution

to form a hemispherical lens-shaped mass at the opposite end of

the tube. The shape of the lens is adjusted by applying a dc

voltage across the coating to decrease its water repellency in a

process called electrowetting. Electrowetting adjusts the liquid's

6

surface tension, changing the radius of curvature in the meniscus

and thereby the focal length of the lens. Only 0.1 micro joules (µJ)

are needed for each change of focus. Extremely shock and

vibration resistant, such a lens is capable of seamless transition

from convex (convergent) to concave (divergent) lens shapes

with switching times measured in milliseconds. In addition, the

boundary between the two fluids forms an extremely smooth and

regular surface, making liquid lenses of a quality suitable for

endoscopic medical imaging and other space-constrained high-

resolution applications like micro cameras and fiber-optic

telecommunications systems.

The aforementioned liquid-formed lenses are a cool technology

as well, and used mostly on image sensors. Tiny drops of epoxy

are placed on each pixel, which then form individual lenses to

increase light-capturing ability. They are also used on novelty

items to create a magnifying effect.

7

WORKING PRINCIPLE:

The magnifying principle of a liquid lens is similar to that of our

eye. When we try to see an object, the light which comes from the

object falls on our eye ball. Our eye ball(pupil) has the ability to

contract or expand itself depending upon the position of the

object. Which then leaves the perfect light ray to fall on the retina

which results visibility of the object.If the pupil can’t adjust itself

then we are not able to see the object.The liquid lens acts on the

same principle.

8

The lens has an actuator which is driven by the dielectric

power. Which results in adjustment of the lens, hence we are

able to take the picture.

The figure below depicts the configuration of a liquid lens

actuated by the dielectric force. The liquid lens consists of a

15μL (liquid) droplet with a low dielectric constant and a

sealing liquid with a high dielectric constant. The bottom

diameter of the droplet was 7mm when no voltage was

applied. The two liquids were injected inside a 3mm thick

PMMA (polymethyl methacrylate) chamber that was sealed

between two ITO glass substrates. The concentric ITO

electrodes on the bottom glass substrate were coated with

1μm thick Teflon® to reduce friction between the droplet and

the glass substrate. The width and spacing of the ITO

electrodes was 50μm. The mass density of the sealing liquid

was adjusted to match that of the droplet to minimize the

gravitational effect, since the gravitational effect may induce

no uniform deformation of the droplet profile, causing optical

aberrations. As the voltage was applied, a dielectric force

arose on the droplet due to the difference in the dielectric

constant between the two liquids. The dielectric force shrunk

the droplet, increasing the droplet's contact angle and

9

shortening the focal length of the liquid lens. The dielectric

force induced is described by equation given below

where ε0 is the permittivity of free space, ε1 and ε2 are

dielectric constants of the sealing liquid and the droplet,

respectively. E denotes the electric field intensity across the

interface of the two liquids

( fig. A typical liquid lens)

Electro wetting Principle:

10

This principle states that whenever no voltage is applied to the drop

of liquid then it is “phobic “of the surface. As the voltage increases

the liquid wets the surface more.

This principle helps in adjusting the lens which can make the lens to

behave like concave & convex as per the requirement.

Two non miscible liquids of same density instead of having a

water drop in air, one works with water and oil. This condition is

necessary for suppressing any optical distortion of the gravity on the

liquid-liquid interface, which enables to use the lens in every

orientation.

11

• Inversion of the conducting and non conducting fluid. In current

electrowetting experiments, the water is used as a drop immersed in

the non conducting fluid (air). For application, it will be preferable to

work with a drop of the insulating fluid (oil) immersed in the

conducting fluid (water). This is to avoid any optical perturbation of

the liquid-liquid interface due to the liquid meniscus at the electrode

touching the conducting fluid. It is preferable to use an oil drop

immersed into a conducting fluid (water based solution) which can be

connected to the outside without perturbing the liquid—liquid

interface. This inversion is not strictly necessary, as in former

publications it is mentioned that contact could be made through the

insulating . Nevertheless, in practical realization the inversion of oil

and water is preferable.

• Centering mean : some publications have mentioned in the past

how to use small liquid droplets as optical lenses [6], but if this lens

12

has to be inserted in a more complex system, it needs precise

alignments of optical lenses. The fig 1 shows that if no centering

mean is applied, the drop can freely move in the transverse

directions while the focal length is changed.

We have the experience of such random displacements which

prevent to use the lens. The liquid-liquid interface thus needs then to

be precisely controlled and any physical realization of lenses have to

incorporate such a centering mean This centering of the liquid-liquid

interface can be obtained by several ways. The following are given

as example, and many others can be found:

• applying electric field gradient using variable thickness of the

insulator film.

• the natural gradient present at the edge of an electrode can be

used. In the case of lenses developed by Lucent, a decentering force

can be applied through angular sector electrodes. Such decent ring

force can only be used if a centering force (restoring force) exists,

such that the balance between the decentering forces and the

centering forces can bring a stable equilibrium. Although this was not

explicitly discussed in the publications of Lucent, we believe that in

their case the centering effect comes either from the edge effect of

the ring electrode, or from the gap between sector electrodes, which

could play this role too, if well designed.

13

it can also be obtained as a result of the geometry of the supporting

surface for the two fluids. It has been shown that inwards cones,

cylinder and some toroidal shapes are centering surfaces for the

liquid-liquid interface. Cylinder the contrary, some surfaces having an

inward high insides and cylinder edges have also been proposed. On

curvature are not suited for centering the liquid-liquid interface.

14

WORKING DIFFERENCE BETWEEN CONVENTIONAL & LIQUID LENS

Liquid lens working like human eye. So here we compare conventional lens with human eye.

Lens characterizations:

The optical characteristic of the liquid lens that were measured

experimentally included the droplet's contact angle and its hysteresis,

15

the conic constant of the droplet, focal length tuning, and focal spot

size. Further, focal length tuning, focal spot size and spherical

aberration were verified using simulation tools and theory. The

contact angle of the droplet in the packaged liquid lens was

measured at various voltages as shown in Figure 2(a). The intrinsic

contact angle of the droplet was measured to be 25°. The contact

angle began to significantly increase at voltages over 50 volts and

reached 58° at 200 volts. Hysteresis of the droplet's contact angle

was observed and its maximum was found to be 12.5° at 120 volts.

Figure 2(b) shows that the conic constants of the droplet were close

to zero at various voltages, implying that the droplet maintained a

spherical profile at all focal lengths. Hence, the surface profile of the

droplet could be assumed to be spherical during actuation. The

actuation of the droplet in the liquid lens was captured by a high-

speed CCD camera. The rise time was measured to be about 650ms

when the liquid lens was actuated from the rest state to 200 volts.

When the applied voltage was switched off, the measured fall time

was 300ms.

Fig. The measured receding contact angles and advancing contact

angles of the droplet in a liquid lens versus the applied voltages. The

insets show the droplets actuated at various voltages. Left: the

droplet was at the rest state. Right: the droplet was actuated at 200V.

16

Focal length measurement of the liquid lens was conducted using a laser

with a wavelength of 532nm and a beam scanner

(0180-XY/LL/SW/1μm/5Hz, Photon Inc.).

The focal length was determined for advancing actuation based on the

minimum spot size resolved along the optic axis. Further, the measured

advancing focal lengths were compared with the paraxial approximation

based on the advancing contact angles in Fig. 2. The measurement

results and the paraxial approximation were in good agreement (see Fig.

3). When the voltage increased from zero to 200 volts, the liquid lens

shortened its focal length from 34mm to 12mm. The electric power

consumed was determined to be less than 1mW.

17

Features:

Applications:

Applications of the liquid lenses based on electro wetting can be

found in many areas. Typical possible sizes for the lens pupil range

from less than a millimeter to one centimeter, using the current

technology. This makes this technology ideal for millimetrtic lenses

needed now in the mobile phone applications. The very small power

consumption (less than one mW dissipated in the lens) is also a

great advantage compared to conventional motorized systems. All

electronic sets integrating optics could benefit from the simplicity of

this technology. Optical pickups, displays, cameras, computers etc...

Again the size under consideration is well fitted between macro- and

microscopic systems. Of course photonic professional applications

18

could also present good opportunities for our technology. Many other

applications could be envisaged. The liquid ends

is one adaptive optical components, with a huge amplitude, but

rather limited flexibility on the pattern of phase shifts, limited to what

can be done with a liquid liquid interface. Directly every application

where Z scanning is required could be of interest: the dynamic

behavior shown in this paper demonstrates s possible to apply to the

lens a triangular ramp (eventually damped in order to avoid shocks

generated at the reversing of the ramp) in order to use the full range

of dioptric correction upon very fast scans. Telemetry could use focus

information in order to produce 2D and 3D images at quite good

resolutions. Medical applications could also be very promising, as

endoscopes develop on many complex optical functions including

confocal microscopy or Optical Coherent Tomography .

19

As a final remark, lasers could be monitored or controlled by the

liquid lens.

Liquids can sometimes produce interesting properties as materials,

which could be of use, even in high power pulsed laser systems.

It has

Dyamic field of view.

Easy to mass produce: manufactured using lithography.

Difficulties:

Far from being a fully developed product.

Lens for cameras:

20

Varioptic and Sunny Optics

announced last week that they were

making the Varioptic Arctic 416 auto

focus oil and water lens available in

high-end camera phones. The oil

and water lens, which has no moving

parts, replaces traditional

mechanical lens focusing systems.

(Oil and water lens uses

electrowetting)

The Varioptic oil and water lens uses a phenomenon called

"electrowetting" to focus the system. A water droplet is deposited

on a metal substrate covered by an insulating layer. The voltage

applied to the substrate modifies the contact angle of the droplet. A

liquid lens uses two liquids with the same density; one is an

insulator while the other is a conductor. The variation of voltage

leads to a change of curvature of the liquid-liquid interface, which

in turn leads to a change of the focal length of the lens.

Liquid lenses have many advantages over their mechanical

counterparts, including ruggedness (no moving parts), faster

response, excellent optical quality, wide operating temperature

21

range and very low energy consumption (ideal for small mobile

devices). Science fiction fans have been waiting for this since

Frank Herbert wrote about oil lenses in his 1964 classic Dune:

Paul lay ... in a slit of rock high on the shield wall rim, eye fixed to

the collector of a Fremen telescope. The oil lens was focused on a

starship lighter exposed by dawn in the basin below them.

(Read more about oil lens from Dune)

Philips is also working on this technology (there may be some

patent fights involved); see Philips FluidFocus: Variable Focus

Fluid Lens. Varioptic is ramping up production in (where else)

Shanghai and expects to produce 100,000 lenses per month in

addition to the production in its plant in Lyon, France. Read more

in the 2MP Autofocus Camera Module with Varioptic Liquid Lens

press release and Varioptic comes into focus with liquid phone

camera lenses. Scroll down for more stories in the same category.

(Story submitted 2/18/2007) .

Schreiber and colleagues worked with Varioptic, French pioneers

of liquid lenses, to come up with a design that switches from a

normal view to 2.5-times magnification. The design consists of four

liquid lenses and three fixed plastic lenses and offers a

magnification of 2.5 times, while when all four lenses are at their

flattest there is no magnification.

“The complete length of the system from outer lens to image

22

sensor is 29mm, but it should be possible to reduce that,” says

Schreiber. Varioptic is now considering how to take the design on

to then prototype stage.

“The lenses are arranged to prevent image distortion while

minimising colour distortion. Red, green and blue images must be

recorded in sequence and then combined digitally, a process that

would increase exposure times,” says Schreiber, “finding less

distorting liquids to build the lenses out of is the answer to that

problem.”So although it potentially sounds like great news, this is

probably another new technology which won’t find its way into 

DSLR cameras for a few years yet. For smaller lenses such as

camera phones it could find a market, but we’ll have to see how

this one pans out.

Conclusion:

23

We might have seen in digital cameras that when it becomes on or

captures or zooms the lens make two and fro. This is done by the

internal motor inside the camera. This lens uses most of the power

of the camera. But now-a-days we

want to save power as much as

possible. So, here liquid lens shows its

ability. It needs very less power as

compared to the typical motor driven

lens. So, it may be the best alternative

of typical motor driven lens.But the

problem is that as liquids are used so

there may be problem in the extreme conditions.Major camera

production companies like Canon, Nikon & cell phone company

Sony Ericson have already tested and might be in the final process

to apply.

IMRE has made a breakthrough in lens technology. The lens is

cheaper to make has optical zooming abilities and uses only a

fraction of the space of most conventional lenses are called as

fluidlens or liquidlens. In the past 2-3 decades, the need for

miniaturization of optical systems has increased dramatically,

especially incoherent light handling, for various applications

including communications, data storage, security or personal

identification. More recently this trend has extended to imaging

24

systems. Nowadays camera modules, integrating a digital sensor

and an optical system altogether, have entered into mobile

phones and slim digital cameras, bringing the need for develop in

miniature optical systems.

The camera module were developed first with low count pixels

and ultra small format sensors (CIF resolution, single element

lens), but the need for better image quality leads now to the

development of mega pixels sensors, 1/4” or less. These sensors

are now commercially available, but the need for auto focus and

zoom compound lenses remains open: no commercial solution

exists up to now at reasonable prices for this very large scale

market. The liquid lens technology that we present here could be

the solution to this demanding application. By using molecular

simulations The structure of interface between liquid layers and

molecular arranges have been understood. The chemical reaction

and by-products were predicted. By modifying the liquid

ensemble composition of the interface depth decreased. The

transmissivity after high-temperature aging improved.

The aforementioned liquid-formed lenses are a cool technology as

well, and used mostly on image sensors. Tiny drops of epoxy are

placed on each pixel, which then form individual lenses to increase

light-capturing ability. They are also used on novelty items to

create a magnifying effect.

25

Reference:.

B. Berge and J. Peseux; "Variable focal lens controlled by

an external voltage: an application of electrowetting”.

Howstuffworks.com

Electronictech.com

Nikoncameras.com

26