Circular Waveguide Research Articles

Topological sensing with photonic arrays of resonant circular waveguides

We propose that a photonic array of resonant circular dielectric waveguides with subwavelength grating can be designed as a robust and sensitive topological chemical sensor. The device can detect trace amounts of a given chemical species through photonic edge modes that are impervious to most sources of disorder. We perform a simulation in the mid-infrared that accounts for the absorption loss introduced by chemical molecules in contact with a strongly coupled photonic lattice of resonators. Due to the topological nature of the device, its chemical sensitivity scales linearly with the system size and can reach parts-per-billion range at the millimeter scale. Our findings suggest that topological chemical sensors could empower the development of novel on-chip integrated photonic sensing technologies.

Design of a 94 GHz Millimeter-Wave Four-Way Power Combiner Based on Circular Waveguide Structure

This paper introduces a four-way power combiner operating in the 94 GHz millimeter-wave based on spatial power combining technology. The four millimeter-waves with Gaussian beams are combined in the waveguide, increasing the output power. The combiner is composed of five circular waveguides connected by four long and narrow coupling slots. Four sub-waveguides are separately connected to four input ports and one main waveguide is connected to a common output port. The TE11-mode is used as the input mode, which has two vertical and horizontal polarization directions. Four sub-waveguides are respectively input corresponding to polarization directions TE11-wave with Gaussian beams. The power of TE11-wave is transmitted to the main waveguide by the coupling slots, combined in the main waveguide, and output with the common port. We analyze the combiner and verify the availability of the design structure by numerical stimulation with CST MWS (Microwave Studio) software. The power-combining efficiency can be over 97%, and the output beams remain Gaussian beams with nearly fourfold increased power. The proposed model provides technological approaches for power combiner application in millimeter-wave.

Etched circular waveguide-based on-chip silicon mode-order converters

Mode-order converters act as the vital higher-order mode sources for on-chip multimode applications. Here, we propose a silicon-based mode-order conversion scheme by leveraging etching slots on the circular waveguide. Through designing and optimizing the etching slots and circular waveguide, the mode-order conversion from input TE0 mode to output TE1 mode has been achieved with the mode conversion efficiency of 99.1%, modal crosstalk of -25.7dB, and insertion loss of 0.21 dB, respectively, in a mode conversion size of ∼8µm×8µm (TE0-TE1). For the device fabrication, only one-step lithography and etching processes will be required, and the requirements of slot width (600 nm) and slot gap (1.49 µm) would be very beneficial for the device fabrication. Moreover, the proposed device scheme can also help achieve other higher-order mode conversions, such TE0-TE2 and TE0-TE3, where their structural parameters and performances are also analyzed. With these features of relatively good device performance, compact size, easy fabrication, and functional scalability, we believe the proposed scheme would be applied in the on-chip multimode applications to enhance their transmission capacities.

РОЗРОБКА КОНСТРУКЦІЇ ПОЛЯРИЗАТОРА ДЛЯ РОБОТИ В КА-ДІАПАЗОНІ

The problems of polarizer`s construction over the basis of the circular waveguide for a work in Ka – range are highlighted in the article. The purpose of the article is to establish the possibility of using the proposed design for the construction of high-tech Ka-band polarizers and to prove the correctness of analytical expressions for determining the structural dimensions by experimentally obtained characteristics. The analysis of the current decisions from the point of view of construction and technology is held. On the conclusion had been drawn more technological polarizer`s construction with the calculation of the main constructive sizes is proposed. Theoretical principles of construction and calculation of structural dimensions of the C and Ku ranges polarizers’ phase-shifting sections are covered in detail in the works of modern researchers and tested on real devices . However, while constructing AFT elements designed to operate in higher frequency operating bands, such as the Ka – band (20/30 GHz), there are certain difficulties, the solution of which continues. In order to check the proposed decision experimental model of polarizer was made and investigation of the main characteristics corroborating the right theoretical assumption was held. For a practical study of the proposed design, a mock-up of a polarizer based on a round waveguide with an inner diameter of 11 millimeters was made. In the prototype, the rod structure was implemented in the form of five pairs of adjusting screws with a diameter of one millimeter. The final length of the polarizing plate, taking into account the smooth transitions designed to align the plate with the waveguide, was defined as the sum of the lengths of its regular part and one smooth transition multiplied by 0.9. The experimentally obtained characteristics confirm the possibility of using the proposed design for the construction of high-tech Ka-band polarizers, and the correctness of analytical expressions for the determining the structural dimensions. A further development of the proposed solution may be the analysis and finding the necessary analytical relationships between the structural dimensions of the rod and dielectric structures in order to expand the operating range of the polarizer.

Propagation of electromagnetic waves in graphene-wrapped cylindrical waveguides filled with magnetized plasma

This manuscript investigates a generalized problem for electromagnetic wave propagation in graphene-wrapped circular waveguides filled with magnetized plasma. Kubo formulism is used for graphene conductivity and impedance boundary conditions are applied to solve the numerical problem. The behavior of the dispersion curves is examined and evaluated computationally. The presented results demonstrate that graphene conductivity has a strong influence on electromagnetic wave propagation for the proposed design. The normalized propagation constant and attenuation phase constant are studied under different values for the operating frequency, radius, plasma frequency, and cyclotron frequency. The presented results may find applications in communication at THz frequency regime, optical sensing and cancer treatment at the specific plasma frequency using magnetized plasma.

Investigation of Oversized Circular Waveguides With Deformed Cross Section for Gradual TE01 Mode Bends

An optimum approach for designing a TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> mode oversized waveguide bend is proposed based on angular-deformed circular waveguide. Due to the deformation of the circular waveguide cross section, the degeneracy of the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> mode and the TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> mode is removed, and the mode conversion inside the waveguide bend is weakened. Characterizations of the angular-deformed circular waveguide with different deformation and its influence on the mode spectrum, the transmission loss, and the power capacity are investigated. Based on the analysis results and the coupling-wave theory, a Ka-band broadband oversized deformed circular waveguide bend with the propagating TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> mode is designed, fabricated, and measured. A good agreement between the calculation results and the S-parameter measurement of a prototype is achieved. The transmission efficiency is over 95% in the frequency range of 26.5-35.9 GHz (the relative band is over 30%). The near-field test results further demonstrate the high output purity of the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> mode in the working frequency band.

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.

Aluminum coated hollow-core fiber for single mode operation in the terahertz spectrum

A hollow-core circular waveguide with a hyperbolic metamaterial cladding is proposed for single-mode operation in the terahertz spectrum. The strong anisotropy of the cladding is achieved by incorporating an aluminum coating on the inner wall of the cladding air holes. It is evident from the numerical study that the proposed model offers a single-mode window covering from 0.22 THz to 0.34 THz. The radially polarized transverse magnetic TM1 mode offers the lowest loss of 0.23 dB/cm at 0.3 THz within the single-mode window. The proposed fiber also offers around 96.8% of the total power in its wavelength scale fiber core. Low bending loss around 0.28 dB/cm with a sharp bend of 5.0 cm makes this fiber a potential choice for a densely integrated terahertz system.

A Linear Microwave Plasma Source Using a Circular Waveguide Filled with a Relatively High-Permittivity Dielectric: Comparison with a Conventional Quasi-Coaxial Line Waveguide

For a conventional linear microwave plasma source (LMPS) with a quasi-coaxial line transverse electromagnetic (TEM) waveguide, a linearly extended plasma is sustained by the surface wave outside the tube. Due to the characteristics of the quasi-coaxial line MPS, it is easy to generate a uniform plasma with radially omnidirectional surfaces, but it is difficult to maximize the electron density in a curved selected region. For the purpose of concentrating the plasma density in the deposition area, a novel LMPS which is suitable for curved structure deposition has been developed and compared with the conventional LMPS. As the shape of a circular waveguide, it is filled with relatively high-permittivity dielectric instead of a quasi-coaxial line waveguide. Microwave power at 2.45 GHz is transferred to the plasma through the continuous cylindrical-slotted line antenna, and the radiated electric field in the radial direction is made almost parallel to the tangential plane of the window surface. This research includes the advanced 3D numerical analysis and compares the results with the experiment. It shows that the electron density in the deposition area is higher than that of the conventional quasi-coaxial line plasma MPS.

Dispersion Analysis of Twist-Symmetric Dielectric Waveguides

We propose a circular twist-symmetric dielectric waveguide that is polarization-selective. In the practical implementation of optical fibers, a selective circular polarization is more convenient than its linearly polarized counterpart where previous knowledge of the emitted polarization from the transmitter is unknown. The analysis of the waveguide was conducted with three methods: an eigenmode approach, simulation of a truncated structure, and the so-called multimodal transfer-matrix method (MMTMM). The presented simulations demonstrate that the operational band can be manipulated by tuning the parameters of the structure. Furthermore, the MMTMM allows for a direct and accurate calculation of the attenuation constant of the rejected circular polarization.

Deep reflector prime focus feed for space communication

In this paper, design of a prime-focus feed for a deep reflector, Earth–Moon–Earth space communication system is described. The feed is based on a circular waveguide equipped with two chokes in order to minimise sidelobes and illuminate the deep dish with a high aperture efficiency of 70 % . Based on sun noise measurements, it is estimated that the antenna system presents very low noise temperature values, below 30 K, making this feed favourable for space communication.

Излучатели скалярных мод круглого волновода.

The frequency characteristics of the radiators of ТМ01 and ТЕ01modes of a circular metal waveguide are investigated. Radiators in the form of an open end of a circular waveguide with a stepped cut, including those with a cylindrical mirror, as well as an open end of a waveguide with an inhomogeneous anisotropic dielectric plate are considered. Numerical simulation and optimization of parameters were carried out using finite element and finite differences in time domain methods.

Wideband Antenna Arrays Based on a Circular Waveguide with the H 01 Mode

Wideband Antenna Arrays Based on a Circular Waveguide with the H 01 Mode

Cutoff Wavenumbers of Multilayered Gyrotropic Circular Waveguides

A coupled-field volume integral equation (CFVIE) method is developed for the calculation of the normalized cutoff wavenumbers of circular metallic walled waveguides having concentric continuously varying highly inhomogeneous gyrotropic (i.e., gyroelectric and gyromagnetic) infill. The normalized cutoff wavenumbers are obtained as the roots of a determinantal equation formed by solving the CFVIEs using the cylindrical Dini series expansion (CDSE) method where the unknown fields inside the waveguide are expanded by entire domain orthogonal Dini-type vectorial basis functions. To account for the electric boundary condition (BC) on waveguide's circular perfect electric conducting (PEC) surface, two modified 2-D tensorial Green's functions (GFs), expanded in cylindrical vector wave functions (CVWFs), are employed in the kernels of the CFVIEs. These modified 2-D tensorial GFs are constructed by enforcing, on their dyadic form, the satisfaction of the electric BC. The CDSE, along with the modified 2-D tensorial GFs, allow for the analytical integration of the volumetric-type integrals and the reduction of the CFVIEs to a set of algebraic equations. We exhaustively demonstrate the validity of the CFVIE-CDSE by a series of comparisons on the normalized cutoff wavenumbers: we first construct the solutions for obtaining the normalized cutoff wavenumbers in homogeneous gyrotropic waveguides by the separation of variables method (SVM), and second, we employ HFSS commercial software for two-layered isotropic and three-layered gyroelectric loaded waveguides. We characterize the type of modes, i.e., TE/TM or hybrid HE/EH, for each configuration presented, and discuss the efficiency of the CFVIE-CDSE method.

Bumbung Gelombang Lingkaran Susun Untuk Aplikasi RF Energy Harvesting pada GSM 1800 MHz

Mobile device for mobile communication, especially GSM communication is one of the most important thing in our daily activities. A massive mobilty and connectivity to make sure everyone is connected to each other is necessary. In a same time, electrical power needs will increase in order to support the increasingly rapid exchange of information. In this research shown the result of circular waveguide array mode TM01 measurement for RF energy harvesting application at frequency GSM 1800 MHz – 1900 MHz. Design of circular waveguide array through parameter study developed an optimum result, return loss at frequency centre 1850 MHz. Realization of this design is measured in unechoic chamber for minimizing a reflected wave from the ambient, so it called an ideal area for waveguide parameter measurement. The measurement results return loss at freuquency 1840 MHz

On the acoustic trapped modes and their symmetry properties in a circular cylindrical waveguide with a cavity

On the acoustic trapped modes and their symmetry properties in a circular cylindrical waveguide with a cavity

Additive manufacturing of a compact Ku-band orthomode transducer

This work presents a compact ortho-mode transducer (OMT) built by additive manufacturing in a single-block, reducing the number of parts and flanges and improving the losses and power handling capability. The single-block approach also reduces potential passive intermodulation issues since the number of interfaces between parts is minimized. The presented OMT is based on the T-junction topology, with a short-circuited common circular waveguide where the two rectangular waveguides ports are attached. Both ports are arranged in opposite direction to maintain a symmetry plane for the whole structure in order to obtain a high isolation. Specific matching elements are introduced for each polarization to route the orthogonal modes to the common waveguide. The device is built by Selective Laser Melting (SLM), which imposes a set of specific mechanical restrictions to the 3D model of the OMT. The proposed design incorporates those restrictions, simplifying the geometry of the OMT as much as possible (especially the routing elements) to simplify the manufacturing. After this process, the experimental results show an OMT working in the band from 13.4 to 15.6 GHz (15.2%) with a return loss level higher than 20 dB for both polarizations, insertion loss lower than 0.18 dB and isolation between polarizations better than 45 dB. The OMT has also been tested in radiation connected to a reference horn, measuring a cross-polarization lower than -45 dB. This experimental performance shows that the proposed combination of compact design with single-block SLM manufacturing provides tested results similar to those obtained by high-accuracy milling or spark erosion suitable for satellite applications.

Возбудители скалярных мод круглого волновода.

Various options for constructing broadband exciters ТМ01and ТЕ01 modes of a circular metal waveguide have been proposed and investigated. Electrodynamic simulation and optimization of parameters were carried out using finite element and finite differences in time domain methods.

Femtosecond laser micromachining of an optofluidics-based monolithic whispering-gallery mode resonator coupled to a suspended waveguide

A monolithic lab-on-a-chip fabricated by femtosecond laser micromachining capable of label-free biosensing is reported. The device is entirely made of fused silica, and consists of a microdisk resonator integrated inside a microfluidic channel. Whispering gallery modes are excited by the evanescent field of a circular suspended waveguide, also incorporated within the channel. Thermal annealing is performed to decrease the surface roughness of the microstructures to a nanometric scale, thereby reducing intrinsic losses and maximizing the Q-factor. Further, thermally-induced morphing is used to position, with submicrometric precision, the suspended waveguide tangent to the microresonator to enhance the spatial overlap between the evanescent field of both optical modes. With this fabrication method and geometry, the alignment between the waveguide and the resonator is robust and guaranteed at all instances. A maximum sensitivity of 121.5 nm/RIU was obtained at a refractive index of 1.363, whereas near the refractive index range of water-based solutions the sensitivity is 40 nm/RIU. A high Q-factor of 105 is kept throughout the entire measurement range.

Calculations on Mode Eigenvalues in a Corrugated Waveguide with Varying Diameter and Corrugation Depth

The present paper addresses numerical calculations on the eigenvalues of hybrid modes in corrugated circular waveguides with varying diameter and corrugation depth. Such calculations are essential for the numerical optimization of advanced mode converters and diameter tapers for future low-loss high-power microwave applications, like broadband high-power radar sensors for space debris observation in low earth orbit (LEO). Corresponding mode converters and diameter tapers may be synthesized based on coupled mode theory. Of particular importance here is the ability to consider varying mode eigenvalues along the perturbed waveguide. The procedure presented here is able to consider arbitrary variations of the corrugation depth as well as the waveguide diameter and therefore is highly flexible. The required computational effort is low. Limitations of the method are discussed.