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Recently, the metastructure absorbers (MSA) have opened up a new sensing approach, whereas the existing designs suffer from a short numerical measurement range and small sensitivity span. In this paper, a photoexcited MSA that enables a transition between three operating states in the terahertz (THz) regime is proposed. The MSA merges two kinds of photosensitive semiconductor materials embedded in the split ring structure. By adjusting the wavelength of the pump light, semiconductor materials can be excited thus realizing the mutual change of three states in absorption. The structure appears to dual peaks absorption at normal incidence with absorptivity of 95.32% at 0.9269 THz and 99.42% at 1.5586 THz without the illumination of the pump light. Furthermore, it is worth emphasizing that we introduce a novel idea to utilize this actively tunable MSA for refractive index sensing. Not only it has the advantage of large sensitivity variation from 0.0471 (THz/RIU) to 0.1239 (THz/RIU) but also it can be applied in five different refractive index numerical measurement ranges spanning from 1 to 4 with preferable performance. Finally, the absorption effect of the MSA is analyzed under different incidence and polarization angles. • Tunability of three states using two photosensitive materials can be achieved. • Refractive index sensing with large sensitivity variation in five different refractive index. • The design has superb tolerance of the angular stability. [ABSTRACT FROM AUTHOR]

In this paper, the properties of the photonic band gaps (PBGs) of three-dimensional (3D) function photonic crystals (PCs) are theoretically investigated by a modified plane wave expansion (PWE) method, whose equations for computations are deduced. The configuration of 3D function PCs is the dielectric spheres inserted in the air background with simple-cubic (SC) lattices whose dielectric constants are the functions of space coordinates, which can be realized by the electro-optical or optical Kerr effect in the practice. The influences of the parameter for 3D function PCs on the PBGs also are discussed. The calculated results show that the bandwidths and number of PBGs can be tuned with different distributions of function dielectrics. Compared with the conventional 3D dielectric PCs with SC lattices, the larger and more PBGs can be obtained in the 3D function PCs. Those results provide a new way to design the novel practical devices. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, an omnidirectional photonic band gap (OBG) which originates from Bragg gap compared to gap or single negative (negative permittivity or negative permeability) gap, realized by one-dimensional (1D) plasma photonic crystals (PPCs) with ternary Thue–Morse aperiodic structure, which is composed of plasma and two kinds of homogeneous, isotropic dielectric is theoretically studied by the transfer matrix method (TMM) in detail. Such OBG is insensitive to the incident angle and the polarization of electromagnetic wave (EM wave). From the numerical results, the bandwidth and central frequency of OBG can be notably broadened by changing the thickness of plasma and dielectric layers but cease to change with increasing Thue–Morse order. The OBG also can be manipulated by plasma density. However, the plasma collision frequency has no effect on the bandwidth of OBG. These results may provide theoretical instructions to design the future optoelectronic devices based on plasma photonic crystals. [Copyright &y& Elsevier]

In this paper, the properties of one-dimensional (1D) photonic crystals (PCs) composed of the semiconductor (GaAs) and dielectric layers are theoretically investigated by the transfer matrix method (TMM). The absorption of semiconductor layers is investigated theoretically. Due to the magneto-optical Voigt effect, the dielectric constant of the semiconductor is modified differently in different modes and frequency ranges. If the frequency range of the incident wave is larger than the plasma frequency, TE and TM modes of the incident wave will be absorbed in a wide incident angle. TM wave will be absorbed but TE wave will be reflected while the frequency range is less than the plasma frequency. The absorption of semiconductor can also be tuned by varying the external magnetic field. The proposed PCs have a reconfigurable application to design a tunable omnidirectional absorber and mode splitter at same time. [ABSTRACT FROM AUTHOR]

A meta-structure (MS) that can realize a conversion between electromagnetically induced transparency (EIT) and electromagnetically induced absorption (EIA) in the Terahertz (THz) range by utilizing phase-transition vanadium dioxide (VO 2) has been reported. This work is controlled by temperature to change the conductivity of VO 2 to achieve the switching function. When the VO 2 is in the insulator state, the MS is designed to achieve EIT based on the principle of bright mode near-field coupling bright mode. The EIT behavior owns a peak of 0.8 at 0.430 THz with a maximum group delay of up to 6.5 ps. The MS behaves the function of EIA accompanied by the maximum absorption rate of 93.8 % at 0.432 THz while the VO 2 film is tuned to the metallic state. The reason for the EIA phenomenon is the magnetic effect of the magnetic dipole generated by the MS in the coupling process. The observed EIT and EIA effects are both theoretically explained by the classic two-oscillator model. In addition, the air columns of the dielectric substrate are utilized for the purpose of frequency approaching. This proposed MS provides a new idea for the design of non-contact regulation and reconfigurable and highly absorbent MSs. [ABSTRACT FROM AUTHOR]

Utilizing metasurface (MS), the transition between dual-peak electromagnetically induced transparency (EIT) and dual-peak electromagnetically induced absorption (EIA) in four states has been proposed in the terahertz (THz) band with the incidence of a circularly polarized (CP) wave. Additionally, the phase-change material vanadium dioxide (VO 2) and photosensitive material silicon (Si) have been adopted. The four state transitions can be achieved by adjusting the pump light and the temperature which is not affected by incident CP waves. With the incidence of the pump light, Si can transform from the insulating state to the metallic state. Similarly, when the temperature exceeds 68 °C, VO 2 enters the metallic state. Two different dual-peak EIT (State 1 and State 2) accompanied by slow light effect can be observed by modulating the state of VO 2 without the action of Si. However, once Si is in metallic state, two different states of dual-peak EIA (State 3 and State 4) are achieved by changing the state of VO 2. Notably, the MS has the property of polarization insensitivity. The theoretical oscillator model and equivalent RLC-circuit model verify the feasibility of dual-peak EIT and EIA. [ABSTRACT FROM AUTHOR]

In this paper, fractal supercells are constructed according to the Thue-Morse theory and arranged in a square lattice to form fractal photonic crystals (PCs), which are called the first-order (1st) and second-order (2nd) approximate of Thue-Morse structure. The multi-circular ring scatterers (MCRSs) are innovatively applied in them and the effect of the number (H) and width (W) variation of the rings on the equifrequency contours (EFCs) of PCs is investigated. To calculate the energy band diagrams and EFC mappings of the first-order (1st) and second-order (2nd) approximate of Thue-Morse structure, an improved plane wave expansion (PWE) method is also introduced. Then, the possibility of achieving polarization-insensitive self-collimation (PISC) in the approximate of Thue-Morse structure and conventional square lattice (CSL) PCs are explored. This phenomenon was verified by simulations at normalized frequencies of 0.128, 0.068, and 0.27 (ωa /2πc), respectively, and the phenomenon of vertical incidence self-collimation of light (VISCOL) was proposed on this basis. Finally, a reflection on the value of the multi-ring nested type of scatterers is presented. Replacing the circular rings in the PCs with square rings, it is found that the EFCs for TE polarization change less while the EFCs for TM polarization have larger variations, which leads to a reduction in the VISCOL frequency range and provides a possibility for beam splitter design. [ABSTRACT FROM AUTHOR]

Based on the transfer matrix method (TMM), the nonreciprocal omnidirectional band gaps (OBGs) of magnetized ferrite photonic crystals (MFPCs), consisting of the Yttrium iron garnet ferrite and general dielectric, are investigated. Herein, a disordered MFPC is modeled by rendering the thicknesses of the general dielectric in the Gauss distribution. With the introduction of D , t , and H 0 to quantitatively describe the disorder degree, the average thicknesses of the general dielectric layers and the external magnetic field, the three parameters are adjusted for multifarious values. It is shown that the disorder effects (DEs) lead the OBGs to the pattern, that the widths primarily expand and then narrow down with the increasing D. Thereinto, the OBG of D = 0.1 attains the maximum. Also, on top of D = 0.2, the OBGs for the negative fully cover the OBGs for the positive. The OBGs are sensitive to the switches in t and H 0 that the ranges vary irregularly with these two variables. For t = 0.2, the OBGs exhibit excellent nonreciprocity, with no overlapping bands in the OBGs for the positive and negative propagation. The results help assume the possible DEs on the OBGs of the MFPCs and give practical advice on the design of filters. [ABSTRACT FROM AUTHOR]

In this paper, the principle of the transfer matrix method (TMM) is applied to derive the dispersion relation of electromagnetic wave propagation in cylindrical photonic crystals (CPCs), and we further deduce the conditional equations for exciting the optical Tamm state (OTS) in the one-dimensional (1D) CPCs based on the excitation conditions for OTS in 1D photonic crystals. Both H- and E-polarization are involved. After that, four CPCs are designed with graphene as the main defect layer to verify the correctness of the formula, and the effects of different defect layer structures, dielectric thickness, chemical potential, and phenomenological scattering rate on the dispersion curve are discussed, separately. In contrast, differences due to defect layer structure and dielectric thickness are more easily to be observed. The chemical potential of graphene dependence on the k ρ - ω curves is more likely to be a kind of positive correlation. While phenomenological scattering rate has the weakest effect on the results. • The formulas for the dispersion relation of CPCs is given. • The conditions to excite optical Tamm states in CPCs are derived. • The graphene is acted as the main part of the defect layer. • The tunable dispersion curvse of CPCs are given. [ABSTRACT FROM AUTHOR]

A new novel of scatterers which is in the form of a multi-ring shape is proposed in this paper. The circular scatterers in the two-dimensional (2D) photonic crystals (PCs) have been replaced by the multi-ring ones based on the honeycomb and Kagomé lattices, and the effects of the number of layers (N), the refractive index (n), and the ring width (W) for the multi-ring scatterers on the photonic band gaps (PBGs) are also researched. After that, the relative properties of the absolute PBGs and all-angle negative refraction (AANR) phenomenon in two different types of inserted scatterers have been probed into. The band structure diagrams of those two lattices and equifrequency contours (EFCs) for two different inserted scatterers are acquired through the plane wave expansion (PWE) method. Through comparison, it is qualified for being figured out that, if the scatterer structure is varied from circular rode to multi-ring one, the bandwidths of some absolute PBGs can be expanded or the number of absolute PBGs can be added. Then, through the diagrams of EFCs and the band structures, the phenomenon that the AANR range shrank after the change has been discovered, and verify it by calculation. • A novel multi-ring structure scatterer with high symmetry is proposed. • The multi-ring structure provides multiple parameters which can be adjusted to control the PBGs for TE and TM polarization PBGs. • The introduction of multi-ring scatterers reduces the frequency range of AANR, which provides a new idea for the design of beam splitters. [ABSTRACT FROM AUTHOR]

In this article, a novel gravity field tailored metamaterial absorber (MA) dealing with polarization separation has been put forward. The proposed MA has two built-in glass grooves of different shapes but equal volume, which contains liquid metal (eutectic gallium-indium) and liquid oil, respectively. Hence, different absorption states can be realized in a way of the gravity field tailored. Unlike the conventional temperature or magnetic field regulation, a gravity field tailored MA does not require additional controllers, and the control technique itself is integrated into the whole structure. Besides, the lumped circuit is used to be equivalent to our MA model for exploring the principle of absorption performance variation. The surface current distributions and the electric field distributions are given to explain its physical mechanism. Simulation results have shown that the absorption peaks shift from 9.24 GHz to 7.4 GHz for the TE wave and from 12.06 GHz to 10.96 GHz for the TM wave when the MA is rotated by 180°, which provides a subverted idea for the promising gravity field tailored optical devices. Also, a 5 × 5 proportional arrangement to achieve two narrow polarization-separated absorption bands is proposed for further research. • A novel gravity field tailored metamaterial absorber (MA) dealing with polarization separation has been put forward. •For the TE wave, the absorption peak moves from 9.24 GHz to 7.4 GHz, when the given MA is rotated 180°. •For the TM wave, the absorption peak shifts from 12.06 GHz to10.96 GHz, when such a MA is rotated 180°. •A 5×5 proportional arrangement to achieve two narrow polarization-separated absorption bands is proposed for further research. [ABSTRACT FROM AUTHOR]

In this paper, an ultra-broadband metamaterial absorber (UBMA) is proposed on basis of plasma metamaterials and lumped elements. For the TE wave, the designed absorber exhibits an ultra-broadband absorption higher than 90% in the frequency regime 1.78 GHz–4.7 GHz. Nevertheless, for the TM wave, the proposed UBMA holds excellent reflection performance, whose reflection coefficient is close to 1. Furthermore, when the different solid-state plasma resonators (PRs) are excited, on the one hand, the single-band and ultra-broadband absorption switching can be realized. When only solid-state PRs along the x -axis are excited, the devised UBMA can form a strong absorption peak at 4.75 GHz whose absorptivity is 97.37%. And the absorption over 90% runs from 1.93 GHz to 4.22 GHz with only solid-state PRs along the z -axis excited (the relative bandwidth is 74.4%). On the other hand, the ultra-broadband absorption performance can be further improved. When all solid-state PRs are excited, the relative bandwidth is 90.1% (1.78–4.7 GHz). • An UBMA based on the SSP is proposed. • For the TE wave, the UBMA operates the frequency regime 1.78 GHz-4.7 GHz. • For the TM wave, the reflection coefficient of UBMA is close to 1. • When the different SSP resonators are excited, the absorption switching can be realized. [ABSTRACT FROM AUTHOR]