Minimalist optical achromatic meta-imaging with extended field of view

Metalenses are revolutionizing frontier fields from consumer products to biological microscopy and astronomical observation^1–5 through their ultrathin planar structures and multidimensional wavefront control, yet large-scale fabrication and broadband achromatism each remain significant challenges, and achieving both simultaneously proves even more demanding⁶. Although traditional phase dispersion engineering is heavily constrained by the aspect ratio limits of nanofabrication^7–11, recent developments in large-aperture meta devices have demonstrated significant progress. By expanding beyond strict continuous phase matching toward more flexible physical modeling and optimization driven design strategies, researchers have successfully scaled achromatic or quasi achromatic performance for continuous broadband light^12–19. Nevertheless, these advancements often necessitate inherent physical trade-offs including diminished focusing efficiency, heightened fabrication complexity, or residual chromatic aberration.

Against this backdrop, the recent work by Wang and colleagues²⁰ makes a significant contribution by proposing a minimalist optical system design. The research team shifts their core optical element from the conventional hyperbolic phase metalens (Fig. 1a) to the meta axicon (Fig. 1b). This choice is rooted in the physical constraints of the optical grating equation. Unlike traditional focusing lenses, the relative intensity distribution of a zero order Bessel beam generated by a meta axicon is fundamentally independent of the incident wavelength. By leveraging this natural dispersion law, the system obtains a point spread function (PSF) that exhibits extraordinarily high spatial consistency across the entire visible spectrum. This strategic shift transfers the burden of chromatic aberration correction from complex dispersion engineering to a physical design that prioritizes wavelength-invariant PSFs jointly with computational algorithms.

Fig. 1  a Ray tracing and PSF illustration of monochromatic metalenses. b Ray tracing and PSF illustration of meta-axicons²⁰.

However, achieving high-resolution imaging with a wide field of view (FOV) remains a significant challenge. Traditional meta axicons are highly sensitive to incident angles, where oblique light disrupts wavefront symmetry and introduces off-axis aberrations that restrict the effective FOV. To overcome this limitation, the researchers²⁰ developed an array of off-axis meta axicons featuring eccentric conical phases. Instead of relying on conventional global phase profiles, they applied a local optical path constraint to ensure that obliquely incident light is converted into uniform and co-propagating Bessel beams. Their experimental system uses a monolithic metasurface integrated with nine distinct elements, including a central 4 mm meta axicon surrounded by eight 3 mm off axis versions.

Each element is responsible for capturing a specific angular region of the field. The system then employs a non-blind deconvolution technique based on total variation (TV) regularization to perform independent, high quality image reconstruction for each region. These local optical fields are fused into a seamless 10-degree FOV, maintaining an angular resolution limit of at least 80% compared to a traditional diffraction limited lens of an equivalent aperture. Table 1 presents main performance comparison for metasurface achromatic imaging research^7–20.

Beyond the conceptual breakthrough, this work points toward a feasible path for developing large-aperture computational imaging systems. However, transitioning from the laboratory to real world applications involves physical challenges. While current performance is validated under specific angles, the system's robustness in complex scattering environments requires further testing. A critical challenge remains in the trade-off regarding the numerical aperture (NA). Because axicons inherently possess a smaller equivalent NA than traditional lenses, increasing light gathering capability while maintaining consistent broadband PSF is a demanding task. Future research should also focus on quantifying the effective depth of field of the meta-imaging system and improving the algorithm's robustness to fabrication errors.

More broadly, these results arrive as researchers in meta-optics focus on how metasurfaces and algorithms can work together. The design, simple yet sophisticated, shows a new way to combine the natural physical laws with computational imaging capabilities. By moving past conventional engineering constraints, this work suggests a practical future for large FOV and large aperture meta cameras. This successful synergy between physical mechanisms and algorithmic reconstruction will likely lead to further investigation into next-generation intelligent imaging systems.