The Institute of Physics, Chinese Academy of Sciences has made significant progress in the research of lithium niobate nanooptics

In recent years, breakthroughs in the preparation technology of lithium niobate single crystal thin films have greatly promoted the important application of lithium niobate crystals in micro nano optical devices such as optical metasurfaces. However, the high hardness and inactive chemical properties of lithium niobate crystals pose significant challenges to micro nano processing; In addition, conventional optical metasurface preparation materials are mostly limited to isotropic materials, and the birefringence characteristics of anisotropic lithium niobate crystals have not been systematically explored in the field of optical metasurfaces.

Li Junjie's team from the Institute of Physics of the Chinese Academy of Sciences/Micromachining Laboratory of the National Research Center for Condensed Matter Physics in Beijing has long focused on the research of micro/nano photonics device processing, design and function integration; In recent years, the team has conducted systematic research on lithium niobate nanooptics and made a series of important progress. Firstly, the team developed a multi-component gas co etching technology, achieving controllable processing of lithium niobate nanostructures (Figure a, Advanced Materials Technology 2024), 9, 2400318). Based on this etching technology, the team designed and processed a nonlinear hyper lens based on lithium niobate nanopore structure, achieving the function of up converting near-infrared beam frequency to ultraviolet band while focusing (Figure b, ACS Photonics 2025, doi. org/10.1021/acphotonics. 4c02259). Recently, the team discovered a new phenomenon caused by lithium niobate birefringence, which is the chiral optical response generated by non chiral structures.

The team established a dual-mode resonant coupled wave model that includes material birefringence response, and thus constructed lithium niobate nanostructures that exhibit non chiral characteristics in spatial structure (Figure c). Theoretical analysis shows that when the optical axis of lithium niobate crystal rotates to a specific angle, birefringence causes the mirror symmetry of the structure to break, and two nearly degenerate resonant states produce strong coupling effects. The hybrid resonance mode exhibits enormous chirality, producing a circular dichroism signal close to 1. In the experiment, the team used self-developed multi-component gas co etching technology to successfully process the designed lithium niobate nanostructure (Figure d), which has excellent surface smoothness and sidewall steepness. The spectral test structure confirmed the core result of the theoretical prediction, and the measured circular dichroism signal reached 0.53. The crystal structure of lithium niobate and the designed nanostructure are both non chiral, and the combination of the two can produce chiral optical response. This new phenomenon will inspire the design of new lithium niobate optical devices and has important scientific significance in the field of micro nano optics.

Figure a. Processing technology of lithium niobate nanostructures; b. Nonlinear superlenses; c. D. Theoretical design and experimental results of lithium niobate chiral metasurface

The research results were published in the recent Physical Review Letters 2025, 134, 113, 802 under the title "Chiral Resonant Modes Induced by Intrinsic Birefringence in Lithium Niobate Metasurfaces", and were included in this issue's Feature in Physics; The highlight column of the American Physical Society's Physics magazine wrote a special report titled "Birefringent Nanocubes Give Light a Circular Boost". The first author of this paper is Associate Researcher Wang Bo from the Microfabrication Laboratory, and the corresponding authors are Researcher Li Junjie and Associate Researcher Pan Ruhao. Zhu Tingyue, Master's student Liu Yunan, and Researcher Yang Haifang participated in the work. This work was supported by the National Natural Science Foundation of China, the National Key R&D Program of the Ministry of Science and Technology, the Chinese Academy of Sciences and the Huairou Comprehensive Extreme Conditions Experimental Device.

Source: opticsky