Liquid Lenses: 5-9MP Phone cameras later this year Digicams next?

There is growing interest in translating and demonstrating capability in liquid lenses where curvature can be altered rapidly and accurately by electric charge.



By controlling the curvature of the meniscus of a liquid droplet it is possible to create a variable focal length lens that mimics the function of the human eye. Here a 2-mm-diameter liquid lens is shown for four different pressures applied by a piezoelectric pump.Source: Duncan Graham-Rowe, Nature Photonics sample, - pp2 - 4 (2006) doi:10.1038/nphoton.2006.2



A 'FluidFocus' lens developed by Philips. The Dutch company says that the lenses are as good as glass optics and has demonstrated their ability to read dual-layer Blu-ray optical discs — a successor to DVDs. Using this technology, the firm has also constructed a miniature autofocus camera that is just 5.5 mm high and has a lens diameter of 3 mm and focusing time of 10 ms. Source

Several practical lenses are becoming available from France (see Breaking news article here and Dutch Company, Phillips!




(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 θ and hence the focal distance of the lens. (C) to (E) Shapes of a 6-mm diameter lens taken at different applied voltages.

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.Source.

What are the implications you see for this new technology?

Asher

Interesting, but not very useful for serious users...?

Hi Asher,
Very interesting idea here for sure, and quite intriguing!
However I can't imagine for a moment that it is 'disruptive' enough for serious photography. Certainly as a cheap lens for a mobile phone, yes.

Any larger lens would in the first case, as far as I can understand, require much more voltage to change the shape, so the savings in energy would decrease as the lens size increases.

At a certain point, the mass of the fluid (and fluid or semi-fluid it must remain!) will be affected by gravity; I sincerely doubt that that can be solved in any way! A large fluidic 'bubble' the size of an old-fashioned silver dollar won't keep its shape very well when held vertically, for instance. Imagine that if you left your camera on the shelf for a week how a large 'wet lens' would look ! Like something from the fun-house perhaps! In fact in the example shown above, it actually looks just like the lens is 'sagging' in the middle since it is relatively horizontal.

The diffraction of light in fluids is a whole new ball game as well; which lens maker in their right mind would throw years of experience away? (Except those mass producing cheap lenses, perhaps?)

And what about multiple lens configurations?
To play the devil's advocate: Actually if the above problems COULD ever be solved, it might be fantastic just for that! Imagine a floating lens concept, where all the lens sections can be 'programmed' with different currents in order to achieve maximised focussing and resolution? That might be something!

Last but not least: What about coatings? They will also be required, and will have to remain in place with the rest of the 'fluids'....

Anyway, just my 2 cents worth of rambling! Thanks for pointing this newfangled gizmo out, I really enjoyed reading it!
Ciao,
Theodore

Good morning Theodore,

The whole treat of the idea is the the new thinking that will stimulate other ideas taking advantage of new materials. Already high quality plastics have been introduced. Many of our lens designs are really the result of work done at the onset of the 20th Century!

Asher

Quality first; production methods second

Good morning- or maybe good night; which time zones are we both in ?
Hi Asher,
For sure, the 'spin-offs' could be tremendous, no disagreement there!
My 'itchiness' on topics of new technology has to do with the possible negative effects on quality that arise when a new technology presents itself. It often takes many, many years before the negatives and positives become truly manifest.

Look the horrible sounding hi-fi equipment that was produced after the change to transistors for instance. It took almost 20 years (at least) before the industry got to grips with creating high quality transistor equipment. In the meantime, everyone suffered from the lower quality. There were many forces behind that of course, although also economic, those of solving heat production, longevity and size considerations marked the death of tubes in general, and of course, the disruptive entrance of transistors was in the end a godsend.

The essence of my (mostly) negative reaction is that I feel new innovations, when driven PRIMARILY by the search for cheap production methods, and not the search for better quality, is invariably doomed to lower the total quality of products in general.

No-one is making these wet lenses for the better picture they produce; they want a cheap solution to eliminate a few cents in the price of a mobile telephone that will deliver millions in savings in the long term. In that same vein, I also don't know of any very high quality lenses made of plastic that exist today; please correct me if I am wrong on that!

The spin-off technology could be beneficial, indeed, no argument there. But cheap thinking will, in my personal opinion, always have a great possibility of an initial lowering of quality, quality that might never be recovered due to the economic nestling of those principles into the mainstream production methods.

Hi Theodore,

For sure, even now tubes still give make finer amplifiers in the hands of an experienced audio engineer. With sufficient effort, digital audio can appear to match that.

With liquid lenses could be calibrated for temperature and focal length and even position. Internally all the needed corrections could be made for every single individual lens. however, likely they wont do that.

I rather think that new glasses and plastics will be present for a long time!

Asher