Smallest U-M logo demonstrates advanced display technology

Smallest U-M logo demonstrates advanced display technology
An optical microscopy image of a 12-by-9-micron U-M logo produced with this new color filter process. Credit: Jay Guo

In a step toward more efficient, smaller and higher-definition display screens, a University of Michigan professor has developed a new type of color filter made of nano-thin sheets of metal with precisely spaced gratings.

The gratings, sliced into metal-dielectric-metal stacks, act as resonators. They trap and transmit light of a particular color, or , said Jay Guo, an associate professor in the Department of Electrical Engineering and Computer Science. A dielectric is a material that does not conduct electricity.

"Simply by changing the space between the slits, we can generate different colors," Guo said. "Through nanostructuring, we can render white light any color."

A paper on the research is published Aug. 24 in Nature Communications.

His team used this technique to make what they believes is the smallest color U-M logo. At about 12-by-9 microns, it's about 1/6 the width of a human hair.

Conventional LCDs, or , are inefficient and manufacturing-intensive to produce. Only about 5 percent of their back-light travels through them and reaches our eyes, Guo said. They contain two layers of polarizers, a color filter sheet, and two layers of electrode-laced glass in addition to the liquid crystal layer. Chemical colorants for red, green and blue pixel components must be patterned in different regions on the screen in separate steps.

Guo's acts as a polarizer simultaneously, eliminating the need for additional polarizer layers. In Guo's displays, reflected light could be recycled to save much of the light that would otherwise be wasted.

Smallest U-M logo demonstrates advanced display technology
An optical microscopy image of seven color filters illuminated by white microscope light. Credit: Jay Guo

Because these new displays contain fewer layers, they would be simpler to manufacture, Guo said. The new color filters contain just three layers: two metal sheets sandwiching a dielectric. Red, green and blue pixel components could be made in one step by cutting arrays of slits in the stack. This structure is also more robust and can endure higher- powered light.

Red light emanates from slits set around 360 nanometers apart; green from those about 270 nanometers apart and blue from those approximately 225 nanometers apart. The differently spaced gratings essentially catch different wavelengths of light and resonantly transmit through the stacks.

"Amazingly, we found that even a few slits can already produce well-defined color, which shows its potential for extremely high-resolution display and spectral imaging," Guo said.

The pixels in Guo's displays are about an order of magnitude smaller than those on a typical computer screen. They're about eight times smaller than the pixels on the iPhone 4, which are about 78 microns. He envisions that this pixel size could make this technology useful in projection displays, as well as wearable, bendable or extremely compact displays.

The paper is called "Plasmonic nano-resonators for high resolution color filtering and spectral imaging."

Guo is also an associate professor in the Department of Macromolecular Science and Engineering. This research is supported in part by the Air Force Office of Scientific Research and the Defense Advanced Research Projects Agency. The university is pursuing patent protection for the intellectual property and is seeking commercialization partners to help bring the technology to market.

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Aug 24, 2010
NICE! Sounds like display technology is getting close to the resolution to be able to reproduce color holographic displays in real time. Give how fast computers are, hopefully we will see true 3D displays coming soon.

Aug 24, 2010
I am very curious when displays will reach "real" resolution, i.e. you couldn't tell the difference between a screen and an open window. That will really be something. I suppose this will also be restricted by the max resolution of cameras too. Unless of course you use only computer generated images.

Aug 25, 2010
Well, trekgeek1, I don't think your vision is that doable. To achieve "open window" level reality, one need not only a high resolution, but also a angle-dependent ray emission to imitate the distance of objects. That is asking for a 180° semi-spherical projector for each "pixel", each projecting a high definition image, such that light of an "object" come to the eye from multiple pixels in accordance to the position of the eye. Yes, "far away" objects must be blurry to short-sighted eyes and vice-versa. Those "3D-glasses" would never cut it.

What's actually achievable in near future is printing level resolution, so that when the screen image is not moving, you can't distinguish it from printed-out photographs. But that's already good enough for most purposes.

Aug 25, 2010
there's more to holography than resolution. Looking from different angles would need to make it look different, and smaller pixels can't help. Holography works by encoding both amplitude (like 2D photography) and phase. You start getting into Fourier optics with this, but the amplitude and phase information combined give a true 3D image. Of course, you still need high resolution, but I suspect that 1080p would be acceptable.

The reason this hasn't been done so far (at least outside of a lab or physicist's garage) is because the Fourier optics is hard, and most holography needs coherent light. But it is technically possible, and now I've got an idea for a new weekend project...

Aug 25, 2010
I am very curious when displays will reach "real" resolution, i.e. you couldn't tell the difference between a screen and an open window. That will really be something.

It has already happened - iPhone 4's retina display (at 326 dpi) exceeds the eye's ability (20/20 vision) to resolve its pixels at normal viewing distances.

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