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2021 China Top Ten Advances in Optics Announced

Wuhan National Research Center for Optoelectronics, Huazhong University of Science and Technology

3 achievements on the list

One of them was selected in the category of basic research

2 items were selected in the applied research category

Top Ten Advances in Optics in China

The "Top Ten Advances in Chinese Optics", initiated by China Laser Magazine since 2005, has always focused on the most cutting-edge optical research results and scientific advances in China, and has been successfully held for 17 times, with 394 optical achievements of great scientific value selected. In addition, 19 other achievements have been nominated for the Top Ten Advances in Basic Research and Top Ten Advances in Applied Research awards.

The selection was made by a recommendation committee and a final evaluation committee composed of 79 academicians and renowned experts from 44 research institutes, including Tsinghua University, Peking University, University of Science and Technology of China, and Institute of Physics, Chinese Academy of Sciences, after several rounds of rigorous review and final selection.

Discovery of "ghost" hyperbolic polarization excitations in birefringent crystals

Selected for Basic Research Category

The international research team led by Xinliang Zhang and Peining Li, in collaboration with Qing Dai of the National Center for Nanoscience and Chengwei Qiu of the National University of Singapore, has theoretically proposed and experimentally demonstrated the existence of a "surface-body" complex hyperbolic polarized excitonic electromagnetic wave in the mid-infrared band in conventional birefringent crystals, expanding the definition of the fundamental physics of polarized excitons, which is of great significance for basic research in condensed matter physics, photophysics and electromagnetism.

Polaritons are "half-light-half-matter" quasiparticles generated by the strong coupling of light and matter, which can break the diffraction limit to compress and focus the light field to a small scale, reduce the physical size of optical devices, and realize exotic micro and nano optical phenomena and important applications.

Polarized excitations are not only a frontier scientific field at the intersection of condensed matter physics, photophysics, and materials science today, but also one of the traditional advantageous research directions in China. As early as 1951, Kun Huang, a famous semiconductor physicist in China, proposed the classical theory of phonon polarization excitons, which opened up this important research direction. At present, these different kinds of polarized excitons are generally grouped into two types of propagation modes: surface modes that propagate along the material interface and bulk modes that propagate inside the material.

The team's research results break through the conventional understanding and demonstrate the existence of a third polarized excitonic mode in anisotropic crystal calcite, the "ghost" hyperbolic polarized excitonic mode, which is a composite of the conventional surface mode and bulk mode polarized excitons, both bound to propagate at the interface and exhibiting tilted wavefront transport within the crystal.

Comparison of the characteristic electromagnetic field pattern distribution of three polarized excitation modes

(top) "ghost" polarization excitation mode, (middle) surface mode, (bottom) body mode

The demonstration and discovery of this new polarized excitonic mode also shows that nearly 150 years after the establishment of Maxwell's system of equations, new fundamental photophysics still exists in the simplest system, the single interface of conventional crystals.

With the help of nanoimaging techniques, the researchers demonstrated the existence of this unique electromagnetic wave, exhibiting a high degree of anisotropy in the plane, with propagation in the form of rays observed on the right side of a circular metal antenna with low-loss transmission up to 20 microns.

Near-field imaging experiments demonstrate anisotropic propagation properties of "ghost" polarized excitations

(left) Schematic diagram of the experiment, (middle) high-resolution near-field image of the measured "ghost" polarized excitations, (right) spatial distribution of the wave vectors

This work expands the "textbook" definition of the fundamental physics of polarized excitations and predicts the feasibility of regulating polarized excitations by the orientation of the optical axis of birefringent crystals, which has great potential for the realization of exotic micro- and nano-optical phenomena.
The research results, titled "Ghost hyperbolic surface polaritons in bulk anisotropic crystals," were published online in Nature on Aug. 18, 2021.

Radiation cooling optical metamaterial fabric based on morphologically graded structural design

Selected in the category of applied research

Based on the morphological hierarchy (Hierarchical-morphology), the team of Prof. Guangming Tao and the team of Yaoguang Ma of Zhejiang University and other research and industrial units have designed and developed a passive cooling optical metamaterial fabric (Metafabric), which can cool down the surface of the human body by nearly 5°C in the outdoor exposed environment.

Since the mid-infrared radiation spectrum of ambient surface objects, including the human body, largely overlaps with the atmospheric transparency window of 8-13 μm, this makes it possible to use the outer space environment for cooling. Based on the principle of radiation cooling, the metamaterial fabric is designed with the concept of morphological grading so that the surface objects facing the sky can radiate heat to the universe through the atmospheric transparent window, using outer space, where the temperature is close to absolute zero, as a "natural cooler", thus realizing zero energy consumption for cooling.

At the same time, the metamaterial fabric acts as an elaborate "labyrinth" for sunlight, with the vast majority of the light scattered around the bend being reflected out, thus avoiding significant warming. Therefore, in the outdoor exposure environment, the metamaterial fabric is like an air conditioner, maintaining a smooth heat exchange channel between the object and the universe, and like a mirror, blocking the solar radiation input. Based on the above design, the metamaterial fabric achieves 92.4% solar radiation reflectivity and 94.5% mid-infrared emissivity, and can cool down the human body by nearly 5 °C and the interior of the car model by nearly 30 °C.

Schematic diagram of passive cooling optical metamaterial fabric

Passive cooling optical metamaterial fabric photo

The results, titled "Hierarchical-morphology metafabric for scalable passive daytime radiative cooling," were published online in Science on July 8, 2021.

Line illumination modulation microscopy enables high-definition imaging

Selected in the category of applied research

The technology was invented by Qingming Luo's team. The fine structures of biological tissues are complex and diverse, and it is a recognized technical challenge to observe them comprehensively and accurately in 3D space by optical methods. In particular, fluorescently labeled neurons have a cell diameter of about 10-30 μm, and the axons extending out from them to project into different brain regions are only 0.2-0.5 μm in diameter, which differ in brightness by 2-3 orders of magnitude, but their spatial distribution is often intertwined. When detecting the weak fluorescence signal on the axons under the interference of the peripheral cytosol, it is like observing small stars around a bright sun. For such cases, conventional optical chromatography methods are difficult to achieve.

Qingming Luo's team has proposed a new principle of optical chromatography microscopy imaging - Line-illumination modulation (LiMo) microscopy, which cleverly uses the Gaussian distribution of line illumination light intensity as a natural modulation, and adopts a multi-line detection method to This method is the first of its kind to achieve a high-resolution, high-resolution, high-resolution microscopy. This method is the first to achieve the simultaneous combination of high resolution, high throughput, high robustness, high background suppression capability, and high sensitivity, which breaks the limit of optical chromatography capability of existing principles and fills the technical gap in the related field. Whether it is the optical path or algorithm, LiMo fully reflects the wisdom of the great road to simplicity.

Schematic of LiMo microscopy imaging principle

Based on this, the team further developed the new technology of high-definition fluorescent micro-optical sectioning tomography (HD-fMOST), which elevates whole brain optical imaging from high resolution to a new standard of high definition, and is currently the fastest whole brain optical imaging technology at similar It is the fastest whole-brain optical imaging technology with similar voxel resolution. The high-definition imaging quality brings significant efficiency improvement in data storage, transmission, processing and analysis from the data source, providing a new solution to the bottleneck of big data in the application of whole brain optical imaging technology. The implementation of this technology is expected to play a great role in standardized and large-scale brain science research and contribute to the mapping of single-cell-resolved mesoscopic brain atlas.

Local magnification of whole brain maximum projection map of mouse brain at the site of virus injection

The results of the study, titled "High-definition imaging using line-illumination modulation microscopy," were published online in Nature Methods on March 1, 2021.

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Source: Huazhong University of Science and Technology official WeChat public number

Editor: Gao Xiang, Ai Ting