With the increase in potential uses of terahertz technology, the need for terahertz transceivers with application-oriented adaptive radiation patterns has emerged. Reconfigurable reflectarrays consisting of actuated sub-wavelength reflectors have been successfully used for terahertz beam steering and beamforming. They do not require a complex feeding network and associated electronics, enabling a compact and power-efficient terahertz beam steering system. However, the current reflectarray-based beam steering is accomplished by forming the reflectarray as a grating structure, which is accompanied by the problems such as grating lobes, limited steering range, and discrete steering angles. Here, we configure a MEMS-based reflectarray with the genetic algorithm to eliminate the grating lobes and open up the possibility of customizing its radiation pattern. We used single- and multi-objective optimization to find the optimal height profile of the reflectarray and verified the results by full-wave electromagnetic simulations. We measured the radiation patterns of four reflectarray phantoms, i.e. reflectarrays without the MEMS actuation systems. The measurement results agree well with the calculated ones, with the main beam deviating at most 2° from the target direction. Our work demonstrates how a genetic algorithm is used to shape a reconfigurable terahertz reflectarray to eliminate the grating lobes and tailor some specific featuress in its radiation pattern.

Micro-optical elements and complex optical microsystems require ultraprecise manufacturing processes. The maximum tolerable roughness is defined by fractions of the used wavelength $\lambda$, e.g., $\frac{\lambda }{100}$ or better, whereas the overall size and shape of the elements can easily reach the millimeter or centimeter range. Next to the industrially established ion beam polishing approaches for optical surfaces with ultra low surface roughness, reactive ion etching (RIE) has been demonstrated for the efficient realization of highly precise microstructured optical surfaces for beam-shaping^1,2 and beam-splitting,³ as well as for imaging⁴ and illumination^5,6 applications. During RIE, material transport is achieved by a combination of physical and chemical (reactive) interaction of ions and reactive gases with the surface in a plasma reactor. The chemical fraction of the process is naturally highly dependent on the substrate/precursor gas composition. Thus, the process has been developed for the semiconductor industry and is well-established and successfully applied for microstructuring of pure materials (e.g., semiconducting alloys such as GaAs, GaN, and others or Si)⁷ as well as pure fused silica (FS) substrates for optical purposes.⁸ Also polymers can be etched in a reactive plasma based on oxygen and in combination with other gases (if required).⁹ Significant advantages are provided as plasma etching does not necessarily require high process temperatures, while the energy of the individual etching species can be very high. This decoupling of temperature and energy is a significant advantage of plasma enhanced etching processes against purely chemical etching in which the activation energy is applied by temperature only. On the other hand, numerous effects influence the local material removal rate, so defined etching profiles require a detailed knowledge of the etching process.

With an increasing number of applications of terahertz systems in industrial fields and communications, terahertz beamforming and beam steering techniques are required for high-speed, large-area scanning. As a promising means for beam steering, micro-electro-mechanical system (MEMS)-based reflection gratings have been successfully implemented for terahertz beam control. So far, the diffraction grating efficiency is relatively low due to the limited vertical displacement range of the reflectors. In this paper, we propose a design for a reconfigurable MEMS-based reflection grating consisting of multiple subwavelength reflectors which are driven by 5-bit, high-throw electrostatic actuators. We vary the number of the reflectors per grating period and configure the throw of individual reflectors so that the reflection grating is shaped as a blazed grating to steer the terahertz beam with maximum diffraction grating efficiency. Furthermore, we provide a mathematical model for calculating the radiation pattern of the terahertz wave reflected by general reflection gratings consisting of subwavelength reflectors. The calculated and simulated radiation patterns of the designed grating show that we can steer the angle of the terahertz waves in a range of up to ± 56.4 ${}^{\circ }$ with a maximum sidelobe level of −10 dB at frequencies from 0.3 THz to 1 THz.

This contribution presents a design approach as well as characterization results for dielectric slot waveguides fabricated in highly resistive (HR) silicon (HR-Si) designed for operation in the terahertz (THz) frequency range. The authors discuss the fundamentals of dielectric slot waveguides and the respective figures of merit. Furthermore, analytical solutions as well as numerical results from field simulations of the propagating mode are presented and discussed. Prototypes are fabricated in a process for HR-Si microelectromechanical systems (MEMSs), including a silicon-based metamaterial to mechanically support the waveguide while preserving a strong field confinement. In addition, actuator concepts to implement device functionalities, such as phase shifting capabilities, are demonstrated. The prototypes are measured and characterized using vector network analyzer (VNA)-based two-port measurements in the frequency range from 220 to 330 GHz. The devices are characterized in terms of their field confinement, loss, and effective mode index. For the first time, the authors report on the experimental validation of dielectric slot waveguides in this frequency range and provide values for the obtained losses.

We present the design, fabrication, and characterization of a MEMS-based 3-bit Digital-to-Analog Converter (DAC) that allows the generation of large displacements. The DAC consists of electrostatic bending-plate actuators that are connected to a mechanical amplifier (mechAMP), enabling the amplification of the DAC output displacement. Based on a parallel binary-encoded voltage signal, the output displacement of the system can be controlled in an arbitrary order. Considering the system design, we present a simplified analytic model, which was confirmed by FE simulation results. The fabricated systems showed a total stroke of approx. 149.5 ± 0.3 µm and a linear stepwise displacement of 3 bit correlated to 2³ ≙ eight defined positions at a control voltage of 60 V. The minimum switching time between two input binary states is 0.1 ms. We present the experimental characterization of the system and the DAC and derive the influence of the mechAMP on the functionality of the DAC. Furthermore, the resonant behavior and the switching speed of the system are analyzed. By changing the electrode activation sequence, 27 defined positions are achieved upgrading the 3-bit systems into a 3-tri-state (3³) system.