Thin lenses have a bright future

Paper-thin optical lenses simple enough to mass produce like microchips could enable a new generation of compact optical devices. A team with researchers at the University of Tokyo and JSR Corp. fabricated and tested flat lenses called Fresnel zone plates (FZPs), but did so for the first time using only common semiconductor manufacturing equipment, the i-line stepper, for the first time. These flat lenses currently lack the efficiency of in-production lenses, but have the potential to reshape optics for industries ranging from astronomy to health care and consumer electronics.

Flat lenses, such as metalenses, exist, but they come with hefty price tags and a high degree of complexity, and only a small number of devices are available. In the race to increase the quality, performance and efficiency of devices whilst reducing costs, manufacturers, through the work of academic researchers, seek alternatives. FZPs have become a good candidate to improve optical devices where space is critical. And for the first time, researchers crafted sample lenses with just a few straightforward steps using industry standard machinery.

“We developed a simple and mass-producible method for FZPs using a common semiconductor lithography system, or stepper,” said Associate Professor Kuniaki Konishi from the Institute for Photon Science and Technology. “This is due to a special type of photoresist or mask called a color resist, which was originally designed for use as color filters. By simply coating, exposing and developing this material, we produced lenses capable of focusing visible light down to only 1.1 microns, around 100 times thinner than a human hair.”

The current drawback with the new FZPs is that they only have a light-gathering efficiency of 7%, meaning they produce excessively noisy images. But already the team is working on ways to increase this fourfold by changing the way they use the color resists. However, this would require a greater degree of control over the color resists’ physical properties than was afforded the researchers at the time of this study, though the ability to do this does exist.

“In addition to efficiently fabricating FZPs, we also devised simulations which are confirmed to match our experiments very tightly. What this means is, we could tailor designs to match specific applications in different fields, such as medicine, before committing to production,” said Konishi. “Furthermore, we envisage environmental and economic benefits too, as unlike traditional manufacturing methods, the FZP production process eliminates the need for toxic etching chemicals and significantly reduces energy consumption.”

So, it might be a while before FZPs help you capture moments in high visual fidelity with your ultrathin smartphone, but this, or technology inspired by it, will likely come along soon.

###

Journal article:

Ryohei Yamada, Hiroyuki Kishida, Tomohiro Takami, Itti Rittaporn, Mizuho Matoba, Haruyuki Sakurai, Kuniaki Konishi. “Optical Fresnel zone plate flat lenses made entirely of colored photoresist through an i-line stepper”, Light: Science & Applications, DOI: 10.1038/s41377-024-01725-6

Funding: This research was supported by JSR-UTokyo Collaboration Hub, CURIE.

Useful links:
Konishi Lab - https://www.kkns.ipst.s.u-tokyo.ac.jp/en/home
Institute for Photon Science and Technology - http://www.ipst.s.u-tokyo.ac.jp/index-e.php
Graduate School of Science - https://www.s.u-tokyo.ac.jp/en/
JSR Corporation - https://www.jsr.co.jp/jsr_e/
JSR-UTokyo Collaboration Hub, CURIE - https://curie.phys.s.u-tokyo.ac.jp/en/

Research contact:
Associate Professor Kuniaki Konishi
Institute for Photon Science and Technology, The University of Tokyo,
7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan
kkonishi@ipst.s.u-tokyo.ac.jp  

Press contact:
Mr. Rohan Mehra
Public Relations Group, The University of Tokyo,
7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan
press-releases.adm@gs.mail.u-tokyo.ac.jp

JSR Corporate Communications

Sayako Kitamura/Yichin Wang    

jsr_koho@jsr.co.jp

About The University of Tokyo:

The University of Tokyo is Japan's leading university and one of the world's top research universities. The vast research output of some 6,000 researchers is published in the world's top journals across the arts and sciences. Our vibrant student body of around 15,000 undergraduate and 15,000 graduate students includes over 4,000 international students. Find out more at www.u-tokyo.ac.jp/en/ or follow us on X (formerly Twitter) at @UTokyo_News_en.

About JSR Corporation:

JSR Corporation is developing its business globally on the strength of its technological capabilities, focusing on the digital solutions business, including semiconductor materials, and the life sciences business, while promoting innovation to provide value to leading industries around the world and exploring next-generation businesses to meet society's challenges.