Mirror-like display creates rich color pixels by harnessing ambient light

June 23, 2015, Optical Society of America

Using a simple structure comprising a mirror and an absorbing layer to take advantage of the wave properties of light, researchers at Qualcomm MEMS Technologies, Inc., a subsidiary of Qualcomm Incorporated, have developed a display technology that harnesses natural ambient light to produce an unprecedented range of colors and superior viewing experience. An article describing their innovative approach appears today in The Optical Society's new high-impact journal Optica.

This technology, which could greatly reduce the amount of power used in multiple consumer electronics products, is the latest version of an established commercial product known as Qualcomm Mirasol. Based on a new color rendering format that the researchers call Continuous Color, the new design helps solve many key problems affecting mobile displays such as how to provide an always-on display function without requiring more frequent battery charging and a high quality viewing experience anywhere, especially in bright outdoor environments.

The innovation was made possible by using a combination of a mirror with a thin absorbing layer separated by a precise and controllable gap. While the mirror by itself would simply reflect all of the incident light energy, the absorbing layer selectively filters out a narrow slice of the spectrum, thus coloring the reflected light. The gap is controlled to produce nearly every conceivable color, not just the red, green, and blue (RGB) of earlier display technologies.

"We have developed an entirely new way of creating a color display," said John Hong, a researcher with Qualcomm MEMS Technologies, Inc. and lead author on the Optica paper. "The incredibly efficient display is able to create a rich palette of colors using only ambient light for viewing, much like the way we would read and view printed material."

Harnessing Ambient Light

Typical color displays are essential yet power-hungry components of virtually every digital product with a human-machine interface, from cell phones and computers to home televisions and massive displays at sporting events. Since even the most energy-efficient models require some form of backlighting, they can quickly draw-down a power supply.

To save on power and extend the life of these devices, engineers have been exploring ways to replace emissive technologies with displays that can reflect .

Earlier attempts to create reflective light color displays, however, presented a number of vexing problems. The designs required using three separate pixels to produce the red, green and blue of a traditional display. Though adequate for certain applications, the fact that only one-third of the incoming light can be reflected back toward the viewer in a typical reflective RGB format limits the gamut of colors and brightness of the display.

The new display reported in Optica is able to overcome these hurdles by reflecting more of the incoming light and enabling the full spectrum of visible light to be displayed, including bright white and deep black.

Hong and his colleagues were able achieve these results by using a property of light they call interferometric absorption to create a broad spectrum of colors. To produce this effect, the researchers designed, in essence, a two-layer device. The first layer consists of a thin absorbing material that lets most of the light pass through to the second mirror layer where it is reflected back upon itself.

With this design, the incoming light and the reflected light interfere with one another, producing a variety of standing waves with each component periodicity producing a unique color in the spectrum.

By adjusting the distance between the reflective and absorbing layers with tiny actuators known as Micro-Electro-Mechanical Systems (MEMS), the absorbing layer is moved to match a node in the standing wave that corresponds to a desired color. The spectral components not associated with that node are efficiently absorbed, allowing only the desired color to leak through the structure and back toward the viewer. Each pixel therefore behaves as a colored mirror, with the color tunable across the entire visible spectrum.

Extending Power and Saving Energy

Depending on how the display is used, the power savings can exceed current backlit technologies tenfold. The greatest benefit is when a particular image is retained on the display, which then operates like a form of analog memory in a virtually power-free display mode.

The design presented in the paper consists of a panel that is about 1.5 inches across and contains approximately 149,000 pixels. Both the resolution and area of the display, however, can be scaled to match those of various mobile devices such as Internet-of-Things (IoT) enabled wearables and smartphones.

Fabrication can be achieved in one piece, with the MEMS, upper layer, and lower layer created using the same deposition, lithography and etching processes that are used to create liquid crystal displays.

"Our goal is to improve the technology and design so it can be easily integrated into manufacturing processes at existing factories." said Hong. The researchers believe that this technology has the potential to change the smartphone experience and that of other personal devices.

"No more squinting at a hard to read display outdoors where we spend much of our time," noted Hong. "We ultimately hope to create a paper-like viewing experience, which is probably the best display experience that one can expect, with only the behind you shining on the page."

Explore further: Engineers create chameleon-like artificial 'skin' that shifts color on demand

More information: J. Hon, E. Chan, T. Chang, T. Fung, B. Hong, C. Kim, J. Ma, Y. Pan, R. Van Lier, S. Wang, B. Wen, L. Zhou, "Continuous Color Reflective Displays Using Interferometric Absorption," Optica, 2, 7, 589 (2015). DOI: 10.1364/OPTICA.2.000589

Related Stories

Making efficient color filter for display applications

August 29, 2012

Flat panel displays, mobile phones and many digital devices require thin, efficient and low-cost light-emitters for applications. The pixels that make up the different colors on the display are typically wired to complex ...

The future of holographic video

February 3, 2015

Holographic video displays, featuring three-dimensional images, are about to "go large" and become a lot more affordable at the same time, thanks to the work of a team of Brigham Young University (BYU) researchers and their ...

Recommended for you

Atomic parity violation research reaches new milestone

November 12, 2018

A reflection always reproduces objects as a complete mirror image, rather than just its individual parts or individual parts in a completely different orientation. It's all or nothing, the mirror can't reflect just a little. ...

Innovative experimental scheme can create mirror molecules

November 12, 2018

Exploring the mystery of molecular handedness in nature, scientists have proposed a new experimental scheme to create custom-made mirror molecules for analysis. The technique can make ordinary molecules spin so fast that ...

3 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

shavera
5 / 5 (2) Jun 23, 2015
How quickly can pixels switch states? Orders of single Hz or slower (eBook speed) or tens-hundreds of Hz (screens)?

Edit: Read source article. Rendered at 60Hz. So monitor/screen/device speeds.
24volts
5 / 5 (2) Jun 23, 2015
If they can make that into an ebook reader it will be a winner. A 10-11 inch one would be a nice size for it.
Eikka
not rated yet Jun 24, 2015
This technology will also highlight the poor quality of light from our modern bulbs, which have discontinuous spectra.

A reflective display cannot reflect a wavelenght that is not present in the ambient light, so the output of the display gets desaturated and dulled down by CFLs and LED lighting. It will only achieve the full possible color gamut under full spectrum light sources such as halogen bulbs, and the sun.

Though some fluorescent tubes come close, it's difficult to find a tube with a CRI rating over 85, whereas any old incandecent bulb gives you a full 100.

"Daylight" fluorescent tubes and plant growing tubes tend to have higher CRI, but they're typically too blue for comfortable indoor lighting in living spaces. The first number in the type sequence, like "830" describes the CRI range (80-89) and the other two give you the color temperature (3000K).

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.