Defects Modes Research Articles

One-Dimensional Photonic Serial Asymmetric Loops Structure Containing Three Defects

We study in this work, the occurrence of defects modes in the transmission spectrum and the band structure of a perfect photonic asymmetric serial loops structure (ASLS) utilized for narrow-band filtering. The perfect structure presents large photonic bandgaps that result from the modes of the loops resonances and the system periodicity. Besides that, the existence of defects within this perfect ASLS, whether at the segment or loop level, or both of them, causes the appearance of two, three, or four defect modes within gaps with good transmission rates and high-quality factors. These defects modes are extremely sensitive to changes in structural parameters. This system can be used to filter or guide the incoming electromagnetic waves. The interface response theory has been used to accomplish the analytical calculation. Green's function of the full system is determinated using this method. It allows us to calculate the dispersion relation and the transmission rate. Therefore, this paper can provide ideas for the design of multi-channel tunable filter using for frequency division multiplexing and microwave and signal processing.

Photonic Hall effect for a 1D-dimensional graphene-based photonic crystal with two defects

The presence of two defect layers in a one-dimensional photonic crystal which could be described numerically by the transfer matrix model becomes important when two defects modes might be controlled by the number of the middle layers. In this work, we compute the transmission spectra of a 1D photonic crystal with two graphene-based defect layers in the presence of an applied constant magnetic field. It is observed that an additional defect mode shows up at the lower edge of the photonic bandgap of the optical structure which could to be tuned by the Fermi energy, the intensity of the magnetic field and also the number of the layers between the defects. In addition, we investigated the effect of decreasing the number of middle layers on the transmission spectra of the photonic device.

Electromagnetic filtering and guiding of three frequencies by the presence of defects in one-dimensional photonic star waveguides structure

In this work, the propagation of electromagnetic waves in a one-dimensional star waveguides photonic structure is shown to present a novel physical phenomenon. This system contains a periodicity of cells; each cell is composed of finite segment of length d1 with two asymmetric resonators of lengths d2 and d3 are grafted in its extremity. This perfect structure consists of photonic pass bands separated by large photonic band gaps where the propagation of electromagnetic waves cannot propagate inside these forbidden regions. Due to the presence of these large gaps, the electromagnetic waves can be controlled and manipulated by a wide range of applications. On the other hand, the presence of defects, either at the segment level, or the asymmetric resonators located in one site, or the two components of the cell (segment–asymmetric resonators) inside this structure, leads to the appearance of two or three localized states (defect’s modes) inside these gaps with a very high transmission rate and a high-quality factor which reach Q=565850. We show that these localized states depend strongly on the defect lengths. The band structure and the transmission spectra are calculated by using the continuous medium interface response theory, which makes possible to calculate the Green function of any composite material. The structure and results provide a good support for the applications of filtering and guiding the defects modes inside the band gaps.

Defects modes in one-dimensional photonic filter star waveguide structure

In this work, by the formalism of the interface response theory, we study the existence of defects’ modes in the transmission spectrum of a one-dimensional photonic star waveguide (SWG) structure. The perfect structure presents large forbidden bands (gaps) that come from the periodicity of the system and the resonance states of the grafted lateral branches which play the role of the resonators. The defects modes result from the presence of the defects of the lateral branches level located in two different sites. The behavior of the defects’ modes is analyzed as a function of the defects’ lengths, the number of defectives resonators, the positions of the defects’ and the number of sites. This system can be considered as a selective filter with high performance.

Propagation of electromagnetic waves in one dimensional symmetric and asymmetric Comb-like photonic structure containing defects

In this paper, we study theoretically the transmission spectrum and the dispersion relation of a periodic photonic comb-like waveguide consisting of periodic segments of length d1 along which two different symmetric or asymmetric resonators of lengths d2 and d3 are grafted in each site. We study the presence of geometrical defects on the transmission spectrum. The creation of defects at the resonators levels of lengths d02 and d03 inside the perfect structure; enable to deduce the localized states (defects modes) inside the band gaps. In this research, we demonstrate the existence of two frequencies filtering with the presence of a single defect at the resonator level. In the same time, we investigate three frequencies filters in the existence of two defect resonators of lengths d02 and d03.

Analysis and characterization of PV module defects by thermographic inspection

Being able to detect, to identify and to quantify the severity of defects that appear within photovoltaic modules is essential to constitute a reliable, efficient and safety system, avoiding energy losses, mismatches and safety issues. The main objective of this paper is to perform an in-depth, onsite study of 17,142 monocrystalline modules to detect every single existing defect, classifying them in different groups, studying the variance of the same kind of defect in different modules and the patterns of each group of thermal defects. Results can be useful in a subsequent development of a software to automatically detect if a module has an anomaly and its classification. Focusing on the results obtained, all faults detected have been classified in five different thermographic defects modes: hotspot in a cell, bypass circuit overheated, hotspot in the junction box, hotspot in the connection of the busbar to the junction box and whole module overheated. An analysis of patterns of the different defects is included, studiyng location within the module, size and temperature statistical results, as average temperature, standard deviation, maximum temperature, median and first and third quartile.

Photonic band gap and defects modes in inorganic/organic photonic crystal based on Si and HMDSO layers deposited by sputtering and PECVD

Hybrid inorganic/organic one dimensional photonic crystal based on alternating layers of Si/HMDSO is elaborated. The inorganic silicon is deposited by radiofrequency magnetron sputtering and the organic HMDSO is deposited by PECVD technique. As the Si refractive index is n = 3.4, and the refractive index of HMDSO layer depend on the deposition conditions, to get a photonic crystal with high and low refractive index presenting a good contrast, we have varied the radiofrequency power of PECVD process to obtain HMDSO layer with low refractive index (n = 1.45). Photonic band gap of this hybrid structure is obtained from the transmission and reflection spectra and appears after 9 alternative layers of Si/HMDSO. The introduction of defects in our photonic crystal leads to the emergence of localized modes within the photonic band gap. Our results are interpreted by using a theoretical model based on transfer matrix.

Compression deformation behaviors of sheet metals at various clearances and side forces

Modeling sheet metal forming operations requires understanding of plastic behaviors of sheet metals along non-proportional strain paths. The plastic behavior under reversed uniaxial loading is of particular interest because of its simplicity of interpretation and its application to material elements drawn over a die radius and underwent repeated bending. However, the attainable strain is limited by failures, such as buckling and in-plane deformation, dependent on clearances and side forces. In this study, a finite element (FE) model was established for the compression process of sheet specimens, to probe the deformation behavior. The results show that: With the decrease of the clearance from a very large value to a very small value, four defects modes, including plastic t-buckling, micro-bending, w-buckling, and in-plane compression deformation will occur. With the increase of the side force from a very small value to a very large value, plastic t-buckling, w-buckling, uniform deformation, and in-plane compression will occur. The difference in deformation behaviors under these two parameters indicates that the successful compression process without failures for sheet specimens only can be carried out under a reasonable side force.

Coupling characteristics of point defects modes in two-dimensional magnonic crystals

The coupling characteristics of two-point defects modes and multi-point defects modes in two-dimensional magnonic crystals composed of Fe square rods/EuO square lattices are studied based on the plane-wave expansion method under supercell approximation. The results show that the coupling degree of these defect modes depends not only on the distance between defect bodies, but also on the arrangement direction of point defects. The phase of precession of defect modes' magnetization distributions varies as the distance between the defects changes. These magnonic crystals with multi-point defects can be used as the fabricating materials of the directional spin-wave filters or the narrow band spin-wave waveguides.

Faceted particles embedded in a nematic liquid crystal matrix: Textures, stability and filament formation

Two dimensional texture simulations, based on the Landau-de Gennes equations of nematodynamics in the absence of flow, were carried out for nematics with embedded faceted binary and multiple particles using temperature, size, and density as topological control variables. The stable modes obtained from kinetic simulations are summarized in texture phase diagrams in terms of temperature, particle separation and particle size. The key novelty in 2D faceted particles is the presence of corners that are sources/sinks of disclination lines or active corner defects. Under close corner-to-corner proximity, disclination lines form inter- or intra- particle links, while under larger distances, surface defects decorate the corners. This generic geometric behaviour is modulated by temperature since the line tension of disclinations decreases with increasing temperature. The characteristic texture diagrams show that for nanoparticles, increasing particle separation results in a disclination mode sequence of linked particles, cross-linked particles, and intra-particle disclinations. For colloidal particles, increasing size results in a mode sequence of linked particles and isolated particles with corner defects. For intermediate particle size, a continuous evolution of the phase diagrams from the former to the latter is demonstrated. At low temperatures, increasing interparticle distances leads to a defect breakage at a critical value independent of particle size. Multimer particle assemblies form stable filaments via a corner-to-corner interparticle disclination linkage mechanism. The stability of the multimers to bending is characterized using curvature as a topological control variable. As stretching-driven instabilities in binary particles give rise to surface defects modes, bending-driven instabilities give rise also to multi-particle rings with corner decorated surface defects. The integrated texture phase diagrams, topological transitions, tension and bending-driven instabilities demonstrate the potential functionality of faceted particle liquid crystal nanocomposites.

Design of mid-IR and THz quantum cascade laser cavities with complete TM photonic bandgap

We present the design of mid-infrared and THz quantum cascade laser cavities formed from planar photonic crystals with a complete in-plane photonic bandgap. The design is based on a honeycomb lattice, and achieves a full in-plane photonic gap for transverse-magnetic polarized light while preserving a connected pattern for efficient electrical injection. Candidate defects modes for lasing are identified. This lattice is then used as a model system to demonstrate a novel effect: under certain conditions - that are typically satisfied in the THz range - a complete photonic gap can be obtained by the sole patterning of the top metal contact. This possibility greatly reduces the required fabrication complexity and avoids potential damage of the semiconductor active region.

Defect modes and transmission properties of left-handed bandgap structures

We analyze transmission of electromagnetic waves through a one-dimensional periodic layered structure consisting of slabs of a left-handed metamaterial and air. We derive the effective parameters of the metamaterial from a microscopic structure of wires and split-ring resonators possessing the left-handed characteristics in the microwave frequency range, and then study, by means of the transfer-matrix approach and the finite-difference time-domain numerical simulations, the transmission properties of this layered structure in a band gap associated with the zero averaged refractive index. By introducing defects, the transmission of such a structure can be made tunable, and we study the similarities and differences of the defects modes excited in two types of the band gaps.