Ultra-thin optical lenses, which can be mass-produced like microchips, may pave the way for a new wave of compact optical devices. A collaborative team from the University of Tokyo and JSR Corp. has successfully designed and tested flat lenses known as Fresnel zone plates (FZPs), utilizing standard semiconductor manufacturing equipment, specifically the i-line stepper, for the very first time. While these flat lenses do not yet match the efficiency of commercially available options, they hold promise to transform optical technology across fields like astronomy, healthcare, and consumer electronics.
Although flat lenses, including metalenses, are available, they tend to be expensive and complicated, limiting the number of devices in circulation. In pursuit of enhancing quality, performance, and efficiency while minimizing costs, manufacturers, aided by academic research, are exploring new alternatives. FZPs have emerged as a solid option for enhancing optical devices where space limitations are a concern. Notably, researchers have succeeded in creating sample lenses using just a few simple procedures with widely used industrial equipment.
“We created a straightforward and mass-producible technique for FZPs utilizing a mainstream semiconductor lithography system, or stepper,” explained Associate Professor Kuniaki Konishi from the Institute for Photon Science and Technology. “This was possible due to a unique type of photoresist known as color resist, originally intended for color filters. By coating, exposing, and developing this material, we engineered lenses that can focus visible light to a minuscule 1.1 microns, approximately 100 times thinner than a human hair.”
The main limitation of these new FZPs is their light-gathering efficiency, currently at 7%, which leads to excessively noisy images. The research team is already exploring methods to quadruple this efficiency by modifying their application of the color resists. This enhancement will necessitate more precise control over the physical properties of the color resists than the researchers had during this study, but the capability to achieve this is available.
“Besides efficiently producing FZPs, we also developed simulations that closely align with our experimental results. This indicates that we could customize designs for specific applications in various fields, such as medicine, prior to beginning the manufacturing process,” stated Konishi. “Moreover, we foresee environmental and economic advantages, as the FZP production method eliminates the use of harmful etching chemicals and considerably lowers energy usage compared to traditional methods.”
While it may take some time before FZPs enable high-quality image capturing with your ultra-thin smartphone, innovations inspired by this technology are likely to emerge in the near future.
Funding: This research received backing from the JSR-UTokyo Collaboration Hub, CURIE.
