Matched dielectric slot waveguide as an all-dielectric terahertz magnetic dipole.

We observe that the modal field distribution of a dielectric slot waveguide closely resembles a magnetic dipole antenna. Such an aperture distribution traditionally demands metals, making it ill-suited to high frequencies due to excessive ohmic loss. By terminating a dielectric slot waveguide with a matched free-space interface, a compact all-dielectric radiating magnetic dipole is realized.

Terahertz disk resonator on a substrateless dielectric waveguide platform.

Resonant cavities are fundamental to and versatile for terahertz integrated systems. So far, integrated resonant cavities have been implemented in relatively lossy terahertz platforms. In this Letter, we propose a series of integrated disk resonators built into a low-loss substrateless silicon waveguide platform, where the resonances and associated quality factor (Q-factor) can be controlled via an effective medium.

Terahertz metasurface for near-field beam conversion.

A uniform illumination over a screen is crucial for terahertz imaging. As such, conversion from a Gaussian beam to a flattop beam becomes necessary. Most of the current beam conversion techniques rely on bulky multi-lens systems for collimated input and operate in the far-field.

In the shadow of the laser phantom needle cross: dynamic air-plasma aperture sheds light on terahertz microscopy.

Two plasma filaments crossing above the target create a subwavelength window for terahertz microscopy that excludes any subwavelength probe in vicinity.

All-silicon, low-cross-talk terahertz waveguide crossing based on effective medium.

All-silicon effective-medium-clad waveguides are a promising candidate for an integrated terahertz platform with high efficiency and broad bandwidth. Waveguide crossings are essential circuit components, allowing for wave routing over shorter paths to increase circuit density. However, the simple intersection of two orthogonal effective-medium-clad waveguides results in terahertz wave scattering, leading to relatively high cross talk.

Terahertz transmissive half-wave metasurface with enhanced bandwidth: publisher's note.

This publisher's note contains corrections to Opt. Lett.46, 4164 (2021)OPLEDP0146-959210.

Terahertz transmissive half-wave metasurface with enhanced bandwidth.

Polarization conversion is useful for studies of chiral structures in biology and chemistry, and for polarization diversity in communications. It is conventionally realized with wave plates, which, however, present challenges due to limited material availability, as well as narrow bandwidth and low efficiency at terahertz frequencies. To enhance bandwidth and efficiency, the concept of the Huygens' metasurface is adopted here for a transmissive half-wave plate.

Assessing frost damage in barley using terahertz imaging.

Frost is estimated to cost Australian grain growers 360 million in direct and indirect losses every year. Assessing frost damage manually in barley is labor intensive and involves destructive sampling. To mitigate against significant economic loss, it is crucial that assessment decisions on whether to cut for hay or continue to harvest are made soon after frost damage has occurred.

Ultra-wideband far-infrared absorber based on anisotropically etched doped silicon.

Far-infrared absorbers exhibiting wideband performance are in great demand in numerous applications, including imaging, detection, and wireless communications. Here, a nonresonant far-infrared absorber with ultra-wideband operation is proposed. This absorber is in the form of inverted pyramidal cavities etched into moderately doped silicon.

Effective-medium-cladded dielectric waveguides for terahertz waves.

Terahertz integrated platforms with high efficiency are crucial in a broad range of applications including terahertz communications, radar, imaging and sensing. One key enabling technology is wideband interconnection. This work proposes substrate-less all-dielectric waveguides defined by an effective medium with a subwavelength hole array.

Dielectric-resonator metasurfaces for broadband terahertz quarter- and half-wave mirrors.

Polarization conversion of terahertz waves is important for applications in imaging and communications. Conventional wave plates used for polarization conversion are inherently bulky and operate at discrete wavelengths. As a substitute, we employ reflective metasurfaces composed of subwavelength resonators to obtain similar functionality but with enhanced performance.

Insulator-metal transition in substrate-independent VO thin film for phase-change devices.

Vanadium has 11 oxide phases, with the binary VO presenting stimuli-dependent phase transitions that manifest as switchable electronic and optical features. An elevated temperature induces an insulator-to-metal transition (IMT) as the crystal reorients from a monoclinic state (insulator) to a tetragonal arrangement (metallic). This transition is accompanied by a simultaneous change in optical properties making VO a versatile optoelectronic material.

All-dielectric integration of dielectric resonator antenna and photonic crystal waveguide.

Two-dimensional photonic crystal waveguides can support guided modes with low loss. Interfacing such a guided mode with free-space propagation modes is crucial for photonic integrated circuits. Here we propose a dielectric resonator antenna (DRA) fully integrated with a photonic crystal waveguide for endfire radiation.

Demonstration of a highly efficient terahertz flat lens employing tri-layer metasurfaces.

We demonstrate a terahertz flat lens based on tri-layer metasurfaces allowing for broadband linear polarization conversion, where the phase can be tuned through a full 2π range by tailoring the geometry of the subwavelength resonators. The lens functionality is realized by arranging these resonators to create a parabolic spatial phase profile. The fabricated 124-μm-thick device is characterized by scanning the beam profile and cross section, showing diffraction-limited focusing and ∼68% overall efficiency at the operating frequency of 400 GHz.

Terahertz near-field imaging of dielectric resonators.

As an alternative to metallic resonators, dielectric resonators can increase radiation efficiencies of metasurfaces at terahertz frequencies. Such subwavelength resonators made from low-loss dielectric materials operate on the basis of oscillating displacement currents. For full control of electromagnetic waves, it is essential that dielectric resonators operate around their resonant modes.

Nanoscale TiO dielectric resonator absorbers.

We demonstrate a narrow-band plasmonic absorber based on a uniform array of nanoscale cylindrical dielectric resonators (DRs) on a metallic substrate at visible frequencies. Under a normally incident plane-wave excitation, the DRs resonate in their horizontal magnetic dipolar mode, which can be seen as localized plasmonic hot spots. Such a localized resonance also couples incident waves into surface plasmon polaritons (SPPs) bidirectionally, and perfect absorption is achieved by creating SPP standing waves.

Analysis of 3D-printed metal for rapid-prototyped reflective terahertz optics.

We explore the potential of 3D metal printing to realize complex conductive terahertz devices. Factors impacting performance such as printing resolution, surface roughness, oxidation, and material loss are investigated via analytical, numerical, and experimental approaches. The high degree of control offered by a 3D-printed topology is exploited to realize a zone plate operating at 530 GHz.

Mechanically Tunable Dielectric Resonator Metasurfaces at Visible Frequencies.

Devices that manipulate light represent the future of information processing. Flat optics and structures with subwavelength periodic features (metasurfaces) provide compact and efficient solutions. The key bottleneck is efficiency, and replacing metallic resonators with dielectric resonators has been shown to significantly enhance performance.

Terahertz Magnetic Mirror Realized with Dielectric Resonator Antennas.

Single-crystal silicon is bonded to a metal-coated substrate and etched in order to form an array of microcylinder passive terahertz dielectric resonator antennas (DRAs). The DRAs exhibit a magnetic response, and hence the array behaves as an efficient artificial magnetic conductor (AMC), with potential for terahertz antenna and sensing applications.

Terahertz reflectarray as a polarizing beam splitter.

A reflectarray is designed and demonstrated experimentally for polarization-dependent beam splitting at 1 THz. This reflective component is composed of two sets of orthogonal strip dipoles arranged into interlaced triangular lattices over a ground plane. By varying the length and width of the dipoles a polarization-dependent localized phase change is achieved on reflection, allowing periodic subarrays with a desired progressive phase distribution.

Limitation in thin-film sensing with transmission-mode terahertz time-domain spectroscopy.

Thin-film sensing with a film thickness much less than a wavelength is an important challenge in conventional transmission-mode terahertz time-domain spectroscopy (THz-TDS). Since the interaction length between terahertz waves and a sample film is short, a small change in the transmitted signal compared with the reference is considerably obscured by system uncertainties. In this article, several possible thin-film measurement procedures are carefully investigated.

Flexible terahertz metamaterials for dual-axis strain sensing.

Utilizing an elastic polymer, we design and experimentally demonstrate a four-fold symmetric flexible metamaterial operating at terahertz frequencies. The fabricated metamaterials exhibit good stretchability and recoverability. Two independent resonances can be observed when the structure is probed with linearly polarized terahertz waves in two orthogonal axes.

Experimental demonstration of reflectarray antennas at terahertz frequencies.

Reflectarrays composed of resonant microstrip gold patches on a dielectric substrate are demonstrated for operation at terahertz frequencies. Based on the relation between the patch size and the reflection phase, a progressive phase distribution is implemented on the patch array to create a reflector able to deflect an incident beam towards a predefined angle off the specular direction. In order to confirm the validity of the design, a set of reflectarrays each with periodically distributed 360 × 360 patch elements are fabricated and measured.

Dielectric resonator nanoantennas at visible frequencies.

Drawing inspiration from radio-frequency technologies, we propose a realization of nano-scale optical dielectric resonator antennas (DRAs) functioning in their fundamental mode. These DRAs operate via displacement current in a low-loss high-permittivity dielectric, resulting in reduced energy dissipation in the resonators. The designed nonuniform planar DRA array on a metallic plane imparts a sequence of phase shifts across the wavefront to create beam deflection off the direction of specular reflection.

Distributed source model for the full-wave electromagnetic simulation of nonlinear terahertz generation.

The process of terahertz generation through optical rectification in a nonlinear crystal is modeled using discretized equivalent current sources. The equivalent terahertz sources are distributed in the active volume and computed based on a separately modeled near-infrared pump beam. This approach can be used to define an appropriate excitation for full-wave electromagnetic numerical simulations of the generated terahertz radiation.