Birefringence is one of the basic optical properties of optical crystals. When a beam of light passes through a birefringent crystal, it will be decomposed into ordinary light (o light) and extraordinary light (e light). Changing the crystal thickness can help people control the phase difference of the two beams, and help people prepare optical components such as 1/2 wave plate and 1/4 wave plate (phase retarder) with different polarization modulation characteristics, which are used in optical communication, display and polarization optics, etc. The field has important application value. Due to the dispersion characteristics of the refractive index, wave plates based on traditional optical design schemes can only work at specific wavelengths, which cannot meet the development of optical system integration. How to prepare achromatic wave plates has become one of the important technical challenges in the optical field. The core of manufacturing achromatic wave plates is to control the phase retardation of each wavelength. The preparation of achromatic quarter-wave plates is generally achieved by bonding multiple uniaxial wafers, or precisely designed metamaterials and metasurfaces. However, both the bonding of uniaxial wafers and the preparation of metamaterials are limited by processing limits. Currently, there is no simple technical route to realize wide-spectrum achromatic quarter-wave plates in the visible light band.

Recently, Professor Zhong Haizheng and adjunct professor Greg Scholes (Professor of Princeton University) of the School of Materials Science & Engineering, Associate Professor Zhang Yongyou of the School of Physics and Professor Wang Yongtian of the School of Optoelectronics of Beijing Institute of Technology cooperated together, discovered the achromatic 1/4 wave plate characteristics of the Cs4PbBr6 crystal embedded with CsPbBr3 nanocrystals, realizing the achromatic polarization modulation in the 532-800 nm wide band. The first author of the paper is Dr. Chen Xiaomei, a 2021 graduate of the School of Materials Science and Engineering, Beijing Institute of Technology, and Dr. Lu Wengao, a 2018 graduate of the School of Optoelectronics (winner of Excellent Doctoral Dissertation of Chinese Optical Engineering Society), and Dr. Tong Jialun, a 2019 graduate of the School of Materials Science and Engineering, are the co-authors of the paper.

The refractive index modulation characteristics of embedded CsPbBr3 nanocrystals on Cs4PbBr6 crystals provide a new idea for the development of intraocular lens optics. Through the adjustment of the microstructure inside the crystal, the limitations of traditional optical materials can be broken, and new optical materials with special optical characteristics can be developed, which provides new ideas for the optimal design and integration of optical systems. Related results were published in Nature Photonics under the title "Solution-Processed Inorganic Perovskite Crystals as Achromatic Quarter-wave Plates", refer to https://www.nature.com/articles/s41566-021-00865-0. This research was supported by the National Natural Science Foundation of China (61722502, 61727808, 12074037, 51761165021). The Advanced Materials Experimental Center and the Micro-Nano Quantum Photon Experimental Center provided platform support for material preparation and optical testing, respectively.