The development of practical terahertz systems requires high-gain, broadband and robust integrated antennas. In recent years, many photonics-inspired all-dielectric components have been demonstrated; however, practical implementation of existing devices usually relies on perforated structures that can be fragile and exhibit cut-offs related to their gratings. In this paper, we present a novel, all-dielectric planar antenna that avoids perforations entirely. The antenna employs a dielectric slab parabolic reflector that collimates incident waves towards radiating rods, producing a fan-shaped beam. A thorough investigation of the optimal guided-wave collimating structure is presented utilizing geometric optics, along with a proof of concept for its use as a beam launcher in integrated terahertz circuits. Thereafter, the device is adapted as an antenna. The novel antenna, 19.83 mm × 20.97 mm in footprint and 200 μm thick, is broadband, low-profile, readily integrable with planar, on-chip components, and exhibits a nearly-flat gain across the 220-330 GHz range, with a maximum value of 21.5 dBi. Input reflection coefficient magnitude is below -20 dB across the entire range, indicating excellent 40% fractional bandwidth, and a sidelobe level reaching as low as -28.4 dB for the E-plane and -39.5 dB for the H-plane.

Terahertz waveguide crossings are critical for compact, integrated signal routing in monolithic platforms, but simple waveguide intersections suffer from high losses and crosstalk due to mode mismatch in the regions where the waveguide channels overlap. The Maxwell fisheye lens with its inherent imaging properties is an excellent solution for multichannel intersections, however its circularshape is not easily integrated with common planar input/output waveguides. Here, we introduce all-silicon waveguide crossings basedon Maxwell fisheye lenses reshaped via conformal transformation optics for improved planar waveguide integration in the terahertzrange. Using effective medium techniques with subwavelength air inclusions, we design and fabricate 2 × 2 and 3 × 3 crossings operating over the 220-330 GHz frequency band. The transformed lenses enable aberration-free imaging without mode mismatch, implemented through a single deep reactive ion etching step. Experimental characterization reveals average insertion losses of 1.2 dB andcrosstalk below -50 dB for the fundamental quasi-TE mode, with a 40% bandwidth across the entire 220-330 GHz band, while thequasi-TM mode is also supported for dual-polarization applications. The transformed lenses have a diameter of just 4 mm (3.66λ₀),while the total device footprint including input and output tapers is 11.5 × 11.5 mm². This approach is scalable to N × N waveguidecrossings, providing a broadband and compact solution for low-loss terahertz integrated optics. 

The development of future 6G communication systems necessitates advanced materials for efficient electromagnetic interference shielding in the sub-terahertz frequency range. This study presents the preparation, porosimetry analysis, compositional and electromagnetic characterization of a highly efficient hierarchically porous carbon-silica composite suitable for shielding and stealth applications in this frequency regime. The composite, fabricated using a mixture of carbon powder and tetraethoxysilane, possesses a highly porous structure with high surface area, which facilitates multiple reflections and scattering of electromagnetic waves. Electromagnetic characterization was conducted using a free-space semi-optical method at 140-220 GHz, focusing on reflection-only measurements due to the sample's large thickness. The results demonstrate that the composite exhibits a qualified bandwidth of 83% over the measured frequency band, with a maximum reflection loss of 35 dB at 187 GHz. Furthermore, measurements demonstrate that electromagnetic power within the sample's volume is effectively attenuated. The composite's shielding efficiency due to reflection is on average 0.26 dB across the band, highlighting its potential for high frequency EMI shielding and stealth applications.

Dielectric waveguides are an emerging platform for terahertz (THz) integrated circuits, but a key challenge for dense integration is the realization of terminations that enable both multi-port device characterization and elimination of electromagnetic interference. Here, we demonstrate a compact, broadband termination by coating silicon waveguides with ultrathin single-walled carbon nanotube (SWCNT) films. Fabricated via a floating-catalyst (aerosol) chemical vapor deposition process, film thicknesses vary from 2 to 53 nm and are characterized in 140-220 GHz. A 53 nm thick film introduces up to 47 dB of attenuation while maintaining over 20 dB reflection loss, confirming nearly reflection-free absorption. Shielding analysis shows absorption dominates over reflection, and a record specific shielding efficiency of 5.5 x 109 dB cm2 g-1 is achieved. This approach offers a footprint-efficient solution for high-density THz circuits without bulky, radiative terminations.

Here, we present the design and experimental directional coupler operating in the low THz frequency range of 60-330 GHz enabled by silicon micromachining technology. Macromachining offers very low losses and high performance due to absence of metals and high precision of manufactured devices. This technology allows fabrication in a single etching step and provides a method for engineering the coupling coefficient. The fabrication of such high-performance directional couplers in the sub-THz frequency range is described, and the measurement results of the fabricated prototypes are reported and discussed.

In this paper, we present a THz 3-dB evanescent wave directional coupler, operating at 300 GHz based on the silicon micromachining waveguides surrounded by effective-medium with subwavelength perforations. This technique offers very low losses due to the absence of metals, allows fabrication in a single etching step and provides a method for engineering the permittivity of the cladding, thus allowing wave manipulation in all-dielectric platforms, extending the concepts of photonics to the THz region.

This article investigates the dichroic properties of aligned γ-Al2O3 nanofibers coated with graphene in the terahertz (THz) regime, revealing significant variance in absorption based on the orientation of the electric field in relation to the nanofibers, arising from the anisotropic nature of the material. Samples are prepared in a hot-wall chemical vapor deposition reactor with varying growth times, resulting in 5 samples with increasing graphene content. Compositional characterization is carried out using scanning electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. The samples are characterized electromagnetically using two distinct measurement techniques. First, a novel waveguide measurement setup is deployed, wherein square waveguide cassettes are used to capture the anisotropic behavior of the material and equally measure both polarization states in 67–500 GHz. Then, the samples are characterized using terahertz time-domain spectroscopy up to 4 THz. Both techniques highlight absorption enhancement when the electric field is parallel to the fibers, opening new possibilities for THz devices using polarization filtering.

We report on the performance of dielectric rod waveguide-coupled CMOS-based sources and detectors. The 252 GHz resonant field-effect-transistors-based THz detector is coupled to a Si rod. A similar rod is attached to a voltage control oscillator based on a Colpitts oscillator topology with optimized third-harmonic emission frequency at the same 252 GHz. A dielectric rod, implemented in this work, is employed as an antenna for coupling into a free space, as a transition element from the source or detector to the standard metal waveguide, or to enable the rod-to-rod coupling of a source-detector system. A dielectric rod-coupled system enables it to reach >60 dB signal-to-noise ratio for an equivalent noise bandwidth of one Hz. The knife-edge scans revealed the minimum half-width at half maximum of 0.24 mm at 252 GHz enabling high-resolution imaging applications. The obtained results demonstrate the high-efficiency coupling CMOS elements and Si rods. This concept can be applied to both sensing and THz imaging.

Recent development of terahertz systems has created the need for new elements operating in this frequency band, i.e., fast tunable devices such as varactors. Here, we present the process flow and characterization of a novel electronic variable capacitor device that is made with the use of 2D metamaterials such as graphene (GR) or hexagonal boron nitride (h-BN). Comb-like structures are etched into a silicon/silicon nitride substrate and a metal electrode is deposited at the bottom. Next, a PMMA/GR/h-BN layer is placed on top of the sample. As voltage is applied between GR and metal, the PMMA/GR/h-BN layer bends towards the bottom electrode thus decreasing the distance between electrodes and changing the capacitance. The high tunability and complementary metal oxide semiconductor (CMOS)-compatible process flow of the platform for our device and its millimeter size make it promising for applications in future electronics and terahertz technologies. The goal of our research is to integrate our device with dielectric rod waveguides, thus making THz phase shifters.

One of the challenges of using carbon nanotubes electronics is achieving precise control of the conductivity type. It is particularly difficult to obtain the n-type conductive nanotubes. One of the most common methods of CNTs modification allowing to change their conductivity type is chemical functionalization. This paper describes the results of studies on non-covalent modification of randomly oriented single-walled carbon nan-otubes (SWCNT) layers with methyl viologen (MV), which allows for the change of the conductivity of SWCNT from p- to n-type. The properties of pristine and MV-modified SWCNT have been compared using Scanning Electron Microscopy, Raman spectroscopy, and X-ray Photoelectron Spectroscopy. The SWCNT conductivity type change was confirmed by photo-conductance under ultraviolet illumination and measurements in the field effect transistor configuration.