Characteristics Of Photonic Band Gaps Research Articles

Pressure-dependent bandgap characteristics in photonic crystals with sensing applications

The present study elucidates a photonic crystal (PhC)-based pressure sensor exploiting the change in refractive index with pressure and the corresponding structural deformation of the dielectric material. The stress-sensitive refractive indices of the constituent materials of the PhC have been considered to study the effect of applied pressure on the photonic bandgap (PBG) characteristics of the structure. The designed pressure sensor, proposed using a two-dimensional hexagonal lattice arrangement of air holes in a dielectric slab, operates in the high-pressure range of 1–6 GPa. A comparative study of the PBG characteristics with the application of high pressure has been reported for three semiconducting materials—GaAs, Ge and Si, used for the dielectric slab in the proposed structure. GaAs is found to exhibit the highest sensitivity to pressure variations and shows more pronounced shifting of the midgap wavelength with pressure in comparison to Ge and Si. The largest PBG is seen in the Ge-based structure, closely followed by the GaAs and Si-based structures. The proposed structure is suitable for high-pressure sensing applications.

Dimer-parity dependent odd–even effects in photoinduced transitions to cholesteric and twist grain boundary SmC* mesophases: PBG characteristics

We describe the first investigations on the influence of flexible spacer parity of the guest photoactive liquid-crystalline dimer on the photonic bandgap (PBG) features of the cholesteric (Ch) and twist grain boundary smectic C* (TGBC*) phases of the host molecule. Both these phases exhibit PBG structure, with the former having it in one and the latter in three dimensions respectively. The concentration of the photoactive dimer is very small in the host liquid crystal (HLC) system that exhibits isotropic (Iso) → Ch → TGBC* sequence. The photoisomerization experiment brings out the feature that the pitch of the Ch phase blue-shifts, with the magnitude being more for the even dimer system compared to the odd one. This effect is accompanied by a reduction in the width of the photonic bandgap, again the effect is more pronounced for the even parity mixture compared to the odd one. The two-dimensional periodicity of the SmC* helix identified with the grid pattern in the TGBC* phase shows the memory effect upon photoisomerization. X-ray diffraction measurements reveal that the odd dimer system shows a larger layer spacing than the even dimer one. Upon UV illumination for one of the materials, layer spacing shows an increase. The investigations discussed in this article reveal that, apart from the actinic light, the spacer and parity of the photoactive dimer play a significant role in controlling the PBG properties in all three directions.

Compact Photonic Crystal Polarization Beam Splitter Based on the Self-Collimation Effect

We propose a new compact polarization beam splitter based on the self-collimation effect of two-dimensional photonic crystals and photonic bandgap characteristics. The device is composed of a rectangular air holes-based polarization beam splitting structure and circular air holes-based self-collimating structure. By inserting the polarization beam splitting structure into the self-collimating structure, the TE and TM polarized lights are orthogonally separated at their junction. When the number of rows in the hypotenuse of the inserted rectangular holes is 5, the transmittance of TE polarized light at 1550 nm is 95.4% and the corresponding polarization extinction ratio is 23 dB; on the other hand, the transmittance of TM polarized light is 88.5% and the corresponding polarization extinction ratio is 37 dB. For TE and TM polarized lights covering a 100 nm bandwidth, the TE and TM polarization extinction ratios are higher than 18 dB and 30 dB, respectively. Compared with the previous polarization beam splitters, our structure is simple, the size is small, and the extinction ratio is high, which meets the needs of modern optical communications, optical interconnection, and optical integrated systems.

Photonic band gap consequences in one-dimensional exponential graded index photonic crystals

We have investigated the photonic bandgap characteristics in one-dimensional (1-D) exponential graded photonic crystals (GPCs) in the microwave region. Proposed 1-D GPC structures are the stacked of the exponential graded index layers. In an exponential graded index layer, the refractive index between the boundaries of the layer modulates in an exponential fashion in terms of the layer's depth. We observe that the number of photonic bands increases with an increase in the graded layer's thicknesses. When the graded layer's thicknesses are proportional to one-quarter of the optical wavelength relative to the mean refractive index, observed photonic bands increase with an integral multiple of λ0/4 (λ0 represents the optical wavelength of the selected frequency). The bandwidth of photonic band gaps can be tuned with the modulations of the initial and final refractive index of the graded layer. Therefore, the desirable photonic bands can be controlled and achieved in a selected frequency range by choosing the GPC structure's convenient parameters. This work will facilitate the design of filters and multi-channel filters and provide more design freedom for other photonic devices. This work may also provide the basis for understanding the effect of exponentially graded material on photonic band gap characteristics in 1-D GPCs.

Photonic bandgap characteristics of GaAs/AlAs-based one-dimensional quasi-periodic photonic crystal

The optical behavior of GaAs/AlAs based 1D multi-layered quasi-periodic photonic crystal is investigated by employing the transfer matrix method (TMM). The complex dielectric constants are employed for analyzing the transmission spectra of the crystal at the long-wave limit. The numerical results are studied for different quasi-periodic sequential arrangements of GaAs/AlAs, which is also compared with the periodic structure. The major portion of optical spectra is affected by different generation numbers of quasi-periodic sequences as compared to the periodic crystal. The shifting of bandgaps around the central frequency with less optical-transmission peaks is observed within a considered frequency range. The mirrored or symmetrical behavior of two different superlattices remains unchanged with varying layer thickness. The scaling property is observed with the change in different incident angles. Moreover, generation number of different quasi-sequences plays a vital role to control the band-gap in the optical spectra. This study will be very helpful in designing the optical pass- and stop-band filters.

Studies on photonic bandgap and its defect mode characteristics of plasma photonic crystals based on S-MRTD scheme

Photonic bandgap (PBG) and its defect mode are two representative characteristics of plasma photonic crystals (PPC), which make them have important industrial applications in photonic crystal waveguides, filters, antennas, and other devices. In this paper, we apply the symplectic multi-resolution time-domain (S-MRTD) scheme to analyze these two properties. Firstly, the characteristics of PBG are analyzed. Secondly, the characteristics of defect mode in the case of a single defect layer and multi-defect layers are adequately studied. Finally, two types of ternary PPC are further simulated. Numerical simulations demonstrate the feasibility and effectiveness of the proposed scheme, a desirable PBG and its defect mode can be obtained by altering the corresponding plasma parameters and dielectric parameters.

Multi-channel photonic bandgap consequences in one-dimensional linear, exponential, and hyperbolic graded-index photonic crystals

We present the structuring of different graded-index materials in the form of one-dimensional (1D) photonic crystals (PCs) for highly efficient light trapping and controlling photonic devices in terms of tuned and controlled photonic bandgap (PBG) performance. We consider hyperbolic, exponential, and linear refractive index variation in the graded-index layer. We systematically study the influence of structural and grading parameters on the bandgap performance for two different graded photonic crystal (GPC) structures formed by stacking different graded-index layers. Compared with conventional PCs, the GPC bandgaps can be changed and tuned by the refractive index profile of the graded-index layer. We show that the number of bandgaps increases with the graded-index layer thickness and the bandgap frequencies can be tuned by the grading profiles. We observe the sequential increment in bandwidth for the complete PBGs in the GPC structures with linear, exponential, and hyperbolic graded-index materials. We also study the influence of the stacking pattern and grading profiles on the bandgap, phase shift, group velocity, delay time, and field distribution. The proposed GPC configurations facilitate the design of reflectors, multi-channel filters, detectors, and other photonic devices. The study may also provide the basis of understanding of the influence of graded-index materials on the PBG characteristics in the GPCs.

A novel symplectic MRTD scheme studies on numerical characteristics of plasma photonic crystals

A novel symplectic multi-resolution time-domain (S-MRTD) scheme is put forward for simulating the one-dimensional unmagnetized plasma photonic crystals (PPCs). The lossless plasma model is taken into account in S-MRTD scheme, and the detailed calculation formulas of the proposed scheme are provided. An one-dimensional perfectly matched layers (PML) technique is used to truncate the computational domain, and the corresponding formulas are also derived. From the perspective of numerical stability and dispersion characteristics, it is shown that the S-MRTD scheme is more effective than the traditional time-domain methods. The propagation process of electromagnetic (EM) waves in one-dimensional PPCs structure are simulated by S-MRTD scheme, and from the perspective of frequency domain, the reflection and transmission cofficients of EM pulse waves through the PPCs are analyzed. Meanwhile, The characteristics of photonic band gaps (PBGs) are studied based on different parameters. Numerical simulations show that plasma frequency, dielectric constant, periodic thickness, number of periods, the thickness ratio of plasma and medium are important factors affecting the characteristics of PBGs.

Photonic bandgaps engineering in double graded hyperbolic, exponential and linear index materials embedded one-dimensional photonic crystals

We present the structuring of different double graded-index materials in the form of one-dimensional (1D) photonic crystals (PCs) for highly efficient light trapping and controlling photonic devices in terms of tuned and controlled photonic bandgap (PBG) performances. Considered 1D graded photonic crystal (GPC) structures are stacked of hyperbolic, exponential, and linear double graded index layers. In the graded index layers, the refractive indices vary in hyperbolic, exponential, and linear fashions as a function of the layer thickness. These configurations show that the operating frequencies and the number of PBGs can be tuned by controlling layer thickness, grading profiles, and grading parameters of the constituted graded layers. The changes in the grading profiles of the graded layers modulate the operation frequencies and also the number of PBGs. We also found that the operating frequencies and bandwidth of PBGs can be tuned by changing the values of initial and final refractive indices of the graded layer. Therefore, the desirable PBG regions and bandwidths can be achieved and controlled by selecting appropriate parameters of the systems. Results can be implemented to design tunable reflectors, multi-channel filters, sensors, and optical detectors. Also, this work may provide an understanding of the effect of different double graded-index materials on PBG characteristics in the GPCs.

Complete photonic band gap characteristics of two-dimensional Kerr nonlinear plasma photonic crystals

In this paper, the characteristics of the complete photonic band gaps for two-dimensional nonlinear plasma photonic crystals are studied theoretically by using the finite-difference time-domain method. The two-dimensional structure comprises nonlinear rods with different geometrical shapes and orientations in a plasma background with square and honeycomb lattices. The embedded dielectric rods containing Kerr nonlinearity have a relative permittivity that is a function of the external light intensity. Our simulation results show that almost all designed nonlinear structures represent noticeable complete band gaps whose position and width can be tuned by altering the light intensity. Furthermore, the influence of geometrical parameters on properties of the band spectra is discussed.

Study on sensing property of one-dimensional ring mirror-defect photonic crystal

Based on the photon localization and the photonic bandgap characteristics of photonic crystals (PCs), one-dimensional (1D) ring mirror-defect photonic crystal structure is proposed. Due to the introduction of mirror structure, a defect cavity is formed in the center of the photonic crystal, and then the resonant transmission peak can be obtained in the bandgap of transmission spectrum. The transfer matrix method is used to establish the relationship model between the resonant transmission peak and the structure parameters of the photonic crystals. Using the rectangular air gate photonic crystal structure, the dynamic monitoring of the detected gas sample parameters can be achieved from the shift of the resonant transmission peak. The simulation results show that the Q-value can attain to 1739.48 and the sensitivity can attain to 1642 nm ⋅ RIU[Formula: see text], which demonstrates the effectiveness of the sensing structure. The structure can provide certain theoretical reference for air pollution monitoring and gas component analysis.

Design of Hollow Core Bragg Fibers for a Compact Fluorescence Sensing Scheme

We propose a compact fluorescence sensing scheme based on hollow core Bragg fibers (HCBFs) that simultaneously serve as a sample cell, a collector, and a delivery channel for the desired fluorescence, as well as a filter for the residual excitation light mixed with fluorescence. The liquid samples filled in the air core are laterally irradiated by the excitation light for the spatial separation from fluorescence. Both the photonic bandgap (PBG) effect in the common HCBF (C-HCBF) and the transverse resonant behavior in the defect HCBF (D-HCBF) can be employed for filtering the residual excitation light mixed with fluorescence. The performance of the fluorescence sensing scheme strongly depends on the characteristics of PBG and modal loss for both types of HCBFs. According to the design principle, we present the design strategies of C-HCBF and D-HCBF for fluorescence sensing, respectively. Two typical examples are demonstrated to confirm the feasibility of our proposed fluorescence sensing scheme. We believe that our proposal would provide a new way to build a compact fluorescence sensing system.

A simple configuration for fabrication of 2D and 3D photonic quasicrystals with complex structures

A simple method using a single-prism common-path interferometer is presented for the fabrication of complex quasicrystals in sub-micrometer scales. Multiple types of two-dimensional (2D) and three-dimensional (3D) quasicrystalline structures are designed and their diffraction patterns are obtained by using Fourier Transform method. Multi-fold rotational symmetries are demonstrated and compared. By using this method, a wide range of quasicrystals types can be produced with arbitrary complexities and rotational symmetries. The transmittance studies of 12-fold and 18-fold structures also reveal the existence of complete photonic bandgaps, which also demonstrates increased symmetry and significantly improved characteristics of photonic band-gaps.

Omnidirectional photonic bandgap of the one-dimensional plasma photonic crystal based on a novel Fibonacci quasiperiodic structure

The binary one-dimensional plasma photonic crystal (1DPPC) based on Fibonacci quasiperiodic structure is studied systematically in this paper. We consider the two simplest cases. In one case, the initial sequences F0 and F1 are both of single layer structure. In another case, one initial sequence (F0 or F1) is of a single layer structure, while the other one (F1 or F0) is of a double layer structure. Thus there are ten different kinds of initial sequences in total. The photonic bandgap characteristics of the 1DPPC with these different initial sequences and numbers of period are analyzed. On these bases, a novel structure of one-dimensional plasma photonic crystal (F3)3 with initial sequence of F0=AP, F1=P and F0=PA, F1=P is proposed in this paper to enlarge the omnidirectional photonic bandgap (OPBG). Compared with previously reported structures in the literature, this structure is simple in configuration with fewer layers and materials, and its OPBG width is wide. The influences of the parameters of the plasma material, such as the thickness, plasma frequency and collision frequency, on the OPBG characteristics of this structure are also discussed. The OPBG width increases with the increase of the thickness and plasma frequency of the plasma layer. Compared with the structures in the literature, the change of OPBG width is the fastest for the proposed structure when the parameters are relatively small. And with the same parameters, the OPBG width for the proposed structure is the widest when the parameters are greater than a certain value. The plasma collision frequency has no effect on the OPBG width for all the structures. But the OPBG width for the proposed structure is the widest when this parameter has the same value. The reason why the proposed structure has an optimal OPBG width is explained by analyzing the dispersion properties of the plasma. The real and imaginary part of the dielectric constant of plasma change with frequency significantly only in the low frequency region. Since the imaginary part of dielectric constant is nearly zero when the frequency is larger than 2 GHz, only the dispersion effect of the real part of dielectric constant needs to be considered in the frequency range we investigate. And its value is much greater than that of conventional medium in the same frequency range. This makes the high-reflectance bands of the 1DPPC broader than those in the case of pure photonic interference phenomena with conventional medium. On the other hand, the corresponding highest proportion of plasma layers in the whole quasiperiodic structure can also be used to explain the broadest band gap of (F3)3. These results can provide important theoretical guidance for designing the novel omnidirectional reflectors.

Analysis of band structure, transmission properties, and dispersion behavior of THz wave in one-dimensional parabolic plasma photonic crystal

The photonic band gap of obliquely incident terahertz electromagnetic waves in a one-dimensional plasma photonic crystal is studied. The periodic structure consists of lossless dielectric and inhomogeneous plasma with a parabolic density profile. The dispersion relation and the THz wave transmittance are analyzed based on the electromagnetic equations and transfer matrix method. The dependence of effective plasma frequency and photonic band gap characteristics on dielectric and plasma thickness, plasma density, and incident angle are discussed in detail. A theoretical calculation for effective plasma frequency is presented and compared with numerical results. Results of these two methods are in good agreement.

Photonic band gap characteristics of one-dimensional graphene-dielectric periodic structures

In this paper, we study theoretically, the transmission properties of a one-dimensional graphene-dielectric periodic structure by using the transfer matrix method. Within the framework of this method, we confirm earlier finding that a periodic structure composed of a stack of monolayer graphene sheets separated by dielectric slabs, possesses photonic band-gap (PBG) properties and supports a series of bandpass and band-stop regions at low-terahertz frequencies. Our calculations showed that the suggested structure possesses in addition to the structural Bragg gaps, a new type of band gap that exhibits a rather versatile behavior with varying angle of incidence. We find this type of band gap is omnidirectional (omni-gap) for both transverse electric (TE) and transverse magnetic (TM) polarizations. Our results show that 1D graphene-dielectric periodic structures are very good candidates for band gap engineering. Specifically, we demonstrate the existence of a band gap region for both polarizations which survives for incident angles as high as 80°. Moreover, we show how our proposed structure can also function as a highly efficient polarization splitter. It is also found that the band gaps can be tuned by tuning the properties of the graphene via a gate voltage. In order to investigate difference between the omni-gap and Bragg PBG, we plot the electromagnetic field profiles for some critical frequencies. The proposed structure is promising and can work as a gate tunable perfect stop filter which completely blocks both polarizations, and may have many other potential applications.

Analysis of the Photonic Bandgaps for Gyrotron Devices

The global bandgaps of photonic crystal are theoretically analyzed in this paper. The electromagnetic-wave propagation characteristics of photonic bandgap (PBG) structures, which is used in the the millimeter-wave, submillimeter-wave, and terahertz regime vacuum electronic devices and accelerators, were numerically simulated using the finite-element method software high-frequency structural simulator. The dispersion curves of the lattices in different rod radius to-rod spacing ratios and the global bandgaps for the general 2-D PBG structures formed by triangular and square arrays of metal rods were simulated. A mode map that shows the relationship between the structures and the contained modes was plotted and a 220-GHz metallic PBG resonator operating in TE $_{\mathrm {\mathbf {04}}}$ mode was designed for a gyrotron device to verify the theoretical and numerical simulations, and a comparison of mode density and quality factor between the PBG resonator and the equivalent cylindrical resonator has been carried out.

基于光子晶体带隙特性的反射式多通道滤光片设计

基于光子晶体带隙特性的反射式多通道滤光片设计

Characteristics of 2D Cylindrical Photonic Crystals Band Gap with Square Lattice

The structure of two-dimensional (2D) photonic crystals (PCs) with square lattice is proposed in this paper, and researches on characteristics of photonic band gap (PBG) are conducted using finite difference time domain (FDTD) method, then the effects of the dielectric constant and the radius of dielectric rods on band gap are analysed, dielectric rods in air (rods/air). The research results indicate that in the case of TE and TM polarization mode, the difference value of dielectric constant of medium and dielectric rods affects forming PBG.The band gap broadens with the difference value increasing. Whats more, the complete band gap (CBG) appears in range of large rods radius structure when dielectric constants of rods are smaller than that of medium.

Extraction-Derived Self-Organization of Colloidal Photonic Crystal Particles within Confining Aqueous Droplets

In this work, we developed a novel and simple microfluidic method for the fabrication of self-assembled monodispersed photonic crystal microbeads with core–shell structures using solvent extraction. Monodispersed aqueous droplets encapsulating colloidal photonic crystal particles were produced in a T-junction microfluidic device, and the controlled transport of water from the aqueous droplets to the oil phase created spherical colloidal crystal microbeads with controlled shell–core structures by extraction-derived self-organization of the colloidal nanoparticles. While the solidification of colloidal particles from emulsion droplets in an oven took tens of hours, the present extraction-derived method reduces the time required for solidification to several minutes. Compared with recent microwave-assisted consolidation methods which showed a particle material dependency, our new method exhibited no such limitation. The results showed that the packing quality of colloidal crystals, which can be precisely controlled by adjusting the extraction rate and surfactant, was high enough to show photonic band-gap characteristics. The reflectance of our photonic microbeads responded precisely to any change in physical properties including the size of colloidal particles and refractive index. A mechanism of the extraction-derived self-assembly of colloidal particles was developed and then supposed by theoretical derivations and experimental results. Finally, the universality of the method was demonstrated by fabricating SiO2 photonic crystal microbeads.