Extended field of view achromatic meta-axicon cluster

Metalenses have transformed optical imaging by enabling ultralight, compact, and multifunctional wavefront control, driving advances in LiDAR, polarization imaging, near-eye displays, microscopy, and astronomy. However, chromatic aberration severely limits broadband metalens performance. Conventional phase-dispersion achromatic designs face fundamental fabrication trade-offs that tightly couple aperture, numerical aperture, and bandwidth, confining most achromatic metalenses to apertures of only hundreds of wavelengths. Moreover, meta-axicon-based approaches suffer from strong off-axis aberrations, drastically reducing the effective field of view (FOV). Previously, no solution simultaneously delivered large aperture, wide FOV, broadband achromaticity, and high resolution.

 

In a new paper published in Light: Science & Applications, a team of scientists, led by Chengmiao Wang, Bin Wang and Yongting Deng from Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, China, together with Jan G. Korvink and Yongbo Deng from Karlsruhe Institute of Technology, Germany, and co-workers have developed a minimalist optical system for achromatic imaging based on a monolithic integrated meta-axicon cluster, breaking the long-standing aperture limitation of achromatic metalenses. Based on the novel imaging paradigm combining the natural wideband consistency of Bessel beams and computational imaging technology, they designed and fabricated a single metasurface integrating 9 meta-axicons with different design field angles, and built a corresponding meta-camera. The meta-camera realizes high-performance achromatic imaging within a 10° stitched FOV after image restoration, with an angular resolution close to that of a near-diffraction-limit lens with the same aperture throughout the entire FOV. This groundbreaking work completely circumvents the aperture constraints of traditional achromatic metasurface systems, and provides a highly valuable solution for the design of large-aperture meta-cameras that can simultaneously achieve broadband operation and wide off-axis FOV.

 

The core innovation of this achromatic imaging system lies in its complete break away from the traditional achromatic design framework based on phase dispersion control. Unlike conventional achromatic metalenses that pursue high-efficiency point focusing through complex phase and dispersion matching of meta-atoms, this work prioritizes the wideband consistency of the point spread function (PSF) to facilitate high-quality terminal image restoration. The team selected meta-axicons as the core optical element, whose unique property is that the relative intensity distribution of the generated zero-order Bessel beam is independent of wavelength under the constraints of the grating equation, forming an achromatic effect that relies on natural dispersion laws. This design fundamentally eliminates the dependence of achromatic performance on the phase dispersion modulation capability of meta-atoms, thus removing the inherent aperture limitation of traditional achromatic metalenses. The team constructed a meta-axicon with a diameter of 4 mm using silicon nitride nano-pillars, and verified that the full width at half maximum (FWHM) of the generated Bessel spots in the RGB channels are highly consistent across the entire visible spectrum from 450 nm to 700 nm, demonstrating excellent wideband achromatic performance.

 

To address the critical drawback of conventional meta-axicons, whose wideband PSF consistency degrades rapidly with increasing incident angle and thus limits the effective FOV, the team further proposed an innovative off-axis meta-axicon design with eccentric conical phases. By shifting the phase solution principle from global phase gradient integration to local equal optical path constraint, the designed off-axis meta-axicons can effectively convert oblique plane waves into wideband uniform off-axis Bessel beams. The team also introduced a wideband constraint to balance lateral chromatic aberration, reducing the focal spot shift across the full visible spectrum from nearly 1 μm to less than 100 nm, achieving precise control of off-axis aberrations. Finally, they integrated a main meta-axicon with a diameter of 4 mm and eight off-axis meta-axicons with a diameter of 3 mm into a single monolithic metasurface, each responsible for achromatic imaging in a distinct FOV region. Combined with a non-blind deconvolution image restoration module based on Total Variation (TV) regularization, the system stitches multiple local high-quality images into a full achromatic image with a 10° FOV. Experimental results show that the limiting angular resolution of the system across the entire FOV can reach no less than 80% of that provided by conventional diffraction-limited lenses with equivalent apertures, and even slightly exceeds the diffraction limit when observing isolated targets in a small FOV.

 

“The design of the meta-axicon cluster effectively overcomes the long-standing limitations of monolithic metasurface imaging in terms of aperture, FOV, and wideband resolution, and significantly promotes the development of minimalist optical systems based on metasurfaces.” the scientists explained. Looking forward, the team will further optimize the system by integrating sidelobe suppression techniques based on high-order vortex Bessel beams and improving wideband chromatic uniformity via meta-atom optimization, to achieve wideband computational imaging with better noise resistance and color authenticity. This technology opens new avenues for the development of large-aperture meta-cameras, and has broad application prospects in astronomical observation, LiDAR, autonomous driving, machine vision, biological microscopy, and consumer electronics.

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