Twisted non-diffracting beams through all dielectric meta-axicons

Area of Science:

• Metasurfaces
• Nanophotonics
• Dielectric Metamaterials

Background:

• Bessel beams are of significant interest due to their non-diffractive properties and diverse applications.
• Existing methods for generating Bessel beams often require additional optical components, limiting miniaturization and integration.

Purpose of the Study:

• To demonstrate highly efficient, transmission-based, all-dielectric meta-axicons for generating Bessel beams.
• To investigate the tunability of Bessel beam characteristics (propagation length and beam width) via numerical aperture (NA).
• To highlight the advantages of hydrogenated amorphous silicon (a-Si:H) as a meta-material.

Main Methods:

• Fabrication and characterization of all-dielectric meta-axicons operating at a visible wavelength (633 nm).
• Utilized the finite difference time domain (FDTD) technique for numerical simulations.
• Experimental validation of simulated results.

Main Results:

• Achieved high efficiency (≈73.4%) and polarization-insensitive generation of Bessel beams.
• Demonstrated control over propagation length (∼2600 λ for NA = 0.1) and full width at half maximum (<0.5 λ for NA ≥ 0.7).
• Showed excellent agreement between FDTD simulations and experimental outcomes.

Conclusions:

• The developed a-Si:H meta-axicons provide an efficient, compact, and cost-effective platform for Bessel beam generation.
• The material choice offers advantages in fabrication, cost, and CMOS compatibility compared to plasmonic and other dielectric metasurfaces.
• This technology enables advanced applications in optical manipulation, alignment, laser machining, and imaging.