Researchers from Taiwan and China Develop Achromatic Metalens Together
Supported by the Academic Summit Program of Taiwan’s Ministry of Science and Technology, NTU Distinguished Prof. of Physics Din-Ping Tsai (蔡定平), who is also Director and Distinguished Research Fellow of the Research Center for Applied Sciences at Academic Sinica, and his collaborator NTU Prof. of Electrical Engineering Chieh-Hsiung Kuan (管傑雄) cooperated with Nanjing University in metalens development. The team adopted the revolutionary concept of integrated-resonant unit elements (IRUEs) they invented to design and fabricate metasurface structures containing IRUEs and develop a broadband achromatic metalens.
Being one of the most important developments in nano-optics worldwide in recent years, the metalens will greatly facilitate the development of flat optical components that are light, thin, small, precise, and accurate. The study was published under the title, “Broadband Achromatic Optical Metasurface Devices, ” in Nature Communications on August 4.
Lenses are a widely used optical component in daily life (e.g., in smartphones, eyeglasses, and microscopes). However, the refractive indexes of optical materials found in nature often exhibit chromatic dispersion. Consequently, most lenses generate different optical resonances under different wavelengths or colors (i.e., causing chromatic aberration). Moreover, optical devices are generally heavy and large due to limits incurred during the design process. Therefore, how to enable lenses to focus light inside a tiny device and how to eliminate chromatic aberration in a wide range of frequency bands are crucial to developing micro-optoelectronic components. The innovative broadband achromatic metalens developed in this study is a basis for all devices that require high-precision flat ultra-micro-optical components.
A study by Prof. Tsai and his team indicated that nano-structured metasurfaces can manipulate incident light by effectively altering its properties such as phase, amplitude, and polarization. Compared with the optical materials existing in nature, metasurfaces provide greater freedom and advantage in developing multifunctional and ultra-thin optical devices. In the last two years, Prof. Tsai and his team have successfully applied this property in designing and develop metasurface devices such as multicolor meta-holograms.
In addition to their larger size, lenses generally exhibit chromatic dispersion, where the focal length varies with the incident wavelength.
The focal length of the IRUE-based achromatic metalens does not vary with the incident wavelength because the chromatic dispersion has been completely eliminated.
Optical image (left) and scanning electron microscope image (right) of the fabricated metalens.