Optical vortices matter because they carry orbital angular momentum, enabling parallel information channels for high-capacity communications, richer quantum photonic states, and improved tools for imaging and optical manipulation. But conventional vortex generators often demand near-perfect alignment with the optical beam’s geometric center, and they can be sensitive to wavelength, fabrication imperfections, beam size, and incidence angle.

The study tackles a known bottleneck in nonlocal metasurfaces: earlier designs worked, but their useful resonances were narrow and overly dispersive, so only a limited slice of the incoming light could be converted efficiently into a high-quality vortex.

Here, the authors introduce a cavity-assisted reflective nonlocal metasurface that forms a Fabry–Pérot cavity using a silicon photonic crystal slab, a silicon dioxide spacer, and a gold mirror. This cavity environment reshapes the optical response so that bound states in the continuum and degeneracy points—both carrying topological signatures—are engineered to hybridize.

That hybridization produces quasi-flat optical bands with strong scattering, effectively creating a broader “working region” across angles and wavelengths. In practical terms, the device can convert a much wider range of incident light into vortex beams without requiring the same stringent alignment that plagues many real-space phase shapers.

Numerical simulations predict near-unity conversion at resonance, more than 90% overall efficiency, and high orbital angular momentum purity. Experiments then confirm broadband operation from 1480 to 1600 nm, with a peak overall efficiency approaching 80% and an OAM purity of 91.7%.

Beyond standard vortex modes, the researchers also demonstrate conversion of a zero-order Bessel beam into a second-order Bessel vortex—often described as a “perfect vortex beam”—showing the approach can maintain mode quality under structured illumination.

Just as importantly, the platform shows robustness against edge effects, beam position, beam profile, and variations in numerical aperture—exactly the kind of resilience needed for real-world photonic systems.

If momentum-space band engineering becomes a reliable design principle, cavity-assisted nonlocal metasurfaces could accelerate compact, efficient, and broadband vortex sources for next-generation meta-optics and integrated photonic platforms, with future directions including visible-wavelength extensions and dynamically tunable or multiplexed vortex generation.

Keywords

nonlocal metasurfaces; orbital angular momentum; bound states in the continuum; band engineering; broadband operation; vortex beam generation
Subject of Research: Cavity-assisted nonlocal metasurfaces for momentum-space broadband optical vortex generation
Article Title: Cavity-assisted nonlocal metasurfaces for momentum-space broadband-operational optical vortice generation with maximum efficiency approaching 80%
Web References: http://dx.doi.org/10.29026/oea.2026.250296
References: Wang KR, Sun KL, Du J et al. Opto-Electron Adv 9, 250296 (2026). DOI: 10.29026/oea.2026.250296
Image Credits: OEA

The work builds on the classic Jackiw–Rebbi mechanism, originally proposed for relativistic particles. In those models, a localized mode appears when a mass term flips sign, effectively creating a domain wall. The authors translate this concept into optics by designing photonic structures where an effective “mass” characterizing light propagation changes across an interface.

What makes the platform especially compelling is the van der Waals architecture. Unlike conventional fabrication routes that can introduce disorder, the layered nature of these materials enables sharp, controllable boundaries and tunable photonic band structures. By adjusting the stacking and interlayer optical responses, the researchers create conditions in which topological modes become robust against typical imperfections.

The study emphasizes that these states are not merely conventional guided resonances. Instead, they are tied to topology: the light modes are associated with an invariant property of the band structure. As a consequence, the Jackiw–Rebbi-like photonic states are expected to persist even when the system’s details vary, so long as the relevant symmetry and band configuration remain intact.

Topological protection is more than a slogan. In photonics, it can translate into reduced sensitivity to fabrication tolerances and a pathway toward devices that rely on stable boundary transport. The paper therefore positions these localized states as building blocks for future optical components that route signals along designed interfaces.

The authors demonstrate the concept theoretically and connect it to experimental observables by focusing on how the interface should host modes localized near the domain wall region. Such localization is a hallmark of the Jackiw–Rebbi scenario, now realized in a controllable, designer photonic environment.

Beyond fundamental interest, the approach could influence the design of reconfigurable photonic circuits. Because van der Waals stacks can be combined and adjusted, the same topology-driven logic may be extended to new material systems, wavelengths, and device geometries.

Overall, the report signals a broader trend: using topological field-theory ideas to engineer light–matter behavior in atomically precise platforms, potentially enabling the next generation of robust, interface-based photonic technologies.

Subject of Research: Topological photonic states (Jackiw–Rebbi) in van der Waals heterostructures.

Article Title: Topological Jackiw-Rebbi states in photonic Van der Waals heterostructures.

Article References: Randerson, S.A., Bouteyre, P., Hu, X. et al. Light Sci Appl 15, 323 (2026). https://doi.org/10.1038/s41377-026-02392-5

Image Credits: AI Generated

DOI: 10.1038/s41377-026-02392-5

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