Posted in | News | Optics and Photonics

Novel Flat Lenses Fabricated with i-line Stepper

A group of researchers from JSR Corp. and the University of Tokyo created and tested flat lenses known as Fresnel zone plates (FZPs) in a study published in Light: Science & Applications. This was the first time that the i-line stepper, a common piece of equipment used in semiconductor manufacturing, was used exclusively.

Photoresist process.
Photoresist process. The process of lithography, on which the researchers’ method is based, is a little like developing a pre-digital chemical photograph. Image Credit: Konishi et al.

A new generation of small optical devices could be made possible by paper-thin optical lenses that are as easy to mass-produce as microchips.

Flat lenses currently lack the efficiency of in-production lenses, but they have the potential to transform optics in various industries, including astronomy, health care, and electronics.

Flat lenses, such as metalenses, exist, but they are expensive and sophisticated, with limited devices available. In the quest to improve device quality, performance, and efficiency while lowering prices, manufacturers seek alternatives through academic research. FZPs have emerged as a promising choice for improving optical systems requiring little area. For the first time, researchers created sample lenses in a few simple steps using industry-standard technology.

We developed a simple and mass-producible method for FZPs using a common semiconductor lithography system, or stepper. 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.

Kuniaki Konishi, Associate Professor, Institute for Photon Science and Technology

The new FZPs' current challenge is that they only have a 7% light-gathering efficiency, resulting in highly noisy images. However, the team is already working on ways to improve this fourfold by modifying how the color resists are used. This would necessitate more control over the physical qualities of the color resists than the researchers had at the time of the study, though the potential to do so exists.

Konishi added, “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.”

He added, “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.

It may be some time before FZPs can help capture moments in high visual fidelity with the ultrathin smartphone, but this technology, or one that is inspired by it, is probably imminent.

Journal Reference:

Yamada, R., et. al. (2025) Optical Fresnel zone plate flat lenses made entirely of colored photoresist through an i-line stepper. Light: Science & Applications. doi.org/10.1038/s41377-024-01725-6

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