Bandgap Waveguides Research Articles

Investigation of Characteristics of Electromagnetic Bandgap (EBG) Waveguide in Electromagnetic Crystal with Capacitive Cylinders

Electromagnetic bandgap (EBG) waveguides formed in a two-dimensionally periodic lattice of capacitive metal cylinders located between two metal screens are considered. The cylinders have a gap between one of the ends and the screen. It is shown that the lower critical frequencies of such waveguides are shifted upwards in comparison with the corresponding waveguide in the array of solid cylinders, which is dueto the possibility of slow waves propagating in the array in the first zone of its transparency. The critical wave frequencies in the second transparency zone of the capacitive grating are lower than in the grating of solid cylinders. The dependences of the dispersion diagrams and the damping of the main wave on the gap are studied.It is shown that, in most of the operating range, the dispersion curves and attenuation characteristics are practicallythe same as for a waveguide without gaps in the walls. The problem of excitation of an EBG waveguide in a capacitive grating by a standard metal waveguide is solved, and the level of their matching in the frequency band is calculated depending on the size of the gap. The working band of the EBG waveguide for different grating periods is determined taking into account the required level of matching and the limitation from above by the highest wave type of the metal waveguide. It is shown that its maximum value is reached at a certainperiod depending on the size of the gap.

Investigation of Characteristics of Electromagnetic Bandgap (EBG) Waveguide in Electromagnetic Crystal with Capacitive Cylinders

Investigation of Characteristics of Electromagnetic Bandgap (EBG) Waveguide in Electromagnetic Crystal with Capacitive Cylinders

Light dynamics around an exceptional point in a 1D photonic bandgap waveguide

Exceptional points (EP) in a system parameter space at which eigenvalues and corresponding eigenvectors coalesce are ubiquitous in non-Hermitian systems. Many unconventional applications have been proposed while encircling around the EPs. One of the unique application is the direction-dependent mode conversion. Here the appearance of an EP has been investigated in a planar 1D Bragg reflection waveguide(BRW) geometry, which has provided an additional degree of freedom to explore EP-based exotic light dynamics. A planar 1D BRW consists of periodic dielectric arrays and a defect dielectric layer forming the core. An inhomogeneous customized gain-loss profile is incorporated in the core region to couple two quasi-guided transverse electric (TE) modes so that the waveguide hosts an EP of order two. Here, we propose a dynamical EP encirclement scheme and corresponding asymmetric mode conversion phenomenon between two photonic bandgap quasi-guided TE modes in a 1D photonic bandgap-guided structure. Our findings will be potentially important to open up a fertile platform using the paradigm of non-Hermitian coupling to meet a wide range of exotic integrated chip-scale applications in the context of mode selectivity for switching and conversion.

Novel Band Gap Waveguide for Low-Loss and Dual Band Applications

In this article, the band gap waveguide (BGW) is proposed and studied. The BGW is formed by a groove gap waveguide (GGW) and a rectangular waveguide, and the former is totally integrated inside the latter. The units of the GGW form a stopband to confine the electromagnetic (EM) wave inside the groove of GGW and propagate the quasi-TE₁₀ mode at high frequencies. When operating at low frequencies, the units cannot block EM waves, and the latter can pass through them and propagate in the entire rectangular waveguide region as a TE₁₀-like mode. Besides, the characteristics, propagation modes, and designing methods of the BGW are illustrated and analyzed. Two transition structures corresponding to high- and low-frequency operations are then designed to verify the transmission performance of the BGW, as well as its integration capability with other passive components. A back-to-back transition prototype has been fabricated to evaluate its performance. The measured results are in great agreement with the simulated results. According to the experimental results, good impedance matchings and low insertion losses are achieved from 6.8 to 8.05 GHz for low frequency and from 71 to 86 GHz for high frequency, respectively.

Interpreting light guidance in antiresonant and photonic bandgap waveguides and fibers by light scattering: analytical model and ultra-low guidance.

Here, we introduce a quasi-analytic model that allows studying mode formation in low refractive index core waveguides through solely focusing on the cladding properties. The model isolates the reflection properties of the cladding from the modes via correlating the complex amplitude reflection coefficient of the cladding to the complex effective index of the fundamental core mode. The relevance and validity of the model are demonstrated by considering a single-ring anti-resonant fiber, revealing unexpected situations of exceptionally low loss. Our model explains mode formation by light scattering, which conceptually provides deep insights into the relevant physics.

Influence of a cylindrical waveguide with a concentric photonic band-gap wall on interatomic resonance energy transfer

We consider how the rate of resonance energy transfer (RET) between an excited atom and a ground-state one is affected by the presence of a cylindrical photonic band-gap waveguide by using the Green’s function approach. Both positions inside and outside the wall and three types of atomic dipole moment orientations, namely radial, azimuthal and axial orientations, are examined. Results for the photonic band-gap structure and those for the perfectly reflecting one are compared. Differences between the two are found to be significant near the surfaces. Frequency dependence of the rate, which is beyond the perfectly reflecting wall model, is investigated. It is shown that when the waveguide is located in between two atoms which have transition dipole moments parallel with the axis and transition frequency falling within the gap region, the RET is suppressed.

Fabrication and Characterization of Woodpile Waveguides for Microwave Injection in Ion Sources

In this article, we study the propagation of high-power RF fields along an air channel realized in a dielectric photonic crystal (PC) woodpile. The resulting hollow-core dielectric waveguide is suitable for high-power applications at 18 GHz and can be used as a dc-break for microwave ion sources. The infinite-periodic electromagnetic bandgap (EBG) waveguide structure has been truncated and coupled to a standard metallic rectangular waveguide operating in the fundamental TE10 mode. The fabricated waveguide structure exhibits a very low insertion loss (IL) of 0.5 dB over a transmission bandwidth of 260 MHz around the operating frequency of 18.25 GHz. A six-period structure has been manufactured, and the experimental characterization exhibits a very good agreement with the simulation results.

Numerical Study of Photonic-Crystal-Based Dielectric Accelerators

All-dielectric electromagnetic band gap (EBG) waveguides structures promise significant improvement of accelerating gradient of laser-driven acceleration with the potential to miniaturize the accelerator itself. In this work we study photonic crystal structures designed for acceleration of relativistic electrons. We explore the performance of the all-dielectric EBG accelerating structures thanks to full wave electromagnetic simulations of couplers and accelerating waveguides. The characteristic interaction impedance, accelerating gradient and all the key parameters that are typically used to characterize linear accelerators are evaluated and used to compare the properties of the accelerating mode field distribution in different geometries.

Additive manufacturing of resonant fluidic sensors based on photonic bandgap waveguides for terahertz applications.

A hollow-core Bragg waveguide-based resonant fluidic sensor operating in the terahertz frequency band is studied. A fused deposition modeling 3D printing technique with a Polylactic Acid filament is employed to fabricate the sensor where the liquid analyte is flowing in the microfluidic channel integrated into the waveguide cladding. The fluidic channel supports a resonant defect state which is probed spectrally using the core-guided mode of the Bragg waveguide. Continuous-wave terahertz spectroscopy is used to characterize the fluidic sensor. The measured signal amplitude shows a dip in the transmission spectrum, while the measured phase shows a sharp change in the vicinity of the anticrossing frequency whose spectral position depends strongly on the real part of the analyte refractive index. The sensor spectral response is further optimized by tailoring the waveguide length and position of the defect layer. Consistent with the results of numerical modeling, the measured sensor sensitivity is ~110 GHz/RIU, while the sensor resolution ~0.0045 RIU is limited by the parasitic standing waves in the spectrometer cavity. We believe that the proposed fluidic sensor opens new opportunities in applied chemical and biological sensing as it offers a non-contact measurement technique for monitoring refractive index changes in flowing liquids.

1-D Periodic Lattice Sums for Complex and Leaky Waves in 2-D Structures Using Higher Order Ewald Formulation

A very efficient and accurate method is proposed to evaluate the lattice sums (LSs) for the analysis of leaky waves in 2-D periodic waveguides. The LSs are the series involving Hankel functions of arbitrary order, which are not convergent for complex wavenumbers. It is shown that by extending Ewald representations to higher order Hankel functions, the LSs can be expressed in terms of spatial and spectral series, granting Gaussian convergence even in the case of complex and leaky waves. The method allows for the appropriate choice of the spectral determination for each space harmonic of a given LS coefficient, thus permitting one to obtain modal solutions that may correspond to physical and nonphysical leaky-wave phenomena. First, the proposed LS calculation is exploited in the evaluation of the free-space 1-D periodic Green’s function for 2-D structures. Then, the same procedure for the LSs is implemented in a cylindrical harmonic expansion method, based on the transition-matrix and the generalized reflection-matrix approach, for the full-wave analysis of leaky modes in 2-D electromagnetic band-gap waveguides formed by layered arrays of cylindrical inclusions. The presented LS formalism is numerically slim, very fast, and thus well suited for the analysis of a significant class of lossy periodic waveguides and leaky-wave antennas.

A Novel Multifunctional EBG-Based Coupled-Line-Defect Directional Coupler Based on Layered Dielectric Substrates

In this paper, a novel multifunctional coupler based on line-defect layered electromagnetic bandgap (EBG) waveguides is proposed and studied. Extensive full-wave simulations are used to establish the critical nature of the coupling region for the realization of different functionalities of the coupler. Changing the separation between the rings or orientation of the rings in the coupling and/or channel regions leads to very interesting and unique coupling mechanisms, such as forward-wave, through-wave, and/or backward-wave quasi-0- and 3-dB couplers that distinguish the proposed topology from conventional proximity directional couplers. In the final analysis, one can switch between configurations by changing the orientation of the rings in the coupling region. These configurations with coplanar-slot-line feeding structures are fabricated and tested at X-band for demonstration purposes. Measurement results validated the design procedure and confirmed the general trends in simulations. The proposed EBG coupler is promising for beamforming matrix and antenna array feeding networks.

Manipulation of negative-index collimation beam using band-gap guidance

We manipulate the source distance, emission position and number of negative-index collimation beam in a two-dimensional hybrid sonic crystal by using band-gap waveguide to control the flow of acoustic waves from a point source. The desired beam manipulations can be achieved at many different frequencies by suitably selecting the first order resonant mode of two crystal components and the waveguide structures. These results have potential applications in acoustic mutifunctional directional emission and acoustic integrated circuits. The proposed approach is also applicable for the similar manipulations of other types of acoustic collimation beams.

Electromagnetic band gap waveguide and bends substrate integrated waveguide

AbstractA planar waveguide and a rounded bend is proposed, designed, and implemented through a hybrid structure of substrate integrated waveguide (SIW) and electromagnetic bandgap (EBG) material. In order to design the EBG waveguide, a square lattice of air holes situated between two metal plates is used. The SIW line and bend are inserted on EBG waveguide to enhance performance. These devices were fabricated and measured. The experimental results show a homogeneous agreement with the simulation. The combination EBG‐SIW covers almost the whole EBG bandwidth of 6 GHz (17%) around 35 GHz. The proposed hybrid integration technique presents a competitive candidate for the development of millimeter‐wave circuits and systems.

Single-polarization hollow-core square photonic bandgap waveguide

Materials with a periodic structure have photonic bandgaps (PBGs), in which light can not be guided within certain wavelength ranges; thus light can be confined within a low-index region by the bandgap effect. In this paper, rectangular-shaped hollow waveguides having waveguide-walls (claddings) using the PBG have been discussed. The design principle for HE modes of hollow-core rectangular PBG waveguides with a Bragg cladding consisting of alternating high- and low-index layers, based on a 1D periodic multilayer approximation for the Bragg cladding, is established and then a novel single-polarization hollow-core square PBG waveguide using the bandgap difference between two polarized waves is proposed. Our results demonstrated that a single-polarization guiding can be achieved by using the square Bragg cladding structure with different layer thickness ratios in the mutually orthogonal directions and the transmission loss of the guided mode in a designed hollow-core square PBG waveguide is numerically estimated to be 0.04 dB/cm.

Gyro-TWT Using a Metal PBG Waveguide as Its RF Circuit—Part II: PIC Simulation and Parametric Analysis

In this paper, 3-D electromagnetic particle-in-cell (PIC) simulation of gyro-TWT amplifier using a metal photonic bandgap (PBG) waveguide as its RF interaction circuit is presented. A commercial finite integration-based PIC simulation code CST Particle Studio has been used to study the beam-wave interaction mechanism. The mode selectivity of a PBG waveguide has been investigated in the absence of an electron beam, so as to obtain the single-mode operation in a gyro-TWT. The simulated PBG gyro-TWT produced a stable RF output power of ~90 kW at 35 GHz for a 72-keV, 10-A annular electron beam with a velocity ratio of 1.05. The instantaneous bandwidth has been obtained as ~14% with respect to the operating frequency. Furthermore, the performance of the simulated PBG gyro-TWT has also been investigated through the parametric variation of the velocity spread, beam voltage, beam current, axial magnetic field, beam pitch factor, and the RF input power to validate the conceptual design of the device.

Gyro-TWT Using a Metal PBG Waveguide as Its RF Circuit—Part I: Analysis and Design

A gyro-TWT using a metal photonic bandgap (PBG) waveguide as its RF circuit has been analyzed using a self-consistent nonlinear analysis. The analysis focuses on single-mode operation of gyro-TWT by eliminating the mode competition problem existing in an overmoded structure using a mode-selective PBG circuit. A Ka-band, TE01 waveguide mode PBG gyro-TWT has been designed, and analytical results have been computed to demonstrate the beam–wave interaction mechanism of the device. The nonlinear analysis predicted $\sim 91$ -kW RF output power with an electronic efficiency of $\sim 13$ % and the saturated gain of $\sim 40$ dB from this device.

Coupling power into accelerating mode of a three-dimensional silicon woodpile photonic band-gap waveguide

Silicon woodpile photonic crystals provide a base structure with which to build a three-dimensional dielectric waveguide system for high-gradient laser-driven acceleration. To realize an on-chip woodpile laser accelerator, a key component is the power coupler to deliver laser power to the fundamental accelerating mode. The woodpile waveguide is periodically loaded in the longitudinal direction; therefore simple cross-sectional mode profile matching is not sufficient to launch the accelerating mode appropriately and will result in significant scattering loss. Several traveling-wave coupler design schemes developed for multicell radio frequency cavity accelerators can be adapted to the woodpile accelerator coupler design. This paper presents design procedures and results using these methods. We present simulations indicating near 100% power transmission between the transverse electric mode of a silicon-guide side coupler and the transverse--magnetic-like accelerating mode of a woodpile waveguide. The coupler launches a full traveling-wave propagation of the accelerating mode, which maintains its propagation quality over long waveguide structures, and provides better tolerance on the structure fabrication uncertainty and material breakdown than standing-wave coupling.

Approximate analysis of planar photonic bandgap waveguides: a simple semi-analytical method

A semi-analytical approximate method, Vopt, is applied to a planar photonic bandgap (PBG) waveguide and a coupler configuration. The variational process of the Vopt method presents simple effective index analysis of the complex two dimensional (2-D) structures. The Vopt method expresses the refractive index profile of the 2-D structure as two 1-D refractive index profiles and obtains the optimized indices for the two structures iteratively. The Vopt method separates the planar PBG waveguide into an effective multilayer waveguide confining optical field in the lateral direction and a 1-D Bragg reflector that gives characteristic reflection/transmission spectra. The results obtained by the Vopt method show good agreement with the numerical results of the finite difference time domain analysis. The present analysis is helpful in understanding the optical properties of such complex waveguides and can be used as starting approximation for optimizing the structures for various applications.

Novel All-Optical Liquid Photonic Crystal Router

A novel design of an easily and fully integrated terabit per second (Tbit/s) optical router is presented and analyzed using the finite difference time domain method. The proposed router consists of three photonic bandgap (PBG) waveguides with two nematic liquid crystal (NLC) layers. The suggested device can be used to divert the light beam to one of the three photonic crystal waveguides based on the biasing states of the two NLC layers. In this way, there are three different modes of operation where each one is used for routing data to the required direction. The suggested device offers crosstalk of 19 dB. In addition, the reported structure opens up the revenue for building multi-port optical routers through the use of a number of appropriately positioned NLC layers within the platform of PBG structure.

Fast analysis for electromagnetic band gap waveguides using compact finite-difference-time-domain method

A fast analysis method, cell modified compact finite-difference time-domain method (CMC-FDTD), is presented to analyze the performance of electromagnetic band gap waveguides. The method calculates band diagrams in orthogonal coordinate system by translating nonorthogonal lattice to orthogonal lattice. It has highly stability for calculating dielectric and metallic material, either TE or TM mode, and reduces the requirement for memory. The comparisons are made among two numerical results and experimental one to validate the method.