Broadband wide-field optical edge detection imaging enabled by helical metalens

Accurate edge detection is essential in biomedical imaging for object identification, segmentation, and quantitative analysis. However, conventional biological samples, including both amplitude-based and phase-based types, often exhibit complex structures and low contrast. Additionally, visible light imaging systems are highly susceptible to chromatic aberration across a broad spectral range and a large field of view. This leads to image edge blurring and the presence of artifacts, significantly degrading the quality of edge information. To overcome these challenges, we propose a double-layer focusing vortex metalens that integrates a conventional focusing function with a spiral phase profile. By modulating the angular wave vector of incident light, this metalens transfers frequency-domain energy to higher spatial frequency components. As a result, edge information can be extracted directly in the image plane without the need for fluorescent dyes, labeling agents, or computational post-processing. During the design process, we combined Zemax optical software with a particle swarm optimization algorithm to jointly optimize the focusing phase for both field of view and chromatic aberration, resulting in a unit structure library that meets the ideal spiral and focusing phase requirements. This structure achieves simultaneous achromatic aberration at three wavelengths: 480nm, 532nm, and 632nm. It also effectively suppresses off-axis aberrations and extends the field of view to 40 degrees. The modulation transfer function approaches the diffraction limit at incident angles of ±20 degrees. This compact and energy-efficient all-optical solution enables real-time, label-free edge enhancement. It is especially promising for biomedical imaging applications such as endoscopy and also offers potential in autonomous driving and machine vision.