Liquid Lens


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.
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.

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.

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 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.

Transmissiveliquid lenses use two immiscible fluids, each with a different refractive index, to create variable-focus lenses of high optical quality as small as 10 ?m (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 surface tension, changing the radius of curvature in the meniscus and thereby the focal length of the lens. Only 0.1 micro joules (J) 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.

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