LENSLENS

A lens may be defined as a piece of A lens may be defined as a piece of glass, plastic or any other glass, plastic or any other transparent material which is curved transparent material which is curved on one or both sides and which on one or both sides and which makes a beam of light passing makes a beam of light passing through it –bend, spread out, become through it –bend, spread out, become narrower or change direction.narrower or change direction.

ZOOMING AND FOCUSINGZOOMING AND FOCUSING Zooming is a phenomenon exhibited by a Zooming is a phenomenon exhibited by a

photographic lens by virtue of which a photographic lens by virtue of which a lens lens can move in from a distant to a close view can move in from a distant to a close view while keeping what is being photographed while keeping what is being photographed in focus .in focus .

It is a It is a method of adjustingmethod of adjusting the focal length the focal length i.e. the distance between the middle of the i.e. the distance between the middle of the lens and the focus such that the image lens and the focus such that the image becomes more clear.becomes more clear.

THE SIMPLEST DEFINITION OF A THE SIMPLEST DEFINITION OF A LIQUID LENSLIQUID LENS

We've all been drinking a cold soda We've all been drinking a cold soda when the condensation on the side when the condensation on the side drips off. You may notice that drips off. You may notice that whatever is under the water drop is whatever is under the water drop is magnified. That's a simple version of magnified. That's a simple version of a liquid lens.a liquid lens.

LIQUID LENS THAT IS USED IN LIQUID LENS THAT IS USED IN VARIOUS ELECTRONIC DEVICESVARIOUS ELECTRONIC DEVICES

A liquid lens is a lens that uses the A liquid lens is a lens that uses the properties of two different liquids within a properties of two different liquids within a small space to provide magnification.small space to provide magnification.

Water and oil do not mix, and are both Water and oil do not mix, and are both safe and inexpensive, so they are perfect safe and inexpensive, so they are perfect for use in a liquid lens. for use in a liquid lens.

The mixture of water and oil is sandwiched The mixture of water and oil is sandwiched between two pieces of clear glass or between two pieces of clear glass or plastic. In this way, a light, cheap liquid plastic. In this way, a light, cheap liquid lens is created. lens is created.

Because water adheres to glass or plastic, Because water adheres to glass or plastic, it naturally forms a bubble shape it naturally forms a bubble shape

This bubble shape within the liquid lens This bubble shape within the liquid lens creates magnification and variable focus. creates magnification and variable focus.

The oil component of the liquid lens fills in The oil component of the liquid lens fills in the rest of the space to keep the water the rest of the space to keep the water from sloshing around. from sloshing around.

ELECTROWETTINGELECTROWETTING

Water is a polar liquid. Thus its molecules can be Water is a polar liquid. Thus its molecules can be attracted by an electric field. It is thus possible to attracted by an electric field. It is thus possible to change the shape of the liquid drop.change the shape of the liquid drop.

To carry out this process of electrowetting a To carry out this process of electrowetting a water drop is deposited on a substrate made of water drop is deposited on a substrate made of metal, covered by a thin insulating layer. The metal, covered by a thin insulating layer. The voltage applied to the substrate modifies the voltage applied to the substrate modifies the contact angle of the liquid drop. The liquid lens contact angle of the liquid drop. The liquid lens uses two isodensity liquids, one is an insulator uses two isodensity liquids, one is an insulator while the other is a conductor. The variation of while the other is a conductor. The variation of voltage leads to a change of curvature of the voltage leads to a change of curvature of the liquid-liquid interface, which in turn leads to a liquid-liquid interface, which in turn leads to a change of the focal length of the lens. change of the focal length of the lens.

DETAILED DESCRIPTIONDETAILED DESCRIPTION(CONSTRUCTIONAL Detail)(CONSTRUCTIONAL Detail)

To start with we take a glass tube which is To start with we take a glass tube which is coated with coated with INDIUM TIN OXIDE (ITO).INDIUM TIN OXIDE (ITO). This This is 50nm thin and acts as an electrode.is 50nm thin and acts as an electrode.

Then we apply another coating of Then we apply another coating of PARYLENE_NITROGENPARYLENE_NITROGEN which acts as an which acts as an insulator between the electrode and water insulator between the electrode and water and this is 3and this is 3µm thick.µm thick.

To force the water volume into a convex To force the water volume into a convex shape, we apply a top coat of a water-shape, we apply a top coat of a water-repelling repelling FLUOROPOLYMER.FLUOROPOLYMER.

CONTD…CONTD… We fill the tube with an insulator—a mixture We fill the tube with an insulator—a mixture

of of PHENYL METHYL SILOXANESPHENYL METHYL SILOXANES that has the that has the same density as water in order to make the same density as water in order to make the curvature of the interface between the curvature of the interface between the liquids perfectly spherical . liquids perfectly spherical .

When a voltage is applied between the When a voltage is applied between the water and the wall electrode, the polar water water and the wall electrode, the polar water molecules are attracted toward the wall. The molecules are attracted toward the wall. The volume of the liquids is constant, so the volume of the liquids is constant, so the curvature of their interface will change. If curvature of their interface will change. If the liquids have different refractive indices, the liquids have different refractive indices, their interface acts as a variable-focus lens .their interface acts as a variable-focus lens .

Why water?Why water?

Water Water reduces the cost of reduces the cost of manufacturingmanufacturing drastically. drastically.

Water cannot be scratched and thus Water cannot be scratched and thus gives us a gives us a flawless lensflawless lens..

WaterWater is is more transparentmore transparent to light to light than any other transparent material.than any other transparent material.

Water is a Water is a polar solventpolar solvent and hence it and hence it is subjected to electrowetting.is subjected to electrowetting.

Contd…Contd…

A drop of water has a A drop of water has a high high surface tensionsurface tension and has a natural and has a natural curvature similar to that of a curvature similar to that of a conventional lens.conventional lens.

Hence the lens obtained is a Hence the lens obtained is a defect free lensdefect free lens..

ApplicationsApplications

It has got an extensive use in It has got an extensive use in cellular cellular phonesphones these days. It actually gives rise to these days. It actually gives rise to a small system which can easily be a small system which can easily be embedded in a small device like that of a embedded in a small device like that of a cellular phone.cellular phone.

It is used in various electronics sets which It is used in various electronics sets which integrate optics with them. For e.g. integrate optics with them. For e.g. displays,cameras,computers.displays,cameras,computers.

CONTD…CONTD…

It is used in It is used in endoscopeendoscope (in the (in the field of medicines) which is field of medicines) which is developed on a number of developed on a number of optical functions.optical functions.

These days it is also used in These days it is also used in tumor detectiontumor detection..

ADVANTAGESADVANTAGES

A liquid lens has got a A liquid lens has got a large focal length large focal length rangerange..

One of its most important properties is its One of its most important properties is its ruggedness i.e. it has got ruggedness i.e. it has got no moving parts.no moving parts.

There is no problem of wear and tear as the There is no problem of wear and tear as the lens lens does not have to change position.does not have to change position.

The time taken by it to respond is very less. The time taken by it to respond is very less. It has got a speedy response of It has got a speedy response of 2/1002/100thth of a of a second.second.

It has got a very It has got a very good transparencygood transparency in in visible range.visible range.

CONTD…CONTD…

It has got a wide operating It has got a wide operating temperature range i.e. temperature range i.e. -50-50°c°c to 180 to 180°c°c . .

The The cost of manufacturingcost of manufacturing is very is very less.less. It is very compact in size i.e. It is very compact in size i.e. 10µm to 10µm to

10mm.10mm.The The curvaturecurvature and the focal length of and the focal length of

the the

liquid lens liquid lens can be switched from can be switched from concave to convex.concave to convex.

CONTD…CONTD…

Zoom lens can be created by combining Zoom lens can be created by combining two liquid lenses.two liquid lenses.

Greatly Greatly reduces spacereduces space taken up by taken up by conventional focus / zoom lens systems.conventional focus / zoom lens systems.

Minimal power usageMinimal power usage . The energy to . The energy to drive the liquid lens is generated by drive the liquid lens is generated by charging the capacitor formed by the charging the capacitor formed by the wall electrode and the water. Charging wall electrode and the water. Charging this approximately 100-pF capacitor this approximately 100-pF capacitor requires less than a micro joule .requires less than a micro joule .

Physical DimensionsPhysical Dimensions

Diameter of lensDiameter of lens: 10µm-: 10µm-10mm10mm

Thickness of lensThickness of lens or or enclosureenclosure: less than 1mm : less than 1mm to 2mm.to 2mm.

Electrical SpecificationsElectrical Specifications

Operating voltageOperating voltage (autofocus)(autofocus): 1.5V: 1.5V

Power not required in Power not required in manual focusing mode.manual focusing mode.

Optical SpecificationsOptical Specifications

MagnificationMagnification: 10x: 10x Focusing latencyFocusing latency: 2 mm : 2 mm

– infinity– infinity

DISADVANTAGESDISADVANTAGES

The only disadvantage of The only disadvantage of the liquid lens is the fact that the liquid lens is the fact that it it should not be subjected to should not be subjected to temperature beyond the temperature beyond the specified rangespecified range or else water or else water will freeze inside it and this will freeze inside it and this may damage our system. may damage our system.

Proposed remediesProposed remedies

The freezing point of the The freezing point of the liquid can be improved by liquid can be improved by adding large quantities of adding large quantities of salt (e.g., salt (e.g., lithium chloridelithium chloride) ) or antifreeze (e.g., or antifreeze (e.g., ethylene glycol). ethylene glycol).