High-efficiency broadband achromatic orbital-angular-momentum metalens for focusing and edge-enhanced imaging in mid-wavelength infrared

This work proposes a general achromatic methodology for broadband edge-enhanced imaging through dispersion engineering in k-space. A high-efficiency broadband achromatic orbital-angular-momentum metalens (NA = 0.45) has been demonstrated. It successfully achieves achromatic focusing of optical vortices and performs two-dimensional spatial differentiation, enabling polychromatic edge-enhanced imaging with potential applications in biomedical imaging and mid-wavelength infrared night vision technologies. • A semi-analytical model controls phase dispersion via heterojunction metasurfaces. • Broadband achromatic focusing achieved with 70% efficiency from 3 to 5 μm. • A novel OAM meta-device is developed for high-efficiency achromatic focusing. • The high-efficiency OAM meta-device performs broadband edge-enhanced imaging. Edge-enhanced detection based on spiral phase contrast imaging driven by orbital angular momentum (OAM) of light, offers a promising way to obtain low-light-level signals. However, the existing OAM elements have severe restrictions on compatibility with chip-scale miniature systems operation at wide bandwidth, due to bulky configurations and chromatic dispersion. Here, we propose a general and high-efficiency achromatic focusing methodology for broadband generation of photonic OAM based on all-dielectric heterojunction metasurfaces. The innovative concept is rooted in the proposed semi-analytical multi-layer films model for control of phase dispersion via the heterojunction metasurface. For the proof of concept, we have implemented broadband achromatic and diffraction-limited focusing with the efficiency up to 70 % across the wide bandwidth ranging from 3 to 5 μm. Based on the high-efficiency achromatism, we have achieved the generation of broadband achromatic focusing optical vortex carrying a topological charge of l = 1. Finally, the OAM-based broadband achromatic meta -device successfully performs the achromatic edge-enhanced imaging. The proposed OAM-based broadband achromatic metalens, with its compact design and high efficiency, serves as a promising foundation for advancements in biomedical imaging and mid-wavelength infrared night vision technologies.