Ultra-compact optical design improves virtual and augmented reality device cameras
Researchers at Seoul National University College of Engineering announced that they have developed an optical design technology that dramatically reduces the volume of cameras with a folding lens system using "metasurfaces," a next-generation nano-optical device.
By arranging metasurfaces on a glass layer so that light can be reflected and folded and rotated on the glass layer, the researchers have realized a lens system with a thickness of 0.7 mm, which is much thinner than existing refractive lens systems. The research was published in the journal Science Advances on October 30.
Traditional cameras are designed to stack multiple glass lenses to refract light when taking pictures. While this structure provides excellent high-quality images, the thickness of each lens and the wide spacing between the lenses increase the overall bulk of the camera, making it difficult to apply to devices that require ultra-compact cameras, such as virtual and augmented reality (VR-AR) devices, smartphones, endoscopes, drones, and more.
To address this limitation, the researchers have developed an ultra-thin camera system that reduces the thickness of a conventional lens system to less than half, using a new lens module design that incorporates metasurfaces.
Metasurfaces, which are being touted as next-generation nano-optical devices, have the ability to precisely control three properties of light—intensity, phase, and polarization—on a pixel-by-pixel basis. This is because the nanostructures that make up a metasurface are arranged in a few hundred nanometer (nm) spacing, which is smaller than the wavelength of light.
According to the team, by designing a metasurface optimized for a specific wavelength (852 nm) and arranging multiple sheets horizontally on a glass substrate, light can be reflected multiple times inside the substrate, thereby securing the light paths in a space-efficient folded manner. . The team presented a framework for a miniature camera that captures images with a system of thin, folded lens modules that adjust the light path.
Comparison of thicknesses between modules. (Center) Microscopic image of metasurface nanofabrication. (Right) Image of a nanostructure composed of metasurfaces. Credit: Science Advances
The system not only overcomes the physical limitations of thick conventional lens modules, but also delivers superior image quality. This is because it provides a 10-degree field of view within a very small system footprint of 0.7 millimeters thick and delivers high-resolution images near the diffraction limit at an aperture of f/4 and a wavelength of 852 nm.
Thanks to this strong competitive advantage, the miniaturized camera technology developed by the researchers is expected to be widely applied in various advanced optical device industries such as VR-AR devices, smartphones, medical endoscopes, and miniature drones.
"This research is significant in that it provides a creative breakthrough to innovatively reduce the thickness of cameras by introducing nano-optical devices," said Youngjin Kim, the paper's first author.
“We will continue our research to lead the innovation of thin and light cameras with metasurfaces that combine their freedom to tune light at the nanometer scale and the excellent performance and industrial advantages of being fabricated through semiconductor processes.”
“Our research focuses on efficiently utilizing the lens space using metasurfaces,” said Tae-won Choi, co-first author of the study. “The folded lens system is very thin, unlike conventional systems that are thick due to the combination of multiple lenses, so it will play an important role in the virtual and augmented reality industries, where device miniaturization and lightweight are essential.”
The Optical Engineering and Quantum Electronics Laboratory, where the research was conducted, is currently headed by Professor Eunchan Jeong after the death of Professor Byung-ho Lee in November 2022. The lab continues its active research in 3D displays, holography, and metasurfaces. Researcher Young Jin Kim will continue his research on overcoming the limitations of imaging devices such as cameras using metasurfaces. Taewon Choi plans to continue his research on the application of metasurfaces in VR-AR devices, camera sensors, image sensors, and other related industries.
