Kristian Altmann

Terahertz beam steering and variable focusing using programmable diffraction gratings

We propose a freely programmable THz diffraction grating based on an electrostatically actuated, computer controlled array of metallic cantilevers. Switching between different grating patterns enables tailoring spatio-temporal profiles of the THz waves. By characterizing the device with spatially resolved THz time domain spectroscopy, we demonstrate beam steering for a wide frequency band extending from 0.15 THz to 0.9 THz. The steerable range at 0.3 THz exceeds 40°. Focusing is also demonstrated by programming a chirped grating. The proposed approach could be employed to mimic arbitrary diffraction optics, enabling highly integrated and extremely flexible systems indispensable for THz stand-off imaging and communications.

Terahertz beam focusing based on plasmonic waveguide scattering

We demonstrate free-space focusing of terahertz (THz) radiation by scattering plasmonic surface-waves into the air. We use a grating of shallow holes which contains non-equidistant defects which act as scattering centers. The scattering occurs with defined phase delays such that the waves emitted in free-space interfere constructively to form a focus above the waveguide surface. In contrast to conventional lenses, this structure does not require any free-space on its backside and has great potential for integrated THz optics.

Polymer stabilized liquid crystal phase shifter for terahertz waves

We propose an electrically tunable phase shifter for terahertz frequencies. The device is based on a polymer stabilized liquid crystal which allows for a simple device geometry. The polymer stabilized liquid crystal enables continuous tuning of the introduced phase shift with only one pair of electrodes. By characterizing the device with terahertz time-domain spectroscopy we demonstrate a phase shift up to 2.5 terahertz, only slightly changed properties of the neat liquid crystal and significantly reduced response times.

Terahertz Parallel-Plate Ladder Waveguide With Highly Confined Guided Modes

In this paper, we introduce a parallel-plate ladder waveguide (PPLWG) for THz waves. The characteristics of the guided modes of this structure which belong to the category of spoof surface plasmons are studied using the generalized multipole technique and its potential applications are discussed. Moreover, the proposed structure is experimentally investigated in a THz time-domain spectroscopy system and a comparison between the calculated and measured amplitude and phase characteristics is given. It is shown that the dominant mode of the PPLWG can be excited by an incident focused beam and a high degree of field confinement in the THz regime can be achieved.

Terahertz beam steering using structured MEMS surfaces for networked wireless sensing

In order to fully explore the great potential of terahertz (THz) waves in networked wireless sensing both as sensing probes and carrier waves, beam steering techniques are required. However, conventional beam steering approaches with delay-line based phased arrays would face technical difficulties due to the too high frequency of THz waves. In this paper, we propose to electrically control the THz beam propagation based on surface-wave scattering from structured MEMS surfaces, which would lead to very compact and low-cost THz phased arrays.