This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: A research team at City University of Hong Kong (CityUHK) has developed a new optical corner-detection imaging method that uses azimuthal Hilbert transform metasurfaces and is designed to work as a universal framework. The study marks an important advance in high-speed, low-power optical information processing and has demonstrated potential for motion-tracking applications.
The study was led by Professor Tsai Din-ping, chair professor in the Department of Electrical Engineering at CityUHK. The project was conducted in collaboration with Professor Tao Li from the College of Engineering and Applied Sciences at Nanjing University. Titled "Optical corner detection with azimuthal Hilbert transform metasurfaces," the study is published in Science Advances.
The inspiration for this research stems from biological vision. Many animals are especially good at noticing geometric features, especially corners. For example, bees are drawn to angular shapes and use their compound eyes to identify sharp structures on flowers, and woodpeckers often peck at the intersections of bark cracks or the edges of holes, where insects are more likely to be hidden.
These examples reflect a common strategy—extracting key information from complex scenes by focusing on local features, such as corners, that stand out clearly. In today's world, where information overload is common, this strategy can help reduce visual complexity and improve both sensing and computational efficiency. Corner detection is widely used in computer vision, including image registration, motion tracking and 3D reconstruction.
Today, most corner detection relies on digital signal processing. However, electronics-based digital processing faces limits in response speed and energy consumption. Photonic or optical processing may offer faster and more energy-efficient performance, but existing optical processing approaches have focused mainly on 2D feature extraction.
Practical optical corner-detection methods have been limited. In this study, the research team built a 4f imaging system and introduced a metasurface at the Fourier plane to modulate the optical field in the angular direction. They used silicon nitride as the metasurface material and optimized the structural parameters based on geometric-phase modulation, enabling efficient broadband operation in the visible spectrum.
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