Hollow Dielectric Waveguide Research Articles

A Low-Loss and High-Bandwidth Hollow Rectangular Dielectric Waveguide for Sub-THz Applications

A Low-Loss and High-Bandwidth Hollow Rectangular Dielectric Waveguide for Sub-THz Applications

Vertically Polarized Planar Transition for Hollow-Dielectric-Waveguide-Based 5G/6G High-Speed mm-Wave Interconnect

Hollow dielectric waveguide (HDW) is a highly anticipated solution for extremely low-loss and high-speed millimeter-wave (mm-wave) interconnect. However, the method for endfire power transition from HDW to planar backplane systems is limited to horizontal polarization in the literature. That is, the potentially available capacity of the HDW within the other polarization is idle and wasted. In this letter, the first vertically polarized (V-pol), endfire transition from tubular HDW to the printed circuit board (PCB) is proposed. The experimental result shows that the minimum calibrated transition loss is only 0.48 dB. And a wideband transition can be designed to achieve a fractional bandwidth of 20%. And a maximum data rate of 34 Gb/s over the proposed 1-m interconnect is demonstrated with 16 quadrature amplitude modulation (16QAM). For the endless race of data rate in 5G/6G communication, this technique provides a new direction for a low-loss and high-speed HDW-based interconnect between planar backplane systems.

Experimental characterization of bending effects for solid and hollow dielectric waveguides at V-band

Mm-wave dielectric waveguides are a promising and low-cost technology for the transmission of ultra-high data rates. Besides the attenuation (losses) and group delay, the bending loss of the dielectric waveguides is also one of the key parameters to establish the capacity and energy efficiency of such wired links, when deployed in realistic scenarios. In this context, we report the experimental characterizations of bending effects for various solid and hollow commercially available dielectric waveguides at V-band (50–75 GHz). A wide-band transition has been designed to carry out the measurements using a Vector Network Analyzer (VNA) and extension modules. The measured results are in very good agreement with full-wave simulations. Our experimental results show an average bending loss of 1.46 dB over the entire V-band for the fundamental {HE}_{11}^{y} mode of a PTFE solid dielectric waveguide (core diameter of 3.06 mm) with a 90° bending angle and 25 mm radius of curvature. This value rises up to 2.88 dB (or 3.25 dB) when bending radius is changed to 15 mm (or bending angle grows up to 140°). The measurements also show that the measured bending losses increase significantly for hollow dielectric waveguides, in particular when the inner to outer diameter ratio gets larger.

Non‐destructive inspection for FRPM pipeline using periodic pattern of microwave guided‐modes on cylindrical dielectric waveguide

The authors propose a new non-destructive inspection method for underground fiberglass-reinforced plastic mortar pipelines utilizing the periodic patterns of microwave guided-modes on a hollow cylindrical dielectric waveguide. By the spatial synthesis of the microwaves utilizing the periodicity in the circumferential direction of a pipe, the authors found that a periodic pattern of the microwaves such as the Talbot effect with producing self-images at the Talbot distance, was observed over the pipe-wall. Further, adjusting the phase relationship between adjoining antenna elements changed the positions of the peak and null in the periodic pattern on the pipe-wall. Additionally, when an unwanted foreign object was attached to the pipe, the periodic pattern of the microwaves can be disturbed according to the size and position of the object, and it is possible to inspect the pipeline using narrow-band microwave signals. This paper experimentally demonstrated the successful detection of a foreign object on the pipe-wall by scanning Talbot-like patterns with a sensor along the pipe-wall. This technique enables the non-destructive inspection of pipelines using only narrow-band, licence-free microwave signals.

Extremely Low-Loss Planar Transition From Hollow Dielectric Waveguide to Printed Circuit Board for Millimeter-Wave Interconnect

An extremely low-loss and high-speed millimeter-wave (mm-wave) interconnect based on hollow dielectric waveguide (HDW) is demonstrated. Though HDW is renowned for its distinguishably low-loss transmission among all dielectric-based competitors, it is criticized for the difficulty of smooth power transition from HDW to planar backplane systems. This article presents a novel approach for planar transition from tubular HDW to printed circuit board (PCB). The proposed transition circuit is composed of a dipole-antenna-like power coupler, a matching metal adapter, and a tapered horn. The experimental result shows only 0.68-dB transition loss at 58 GHz, which is the best value compared to other approaches in the literature. In addition, thorough analysis and modeling for the proposed technique are obtained. It implies the opportunity to apply this approach for applications in higher frequency by scaling. The 16 quadrature amplitude modulation (16QAM) communication over the proposed 1-m interconnect is demonstrated with a maximum data rate of 34 Gb/s. This technique provides an extremely low-loss and structurally stable solution for HDW-based interconnect and transition, which is expected to be applied for 5G/6G high-throughput communication in the near future.

Control of tightly focused laser beams in the THz range

AbstractThe possibility for control of tightly focused laser beams excited by the resonator modes of a THz laser based on a hollow circular dielectric waveguide is studied theoretically and experimentally. The wavelength of the radiation under study is 0.4326 mm corresponding to the generation line of the optically pumped HCOOH‐molecule THz laser. The focusing system is implemented by a short‐focus lens covered by absorbing masks in the central region. The focal area parameters were controlled by changing the size of the masks. The electric field components of the laser modes are calculated using the Rayleigh‐Sommerfeld integral transformations under non‐paraxial approximation. The use of absorbing masks made it possible to reduce the beam diameter in the focal region and increase the depth of focus of the linearly polarized EH11‐mode and azimuthally polarized TE01‐mode as well. In this case, despite of the presence of an absorbing mask, the distribution of the total field intensity of the TE01‐mode retained its annular shape, and the field maximum of the EH11‐mode is observed at center of the focal spot. The results of this work can be implemented in medical diagnostics, high‐speed communications, and environmental monitoring.

Significant Crosstalk Reduction in High-Density Hollow Dielectric Waveguides by Photonic Crystal Fence

Hollow dielectric waveguides (HDWs) are renowned for their extremely low-loss transmission among all dielectric -based solutions. Highly-integrated multilane HDWs are expected to be applied for increasing demand on high-throughput communication. Unfortunately, severe crosstalk and loosely confined electromagnetic field have been a critical issue for a long time. In this article, we demonstrate a novel 1-D photonic crystal fence. Photonic particles represent a series of guard lining up beside the waveguides. Over 30-dB crosstalk reduction can be realized for closely placed HDWs. This proposed method, without altering the original structure of HDWs, offers high degrees of freedom for the HDW design. The experimental results show good field confinement in the mm-wave range, but not limit to it. This all-dielectric -based solution implies its opportunity for subterahertz to optical frequency application. Moreover, photonic crystal fence with only 1-D arrangement makes this concept feasible for both tubular HDWs and other planar integrated dielectric -based waveguides on board. This technique takes a key step for highly integrated multilane HDWs in the near future.

Diffraction properties of azimuthally symmetric gratings in a hollow circular dielectric waveguide

Diffraction gratings can be used in cavities of terahertz lasers for generating wave beams with special polarization. Adequate using of such gratings needs preliminary theoretical investigation of their diffraction properties. To solve the problem a specially adopted numerical method should be used because the structures under study frequently have many elements (many periods) and well-known theoretical approaches or commercial solvers cannot cope with such task. In this paper, a Finite Difference in Time Method for Body of Revolution (BOR FDTD) is applied to the problem. Updating formulae for electromagnetic field and some calculation features of the method are presented. Different types of diffraction gratings that homogeneously and inhomogeneously change their properties with the radial coordinate are studied. Some physical peculiarities of diffraction modes of a hollow dielectric waveguide with different polarization are revealed and discussed.

FOCUSING OF MODES WITH AN INHOMOGENEOUS SPATIAL POLARIZATION OF THE DIELECTRIC RESONATOR OF A TERAHERTZ LASER

Wave beams with non-uniform spatial polarization of radiation are necessary for solving important fundamental and applied problems related to the interaction of electromagnetic waves of the terahertz range with matter - surface diagnostics of materials, thin films, biological objects, information transmission, and processing systems, achieving subwave resolution in tomography, communication systems, etc. The results are presented in the literature on focusing on pulsed radiation beams in the terahertz range. Data on the focusing of continuous radiation beams are practically absent. The spatial-energy characteristics of laser beams having an inhomogeneous spatial polarization at their moderate and sharp focusing are theoretically investigated. As the radiation understudy, in the numerical simulation of the focusing of wave beams in the terahertz range, we used the modes of a laser waveguide dielectric resonator that coincide with the eigenmodes of a hollow dielectric waveguide. Symmetric and asymmetric modes with both spatially inhomogeneous azimuthal, radial, and homogeneous linear field polarizations are studied. The components of the electric field of laser beams during their propagation in free space were studied using the Rayleigh-Sommerfeld integrals in the nonparaxial approximation. The effect of the focusing lens on laser radiation was taken into account using the amplitude-phase correction function. The distributions of the total intensity of the resonator modes and their individual field components in the focal region of the lens are studied. The obtained results expand the knowledge about the features of focusing terahertz laser beams.

Ray Tracing and Modal Methods for Modeling Radio Propagation in Tunnels With Rough Walls.

At the ultrahigh frequencies common to portable radios, tunnels such as mine entries are often modeled by hollow dielectric waveguides. The roughness condition of the tunnel walls has an influence on radio propagation, and therefore should be taken into account when an accurate power prediction is needed. This paper investigates how wall roughness affects radio propagation in tunnels, and presents a unified ray tracing and modal method for modeling radio propagation in tunnels with rough walls. First, general analytical formulas for modeling the influence of the wall roughness are derived, based on the modal method and the ray tracing method, respectively. Second, the equivalence of the ray tracing and modal methods in the presence of wall roughnesses is mathematically proved, by showing that the ray tracing-based analytical formula can converge to the modal-based formula through the Poisson summation formula. The derivation and findings are verified by simulation results based on ray tracing and modal methods.

Theoretical analysis of the radiating system for treatment of ovarian diseases of the cows

Conducted in this article theoretical studies are focused on calculation of the geometry parameters and directional diagram of the radiating system for millimeter wavelength range for intrauterine treatment of ovarian diseases of cattle. Theoretical studies have shown that radiating system for intrauterine treatment of ovarian diseases of the cows can be created based on the hollow dielectric waveguide system coordinated with pyramidal horn radiator and the dielectric lens at the output of waveguide

Study on the Dispersion Characteristics of Surface TM Modes in Hollow Slab Waveguide with a Left-Handed Material Cover

The dispersion characteristics of surface TM modes in a hollow slab waveguide which consists of the core and substrate of right-handed material (RHM) and the cover of left-handed material (LHM) are investigated. Normalized frequency, normalized propagation constant and asymmetry measure are introduced to the left-handed material hollow slab waveguide. The dispersion relation is derived by using these normalized parameters, and universal dispersion curves are obtained by solving transcendental dispersion equations analytically. Existence condition and other dispersion characteristics of guided surface TM modes have been discussed in detail for different permittivity of three layers for this left-handed material hollow dielectric slab waveguide.

Simulation and analysis of single negative metamaterial sensor based on microring resonator

A novel microring resonator sensor coated with a single negative metamaterial (SNM) layer is proposed. The dispersion relation of hollow cylindrical dielectric waveguide covered with a SNM layer is derived, and resonant frequencies of the corresponding whispering gallery mode are computed. We find that there is a good agreement between the theoretical results and numerical results of resonant frequencies and electric field distributions. Compared with traditional resonator sensor, the sensitivity and resolution are significantly enhanced by SNM, and the Q factor can be tailored by adjusting the distance between the waveguide and the microring.

Analysis of periodic structure and distorted characteristic in hollow dielectric waveguide fibers

In this paper, using numerical methods, first, the transmittance characteristic of single mode OmniGuide fibers – the hollow dielectric waveguides in which light is confined by a large index-contrast omnidirectional dielectric mirror is analyzed. We found that the minimum periodic number of omnidirectional mirror of high transmission OmniGuide fibers with small bend radius is three layers. Then, the distortion characteristics of the elliptical and cylindrical OmniGuide fibers are analyzed, and we found that maintaining transverse mode field distribution in single mode OmniGuide fiber is almost changeless when fiber is obviously bent or distorted. Therefore, the hollow dielectric waveguide fibers will be useful as large mode area fiber for advanced high-power amplifiers and lasers.

Simulation and Analysis of a Metamaterial Sensor Based on a Microring Resonator

Metamaterials are artificial media structured on a size scale smaller than the wavelength of external stimuli, that may provide novel tools to significantly enhance the sensitivity and resolution of the sensors. In this paper, we derive the dispersion relation of hollow cylindrical dielectric waveguide, and compute the resonant frequencies and Q factors of the corresponding Whispering-Gallery-Modes (WGM). A metamaterial sensor based on microring resonator operating in WGM is proposed, and the resonance intensity spectrum curves in the frequency range from 185 to 212 THz were studied under different sensing conditions. Full-wave simulations, considering the frequency shift sensitivity influenced by the change of core media permittivity, the thickness and permittivity of the adsorbed substance, prove that the sensitivity of the metamaterial sensor is more than 7 times that of the traditional microring resonator sensor, and the metamaterial layer loaded in the inner side of the microring doesn’t affect the high Q performance of the microring resonator.

PHYSICAL MODELING OF ELECTROMAGNETIC SCATTERING IN THE TERAHERTZ BAND QUASI-OPTICAL DIRECTIONAL STRUCTURES

The paper is devoted to elaboration of the theoretical and experimental basis, methods and recommendations aimed at the development of a new trend in the experimental radio physics -physical quasi-optical waveguide modeling (QWM) of the processes of electromagnetic scattering in the near millimeter (NMM) and submillimeter (SMM) wavelength ranges. The methods of experimental research of the electromagnetic scattering processes in the quasi-optical (QO) directional structures of a «hollow dielectric waveguide» (HDW) class have been developed and generalized. The basis for development of the radio measurement facilities used for physical electromagnetic modeling (EMM) of the object’s scattering characteristics in the NMM and SMM wavelength bands has been elaborated.

Minimum loss condition of a bent rectangular hollow waveguide

AbstractThe leakage loss of a hollow dielectric waveguide is analyzed analytically and numerically. A minimum loss condition of a bent rectangular hollow waveguide is derived in terms of the refractive index of the cladding using the perturbation method. The validity of the derived minimum loss condition is confirmed by the beam‐propagation method. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2901–2902, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24761

A Semianalytical Technique for Leaky-Mode Loss Calculation in Hollow Dielectric Waveguides With Arbitrary Cross Sections

We present an approximate semianalytical technique for the calculation of the loss coefficient of leaky modes in 3-D hollow dielectric waveguides having an arbitrary cross section. The hollow waveguides are assumed to have an axis of symmetry and to have a cladding with a higher refractive index than the core. An expression for the modal loss coefficient is derived using a ray-optics approach with paraxial approximation. For the special cases of specific cross sections with known solutions, our technique gives results that are identical to the available analytical solutions. The technique is then applied on practical waveguide geometries, allowing the calculation of polarization- and wavelength-dependent losses. Full numerical alternatives to the technique involve time-consuming simulations and, sometimes, difficulty in incorporating a suitable boundary condition to obtain leaky-mode solutions.

Waveguide submillimetre laser with a uniform output beam

A method for producing non-Gaussian light beams with a uniform intensity profile is described. The method is based on the use of a combined waveguide quasi-optical resonator containing a generalised confocal resonator with an inhomogeneous mirror with absorbing inhomogeneities discretely located on its surface and a hollow dielectric waveguide whose size satisfies the conditions of self-imaging of a uniform field in it. The existence of quasi-homogeneous beams at the output of an optically pumped 0.1188-mm waveguide CH3OH laser with a amplitude-stepped mirror is confirmed theoretically and experimentally.

Design of Stark-tuned far-infrared laser with circular hollow waveguide

A novel design of a Stark-tuned far-infrared laser using a circular hollow dielectric waveguide is proposed, and its characteristics are studied. Supplementary electrodes are inserted inside the circular hollow dielectric tube to suppress charge accumulation while keeping field uniformity. In what is believed to be a new design, the mode property is found to be improved, and the angular dependency of the attenuation loss according to the beam polarization is estimated to be much smaller than that of the conventional rectangular hybrid waveguide design. In this new design, DeltaM=0 far-infrared (FIR) transition as well as DeltaM=+/-1 transition can be observed, and the power enhancement for the DeltaM=0 FIR transition is expected.