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Philips Develops Fluid Lenses
Lars T. writes "Digital Photography Review has a short report indicating: 'Philips Research at the CeBIT exhibition is demonstrating a unique variable-focus lens system that has no mechanical moving parts. Suited to a wide range of optical imaging applications, including digital cameras.' Here is Philips' press release and the Heise News article (in German) where I first heard about it. The latter also mentions that Philips has recently used the same electrowetting effect in an 'ePaper' display prototype."
There was an article in New Scientist a few weeks ago about a lense that changed it's focus in response to an electric current, iirc.
It was made of some plastic and I think the current changed the density of the plastic at some point in the structure in order to change the focus.
Of course, the aim was the same: "Make a lense without moving parts" - these guys must have developed a better solution because the Lense was very poor in the NS article.
Simon.
Philips' Fluid Lenses
Wednesday, 3 March 2004 21:40 GMT
Philips Research at the CeBIT exhibition is demonstrating a unique variable-focus lens system that has no mechanical moving parts. Suited to a wide range of optical imaging applications, including digital cameras. Philips' FluidFocus system mimics the action of the human eye using a fluid lens that alters its focal length by changing its shape. The new lens, which lends itself to high volume manufacturing, overcomes the fixed-focus disadvantages of many of today's low-cost imaging systems.
Press Release:
Philips' Fluid Lenses Bring Things into Focus
At this year's CeBIT Exhibition in Hannover Germany, Philips Research is demonstrating a unique variable-focus lens system that has no mechanical moving parts. Suited to a wide range of optical imaging applications, including such things as digital cameras, camera phones, endoscopes, home security systems and optical storage drives, Philips' FluidFocus system mimics the action of the human eye using a fluid lens that alters its focal length by changing its shape. The new lens, which lends itself to high volume manufacturing, overcomes the fixed-focus disadvantages of many of today's low-cost imaging systems.
The Philips FluidFocus lens consists of two immiscible (non-mixing) fluids of different refractive index (optical properties), one an electrically conducting aqueous solution and the other an electrically non-conducting oil, contained in a short tube with transparent end caps. The internal surfaces of the tube wall and one of its end caps are coated with a hydrophobic (water-repellent) coating that causes the aqueous solution to form itself into a hemispherical mass at the opposite end of the tube, where it acts as a spherically curved lens.
The shape of the lens is adjusted by applying an electric field across the hydrophobic coating such that it becomes less hydrophobic - a process called 'electrowetting' that results from an electrically induced change in surface-tension. As a result of this change in surface-tension the aqueous solution begins to wet the sidewalls of the tube, altering the radius of curvature of the meniscus between the two fluids and hence the focal length of the lens. By increasing the applied electric field the surface of the initially convex lens can be made completely flat (no lens effect) or even concave. As a result it is possible to implement lenses that transition smoothly from being convergent to divergent and back again.
In the FluidFocus technology demonstrator being exhibited by Philips Research at CeBIT 2004, the fluid lens measures a mere 3 mm in diameter by 2.2 mm in length, making it easy to incorporate into miniature optical pathways. The focal range provided by the demonstrator extends from 5 cm to infinity and it is extremely fast: switching over the full focal range is obtained in less than 10 ms. Controlled by a dc voltage and presenting a capacitive load, the lens consumes virtually zero power, which for battery powered portable applications gives it a real advantage. The durability of the lens is also very high, Philips having already tested the lens with over 1 million focusing operations without loss of optical performance. It also has the potential to be both shock resistant and capable of operating over a wide temperature range, suiting it for mobile applications. Its construction is regarded as compatible with high-volume manufacturing techniques.
(A) Schematic cross section of the FluidFocus lens principle. (B) When a voltage is applied, charges accumulate in the glass wall electrode and opposite charges collect near the solid/liquid interface in the conducting liquid. The resulting electrostatic force lowers the solid/liquid interfacial tension and with that the contact angle q and hence the focal distance of the lens. (C) to (E) Shapes of a 6-mm diameter lens taken at different applied voltages.
Prototype FluidFocus lenses
Photos courtesy of Philips
I remember that fluid lenses have been used by holographers for a long time, because they can be of quite high quality even with large diameter. Vari*lite also uses fluid lenses in some of their intelligent lighting fixtures.
The News here is that the Philips lens can be focused by an electric field with no part moving other then the lens. The size of their prototype is tiny; IMHO they need at least to triple the size of it to make it useful for digital cameras.
-- www.linux-laser.org - Open Source Laser Show Software for Linux
A lone researcher did it to make cheap bifocals a few years back. It is an extremely inexpensive way to provide a "one size fits all" pair of glasses for everyone who needs them. No custom lenswork needed - just pump liquid in or out :)
I guess you where sleeping your way through the optics lectures: These lenses could definitely work. If you look at the picture
you see that there are two fluids: brown one on top and a blue one on the bottom. If you remember Snell's law (ray bends towards the normal in the denser medium), you can conclude from the picture that the 'brown' fluid has a higher refractive index than the 'blue' fluid. The left picture thus resembles a hollow/concave/negative lens and the right picture resembles a convex/positive lens. Of these the positive (on the right) can be used to form a real image (one you can capture on a CCD or a retina), whereas the negative only forms a virtual image.
A colleague of mine did his internship at the group that invented these and my boss still works part-time at Philips.
karma police: arrest this man, he talks in maths; he buzzes like a fridge, he's like a detuned radio. [radiohead]
According to the article, it takes 10 ms to focus.