High NA Broadband Fiber Facet Flat Orbital Angular Momentum Graphene Oxide Metalens

Optical vortex beams with orbital angular momentum (OAM) are promising for applications in communications, imaging, and nanomanipulation. Integrating such a function onto fibers offers a transformative approach to expand their applicability in communications and biomedical optics. While advancements in varied fiber OAM lenses have addressed some of the challenges, there are still issues such as low numerical apertures (NA), limited bandwidths, and integration difficulties. This study presents a high-NA, broadband OAM graphene oxide metalens designed by the detour phase method and directly integrated onto fiber facets, using a one-step femtosecond laser direct writing technique. Specifically, a metalens works in the communication bands with a topological charge of l = 1, covering the wavelength range from 1310 nm to 1625 nm, achieving a NA of 0.93. Additionally, two distinct metalenses work at 850 nm, with topological charges of l = 1 and l = 2, corresponding to NAs of 0.85 and 0.71, respectively. These lenses demonstrate excellent focusing and OAM generation, advancing compact, high-performance, and high-performance OAM devices for optical communications, integrated photonics, and biomedical systems.