Lenses are essential elements of optical technology that have played a crucial role in different applications, ranging from eyewear to space telescopes. However, traditional refractive lenses are bulky, which can limit their usage in certain areas. In the last two decades, researchers have developed metalenses as a promising alternative to conventional refractive lenses. These devices are thinner than traditional lenses and offer diffraction-limited focusing performance while avoiding some problems associated with refractive lenses such as aberrations.

Production process: the silicon master stamp (left), metalenses (centre), and SEM image of the metalenses (right). 

Metalenses consist of thin structures with arrays of "meta-atoms" that interact with light, changing its direction of propagation. These meta-atoms have dimensions smaller than the wavelength of light. Conventional refractive lenses rely on the shape of the lens and its refractive index to control light. In contrast, metalenses are macroscopically flat, so their shape and composition of meta-atoms define their optical properties.

Due to the intricate design and material requirements, metalenses have yet to be mass-produced with reasonable feasibility and cost. However, researchers have recently developed a method to fabricate large quantities of metalenses. The team at Pohang University of Science and Technology in South Korea integrated three fabrication technologies to simplify the production of metalenses: photolithography, nanoimprint lithography, and atomic layer deposition.

The researchers patterned a master stamp using deep ultraviolet photolithography, imprinted the inverse of the meta-atom structure in a replica mold made of silicone, and poured liquid resin into the silicone mold. The resin flowed into the nanogrooves before hardening, and the team produced hundreds of metalenses at once. By integrating these three already mature fabrication technologies, the researchers have simplified and scaled up the production of metalenses.

The researchers have tested the potential of metalenses by integrating them into a prototype virtual reality (VR) display. In commercial VR devices, reflection or diffraction is used to project virtual images, resulting in bulky devices that must accommodate the appropriate focal length for the optics. The metalens-based VR display reduces the distance the light has to travel by using a transmission-based design, making the display lightweight and comfortable to wear. The researchers created images using red, green, and blue light, indicating the potential for all-color displays.

The scalable fabrication method produces metalenses with higher performance than devices made using more conventional methods. The mass-produced metalenses open up possibilities for use in biosensors, color printing, holograms, and virtual reality displays, among other applications. The development of metalenses is a game-changer in optical technology that could revolutionize various fields, including medicine, communications, and entertainment.