Dielectric Rod Research Articles

RETRACTED: Chupradit et al. Ultra-Sensitive Biosensor with Simultaneous Detection (of Cancer and Diabetes) and Analysis of Deformation Effects on Dielectric Rods in Optical Microstructure. Coatings 2021, 11, 1564

The journal retracts the article, “Ultra-Sensitive Biosensor with Simultaneous Detection (of Cancer and Diabetes) and Analysis of Deformation Effects on Dielectric Rods in Optical Microstructure” [...]

Enhancing circular dichroism with anisotropic heterogeneous-structure based on MQBIC resonance

Metasurfaces based on quasi-bound states in the continuum (QBIC) typically require careful tuning of structural parameters to meet critical coupling condition, thereby maximizing circular dichroism (CD). In this study, we propose an innovative heterogeneous-structure comprising four pairs of symmetry-breaking silicon dielectric rods embedded in an anisotropic polymer. The resonance of magnetic QBIC (MQBIC) within the dielectric rods generates a CD response, while the polymer effectively modulates the chirality of the heterogeneous-structure and enhances the CD. This enhancement occurs because the resonance of the MQBIC in the diagonal direction of the heterogeneous-structure is confined, leading to a break in mirror symmetry. Further investigations reveal that even when critical coupling condition are not satisfied, CD can still be maximized through rotational modulation. Additionally, the critical coupling condition for the resonance of MQBIC in the heterogeneous-structure are more readily achievable, allowing the CD response to remain unconstrained by lattice constants. This research is anticipated to have a significant impact on the fields of biosensing and medical imaging in the future.

Design of a beam splitter based on an adjustable beam-splitting ratio of a hexagonal star-like topological photonic crystal

We propose a new, to the best of our knowledge, mechanism to realize topological phase transition, that is, in a hexagonal star-like honeycomb lattice photonic crystal (PC), the optical quantum spin Hall effect (QSHE) can be realized by changing the materials of the outer or inner ring dielectric rods in the cells. We calculated the energy band and analyzed the topological phase transition law of a hexagonal star-like honeycomb PC. By changing the permittivity of the PC, the disturbance is introduced to the edge state. It is found that with the decrease of the permittivity of the PC, the gap decreases, the lower boundary state gradually redshifts, and the maximum transmittance in the straight waveguide can reach 98.8%. On this basis, a topological beam splitter was designed and analyzed. Results show that the beam splitting ratio obtained by the system is in the wide range of 0.2–3.5. Our research enriches the implementation of topological photonics, provides potential applications for topological boundary states in terahertz technology, and offers a new avenue for the design of current optical integrated devices.

Multiple parameters control of square superlattice plasma photonic crystal

We present a novel square superlattice plasma photonic crystal (PPC) fabricated by periodic arrangement of different-sized gas discharge tubes and Al2O3 dielectric rods. The effects of the plasma, the number and location of Al2O3 rods, and the angular orientation of PPCs on the microwave transmission characteristics have been demonstrated. For the simple square lattice, a PBGa in the range of 13.40–14.20 GHz is obtained. For the square superlattice, an additional PBGb in the range of 14.35–15.10 GHz develops. While PBGa and PBGb are primarily dependent on the square sublattices of plasma rods and Al2O3 rods, respectively, a synergistic effect arising from the interplay between these two sublattices is suggested. Moreover, a new PBGc is achieved by changing the rotation angle of the PPC to 45° The multiple parameters control of square superlattice PPC may inspire new strategies for designing fully bandgap-tunable PCs and may find potential applications in various fields.

Chirally-coupled-ring fibers for arbitrary-order orbital angular momentum mode generation and detection.

A novel chirally-coupled-ring fiber (CCRF) is proposed for efficiently generating and detecting arbitrary-order orbital angular momentum (OAM) modes in ring-core fibers (RCFs). The CCRF comprises inner and outer cores, N angularly uniformly distributed dielectric rods, and a cladding layer. These rods, twisted along the fiber axis between the cores, introduce angular geometry perturbations to manipulate the core modes. Through meticulous theoretical modeling and systematic analysis grounded in coupled-mode theory, we reveal CCRF eigenmodes carrying spin-entangled OAM, elucidate the mode coupling and power transfer in CCRFs, and present the CCRF design principle. Utilizing the full-vector beam propagation method, we carry out a proof-of-principle experimental system to demonstrate the capability of CCRFs in OAM mode manipulation and their feasibility and superiority in system-level applications. Additionally, we generate OAM modes across a wide range of topological charges from ℓ = -8 to ℓ = 8 using CCRFs, with conversion efficiencies from 92.10% to 99.63% and mode purities from 90.28% to 99.48%. Attributed to a coaxial dual-core structure with core-separated geometry perturbations, CCRFs enable flexible manipulation of arbitrary-order OAM modes without altering core geometry parameters, effectively solving design flexibility and compatibility problems in conventional single-core fiber devices. The proposed CCRF holds great promise for fiber-based OAM applications, especially for RCF-based OAM multiplexing communications.

Experimental verification of guided-wave lumped circuits using dielectric rod

Abstract This paper presents a method to realize equivalent lumped inductance/capacitance by adjusting the relative permittivity, diameter, and offset of the dielectric rod. The dielectric rod is used to replace the traditional reactance matching elements (metallic diaphragm, pin, and resonant window) in the substrate integrated waveguide, which avoids the problem of short circuit in the upper and lower metal plate of the substrate integrated waveguide, and has the advantage of high regulatory freedom, low radiation loss, and low crosstalk. Based on this method, three air rod filters are designed and verified by experiments. The three filters are designed based on the diameter and offset of a single dielectric hole and the offset of symmetrical dielectric rods. Compared with conventional filters, this method greatly adjusts the degree of freedom of media regulation in the substrate integrated waveguide. The experimental results are in good agreement with theoretical analysis and simulation results. It provides an effective platform for the design of substrate integrated waveguide functional lumped circuits.

Back-focal plane scanning spectroscopy for investigating the optical dispersion of large-area two-dimensional photonic crystal fabricated by capillary force lithography

In this article, we introduce our custom-built back-focal plane (BFP) scanning spectroscopy to explore an angle-resolved optical dispersion in two-dimensional (2D) photonic crystal (PhC) constructed with hexagonal lattice of nano-scaled dielectric rods. We fabricated a uniformly large-area photonic crystal measuring 1 cm by 0.5 cm, featuring a polymer-based hexagonal lattice on a gold layer, using capillary force lithography. This precision enables the effective confinement of photonic modes, leading to enhanced optical interactions. We successfully map out the angle-resolved reflectance spectra by directly scanning BFP, revealing the structure's angle dependent optical response and providing insights into its iso-frequency contours. Our approach simplifies the exploration of advanced optical materials, highlighting the role of precise fabrication and measurement techniques in understanding and utilizing the optical properties of structured materials for various technological applications.

THz plane wave scattering by azimuthally periodic array of conformal graphene patches on circular dielectric rod

THz plane wave scattering by azimuthally periodic array of conformal graphene patches on circular dielectric rod

Recent advances in all-optical half-subtractor and full-subtractor based on photonic crystal platforms

Abstract A half-subtractor is a digital circuit that subtracts two inputs and displays the result in two outputs. Photonic crystals (PhCs) are used in optical circuits, including encoders, multiplexers, adders, subtractors, timers, counters, etc. This paper reviews and compares some of the all-optical half-subtractors and full-subtractors based on PhCs reported to date. We study physical parameters, including the arrangement of dielectric rods, rod radius, lattice constant, structure area, background material, and resonator type and illustrate the structure with a small size is suitable for integration in a photonic chip. Another crucial factor is the optical power difference between the two logic states of 0 and 1. A large difference between these two values increases the contrast ratio and reduces the detection error in the output. Delay time as a key parameter specifies that the input signal will leave the desired output after a few femtoseconds. Linear structures have the lowest delay time, fall time, and rise time among compared structures. But on the other hand, non-linear structures have the highest amount of contrast ratio. In the recent papers, relatively favorable delay times are obtained, equal to 0.06, 0.1, and 0.85 ps, respectively. Also, the fall times are a small value and are equal to 0.05, 0.1, and 0.25 ps, respectively, and the rise times are equal to 0.1, 0.5, and 0.7 ps, respectively. Also, the contrast ratio values are high and acceptable which are equal to 25.88, 18.80, and 18.40, respectively.

Dual high-Q Fano resonances metasurfaces excited by asymmetric dielectric rods for refractive index sensing

Abstract The metasurface refractive index sensor has a high degree of tunability and flexibility, providing excellent performance for high precision refractive index sensing applications. The metasurface absorber with metallic structure has been hindered in further sensor applications due to the inherent Ohmic loss of the metallic material. In this study, a dual nanorod metasurface structure based on semiconductor Si was designed, introducing a symmetry-breaking structure to excite dual ultra-narrow q-BIC resonance peaks with Fano line shapes. Both peaks are located in the near-infrared region, and multipole analysis shows that this strong field enhancement effect is induced by a magnetic dipole. Experimental results demonstrate the potential of this sensor to provide dual-channel detection while achieving high sensitivity and high Q-factor. We believe that this device exhibits outstanding performance and high practicality, providing a reference for the development and application of biological and environmental sensors.

Sensitivity and quality factor improvement of photonic crystal sensors by geometrical optimization of waveguides and micro-ring resonators combination

In this work, the process of designing and simulating optical sensors based on photonic crystal (PC) micro-ring resonators (MRRs) has been investigated. According to the PC type, different waveguides and resonators can be designed, and various topologies can be proposed from their combination, for optical sensor applications. Here, the investigated MRR is of the symmetrical micro-hexagonal ring resonator (MHRR) type. Different arrays of MHRR arrangement have been designed to investigate their effects on the output spectrum. The results of the design and simulation of different topologies have been analyzed and compared with other numerical researches. Considering all the necessary aspects of PC optical sensors, a detailed and comprehensive algorithm has been presented for designing these devices and choosing the optimal structure. In a more complementary process, the effects of reflector rods have been investigated, which indicates the existence of similarity and compatibility in the design between the distance of reflector rods and the length of MHRRs to obtain the optimal structure. Finally, the effect of different values of lattice constant and radius of dielectric rods on FWHM, transmission (TR) and resonant wavelength is studied, and the most optimal mode is presented. In order to measure the performance of the proposed optimal sensor, its application for gas detection has been analyzed. TR, FWHM, quality factor (QF), sensitivity (S) and figure of merit (FOM) of the proposed sensor were equal to 96%, 0.31 nm, 2636, 6451 nm/RIU and 2960 RIU−1 respectively. An examination of results from similar research indicates a rational and effective approach for generating diverse topologies, aiming to attain the most optimal configuration for optical sensors employing MRRs. Furthermore, employing a systematic design process based on established principles and the proposed algorithm helps prevent arbitrary parameter variations, facilitating the attainment of desired outcomes in a more streamlined and efficient manner. Given the comprehensive nature of this research, it presents a viable solution for designing optical devices based on MRRs for use in optical integrated circuits (OICs) applications.

A novel design of an all‐optical D flip‐flop based on 2D photonic crystals

AbstractIn this study, we endeavored to create and simulate a D‐type flip‐flop utilizing two‐dimensional photonic crystals featuring a square lattice. This flip‐flop, composed of just two intersecting waveguides, is both compact and straightforward. Constructed from 10 × 10 dielectric rods suspended in air, it boasts low output power in logic mode 0, creating a significant distinction between optical powers in modes 0 and 1, lending it a logical aspect. Optimized for operation at a communication wavelength of 1.55 µm, this flip‐flop proves suitable for optical communication systems. The third window optical fiber communication system is suitable for 1.55 μm wavelength because the fiber has the lowest loss. Our analysis involved calculating the band structure via the plane wave expansion method and determining the optical power distribution using the finite difference time domain method.

Conductivity Measurement Technique for Interface and Surface Using Dielectric Rod Resonator Based on Calibration

Conductivity Measurement Technique for Interface and Surface Using Dielectric Rod Resonator Based on Calibration

Design, simulation, and measurement of near-zero-index shells for electromagnetic beam generation

We present design and simulation of three-dimensional (3D) shell structures, which generate directional radiation patterns from isotropic sources thanks to their near-zero-index (NZI) characteristics, as well as realizations of these shells via low-cost 3D printing. Throughout the design process of NZI beam generators, both homogenized structures, for which near-zero relative permittivity and/or permeability values are enforced, and actual models involving periodic arrangements of dielectric rods are considered. Solutions of the electromagnetic problems are obtained by using rigorous implementations of the state-of-the-art surface-integral-equation (SIE) formulations in frequency domain. Iterative solutions of matrix equations derived from SIEs are accelerated by different forms of the multilevel fast multipole algorithm (MLFMA) and suitable preconditioners, when necessary. In the design process of NZI shells, alternative strategies are employed to obtain customized radiation patterns. In this context, various cavities with strong resonance behaviors are designed as source regions. At the same time, outer surfaces are modified to either enhance or suppress outgoing electromagnetic fields. In addition to comprehensive simulations and analyses of NZI beam generators, their capabilities are verified by measurements, specifically at 10.3 GHz, on different prototypes fabricated via 3D printing. Measurements of diverse NZI shell structures are presented to demonstrate that NZI properties can successfully be achieved by well-designed arrangements of dielectric rods with proper materials. The results demonstrate the feasibility of efficient, effective, low-cost, and reconfigurable NZI shells to generate alternative beam configurations that can be useful in a plethora of microwave applications.

Inverse design of polymorphic Dirac-like cone dispersion relationship in photonic crystals

Dirac-like cone linear dispersion relations in photonic crystals (PhCs) often endow them with unique properties, yet searching for such relations can be challenging. We introduce a generalized inverse design system that, given the dielectric constants and lattice of two-dimensional PhCs, can efficiently determine its structural parameters to obtain its Dirac-like cone dispersion. Employing this inverse design strategy, we design three types of Dirac cone PhCs, including triple degenerate, quadruple degenerate, and triple degenerate under dual polarization with the same frequency. Further investigations reveal a systematic relationship between the radius of the dielectric rods in these PhCs and their corresponding Dirac frequencies across varying dielectric constants. The zero refractive index characteristic is validated in two of the three PhCs studied, as confirmed through numerical simulations. Additionally, by leveraging our proposed inverse design method, we introduce an innovative shell dielectric rod model, which encapsulates a dielectric material, achieving a quadruple degenerate dispersion structure with dual Dirac cones. This research provides a potent tool for the inverse design of PhCs and expands its application in Dirac cone dispersion design.

An FCC-FDTD Method on Nonuniform Grids With Guaranteed Stability for Electromagnetic Analysis

The finite-difference time-domain (FDTD) method based on nonuniform face-centered cubic (FCC) grids, termed as NU-FCC-FDTD method, is proposed in this article. The FCC-FDTD method with uniform grids has a smaller numerical dispersion error than the traditional FDTD methods. To further enhance its efficiency and scalability, the NU-FCC-FDTD method is proposed to solve complex electromagnetic problems. Unlike the traditional FDTD methods based on Yee’s grids, for which the nonuniform grid technique is relatively straightforward, instability may occur when trying to apply nonuniform grids into the FCC-FDTD method. To ensure stability, cell-size-based correction factors are carefully defined in the time-marching formulations after taking cell sizes into consideration. Through comprehensive numerical dispersion analysis, the NU-FCC-FDTD method shows numerical dispersion advantage over the FDTD methods and the FCC-FDTD method with uniform grids. Furthermore, the stability condition is also given by using the parameter scanning method and verified in numerical examples. Four examples, including electromagnetic wave propagation, a dielectric rod (DR) resonator, a composite metallic-dielectric radome and the electromagnetic energy absorption of human head, are carried out to demonstrate its performance. Results show that the proposed NU-FCC-FDTD method can significantly improve efficiency compared with that of the FCC-FDTD method without compromising accuracy.

Stability of the homogeneous mode in the metamaterial regime with structural disorder

This research considers the stability of the ε-near-zero homogeneous mode in the metamaterial composed of dielectric rods. The homogeneous mode is shown to be tolerant to modification of the geometrical shape of metamaterial boundaries as well as to introduction of internal boundaries associated with super-wavelength voids inside the structure. Additionally, we study the influence of structural disorder, namely, the deviation of the rod position from the lattice sites, which is the inherent feature of any real structure. We investigate the influence of the disorder degree on homogeneous mode stability. The closer parameters of the structure are to the boundary of the “photonic crystal–metamaterial” transition, the less stable the ε-near-zero homogeneous mode is. The homogeneous mode collapses at a fixed frequency; however, there is a range of disorder degree at which the homogeneous mode is still observed but at a lower frequency. While the change in frequency is weak, the ε-near-zero homogeneous mode is robust against the introduction of structural disorder.

Terahertz photodiode integration with multi-octave-bandwidth dielectric rod waveguide probe.

Photonic integrated circuits play a vital role in enabling terahertz (THz) applications that require multi-octave bandwidth. Prior research has been limited in bandwidth due to rectangular waveguide (WRs) interconnects, which can only support single octave at low loss. To overcome this fundamental limitation, we exploit the ultra-wideband (UWB) near-field coupling between planar waveguides and silicon (Si)-based subwavelength dielectric rod waveguides (DRWs) to interconnect THz bandwidth uni-traveling-carrier photodiodes (UTC-PDs) at 0.08-1.03 THz. In a proof-of-concept experiment, the on-chip integrated UTC-PDs demonstrate a UWB operation from 0.1 THz to 0.4 THz. Furthermore, by employing Si DRWs as probes, multi-octave device-under-test characterization of UTC-PDs integrated with UWB transition is enabled with only one DRW probe. The proposed UWB interconnect technology is distinct from previously used WR-based ground-signal-ground probes or quasi-optical free-space coupling since it can provide multi-octave bandwidth and enable on-chip THz circuit integration.

Pressure sensor based on two-dimensional photonic crystal ring resonator

This paper proposes a novel pressure sensor utilizing a two-dimensional photonic crystal (2DPC) based on a ring resonator design. The sensor consists of a square ring resonator that is connected to two photonic crystal waveguides. The photonic crystal is comprised of a square lattice of circular Silicon dielectric rods with air serving as a background. The proposed sensor operates within a pressure range of 0 to 6 GPa, corresponding to a wavelength range of 1554 nm to 1569 nm. The band structures and transmission characteristics of the proposed sensor are studied using the plane wave expansion (PWE) and finite-difference time-domain (FDTD) methods. The normalized transmission spectra of the sensor are observed by varying parameters such as the refractive index, radius, lattice constant, and pressure value, resulting in corresponding wavelength shifts. The proposed sensor design offers a compact size, a wide dynamic range of 6 GPa pressure, and a high sensitivity of 3 nm/GPa. These properties make it highly suitable for a range of applications such as high-pressure or stress-sensing, medical applications, and long pipeline strain monitoring.

Full cycle, self-consistent, two-dimensional analysis of a packed bed DBD reactor for plasma-assisted splitting: spatiotemporal inhomogeneous, glow to streamer to surface discharge transitions

We investigate the full-cycle operation of a coaxial Packed Bed Dielectric Barrier Discharge (PB-DBD) reactor operating in pure . The reactor is packed with high permittivity dielectric rods and is analyzed with a two-dimensional (2D) self-consistent plasma model. We show that the PB-DBD operation is governed by both glow and volume/surface streamer discharges, forming alternatively and non-uniformly inside the gas volume. The presence and surface charging of the dielectric rods and dielectric layer is crucial for the initiation, propagation, annihilation and afterglow of these microdischarges. Our calculations show maximum electron and densities in the order 1020 m−3, an average discharge power of 353.42 W m−1 in the first cycle, microdischarge peak currents in the order of 50–400 A m−1, total half-cycle plasma charge of around 6 µC m−1, which compare well with experimental findings. Dominant negative ions are found to be . CO molecules and O atoms are mainly formed during the MDs development and the streamer-surface ionization waves. Molecular oxygen () is preferentially formed during the glow, current-decaying and afterglow phase of each microdischarge. The spatially average reduced electric field inside the reactor lies in the 20–100 Td range. Each MD, presents distinct non-uniform and non-repeatable glow and volume/streamer discharges owed to the non-uniform surface charging processes which dictate the complex spatial distribution of produced neutral (and ion) species. These detailed results shed light on crucial, largely non-uniform plasma spatiotemporal characteristics that can help design efficient PB-DBD reactors for splitting and beyond, while emphasizing the important insights obtained by 2D simulations which can not be captured with 0D-global or 1D models.