Photonics-based Bessel beam launcher with an air-filled core and cylindrical Bragg gratings in the cladding

In this study, we develop a photonics-based Bessel launcher characterized by a hollow-core cylindrical waveguide surrounded by Bragg gratings composed of concentric silicon rings, each 375 nm thick. The metasurface is constructed on a 5 µm high silicon cylindrical substrate. This configuration effectively generates a Bessel beam at the commonly used telecom infrared optical wavelength of 1.55 µm. We explore three variations of this optical antenna, featuring 3-, 6-, 16-, and 32-ring arrays, respectively. We compare the results with the geometrical optics approach as well as the Rayleigh hypothesis. The performance of the optical antenna configuration is assessed through simulated far-field polar plots and z-directed intensity distributions up to a non-diffracting range (NDR) of 1 mm using CST Microwave Studio and Lumerical FDTD INTERCONNECT. These simulations reveal that the optical antenna gain of the launcher in the far field varies from 20 to 26 dBi as the number of concentric rings increases from 6 to 32. We report the S₁₁ reflection coefficient of −33 dB and the radiation efficiency of 0.01 dB. To independently verify the angular spectrum of the antenna, we employ dyadic Green’s functions, orthogonal vector wave functions, and Bloch’s theorem in MATLAB, demonstrating exceptional coupling of the Gaussian beam into the photonic device with a radiation efficiency of 99%.