Professor Byoungho Lee, Introduces to the world, an ‘ultra-thin lens’ that controls light on demand (Donga Science, 20181119)

2018-11-21l Hit 235

[Professor Byoungho Lee of SNU department of electrical and computer engineering is holding up the ultra-thin ‘metalens’ recently developed by his team. From the left: Researcher Gun-Yeal Lee, Professor Lee, and Researchers Jong-Young Hong and Seokil Moon. Photo credit: Professor Byoungho Lee]

A research lab in 301 building of SNU College of Engineering. SNU ECE researcher Jong-Young Hong pointed to a chair in the corner, offering a seat. There was a slanted, clear glass window in front of the chair. Beyond the glass, lab equipment could be seen. “Try moving your head up and down, left and right.” Suddenly, a 3-color sign appeared in front of the eyes. The letters ‘2m’, ‘4m’, ‘6m’, ‘8m’, and ‘10m’ were overlaid on the lab surroundings reflected on the transparent glass slide. ‘2m’ appeared near, and ‘10m’ seemed further away.

This is an 3D augmented reality(AR) image developed for ‘Head-Up Display(HUD)’ system in which information is displayed in the windshield of the car. This shows a three-dimensional image even without glasses,” said Professor Byoungho Lee of SNU ECE. “This is possible thanks to a special lens called ‘lenticular lens’.”

The augmented reality system in which the research team used a ‘lenticular lens’ to superimpose a three-dimensional image onto the actual scenery. Photo credit: Professor Byoungho Lee

A lenticular lens is a special type of lens with a structure of several half-cylindrical lenses connected in parallel. One can easily picture the bumpy surface of corduroy pants often worn in winter. Since each of the bumps acts as a lens, the information of the display pixels situated behind the lenses propagate in different directions. Using this fact, it is possible to project slightly different images according to the location of the two eyes. Following the same principle with which our eyes can view the real world, it is possible to see three-dimensional images through the eyes in an artificial manner.

Professor Lee and the research team of Jong-young Hong and Seokil Moon installed, on top of a flat display, an accurately manufactured lenticular lens whose diameter for each of the bumpy structures is 0.5mm. The precisely designed image display was manipulated as desired as it passed the lens, and this was reflected on the glass(windowshield) where it was transformed into a three-dimensional image in front of the eyes. To an extent, the image was maintained even when the body and head moved, and it synchronized well with the background beyond the window, not causing any dizziness.

There is also ‘meta lens’, which is thinner than lenticular lens. It is a novel, ultra-thin flat lens that can easily focus or bend an intended amount of light to the direction of choice even though it is extremely thin. It can reproduce desired images by controlling light even without heavy lenses that are several centimeters thick.

Holding up the metalens developed by Professor Lee and the research team of Gun-Yeal Lee and Jong-Young Hong, its weight and thickness could barely be felt. “It’s 100nm(nanometer. 1nm is one-billionth of 1m) thick,” explained Researcher Lee. Although unperceivable with the naked eye, this lens is filled with tiny bumps that are smaller than the wavelength of light. On the transparent plane composed of silicon dioxide, tiny parallelepiped structures that are 60nm in width, 220nm in length, and 100nm in height are densely packed every 400nm. As the structures are tiny, even when they are attached to the glass surface, the glass sustains its transparency, and the actual scenery can be seen as before. However, when a particular light was projected onto the structures, light was bent or focused in an unusual angle not found in nature, thus superimposing an image onto the background.

Professor Lee commented, “Research teams overseas are still limited to creating meta-lenses of less than 1mm in diameter. We are the world’s first to manufacture meta-lenses of practical size, 2cm in diameter. We have also significantly widened the field of view from the conventional 25 degrees to a maximum of more than 100 degrees, thus raising the level of immersion for AR.” On the 1st, the research team published this work on meta lens in the ‘Nature Communications’, and is continuing research to apply this to next-generation display for augmented reality.

Translated by: Jee Hyun Lee, English Editor of Department of Electrical and Computer Engineering,