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| Source: Qualcomm. Single Mirror Interferometric Modulation (SM IMOD or SMI) Mirasol displays (1.6” diagonal, 343 ppi) illuminated only by average office (fluorescent) ambient light. The content shown is refreshed at 60Hz. The frame rate is variable, between 1 and 120 Hz. |
Using a structure comprising a mirror and an absorbent layer to take advantage of the wave properties of light, researchers at Qualcomm MEMS Technologies, a subsidiary of Qualcomm, have developed a display technology that harnesses ambient light to produce an unprecedented range of colours and superior viewing experience. An article* describing their innovative approach has been published in The Optical Society’s journal Optica.
This display 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 colour 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, colouring the reflected light. The gap is controlled to produce nearly every conceivable colour, not just the red, green, and blue (RGB) of earlier display technologies.
“We have developed an entirely new way of creating a colour display,” said John Hong, Researcher, Qualcomm MEMS Technologies 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.
“We ultimately hope to create a paper-like viewing experience, which is probably the best display experience that one can expect, with only the light behind you shining on the page.”
Typical colour displays are power-hungry. Since even the most energy-efficient models require some form of backlighting, they can quickly deplete 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 ambient light.
Earlier attempts to create reflective light colour displays presented 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 colours 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. The incoming light and the reflected light interfere with one another, producing unique colours 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 colour. The spectral components not associated with that node are absorbed, allowing the desired colour to leak through the structure and back toward the viewer. Each pixel therefore behaves as a coloured mirror, with the colour tunable across the entire visible spectrum.
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 analogue memory in a virtually power-free display mode.
The design presented in the paper consists of a panel that is about 1.5" across and contains approximately 149,000 pixels. Both the resolution and area of the display can be customised. “Our goal is to improve the technology and design so it can be easily integrated into manufacturing processes at existing factories.” said Hong.
*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
Typical colour displays are power-hungry. Since even the most energy-efficient models require some form of backlighting, they can quickly deplete 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 ambient light.
Earlier attempts to create reflective light colour displays presented 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 colours 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. The incoming light and the reflected light interfere with one another, producing unique colours 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 colour. The spectral components not associated with that node are absorbed, allowing the desired colour to leak through the structure and back toward the viewer. Each pixel therefore behaves as a coloured mirror, with the colour tunable across the entire visible spectrum.
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 analogue memory in a virtually power-free display mode.
The design presented in the paper consists of a panel that is about 1.5" across and contains approximately 149,000 pixels. Both the resolution and area of the display can be customised. “Our goal is to improve the technology and design so it can be easily integrated into manufacturing processes at existing factories.” said Hong.
*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
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