Dielectric Rod Waveguide Research Articles

Terahertz photodiode integration with multi-octave-bandwidth dielectric rod waveguide probe.

Photonic integrated circuits play a vital role in enabling terahertz (THz) applications that require multi-octave bandwidth. Prior research has been limited in bandwidth due to rectangular waveguide (WRs) interconnects, which can only support single octave at low loss. To overcome this fundamental limitation, we exploit the ultra-wideband (UWB) near-field coupling between planar waveguides and silicon (Si)-based subwavelength dielectric rod waveguides (DRWs) to interconnect THz bandwidth uni-traveling-carrier photodiodes (UTC-PDs) at 0.08-1.03 THz. In a proof-of-concept experiment, the on-chip integrated UTC-PDs demonstrate a UWB operation from 0.1 THz to 0.4 THz. Furthermore, by employing Si DRWs as probes, multi-octave device-under-test characterization of UTC-PDs integrated with UWB transition is enabled with only one DRW probe. The proposed UWB interconnect technology is distinct from previously used WR-based ground-signal-ground probes or quasi-optical free-space coupling since it can provide multi-octave bandwidth and enable on-chip THz circuit integration.

Ultra-Wideband Multi-Octave Planar Interconnect for Multi-Band THz Communications

An ultra-wideband (UWB) interconnect technology using indium phosphide (InP)-based transitions for coupling the output signals from terahertz (THz) photodiodes featuring coplanar waveguide (CPW) outputs to low-loss dielectric rod waveguides (DRWs) is presented. The motivation is to exploit the full bandwidth offered by THz photodiodes without limitations due to standard rectangular waveguide interfaces, e.g., for future high data rate THz communications. Full electromagnetic wave simulations are carried out to optimize the electrical performance of the proposed InP transitions in terms of operational bandwidth and coupling efficiency. The transitions are fabricated on 100-µm-thin InP and integrated with silicon (Si) DRWs. Experimental frequency domain characterizations demonstrate efficient THz signal coupling with a maximum coupling efficiency better than − 2 dB. The measured 3-dB and 6-dB operational bandwidths of 185 GHz and 280 GHz, respectively, prove the multi-octave ultra-wideband features of the developed interconnect technology. The 6-dB operational bandwidth covers all waveguide bands between WR-12 to WR-3, i.e., a frequency range between 60 and 340 GHz. In addition, the multi-octave performances of the fabricated interconnects were successfully exploited in proof-of-concept THz communication experiments. Using intermediate frequency orthogonal frequency division multiplexing (OFDM), THz communications are demonstrated for several frequency bands using the same interconnect. Considering soft-decision forward error correction, error-free transmission with data rates of 24 Gbps at 80 GHz and 8 Gbps at 310 GHz is achieved.

Composite Feedstock Filaments for Fused Deposition Modeling (FDM) of Microwave Interconnects

Improved manufacturing methodology of ceramic-thermoplastic composite feedstock filaments using solvent assisted dispersion is presented with one of the highest reported ceramic particle filler volume concentration of 50%. Relative permittivity values up to 12.35 along with a low loss tangent of 0.003 have been achieved for newly developed feedstock filaments. They have been employed for fuse deposition modelling (FDM) of test specimens for characterization of complex permittivity, which exhibited dielectric loss tangent in the range of 0.001-0.007 at frequencies ranging from 4 GHz to 12 GHz. This is on par with that of the best microwave laminates. Also, surfactant-assisted ball milling was used to downsize ceramic fillers, while simultaneously applying a surface treatment by a strategically chosen surfactant to improve the interfaces between organic matrix and inorganic particles. The effect of the surfactant surface treatment on the dielectric and loss properties of the composite feedstock materials has been explored, which is compared with analytical model predictions. Two 40 mm-long dielectric rod waveguides (DWG’s) were 3D printed by using an in-house developed composite filament and a commercial counterpart. The former exhibited a much lower attenuation of 0.012 dB/mm as compared to 0.038 dB/mm shown by the latter. Measurements were compared to 3D EM simulation results to extract effective permittivity of DWG fabricated by FDM printing using in-house developed composite feedstock filament, which agrees very well with measured permittivity values.

A graphene/h-BN MEMS varactor for sub-THz and THz applications.

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.

A Low-Scattering Pixelated Dielectric Rod Waveguide Probe for Near-Field Measurement

A 3.4–3.7 GHz dielectric rod waveguide probe for near-field measurements is proposed for applications on the 5G sub-6 GHz band. By implementing a dielectric-filled waveguide, the probe achieved a higher resolution and low scattering characteristics through a miniaturized aperture compared to the open-ended waveguide (OEWG) used for conventional near-field probes. An <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8\times 8$ </tex-math></inline-formula> pixelated grid structure in the dielectric launcher section of the probe is implemented to further reduce the scattering characteristics of the probe. The proposed probe is fabricated and experimentally verified. A coating of silver is applied to the dielectric during a production process. Measurement shows that the −10 dB reflection coefficient bandwidth meets 3.4–3.7 GHz requirement and that the radiation pattern shows a broadside gain of about 3.8 dBi with no null at the forward hemisphere. The results of a scattering characteristic experiment indicate decreased interferer level of 7.3 dB compared to an OEWG.

Transition Structure Between Coaxial Cable and Dielectric Rod Waveguide in Microwave Frequency

The dielectric waveguide in THz and millimeter circuit is widely researched. However, it is rarely researched in a microwave frequency. In this article, a dielectric rod waveguide (DRW) is proposed with low transmission loss in microwave frequency. For the purpose of impedance matching, a transition section composed of the metal-coated dielectric cavity, and a dielectric horn is presented to match the impedance between the coaxial cable and the dielectric rod waveguide. Finally, the dielectric rod waveguide and the transition section have been fabricated for experimental verification. To obtain the propagation constant of the DRW, the thru-line (TL) calibration is used in measurement. The simulation and measurement results show an effective conversion between the coaxial cable and the dielectric rod waveguide.

Analytical and Experimental Study of Multilayer Dielectric Rod Waveguides

This article presents a comprehensive study of the design and performance of a multilayer dielectric rod waveguide (MDRW) with a rectangular cross section. The design is comprised of a high permittivity core encased by a low permittivity cladding. A mathematical model is proposed to predict the fundamental mode cutoff frequency in terms of the core dimensions and the core and cladding permittivity. The model is useful for design purposes and it offers an excellent match to full-wave electromagnetic (EM) simulation results. The MDRW performance is measured for the extended Ku-band (10-18 GHz) considering straight and bent waveguides with different radius of curvatures. The particular multilayer configuration shows a 16.7% and 24% extension of the 1 dB low-band cutoff frequency for a 10×10 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and 20×20 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> cladding area, respectively, when compared to a single layer dielectric rod waveguide (DRW) design of the same core dimensions. MDRW bends also exhibit a significant reduction of the 1 dB low-band cutoff frequency from 20% to 40% when compared to single-layer designs, for the different radius of curvature bends.

Planar Lens–Based Ultra-Wideband Dielectric Rod Waveguide Antenna for Tunable THz and Sub-THz Photomixer Sources

In this manuscript, the use of dielectric rod waveguide antenna (DRW) with an embedded planar lens is proposed as a highly directional alternative to an electrically large hyper-hemispheric silicon ...

Wideband Method to Enhance the Terahertz Penetration in Human Skin Based on a 3-D Printed Dielectric Rod Waveguide

In this paper, a wideband method based on a three-dimensional (3-D) printed dielectric rod waveguide (DRW) is proposed to enhance the terahertz (THz) penetration in the human skin. Two skin models are established to mimic the electromagnetic environments in the hydrated and dehydrated skin tissue, and the characteristics of the DRW are analyzed in detail. Three human tissues embedded in paraffin are measured to test the performance of the DRW. Experimental results demonstrate that the DRW generates an average penetration enhancement of 28% from 140 to 220 GHz compared with the conventional waveguide, which is rather close to the simulation prediction. Meanwhile, the DRW can significantly increase the dynamic range of the reflection signal from the skin tissue, which is meaningful in clinical application. The design of the DRW described here can be easily applied to other THz band, and the 3-D printing technique makes the fabrication flexible.

Building Blocks for a Millimeter-Wave Multiport Multicast Chip-to-Chip Interconnect Based on Dielectric Waveguides

A multichip multiport communication network technology is proposed based on a network of dielectric waveguides. For optimum performance and best versatility, a combination of high-permittivity dielectric slab waveguide and low-permittivity flexible dielectric rod waveguide is proposed. Additional building blocks are a dielectric waveguide Y junction and transitions between waveguide types as well as between chip and waveguide. The resulting multichip multicast multiport interconnect network features low overall transmission loss and small chip-area consumption for the chip-to-waveguide transitions. Measurement results for all components are presented for frequency bands around 60 GHz and around 100 GHz. The insertion loss of the transition from on-chip microstrip line to dielectric slab waveguide, extracted from end-to-end measurements, is 3.3 dB around 60 GHz and 2.2 dB around 100 GHz. Experimental four-terminal networks, each comprising four chip-to-waveguide transitions and two dielectric waveguide Y junctions, show measured end-to-end insertion loss (including pass through two Y junctions and two chip-to-waveguide transitions) of 21 dB (around 60 GHz, covering 26-mm distance) and of 17 dB (around 100 GHz, covering 20-mm distance), respectively. These values outperform wireless interconnects by far and emphasize the performance and versatility of the proposed approach for chip-to-chip multicast multiport interconnects.

Circularly Polarized Dielectric Rod Waveguide Antenna for Millimeter-Wave Applications

This paper presents a novel wideband circularly polarized dielectric rod waveguide (DRW) antenna for millimeter-wave applications. The rotated tapering rod that consists of a matching taper and a radiation taper is the first time adopted to realize circular polarization in the DRW antenna design. The circular polarization is realized by generating two orthogonal electric fields through rotating the radiation taper to an angle of $\varphi$ relative to the matching taper. The proposed antenna achieves a wide impedance bandwidth throughout the whole Ka-band as well as a wide 3 dB axial ratio bandwidth (ARBW) of 37% from 27.5 to 40 GHz. The main advantages for this antenna design are its wide impedance bandwidth, 3 dB ARBW, simple structure, and easy fabrication.

Near-zero-index wires.

In this work, near-zero-index material boundary properties have been exploited to achieve new electromagnetic functionalities. The extraordinary guiding properties of a cylindrical dielectric rod waveguide surrounded by a thin epsilon-mu-near-zero shell is analyzed and discussed. A closed-form solution for the dispersion equation has been developed, able to model and design such properties at will. Analytical and numerical results will confirm that the use of near-zero cover materials leads to extraordinary properties in terms of field configurations, low attenuation, and bandwidth. The dielectric wire acts as an efficient "waveguide" with great potentials for advance nanocircuit and electronics.

Conductivity of Carbon Nanotube Layers at Low-Terahertz Frequencies

Wave propagation in a dielectric rod waveguide loaded with carbon nanotube (CNT) layers was studied experimentally at the wide frequency range of 75–320 GHz. Analytical calculations and computer modeling indicate that the measured losses at low-terahertz frequencies are due to conductivity of the CNT layer. The observed rapid decrease of the conductivity with increasing frequency is related to finite lengths of CNTs.

Design of a Dielectric Rod Waveguide Antenna Array for Millimeter Waves

In this manuscript, the use of dielectric rod waveguide (DRW) antennas in the millimeter and sub-millimeter wave range is presented as a solution for covering two issues: getting more radiated power and filling a technological gap problem in the terahertz band, namely a fully electronic beam steering. A 4x4 element array working at 100 GHz fed by a rectangular waveguide is manufactured and measured for showing its capabilities. This topology can be used as a cost-affordable alternative to dielectric lenses in photomixer-based terahertz sources.

Excitation of THz hybrid modes in an elliptical dielectric rod waveguide with a cold collisionless unmagnetized plasma column by an annular electron beam

The dispersion relation of electromagnetic waves propagating in an elliptical plasma waveguide with a cold collisionless unmagnetized plasma column and a dielectric rod is studied analytically. The frequency spectrum of the hybrid waves and the growth rate for excitation of the waves by a thin annular relativistic elliptical electron beam (TAREEB) is obtained. The effects of relative permittivity constant of dielectric rod, geometrical dimensions, plasma frequency, accelerating voltage, and current density of TAREEB on the growth rate and frequency spectra of the waveguide will be investigated.

Dielectric Constant Estimation of a Carbon Nanotube Layer on the Dielectric Rod Waveguide at Millimeter Wavelengths

A method has been developed to estimate dielectric properties of a layer containing carbon nanotubes (CNTs) randomly arranged in plane, deposited on a dielectric rod waveguide (DRW). In the framework of this method, a theoretical model of a layered DRW with extended narrow walls and perfect electric conductor walls was used to fit the experimental results. The experimental results were obtained by measuring the wave propagation characteristics ( S11 and S21) of a DRW unloaded and loaded with different CNT layers at 75-110 GHz. The developed model allows derivation of the dispersion equation of the wave excited in the loaded DRW in an analytical form. The propagation constant is then found numerically through the fitting process with measurement results. Additionally, the complex permittivity of the CNT layer can be estimated using the surface conductivity model of the CNT and mixing formulas. Both methods give reasonable and comparable results. The obtained results (ε = 1- j5×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ) allow full-wave simulation (e.g., HFSS) of DRW structures loaded with CNT layers with a thickness of 60 nm or more. Simulation and measurement results agree rather well.

Dielectric Rod Waveguide Antenna as THz Emitter for Photomixing Devices

We propose a dielectric rod waveguide antenna (DRW) integrated with a photomixer as a THz emitter. This represents a different approach as opposed to the classical solution of a substrate lens. Main goals are an inexpensive alternative to substrate lenses, reduction of both reflections on the semiconductor-air interface and scattering of terahertz-generated power into the substrate. A radiation pattern measured at 137 GHz is shown as a proof-of-concept. In order to increase radiated power, the improvement of the rod antenna is discussed. Finally, as an application example, evanescent coupling of the DRW into a high index whispering gallery mode resonator is shown.

Millimeter-Wave Near-Field Probe Designed for High-Resolution Skin Cancer Diagnosis

This paper presents a detailed technical characterization of a micromachined millimeter-wave near-field probe developed for skin cancer diagnosis. The broadband probe is optimized for frequencies from 90 to 104 GHz and consists of a dielectric-rod waveguide, which is metallized and tapered towards the tip to achieve high resolution by concentrating the electric field in a small sample area. Several probes with different tip sizes were fabricated from high-resistivity silicon by micromachining and were successfully characterized using silicon test samples with geometry-defined tailor-made permittivity. The probes show a high responsivity for samples with permittivities in the range of healthy and cancerous skin tissue at 100 GHz (from $3.2-{\rm j}2.3$ to $7.2-{\rm j}8.0$ , loss tangent of approximately 1.26). The sensing depth was determined by simulations and measurements from 0.3 to 0.4 mm, which is adapted for detecting early-stage skin tumors before they metastasize. The lateral resolution was determined to 0.2 mm for a tip size of 0.6 $\,\times\,$ 0.3 mm, which allows for resolving small skin tumors and inhomogeneities within a tumor.

Wide Band mm- and Sub-mm-Wave Dielectric Rod Waveguide Antenna

The design of a dielectric rod waveguide (DRW) antenna for frequencies of 75-325 GHz is presented. The optimal broadband antenna geometry is determined using numerical simulations . A single DRW antenna is matched with metal waveguides of different sizes for different frequency bands. Measurement results agree very well with the simulation results up to 325 GHz; the gain of the antenna stays nearly constant ( G ≈ 10 dB) over the whole frequency range measured from 75 to 325 GHz (160% relative bandwidth). The upper limit is due to our limited manufacturing capability to produce sharp antenna tips. The return loss of the antenna is better than 15 dB. The radiation patterns are nearly independent of frequency. The 3 dB beamwidth is 50 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> -60 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> , and the 10 dB beamwidth is about 95 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> . This indicates that the aperture size of this end-fire antenna decreases as a function of frequency, and this observation agrees well with the earlier observation that the phase center of a DRW antenna moves towards the antenna tip as a function of frequency. Also the cross polarization was studied. The cross-polarization level is better than -15 dB at all frequencies .

Field Distributions Around a Rectangular Crack in a Metallic Half-Space Excited by Long Current-Carrying Wires With Arbitrary Frequency

In this paper, we propose a semianalytical solution for evaluation of field distributions around a short rectangular crack in a metallic half-space excited by long current-carrying wires with arbitrary frequency. The governing Helmholtz equation is solved in three dimensions by separation of variables. The solution is obtained by developing 2-D Fourier series model and using exponential functions in the third dimension. To expand all possible field components in the metal, we first hypothesize a shielded dielectric rod waveguide where the shield enclosure lies at infinity, the surrounding dielectric (i.e., the metal) is a lossy material, and the rod dielectric is the crack opening. We then introduce hybrid modes each of which consists of two components, representing the TMy and TEy modes. The mode-matching technique is finally used to numerically solve the resultant boundary value problem. The unknown eigenvalues and field coefficients are found by searching for small singular values, using the singular value decomposition (SVD) in the resultant homogeneous linear system. The validity of our modeling technique is confirmed by comparison of our results with those obtained by measurement and finite integration code.