Catenary optics for achromatic generation of perfect optical angular momentum

TLDR

The catenary curve, a classic mechanical shape, has not previously been linked to optical phenomena. The study aims to demonstrate that an optical catenary can act as a metasurface element to generate a continuous 0–2π phase shift, a capability beyond current technology. The authors design planar devices using catenary arrays and experimentally characterize them to produce beams carrying orbital angular momentum. The devices exhibit ultra‑broadband operation and, by integrating optical and topological properties, enable complete photon control within a single nanometric layer.

Abstract

The catenary is the curve that a free-hanging chain assumes under its own weight, and thought to be a "true mathematical and mechanical form" in architecture by Robert Hooke in the 1670s, with nevertheless no significant phenomena observed in optics. We show that the optical catenary can serve as a unique building block of metasurfaces to produce continuous and linear phase shift covering [0, 2π], a mission that is extremely difficult if not impossible for state-of-the-art technology. Via catenary arrays, planar optical devices are designed and experimentally characterized to generate various kinds of beams carrying orbital angular momentum (OAM). These devices can operate in an ultra-broadband spectrum because the anisotropic modes associated with the spin-orbit interaction are almost independent of the incident light frequency. By combining the optical and topological characteristics, our approach would allow the complete control of photons within a single nanometric layer.