A Terahertz Metasurface for Frequency-Controlled Bessel Beam Steering

This paper presents a nondiffractive Bessel beam launcher with frequency-controlled beam steering capability operating from 0.8 to 1.1 THz. The launcher is composed of a THz reflective metasurface fed by a diagonal horn. Four components dictate the phase distribution across the metasurface aperture at a designated frequency: phase of the incoming plane wave, axicon angle for the Bessel beam, phase of the outgoing plane wave, and a constant reference phase. The total phase is optimized by having four reflection directions from 0.8 to 1.1 THz with a 0.1 THz step. The metasurface consists of 79x79 elements with dimensions of 150x150 mu m. Each element includes a double-headed arrow geometry enclosed by a diamond frame whose dimensions are chosen to satisfy the phase distributions at the four design frequencies. The aluminum patterning is printed on a 30 mu m thick benzocyclobutene (BCB) substrate with a dielectric constant of 2.6. The BCB substrate is backed by an aluminum ground plane. The designed element can cover around 700 degrees phase range by tuning its dimensions. Experimental results demonstrate that the generated beam can be deflected from 6 degrees to 15 degrees off normal from 0.8 to 1.1 THz.