Dielectric Rod Research Articles

A 3‐D ‐printed Luneburg lens antenna with consistent multibeams based on quasi‐pyramid structure

A wide-scanning dual-polarized Luneburg lens antenna based on the quasi-pyramid structure is proposed. To achieve beam consistency, 18 identical quasi-pyramid sections are employed to approximate a spherical lens antenna, and each section is divided into 12 layers. The 6-stepped gradient permittivity index is achieved by the diced ring-type periodic unit cells in accordance with the Effective Medium Theory. Each quasi-pyramid is incorporated with the same connecting structure to form an integrity. And a dielectric rod is penetrated parallelly to the center axis of the lens, thus improving the robustness of the overall structure. The radius of the whole lens is merely 0.88λ0. The spherical Luneberg lens antenna is fabricated and measured, with an impedance bandwidth of 45.5%, a measured peak gain of 15.4/15.1 dBi and a cross-polarization level of higher than 17/17.5 dB. Placing the feed antenna at different locations during the measurement, results attest that those beams possess an excellent consistency. The multibeams are able to achieve an ultra-wide beam coverage of 165°, promising it a serviceable candidate for mobile communication base stations and wireless networking.

Chaotic Analysis as a Tool for Sensing Long-Term Degradation of High Voltage Fibre Reinforced Plastic Core Used in Composite Insulators

The leakage current which flows on the surface of dielectric rods under high voltage involves a series of events which include partial arcing, discharges and corona, these phenomenon are highly non-linear. These sequence of events render the leakage current signal to be very much chaotic. In the present work, the process of delay-embedding is employed to study the phase-portrait of the signal, further Lyapunov Exponents are computed to characterize the chaotic nature of the leakage current. The main focus of the study is intended to understand the chaotic nature of leakage current behaviour over the ageing period and to determine the degree of degradation on the dielectric rod surface.

A promising Ka band leaky-wave antenna based on a periodic structure of non-identical irregularities

This paper presents a new periodic grooved dielectric leaky-wave antenna with non-identical irregularities for an extremely high-frequency range capable of performing efficiently in the Ka band through a stable gain, a decrease in the level of the side lobes, and the achievement of a narrower main lobe beam. It consists of a dielectric waveguide antenna placed inside a channelled rectangular metallic waveguide to improve performance. A dielectric rod was used to overcome the losses related to the propagation of electromagnetic waves in metal conductors. A grooved dielectric of a 21-element linear array is used to propose a simple approach for the synthesis of such antennas based on a modified energy method and is fed by a standard waveguide. It was designed and simulated at 37.2 GHz for satellite, 5G antenna, and radar applications. The major novelty of this study is the ability to control the direction of the main lobe through non-identical irregularities in geometric parameters such as the width, height, and distance between each element. Radiation techniques have been extensively studied using simulations. A performance antenna with radiation efficiency of 99.35%, gain of 22 dBi, width of radiation pattern of 3.2 ^{circ }, and side lobe level (SLL) of {-} 18.3 dB has been achieved.

Reconfigurable double-band valley topological edge states through rotating the dielectric rod with holes in triangular lattice

The valley topological edge states (VTESs) have become a new research hotspot in topological photonics because of its flexibility and diversity. The major challenge for them comes from the dynamical modulation and the weak ability of direction-locked. In this paper, a triangular lattice made of rotatable dielectric rods with three circular holes is designed. Through the rotation of rod, the lifting of the valley points leads to double nontrivial bandgaps and double-band VTESs. The spin-locked excitation of the VTESs, is dependent on whether the nontrivial bandgaps is closed by the VTESs. The reconfigurable VTESs have been achieved with the idea of programmable coding, which provides potential applications in on-chip photon routing. • A triangular lattice made of rotatable dielectric rods with three circular holes is constructed. • The double-band valley topological edge states are achieved. • The valley topological edge states are reconfigurable with the idea of programmable coding.

Stable phase‐centre horn antenna using 3D printed dielectric rod for aperture efficiency improvement of space‐fed antennas

The design strategy to stabilise the phase centre (PC) of the conventional horn antenna using a shaped dielectric rod is presented for aperture efficiency improvement of space-fed antennas. In most practical horn antennas, PC location has significant variations with frequency leading to phase error loss and aperture efficiency reduction over the bandwidth of interest. To overcome this drawback, based on physical reasoning, shaped dielectric rods with appropriate excitation mode are designed and placed on the aperture of conventional rectangular and conical horn antennas. The simulation results show that using a shaped dielectric rod inside the horn antenna leads to a decrease in phase-centre variations versus frequency without disturbing the radiation pattern and reflection coefficient. To investigate the performance, a conical corrugated horn antenna loaded by a conical tapered dielectric rod is used as a feed of the transmitarray antenna. Using a shaped dielectric rod fabricated by 3D printing technology, the PC variations of the proposed horn decrease from 1.06 λ to 0.08 λ over the X-band (λ at 8 GHz). The measurement of the fabricated transmitarray antenna shows an improvement of maximum aperture efficiency from 55% to 64.7% at 10 GHz. The aperture efficiency bandwidth above 50% level is also increased from 1 to 2.2 GHz.

Irregularities in a metal-dielectric shielded waveguide with low losses for the frequency range 90–100 GHz

This article is devoted to the study of waveguide metal-dielectric structures in the frequency range of 90100 GHz with low losses up to 0,05 dB/m. The paper considers the effect of sharp irregularities on a section of a regular line, which leads to a change in the parameters of a metal-dielectric closed waveguide path. In practice, irregularities have a negative impact on the transfer characteristic of the waveguide. Therefore, the types of irregularities often found in modern devices were investigated. As a result of the analysis of the losses caused by the rupture of the dielectric rod and the rotation of the polarization plane, the approximated characteristics of the transfer function of the waveguide line with irregularity were obtained.

Multiple topological transitions and topological edge states of triple-site honeycomb lattice photonic crystals

We propose a two-dimensional (2D) triple-site honeycomb lattice (TSHL) photonic crystal (PC) by rotating the three dielectric rods six times, forming unit cell, and then arraying the unit cells in the triangular lattice. The TSHL PC structure can achieve topological phase transitions in three ways, which are changing the position or size of the rods, and rotating the rods. By calculating the band structure under different parameters, the law of topological phase transition for TSHL PC is analyzed. The topological edge state can be adjusted by changing the rotation angle of the dielectric rods. Based on this, a frequency-selective beam splitter is designed. Compared with previous studies, this flexible topological system shows more abundant physical phenomena, enriches the implementation of topological photonics , and promotes the research of topological edge states and the development of topological insulators in practical applications. • We propose a two-dimensional triple-site honeycomb lattice photonic crystal, which has the high degrees of freedom. • The triple-site honeycomb lattice unit cell can achieve topological phase transitions in three ways, which are changing the position or size of the cylinders, and rotating the cylinders. • We design a frequency-selective beam splitter, by changing the rotation angle of the dielectric rods.

Design and optimization of nanooptical couplers based on photonic crystals involving dielectric rods of varying lengths

This study presents design and optimization of compact and efficient nanooptical couplers involving photonic crystals. Nanooptical couplers that have single and double input ports are designed to obtain efficient transmission of electromagnetic waves in desired directions. In addition, these nanooptical couplers are cascaded by adding one after another to realize electromagnetic transmission systems. In the design and optimization of all these nanooptical couplers, the multilevel fast multipole algorithm, which is an efficient full-wave solution method, is used to perform electromagnetic analyses and simulations. A heuristic optimization method based on genetic algorithms is employed to obtain effective designs that provide the highest efficiency values. Two types of optimization strategies are applied using nanorods with a fixed length and using nanorods with varying lengths. This way, photonic crystals consisting of irregular arrays of both identical and nonidentical dielectric elements are designed for the realization of nanooptical couplers. The designs and their numerical results show that it is possible to design and further improve efficient nanooptical couplers with simple and compact geometries based on the principles of photonic crystals. Using relatively simple geometries and a single material, the designed nanooptical couplers are more preferable than the available designs in the literature.

Radial bound states in the continuum for polarization-invariant nanophotonics

All-dielectric nanophotonics underpinned by the physics of bound states in the continuum (BICs) have demonstrated breakthrough applications in nanoscale light manipulation, frequency conversion and optical sensing. Leading BIC implementations range from isolated nanoantennas with localized electromagnetic fields to symmetry-protected metasurfaces with controllable resonance quality (Q) factors. However, they either require structured light illumination with complex beam-shaping optics or large, fabrication-intense arrays of polarization-sensitive unit cells, hindering tailored nanophotonic applications and on-chip integration. Here, we introduce radial quasi-bound states in the continuum (radial BICs) as a new class of radially distributed electromagnetic modes controlled by structural asymmetry in a ring of dielectric rod pair resonators. The radial BIC platform provides polarization-invariant and tunable high-Q resonances with strongly enhanced near fields in an ultracompact footprint as low as 2 µm2. We demonstrate radial BIC realizations in the visible for sensitive biomolecular detection and enhanced second-harmonic generation from monolayers of transition metal dichalcogenides, opening new perspectives for compact, spectrally selective, and polarization-invariant metadevices for multi-functional light-matter coupling, multiplexed sensing, and high-density on-chip photonics.

Design of 2D photonic crystal biosensor to detect blood components

Photonic crystals are periodic structures made of insulators. They are the best option to design biosensors. In this paper, a photonic crystal biosensor containing insulation rods in the air was designed and simulated. This biosensor was used as a photonic crystal circular nano-ring between the internal and external waveguides. At the end of the internal waveguide, a defect exists to create an increase in the coupling distance. This causes the quality factor and resonant wavelength displacement to increase. The purpose of designing this sensor is to check blood ingredients. After connecting to a measuring rod, this sensor shows different refractive indices. Another important characteristic of the proposed structure is that most radiuses of dielectric rods are identical. This causes the sensor construction to be easy. The plane-wave expansion method is utilized to calculate the band structure. The results show that a photonic band gap with a wavelength from 1.26 to 1.92 $$\mathrm{\mu m}$$ is created at this distance where no wavelength can spread. In this work, the Q-factor, detection limit, figure of merit, and sensitivity of the proposed photonic crystal were recorded as 5166, 0.021RIU−1, 9.84 nm/RIU, and 2.94 nm/RIU.

Channel switch based on the transformation of two kinds of topological edge states

In this paper, we have constructed a compound triangular lattice in which the optical quantum spin Hall effects and quantum valley Hall effects can simultaneously occur. Through the rotation of the dielectric rods in the lattice, two complete photonic band gaps with nontrivial topology can be created, one of which is due to the band inversion associated with the pseudospin degree of freedom at point in the first Brillouin zone (BZ) and the other due to the gapping out of Dirac cones associated with the valley degree of freedom at K point in the first BZ. The transformation between the two kinds of topological edge states can be also achieved through the rotation of the dielectric rods. A four-channel structure model is proposed to demonstrate the transformation and to achieve the channel switch of the topological edge states.

Desktop laboratory of bound states in the continuum in metallic waveguide with dielectric cavities

A metallic waveguide with an integrated dielectric rod is equivalent to a periodic array of rods and readily allows to achieve bound states in the continuum, dependent on the position and orientation of the rod relative to the waveguide. This significantly facilitates experimental studies in comparison to the infinite arrays of cavities. However, the main advantage is related to material losses and structural fluctuations in long arrays of rods which quickly saturate the growth of the Q-factor with the number of rods in the periodic array in the GHz range, at least.

Deep Complex Convolutional Neural Networks for Subwavelength Microstructure Imaging

To take the advantages of a convolutional neural network (CNN), U-net, and a complex-valued CNN (complex-CNN), a new complex-valued U-net (CU-net) is proposed for deep learning (DL)-based methods to solve inverse scattering problem (ISP). With the proposed CU-net, the complex scattered data carrying rich information of object can be directly used for inversion without any preprocessing, which is very helpful for the accuracy improvement of the final result. To validate the performance of proposed method, a microstructure, consisting of a finite periodic set of circular cylindrical dielectric rods, is considered and detected for textural abnormalities, which contains the missing, flaw, and displacement of the rods. The distances between rods and diameters of rods are both subwavelength, well beyond the Rayleigh criterion, which causes this ISP extremely ill-posed. For comparison, both the conventional iterative method and DL-based method are used to solve this nonlinear problem. Numerical simulations demonstrate that the well-trained DL-based methods can successfully produce excellent results almost in real time and can greatly outperform the conventional iterative methods in terms of quality and efficiency.

Optimization of hexagonal boron-doped silicate photonic crystal fiber to obtain near zero flattened dispersion for nonlinear waves by finite difference method

The B2O3-doped silicate photonic crystal fiber (PCF) containing small core and dielectric rods built of lead silicate SF57 has been most intensively explored for diverse pump signals centered at a 0.65 µm, communication band. This type of doping has been carried out to diminish the upgraded refractive index of silica by a significant amount. This enhances special capabilities that lead to an outstanding potential to PCF for the profoundly intense field in the optical Kerr effect. In this study, the mode analysis has been done by solving a nonlinear wave equation for a Gaussian input beam using the finite difference method under analytical boundary conditions. Numerical results show that due to ultra-low changes in nonlinear behaviour, extremely small doping of B2O3 is needed to enable sustained confinement of a beam with flattened dispersion.

Low Profile Dielectric Rod Tuned Reconfigurable Band Pass Filters

A novel low profile mechanical tuning technique is introduced in this paper to change the center frequency of substrate integrated waveguide (SIW) based reconfigurable bandpass filters (BPF), by loading dielectric rods of different permittivity in resonant cavities and coupling apertures. The technique is simple, cost-effective (rods are machined from conventional substrates), and the same physical structure provides a wide frequency tuning. First, the tunability of center frequency of the SIW cavity resonator is theoretically explained and then estimated with the help of full-wave 3D EM simulator and electrical equivalent circuit. This concept is extended to the tuning of coupled resonator BPF loaded with dielectric rods followed by the analysis of maintaining constant bandwidth. Following the analysis technique, the tunability concept is studied for different arrangements of dielectric rods inside the SIW BPFs. The characteristics of the fabricated filters are experimentally validated. It is shown that center frequency tunability can be achieved by simply varying the permittivity of all the dielectric rods simultaneously. The proposed technique is further extended for obtaining wider tunability and constant bandwidth by using dielectric rods of dissimilar permittivities from a look up table. These designs demonstrate a simple and cost-effective passive tuning technique achieving high Q-factors in the range of 102–210.5, lowest insertion loss <2dB above 10 GHz, and wide tuning bandwidth in X-band. The reconfigurable filters are developed for advanced high-speed, long-distance, and fixed wireless connectivity in a rural area at a low cost. The technique can also be used for temperature compensation and overcoming fabrication uncertainty.

A Broadband Circularly Polarized Endfire Loop Antenna for Millimeter-Wave Applications

In this letter, a broadband circularly polarized (CP) endfire loop antenna is proposed for millimeter-wave (mmW) applications. The loop consists of two arms constructed by printed strips with straight edge connections implemented by metalized via-holes, and is fed by substrate integrated waveguide differentially. The quasi-traveling wave currents flowing along strips and via-holes, which generate horizontal and vertical polarizations, respectively. By using the offset strip, comparable amplitudes of two polarizations are realized to achieve a good CP radiation. Furthermore, a dielectric rod is applied for higher gain. The experimental prototype reported that the impedance bandwidth of 28.3% from 23.75 to 31.4 GHz, the 3 dB axial-ratio bandwidth of 25% from 24.25 to 31 GHz, and the gain no less than 9 dBic for endfire radiation. In addition, the whole antenna is curved on one substrate with a low profile of 0.14 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> (λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is the free-space wavelength at 27 GHz). Thus, the antenna is attractive for fifth-generation (5G) applications in mmW integrated circuits.

Broadband High-Gain SIW Horn Antenna Loaded With Tapered Multistrip Transition and Dielectric Slab for mm-Wave Application

A substrate integrated waveguide (SIW) H-plane horn antenna loaded with tapered multistrip transition and dielectric slab is proposed for broadband high-gain operation. The broadband characteristic of the proposed antenna is obtained by loading a tapered multistrip transition. The theory of coupled resonator is introduced to reveal the mechanism of bandwidth enhancement. On the other hand, a dielectric slab is used to enhance the gain of the proposed antenna. The optimal length of this dielectric slab is determined based on the design principles of a dielectric rod with maximum gain. Besides, the tapered multistrip transition also contributes to the gain improvement by suppressing the feed radiation and prompting the transverse expansion of the surface wave. To verify the design theory and concept, a prototype operating at the K- and Ka-bands is fabricated and measured. The measurement results show that the impedance bandwidth of the proposed antenna is from 20.6 to 38.4 GHz (60%). Within the operating band, a peak realized gain of 19.1 dBi and excellent endfire radiation patterns with low cross polarization (<−30 dB) and high front-to-back ratio (FBR >20 dB) are achieved simultaneously. With its broad bandwidth, high gain, low cross polarization, and high FBR, the proposed antenna is promising for various millimeter-wave applications.

Bandgap structure and density of states of two-dimensional magnetized plasma photonic crystals

In this paper, we study dispersion properties in a two-dimensional magnetized plasma photonic crystal, based on the modified plane wave expansion method. Transverse electric polarization is considered. The influence of different factors such as external magnetic field, lattice constant, dielectric constants of background and central rod, and electron density of plasma in photonic bandgap structure and photonic bandgap map is studied. The photonic density of states is also demonstrated. Results show that a large magnetic field produces more band gaps in higher frequencies. The lattice constant is an important factor in controlling the bandgap structure and it can compensate low magnetic field effect. Using a larger dielectric constant in the background compared to the central dielectric rod leads to more and sharper band gaps in higher frequencies. Electron density of plasma plays an important role in tuning bandgap structure. There would be three or four band areas in the band structure and the band frequencies are larger than the cutoff frequency of plasma.

Design and simulation of high-quality factor all-optical demultiplexers based on a two-dimensional photonic crystal

The present study proposes a new type of wavelength division multiplexing as an optical demultiplexer with four, eight, and sixteen output channels. The proposed structure consists of a two-dimensional square array of dielectric rods. The wavelength selection is performed by two defect rods and one defect with a rectangular cross-section. The values of the parameters related to each defect are selected so that the resonant wavelength associated with each output channel is located in the third telecommunication window (1.55μm). It is observed that the proposed demultiplexers demonstrate a high transmission efficiency and low crosstalk. As it is wanted to see just one sharp wavelength at the output of each channel, the quality factor needs to be maximized. Based on the results, the maximum values for demultiplexers with four, eight, and sixteen channels are 19863.89, 14264.57, and 32304.46, respectively. Due to the device’s small size, it can be used for wavelength division multiplexing (WDM) systems in photonic integrated circuits.

Simultaneous Appearance of Different Topological Phases in a Single Photonic System: Coexisting Phases Characterized by Bulk Polarization and Valley‐Chern Number Enabling Dual‐Band Second‐Order Topological States

Topological phases appearing in photonic systems have recently attracted much attention in the community of photonics due to the fundamental and practical significances. Despite extensive investigations, the preceding results show that the photonic systems exhibit single topological phases with few exceptions. This work presents the simultaneous appearance of different topological phases in a single photonic crystal structure, which are characterized by bulk polarization and valley‐Chern number. Square‐lattice photonic crystals with unit cells consisting of four dielectric rods, one of which has the size different from the other three ones, exhibit the topological phase characterized by bulk polarization in the first bandgap, depending on the distance between the dielectric rods. Due to the broken inversion symmetry, in the meantime, the photonic systems show the valley‐Hall topological phase in the fourth bandgap. The proposed structures have the advantage of flexible design for generating the dual‐band topological edge and corner states compared with other photonic systems exhibiting single topological phases. From the fundamental and practical significances, the presented results will trigger the extensive investigations for exploring the photonic systems with multiple topological phases and find important practical applications.