Rectangular Dielectric Waveguide Research Articles

Chiral forces in longitudinally invariant dielectric photonic waveguides

We calculate numerically the optical chiral forces in rectangular cross-section dielectric waveguides for potential enantiomer separation. Our study considers force strength and time needed for separating chiral nanoparticles, mainly via quasi-TE guided modes at short wavelengths (405 nm) and the 90°-phase-shifted combination of quasi-TE and quasi-TM modes at longer wavelengths (1310 nm). Particle tracking simulations show successful enantiomer separation within two seconds. These results suggest the feasibility of enantiomeric separation of nanoparticles displaying sufficient chirality using simple silicon photonic integrated circuits, with wavelength selection based on the nanoparticle size.

Waveguide Eavesdropping Threat for Terahertz Wireless Communications

As wireless communications move to higher frequency band for 5G networks and beyond, resiliency against eavesdropping and other security threats is still one of the key system-design considerations. Compared to data transmissions by lower frequencies, terahertz links are inherently more robust against eavesdropping attacks due to their propagation characteristics (such as high free-space path loss) and aligned link path by high-gain antennas. However, it does not indicate that eavesdropping is always impossible. Line-of-sight terahertz links have proven to be vulnerable to active/passive eavesdroppers by placing scatters in the path of data transmission, or by collecting side-lobe leakages. Here, we demonstrate a waveguide-based approach for signal eavesdropping which can be operated much more feasibly with several advantages, such as lower propagation loss and reliable data interception. Our method relies on a 3D printed rectangular dielectric waveguide and can overcome spatial limitations caused by directional modulation or near-field modulation. We demonstrate successful eavesdropping attacks for a 16 quadrature amplitude modulated (16-QAM) data link at rates up to 5 gigabits per second. Our work highlights the importance of system designs in resisting waveguide-based eavesdropping strategies and identifies aspects where

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

Sub‐THz Phase Shifters Enabled by Photoconductive Single‐Walled Carbon Nanotube Layers

Materials with tunable dielectric properties are highly relevant for terahertz (THz) applications. Herein, the tuning of the dielectric response of single‐walled carbon nanotube layers by light illumination is studied for applications to THz phase shifters. The dependence of the length of individual nanotubes on the THz photoconductivity of the network is experimentally investigated in the frequency range of 0.2–1 THz by time‐domain spectroscopy (TDS). The effective conductivity of the networks is described by a theoretical model that fits the measured dielectric function. Terahertz phase shifters are realized with the carbon nanotube layers as the optically tunable element deposited on the wall of rectangular dielectric waveguides. The phase of the electromagnetic wave propagating in the waveguide is shown to be tunable by illuminating the nanotubes. A linear phase shift with the frequency is measured between 75 and 500 GHz with a low change in amplitude due to the illumination.

Volumetric integro-differential equations in diffraction and eigenvalue problems (r e v i e w)

Volumetric integral and integro-differential equations are considered that describe problems of diffraction by three-dimensional bodies with given macroscopic permittivity and magnetic permeability, as well as problems on free vibrations of such bodies. Similar equations are obtained for waveguide structures: hollow shielded waveguides with dielectric filling, dielectric waveguides (optical beamguides), photonic-crystal waveguides. Dominantly stationary linear electromagnetic problems are considered. Non-stationary and nonlinear problems are mentioned casually. Numerical results are given for oscillations H01delta and H011 of a cylindrical dielectric resonator, for waves of a rectangular dielectric waveguide and a plasmonic waveguide, dispersion in a photonic crystal, and diffraction by a rectangular dielectric cylinder. Keywords: ...

Space-Mapping Based Automatic Design of SIW-Based Directional Coupler With Arbitrary Power Ratio

In this paper, an automatic design method allowing efficient design of substrate integrated waveguide (SIW) directional coupler with any given power ratio between 3 dB and 20 dB has been proposed. Due to excessive electromagnetic (EM) simulation time of SIW structure, the space mapping technique is exploited to accelerate the design process. An EM-simulation based dielectric rectangular waveguide (RWG) model acts as the surrogate to reduce the simulation time. A two-stage optimization scheme including a differential evolution (DE) algorithm and a Nelder-Mead (NM) simplex algorithm is used to obtain initial surrogate design. Suitable objective functions are proposed for surrogate optimization and for parameter extraction procedure of space mapping technique. Our proposed method is verified with an X band SIW directional coupler with four different power ratio designs, which are 3dB, 10dB, 15dB and 20dB. The experimental results confirm the effectiveness and efficiency of the method.

Broadband microwave absorber using pixelated FSS embedded in CISR sheets in frequency range of 3.95 to 8.2 GHz

In this paper, pixelated Frequency Selective Surface (FSS) layer embedded in two carbonyl iron-filled silicon rubber (CISR) sheets are used for design of broadband microwave absorber in frequency range of 3.95 to 8.2 GHz. Top and bottom layers of CISR sheets are prepared with 24% and 33% of Carbonyl Iron (CI) powder by volume, respectively. Reflectivity of microwave absorber, complex permittivity and complex permeability of CISR sheets are evaluated using two Rectangular Dielectric Waveguide (RDWG) measurement systems in 3.95 to 5.85 GHz frequency band (WR-187) and 5.85 to 8.2 GHz frequency band (WR-137). An algorithm was developed using Geometry-Refinement Method (GRM) and Genetic Algorithm (GA) optimization technique to design pixelated FSS layer. Measured as well as simulated reflectivity of composite microwave absorber is better than −10 dB at normal incidence in the frequency range of 3.95–8.2 GHz. For oblique incidence from 0 to 40, simulated reflectivity of TE and TM polarizations carried out for all angles of incidence.

Design and modeling of a photonic integrated device for optical vortex generation in a silicon waveguide

We propose and numerically verify a design of the photonic integrated circuit for in-plane generation of a 1st azimuthal order vortex mode in dielectric rectangular waveguides. Radiation is introduced into the proposed structure in a standard way through two grating couplers. Applying a mode coupling and specific phase shift, a field with the required amplitude-phase distribution is formed directly in the output waveguide. The geometric dimensions of the device are simulated and optimized to fit the technological parameters of the silicon-on-insulator platform.

Waveguide platform for quantum anticentrifugal force.

This work is a proposition of an experimental platform to observe quantum fictitious anticentrifugal force. We present an analytical and numerical treatment of a rectangular toroidal dielectric waveguide. Solving the Helmholtz equation, we obtain analytical solutions for transverse spatial modes and estimate their number as a function of system characteristics. On top of that, the analysis of the structure is extended onto a real material platform, a thin-film lithium niobate on insulator rib waveguide. The framework presented here can be applied directly to analyze the phenomenon of quantum anticentrifugal force.

Modeling and Optimization of Vortex Modes Propagation in Rectangular Dielectric Waveguides

We study analytically and numerically the possibility of vortex modes propagation over planar dielectric rectangular waveguides, and consider the problem of waveguide geometry optimization for the support of vortex modes. The results show, that theoretically rectangular waveguides can provide transmission of quasi-TE and quasi-TM modes with high purity states of orbital angular momentum (OAM) in the dominant field component. However, only for the quasi-generate mode of azimuthal order ±1 the constituent eigenmodes can propagate in a phase-matched regime, and the vortex modes of higher azimuthal orders can propagate only with a certain beat length. Moreover, as the target azimuthal order increases, the normalized power of the corresponding OAM state in the modal superposition decreases. The analytical predictions have been verified by numerical electromagnetic simulations of silicon nitride waveguides providing field distributions and OAM spectra of the corresponding modal superpositions.

Low-Loss, Thermally Insulating, and Flexible Rectangular Dielectric Waveguide for Sub-THz—Signal Coupling in Superconducting Receivers

Dielectric waveguides have potential as transmission lines in subterahertz (sub-THz) applications due to their low-loss. A new application of a rectangular dielectric waveguide (RDW) for a THz superconducting receiver system for radio astronomy is investigated and demonstrated for the first time. The RDW can be used to transmit sub-THz local oscillator (LO) signals into the cryostat for driving the superconductor insulator superconductor mixer, with very low heat transfer. A series of RDWs with different lengths are fabricated. The measured average attenuation constants of the RDW are 0.034 and 0.069 dB/mm at 3.4 and 300 K measurement environments over 240–300 GHz, respectively. The double-sideband system noise temperature of the receiver system is also measured. With this LO signal feeding system, there is only 0.69 mW thermal transfer power from the 300 to the 3.4 K cold stage. Compared to traditional pumping signal feeding schemes, such as the horn-to-horn structure and beam splitter method, this approach outperforms the traditional schemes in terms of feeding flexibility, insertion loss, and thermal isolation for the cryostat. The proposed RDW can be widely applied to superconducting receivers for radio astronomy in the future.

3D-Printed Dual-Reflector Antenna With Self-Supported Dielectric Subreflector

A dual-reflector antenna with a self-supported subreflector is proposed. The supporting structure is made of dielectric material and it is part of the feeding of the antenna, which is based on Cassegrain optics and works at X-band. The feeding subsystem includes the primary feed, subreflector supporting structure and subreflector surface in a single dielectric piece, resulting in a compact, light and low-cost solution. First, the subreflector and its feeding subsystem, based on a Dielectric Rectangular Waveguide (DRW) along with a hyperboloid, are described, and the phase center of the DRW and the antenna optics are defined. Then, two effective techniques to mitigate the refraction caused by the dielectric were proposed. Finally, the design was validated through the fabrication of a Cassegrain antenna using a 3D printing technique. Measurements and simulations show a very good agreement and an antenna of 26 dBi of directivity with overall very good performances is obtained, validating both the proposed subreflector and the design technique.

Cherenkov Radiation Generated by an Electron Bunch in a Rectangular Dielectric Waveguide Filled with a Transversely Isotropic Medium

Dielectric waveguides are being intensively studied as accelerating structures excited by an electron bunch. Rectangular dielectric structures are used both to test the principles of new accelerating schemes and to study the electric properties of filling materials. Several dielectric materials used as fillers of waveguides have anisotropic properties (sapphire, ceramic films). Anisotropy can have a significant effect on the wakefields generated by an electron bunch in a structure. The paper presents an analytical calculation of Vavilov–Cherenkov radiation generated by a relativistic electron bunch in a rectangular waveguide filled with a transversely inhomogeneous transversely isotropic dielectric. A method for constructing an orthogonal basis of the transverse operator with its subsequent use to find the wakefield is presented. A dispersion relation for the structure and expressions for the wakefield created by a point electron bunch in a transversely isotropic rectangular dielectric structure are obtained. Based on the formalism presented, parameters of an accelerating structure based on sapphire, allowing the generation of fields above 100 MV/m, are calculated.

Analysis of electron beam dynamics in a rectangular dielectric waveguide

Wakefield acceleration of electron bunches is effective method developed for linear accelerator techniques. The main problem of this method is transverse beam dynamics which limits the propagation length of bunch. This work is dedicated to beam dynamics in dielectric waveguide with rectangular geometry. This type of waveguide has complex mode composition including LSM and LSE modes. The main purpose is a study of modes influence in rectangular dielectric waveguide on beam dynamics with different types of dismission of driver from waveguide’s axis. It is shown that the LSM asymmetric modes make a major contribution to wakefield and transverse dynamics.

Guided-Mode Filters for Terahertz Frequencies Fabricated by 3D Printing

In this article, we present the design and characterization of the first 3D-printed guided-mode filter for terahertz frequencies. The device consist on a diffractive grating fabricated on top of a rectangular dielectric waveguide by 3D printing. Finite difference numerical modeling shows this device acts as a filter at a frequency that can be geometrically engineered and tuned around such frequency by varying the radiation incidence angle. Three devices were designed to operate at 200 GHz, 250 GHz, and 300 GHz; the devices were fabricated and successfully characterized using terahertz time-domain spectroscopy.

Propagation of THz pulses in rectangular subwavelength dielectric waveguides

Rectangular subwavelength waveguides are necessary for the development of micro/nanophotonic devices and on-chip platforms. Using a time-resolved imaging system, we studied the transient properties and the propagation modes of THz pulses in rectangular subwavelength dielectric waveguides. The dynamic process of THz pulses was systematically recorded to a movie. In addition, an anomalous group velocity dispersion was demonstrated in rectangular subwavelength waveguides. By using the effective index method, we theoretically calculated the modes in rectangular subwavelength waveguides, which agree well with the experiments and simulations. This work provides the opportunity to improve the analysis and design of the integrated platforms and photonic devices.

On Calculation of the Amplitude–Phase Distribution of the Field Radiated from an Open End of a Rectangular Dielectric Waveguide

The problem of calculating the amplitude–phase distribution of the field radiated from an open end of a rectangular dielectric waveguide expanding along one of its sides (a plane dielectric horn) is considered. The problem of diffraction on the junction of a feed dielectric waveguide and the horn is solved by the domain decomposition method using a model in the form of a screened dielectric waveguide. The amplitude–phase distributions over the distance from the end of the radiator are studied. The possibility of using the screened model for solving the problem of radiation from the open end of a dielectric horn is shown.

Coherent-perfect-absorber and laser for bound states in a continuum.

It is shown that two fundamentally different phenomena, the bound states in continuum and the spectral singularity (or time-reversed spectral singularity), can occur simultaneously. This can be achieved in a rectangular core dielectric waveguide with an embedded active (or absorbing) layer. In such a system a two-dimensional bound state in a continuum is created in the plane of a waveguide cross section, and it is emitted or absorbed along the waveguide core. The idea can be used for experimental implementation of a laser or a coherent-perfect-absorber for a photonic bound state that resides in a continuous spectrum.

A Fully Integrated Broadband Sub-mmWave Chip-to-Chip Interconnect

A new type of broadband link enabling extremely high-speed chip-to-chip communication is presented. The link is composed of fully integrated sub-mmWave on-chip traveling wave power couplers and a low-cost planar dielectric waveguide. This structure is based on a differentially driven half-mode substrate integrated waveguide supporting the first higher order hybrid microstrip mode. The cross-sectional width of the coupler structure is tapered in the direction of wave propagation to increase the coupling efficiency and maintain a large coupling bandwidth while minimizing its on-die size. A rectangular dielectric waveguide, constructed from Rogers Corporation R3006 material, is codesigned with the on-chip coupler structure to minimize coupling loss. The coupling structure achieves an average insertion loss of 4.8 dB from 220 to 270 GHz, with end-to-end link measurements presented. This system provides a packaging-friendly, cost effective, and high performance planar integration solution for ultrabroadband chip-to-chip communication utilizing millimeter waves.

LED-Switchable High-QPackaged THz Microbeam Resonators

This paper describes the design, fabrication, and experimental characterization of photonic crystal microbeam cavity resonators for the terahertz band implemented using suspended dielectric rectangular waveguide (DRW) in high-resistivity silicon. Electrical quality factors of up to 11 900, combined with small modal volumes of 0.28 and 0.077 mm3, are demonstrated for devices operating at 100 and 200 GHz, respectively. The devices are found to be extremely light-sensitive, opening up new opportunities for light-controlled switching devices at terahertz frequencies. It is shown that the quality factor of the resonator can be tuned and the resonance extinguished through photo-illumination with an infrared light-emitting diode (IR LED). Additionally, the questions of thermal tunability and thermal stability of the resonators are examined. The demonstrated resonators are inherently suited to integration with DRW and, by silicon bulk micromachining, represent an attractive approach for realizing microphotonic-integrated circuits for terahertz systems-on-a-substrate.