With their ability to manipulate light and potential to drastically reduce the size and thickness of optical components, metalenses show great promise, especially for applications in the NIR region. Fabrication, however, is expensive. A single metalens the size of a fingernail currently costs thousands of dollars to produce. Beyond excessive production costs, limitations in conventional manufacturing techniques, including small patterning areas and low throughput, impede the commercialization of metalens technology. To support the mass production of metalenses for use in applications like lidar and miniature medical devices, researchers at Pohang University of Science and Technology (POSTECH) and Korea University collaborated to develop two methods for the scalable, wafer-scale manufacture of metalenses operating in the NIR region. The techniques devised by the team could reduce the cost of metalens production by as much as 1000×. (From left) Professor Junsuk Rho, researcher Seong-Won Moon, and researcher Joohoon Kim from the Pohang University of Science and Technology (POSTECH) worked to develop two methods for wafer-scale manufacturing of metalenses. Courtesy of POSTECH. Metalenses are made using photolithography, a process that uses light to imprint patterns on silicon wafers. Typically, the resolution of light is inversely proportional to its wavelength, which means that shorter wavelengths result in higher resolution, enabling the creation of finer, more detailed structures. For their metalenses, the team opted to use deep-UV photolithography, a process that uses the shorter wavelengths of UV light. The first method developed by the researchers was designed for the production and manufacture of polarization-independent metalenses (i.e., lenses that perform consistently, regardless of the polarization state of the incident light). To construct a metalens that was efficient in the IR region, the team developed a material with a high refractive index and low loss for the IR region. They integrated this material into the mass production process to create a polarization-independent, IR metalens with a diameter of 1 cm and a numerical aperture of 0.53 on an 8-in wafer. The metalens demonstrated exceptional light-collecting capabilities and high resolution approaching the diffraction limit. The cylindrical structure of the metalens reinforced its polarization-independent properties, ensuring good performance regardless of the direction of light vibration. The researchers confirmed the focusing efficiency of the metalens at a 940-nm wavelength. The team also developed a method for mass-producing polarization-dependent metalenses (i.e., lenses that exhibit different optical properties based on the polarization direction of the incident light). For this method, the team used nano imprinting, a cost-effective process that prints nanostructures using a mold. The researchers fabricated the metalenses using rectangular structures made from silicon and nanoparticle-embedded resin. They mass-produced a polarization-dependent metalens with a 5-mm diameter, comprised of about one hundred million rectangular nanostructures on a 4-inch wafer. The metalens has an numerical aperture of 0.53. The polarization-dependent properties of the metalens’s rectangular structure were found to respond effectively to the direction of light vibration. Wafer-scale manufacturing of a NIR metalens (left) and a high-resolution image of an onion epidermis captured using the metalens technology (right). Courtesy of POSTECH. The researchers demonstrated the high-resolution capabilities of both types of metalens, made according to the methods for mass-producing the lenses on large surfaces, by imaging a 1951 USAF resolution test target and through bioimaging. They integrated a high-resolution imaging system to observe samples like an onion epidermis and confirm the potential to commercialize their method for making the metalenses. The researchers’ methods for producing metalenses could overcome the limitations of the traditional, one-by-one metalens production process. The new methods facilitate the creation of optical devices with both polarization-independent and polarization-dependent characteristics, tailored to specific applications, while reducing the production to one thousandth of the price of traditional methods. The techniques could provide a cost-effective pathway for the mass production and large-scale fabrication of metalenses, accelerating the commercialization of metalenses for advanced optical technologies. “We have achieved the precise and rapid production of high-performance metalenses on a wafer-scale, reaching centimeter dimensions,” professor Junsuk Rho, who led the research, said. “Our aim is for this research to expedite the industrialization of metalenses, fostering the advancement of efficient optical devices and optical technologies.” The research was published in Laser & Photonics Reviews (www.doi.org/10.1002/lpor.202300929).
