A prototype display developed by Opalux.

Last week, a panel of experts at EmTech@MIT discussed technologies that could hasten the arrival of color e-readers.

While the panelists agreed that high-quality color displays could make portable reading devices more attractive to advertisers and deliver a richer experience for readers, they were less unanimous on the best way to deliver color screens.

Two companies are hoping to use reflective microstructures--the same kind seen in opals and on butterflies' wings--to develop color displays.

Opalux uses a sponge-like polymer structure that mimics that of an opal. When a voltage is applied, the material expands, changing the wavelength of light that it reflects."So you can basically take one material and get all the colors you want," says the company's CEO, Andre Arsenault.

Qualcomm is also making color displays with photonic microstructures. The company has developed a MEMs structure that sits on glass and opens and closes depending on the voltage applied, imitating the way gaps on the surface of a butterfly's wings allow certain wavelengths of light to reflect back.

Achieving high quality shades of black, white and gray remains a challenge for such screens. And, just like a stone sparkling at a certain angle of light, the color can sometimes change when viewed from different angles.

Another company, Kent Displays, has developed a technology that reflects different colors using three colored layers of liquid crystals placed on top of glass or plastic LCDs. The company has so far made thin, flexible displays that consume little power, says CTO Asad Khan.

E-Ink, which makes the displays for Amazon's Kindle, uses micro-encapsulated charged particles that move in response to an electric field. In 2010, the company plans to put a color filter over the electronic paper to add color. However, E-Ink's product director Lawrence Schwartz says that the industry needs to make sure the devices are low cost and low power and are usable in direct sunlight.

Varying etching conditions influences the angles formed by the panels in these nanoboxes. The left column is a close-up of the tin hinge material. The other columns show the boxes at different magnifications. The panels are patterned with the letters "JHU" with line-widths of 15 nanometers. Credit: ACS/Nano Letters

Chemists have become very skilled at building 2-D nanostructures, but making 3-D patterned structures for drug delivery, electronics and other applications has proved more challenging. In particular, no one has been able to make 3-D structures with patterned surfaces.

David Gracias and Jeong-Hyun Cho of Johns Hopkins University in Baltimore have overcome this problem. They first made arrays of patterned, cross-shaped nickel structures on a silicon wafer, then added tin hinges. When placed in a plasma etching chamber, the flat structures folded up into cubes and released from the wafer. To make nanocubes as small as 100 nanometers a side, the researchers added another panel.

The work is described online in the journal Nano Letters, where the researchers write that it should apply to other polyhedral shapes as well.

Metamaterials can be designed to interact with light in strange ways. By carefully structuring metal arrays at the nanoscale, for example, physicists can cloak an object from microwaves, or make superlenses that focus in on objects too small to be seen with conventional optics.

Now physicists have made designs for metamaterial optical fibers. Conventional optical fibers carry telecommunications data and are important components of some sensors and medical equipment. Fibers made up of metamaterials could carry light in ways that aren't possible using naturally existing materials. According to research published online this week in Nano Letters, metamaterial fibers could guide both light and plasmons, surface energy waves induced by photons. Plasmonic fibers, say the paper's authors, could do what optical fibers do, but much faster, speeding telecommunications and making for faster sensors. While conventional optical fibers are made up of layers of glass, the metamaterials proposed this week would be made up of nano-patterned aluminum oxide and silver. The designs were made by researchers at the University of California, San Diego, and the Institute for Integrative Nanosciences at IFW Dresden, Germany.

These simulations show how light and plasmons would move through newly designed metamaterial fibers. The line drawings are ray diagrams; the colored circles show the intensity of light through the theoretical fibers' cross sections. Credit: ACS/Nano Letters