Generation of non-diffractive Bessel beams by inward cylindrical traveling wave aperture distributions.

M Albani,M Casaletti,S C Pavone,M Ettorre

doi:10.1364/oe.22.018354

Abstract

The focusing capabilities of an inward cylindrical traveling wave aperture distribution and the non-diffractive behaviour of its radiated field are analyzed. The wave dynamics of the infinite aperture radiated field is clearly unveiled by means of closed form expressions, based on incomplete Hankel functions, and their ray interpretation. The non-diffractive behaviour is also confirmed for finite apertures up to a defined limited range. A radial waveguide made by metallic gratings over a ground plane and fed by a coaxial feed is used to validate numerically the analytical results. The proposed system and accurate analysis of non-diffractive Bessel beams launched by inward waves opens new opportunities for planar, low profile beam generators at microwaves, Terahertz and optics.

Highlights

The spreading of the transverse profile of a propagating wave is an all-present phenomenon known as diffraction
Note that this structure is different from the one proposed in [6], where an incident field generated by an external horn antenna was used to illuminate a subwavelength annular aperture on the back side of a radial waveguide loaded with metallic gratings of same size and periodically placed over the aperture
We have shown that Bessel beams can be created by radiating apertures taking on tangential inward Hankel distributions

Summary

Introduction

The spreading of the transverse profile of a propagating wave is an all-present phenomenon known as diffraction. Non-diffractive radiation is generated by resonant apertures having a Bessel-like distribution given by a combination of inward and outward cylindrical waves, simplifying the beam generator synthesis. The. position and size of the metallic gratings are properly chosen to sample the outward feeding wave launched by the feed for synthesizing the required inward aperture distribution. Position and size of the metallic gratings are properly chosen to sample the outward feeding wave launched by the feed for synthesizing the required inward aperture distribution Note that this structure is different from the one proposed in [6], where an incident field generated by an external horn antenna was used to illuminate a subwavelength annular aperture on the back side of a radial waveguide loaded with metallic gratings of same size and periodically placed over the aperture. The presented approach for the analysis and generation of non-diffractive Bessel beams and the proposed simple structure may find several applications in optics and at radio frequencies [5] or for the generation of surface plasmon polaritons [17]

Analytical derivation: infinite case

Finite case

Proposed structure: radial waveguide loaded with metallic gratings

Conclusion