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 79×79 elements with dimensions of 150×150 µm. 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 µm thick benzocyclobutene (BCB) substrate with a dielectric constant of2.6. The BCB substrate is backed by an aluminum ground plane. The designed element can cover around 700° phase range by tuning its dimensions. Experimental results demonstrate that the generated beam can be deflected from 6° to 15° off normal from 0.8 to 1.1 THz.