Spectra Of Photonic Crystals Research Articles

The effect of singularities and damping on the spectra of photonic crystals

Understanding the dispersive properties of photonic crystals is a fundamental and well-studied problem. However, the introduction of singular permittivities and damping complicates the otherwise straightforward theory. In this paper, we study photonic crystals with a Drude–Lorentz model for the permittivity, motivated by halide perovskites. We demonstrate how the introduction of singularities and damping affects the spectral band structure and show how to interpret the notion of a “band gap” in this setting. We study a one-dimensional model for which we present explicit solutions.

High-purity foam-like micron-sized gold cage material with tunable plasmon properties

Herein, by growing mono dispersed gold nanoparticles (MNPAu) on the surface of polystyrene (PS)/nanogold (Au) core–shell composites (PS@Au), we successfully synthesized a micron-sized gold cage (2.6–10.7 μm), referred to as PS@Au@MNPAu for the first time. The new micron-gold cage materials exhibit broadband absorption range from near-ultraviolet to near-infrared, which is unlike the conventional nanogold core–shell structure. The uniform growth of MNPAu on the surface forms a new photonic crystal spectrum. The strong coupling of the spectra causes anomalous absorption in the ultraviolet-near infrared band (400–900 nm). Furthermore, by removing the PS core, a nanogold cavity structure referred to as Au@MNPAu was prepared. This structure demonstrated a high purity (> 97 wt%), low density (9–223 mg/cm3), and high specific surface area (854 m2/g). As the purification process progressed, the MNPAu coupling on the surface of the micro-gold cage strengthened, resulting in the formation of peaks around 370 nm, plasma resonant peaks around 495 nm, and structural bands of photonic crystal peaks around 850 nm. The micron-sized gold cage provides hybridized and tunable plasmonic systems. The theoretical simulations indicate that this plasmon anomalous absorption phenomena can be understood as the novel form of the topological structural transitions near the percolation threshold, which is consistent experimental measurements.

Nonlocal electrodynamics of homogenized metal-dielectric photonic crystals

The nonlocal effective permittivity tensor for photonic crystals (PCs), having dielectric and metallic inclusions in the unit cell, is calculated and analyzed within the homogenization theory based on the Fourier formalism and the form-factor division approach. A method allowing us to extract the effective bianisotropic metamaterial parameters (permeability and chirality) from the wave vector dependence of the nonlocal effective dielectric response is proposed. Both the original nonlocal dielectric response parameters and the new bianisotropic metamaterial ones reproduce the photonic band structure of the artificial crystal far beyond the long wavelength limit and for a wide class of metal-dielectric structures. To calculate the optical spectra (reflection and transmission) of finite-size PC, the nonlocal homogenization approach is extended with the method of expansion into photonic bulk-modes (Bloch waves). The application of the developed theory is illustrated with well-known forms of metallic inclusions (slabs, thin wires, split-ring resonators) and experimentally confirmed with novel designs based on metallic crosses.

Thermal darkening of one-dimensional photonic crystal containing tellurium suboxide

The purpose of this study is to experimentally and theoretically evaluate the optical properties of a one-dimensional photonic crystal (PC) with a defect layer before and after an annealing procedure. A sputtering technique with high index (TeOx) and low index (SiO2) materials was used to fabricate the 1D PC with a defect layer. The chemical and structural analysis of a single layer TeOx thin film was evaluated by X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX), and X-Ray Diffraction (XRD). The optical constant of the single layer was also determined based on the envelope method from transmittance spectra measured by ultraviolet visible near-infrared spectrophotometry (UV-VIS-NIR). The measured reflectance spectra of the 1D PC were compared with the results simulated using the transfer matrix method (TMM) before and after the annealing procedure. A photonic bandgap (PBG) appears within the desired, near-infrared (NIR), region. The defect mode in the 1D PC was observed at λ = 1455 nm within the PBG of λ = 1235–1723 nm (Δλ = 488 nm). The reflectance spectra overall shifted toward longer wavelength due to thermal darkening effect resulting from the thermally induced optical property changes.

Wavelength-selective thermal emitters using Si-rods on MgO

Supporting substrates for Si rod-type photonic crystals (PCs) are investigated for realizing highly wavelength-selective near-infrared thermal emitters. Three materials—SiO2, Al2O3, and MgO—are considered for their low infrared emission (transparency) and remarkable heat resistance. Theoretical calculations of the emissivity spectra of Si-rod PCs (rod height = 500 nm, rod diameter = 300 nm, and lattice constant = 600 nm) on 50 μm-thick supporting substrates at 1400 K indicate that the long-wavelength (>3 μm) emission power from the emitter using MgO is less than 1/10 of that of the other two materials. Fabrication of the Si-rod PCs on the 50 μm-thick MgO substrate requires the insertion of a thin (30 nm) HfO2 film between MgO and Si to improve the stability at high temperatures (>1400 K). Experimental results of the fabricated structure show that at 1400 K, the ratio of emissive power at wavelengths <1.8 μm to the total emissive power is 34% and that this can be increased to over 53% in an optimized rod-array structure with a 10 μm-thick MgO substrate.

Influence of dielectrics with light absorption on the photonic bandgap of porous alumina photonic crystals

In this work, the influences of dielectrics with light absorption on the photonic bandgaps (PBGs) of porous alumina photonic crystals (PCs) were studied. Transmittance spectra of porous alumina PCs adsorbing ethanol showed that all the PBGs positions red-shifted; however, the transmittance of the PBG bottom showed different trends when the PBGs were located in different wavelength regions. In the near infrared region, liquid ethanol has strong light absorption, and, with the increase in adsorption, the PBG bottom transmittance of porous alumina PCs first increased and then decreased. However, in the visible light region, liquid ethanol has little light absorption, and thus, with the increase in adsorption, the PBG bottom transmittance of porous alumina PCs increased gradually all the time. Simulated results were consistent with the experimental results. The capillary condensation of organic vapors in the pores of porous alumina accounted for the change in the PBG bottom transmittance. The nonnegligible light absorption of the organic vapors was the cause of the decrease in the transmittance. The results for porous alumina PC adsorbing methanol, acetone, and toluene further confirmed the influences of light absorption on the PBG bottomed transmittance.

Interaction of a Gaussian pulse with a one-dimensional photonic crystal

A computer analysis of the profiles of reflected pulses and pulses passed through a photonic-crystalline medium has been performed. The time shift of the frequency component and its influence on the general pattern of signal distortion have been investigated. It is shown that the profiles of reflected and transmitted pulses are distorted even when they are normally incident on a defect-free one-dimensional photonic crystal. Distortions of the pulse profiles at the boundaries of the forbidden band of the photonic-crystal spectrum are most significant.

Colloidal particles with various glass transition temperatures: preparation, assembly, and the properties of stop bands under heat treatment

Monodisperse P(St-co-nBA-co-AA) colloidal microspheres with various glass transition temperatures (T gs), whose average particle sizes were about 300 nm, were prepared using soap-free emulsion polymerization by adjusting the ratio of styrene and n-butyl acrylate. Colloidal photonic crystals were assembled with these microspheres by vertical deposition method. Stop bands of colloidal crystals under different temperatures have been characterized. The relationship between the stop band and temperature was indicated. The microstructure and reflectance spectra of photonic crystals were characterized by SEM and fiber spectrometer, respectively. Results showed that as the temperature increased, only a little red shift of stop band appeared in the vicinity of T g and the intensity of the maximum reflection peak decreased until the stop bands disappeared. Furthermore, enough heating time at the T g ±2 °C could also lead to the disappearance of stop bands. What’s more, colloidal crystal films with certain connection strength were obtained by simple heating.

Two Dimensional Photonic Crystal Biosensors

Based on the rigorous coupled wave theory, the narrowband reflect spectral imaging characteristics on two-dimensional photonic crystal are analyzed, and two-dimensional photonic crystal sensor probe biological structure and photonic crystal biosensor system are constructed. The simulation proved that, when the adsorption medium at the surface of two-dimensional photonic crystal are different, the white light narrowband reflection resonance mode peak wavelength would drift, and the drift quantity of the peak wavelength and the refractive index of the adsorptive medium is in a linear relationship. Colored the space imaging spectra of photonic crystal, the changes of the adsorbate refractive index in different area of the photonic crystal surface can be observed , the adsorbate concentration changes can also be got. This conclusion can be applied to biochemical substances, pharmaceutical, biological molecules and environmental pollution detection.

Spectral properties of a two-dimensional resonant metal-dielectric photonic crystal

We have studied the transmission spectra of resonant two-dimensional photonic crystals of two types, one of which consists of nanocomposite cylinders that form a square lattice in vacuum and the other of which consists of cylindrical holes that form a square lattice in nanocomposite matrix. The nanocomposite consists of metallic nanospheres that are dispersed in a transparent matrix and is characterized by an effective resonant dielectric permittivity. We show that, depending on the position of the resonant frequency of the nanocomposite with respect to the boundaries of the band gap, there arises either an additional transmission band in the transmission spectrum in the band gap or an additional band gap in the continuous spectrum of the photonic crystal. As the structural and geometric parameters of the system change, both the additional transmission band and the additional band gap are considerably modified. We analyze particular features of the spatial distribution of the electromagnetic field intensity in crystals. The considered effects can be used to extend the possibilities of creating new photonic crystals with specified properties.

Local spectroscopy of band gaps in ferroelectric photonic crystals

We have measured visible to near-UV reflection spectra of opal photonic crystals infiltrated with ferroelectrics: barium titanate, sodium nitrite, potassium iodate, and triglycine sulfate. An experimental procedure has been developed for the infiltration of various ferroelectrics into opal pores through laser ablation and laser implantation. Using a fiber-optic probe, we were able to analyze surface reflection spectra of photonic crystals with a 0.2-mm resolution. A deuterium lamp was used as a broadband UV source, which allowed us to observe both the first and second [111] photonic band gaps in the reflection spectrum of opal crystals.

Transmission of light through a plane-parallel plate of a two-dimensional resonant photonic crystal

The transmission spectra of two-dimensional resonant photonic crystals of two types have been investigated. Crystals of one type consist of dielectric cylinders forming a square lattice filled by a resonant gas with mercury atoms, and crystals of the other type consist of cylindrical holes filled with a gas and forming a square lattice in a dielectric matrix. It has been established that characteristics of the spectrum of additional transmission arising in the band gap of the photonic crystal can be changed significantly by varying the gas pressure and the angle of incidence. It has been demonstrated that the calculated features in the transmission spectrum of the photonic crystal are stable with respect to a significant increase in the width of the atomic resonance.

Experimental Demonstration on Structure-Parameter Dependence of Photonic Crystal Optical Spectrum

We present fabrication and experimental measurement of a series of photonic crystal waveguides and coupled structure of PC waveguide and PC micro-cavity. The complete devices consist of an injector taper down from 3 microm into a triangular-lattice air-holes single-line-defect waveguide. We fabricated these devices on a silicon-on-insulator substrate and characterized them using tunable laser source. We've obtained high-efficiency light propagation and broad flat spectrum response of photonic-crystal waveguides. A sharp attenuation at photonic crystal waveguide mode edge was observed for most structures. The edge of guided band is shifted about 31 nm with the 10 nm increase of lattice constant. Mode resonance was observed in coupled structure. Our experimental results indicate that the optical spectra of photonic crystal are very sensitive to structure parameters.

Optically excited secondary emission spectra of photonic crystals based on synthetic opals

The photonic dispersion, the group-velocity dispersion, the effective mass, refractive index, and the spectral distribution of the density of photonic states near the edge of the photonic stop band are numerically calculated in the one-dimensional model for photonic crystals based on synthetic opals. The fluorescence spectra of rhodamine 6G and 2,5-bis(2-benzoxazolyl)hydroquinone molecules infiltrated into a synthetic opal are measured. For both substances, it is observed that the spontaneous emission intensity in the range of the photonic stop band is appreciably suppressed. A blue shift of the fluorescence spectrum of rhodamine 6G molecules is revealed. Secondary emission of synthetic opals infiltrated with colloidal silver is observed in the Stokes range under excitation of opals by radiation at λ = 400 nm. The spectrum of the secondary emission is located in the range 450–590 nm, which contains the stop band and intervals near its edges.

Absorption spectra versus field distribution for metal-dielectric three-dimensional photonic crystals

The absorption spectra of three-dimensional metal-dielectric photonic crystals (PCs) are studied using computer simulation by the finite difference time domain method and the layered Korringa-Kohn-Rostoker method. The band structure of a three-dimensional dielectric PC is obtained by the plane wave expansion method. The explanation of absorption spectra of PC based on its comparison with the band structure and Fabry-Perot resonances inside a PC plate is given. The intensity distribution of an electric field using FDTD inside the metal-dielectric PC for three various structures is analyzed. It is shown that spherical cavities in a dielectric PC “focus” the field inside cavities at certain wavelengths. This leads to an increase of absorption at these wavelengths if metal spheres are located in the centers of those cavities. This effect can be considered as an analogue of the Borrmann effect in X-ray spectroscopy.

Absorption spectra versus field distribution for metal-dielectric three-dimensional photonic crystals

The absorption spectra of three-dimensional metal-dielectric photonic crystals (PCs) are studied using computer simulation by the finite difference time domain method and the layered Korringa-Kohn-Rostoker method. The band structure of a three-dimensional dielectric PC is obtained by the plane wave expansion method. The explanation of absorption spectra of PC based on its comparison with the band structure and Fabry-Perot resonances inside a PC plate is given. The intensity distribution of an electric field using FDTD inside the metal-dielectric PC for three various structures is analyzed. It is shown that spherical cavities in a dielectric PC “focus” the field inside cavities at certain wavelengths. This leads to an increase of absorption at these wavelengths if metal spheres are located in the centers of those cavities. This effect can be considered as an analogue of the Borrmann effect in X-ray spectroscopy.

FLAT PASS-BANDS OF ONE-DIMENSIONAL PHOTONIC CRYSTALS COMPOSED OF MULTIPLE QUANTUM WELLS WITH GAUSSIAN-DISTRIBUTED REFRACTIVE INDICES

Transmissions of one-dimensional (1D) photonic crystals (PCs) containing multiple quantum wells with Gaussian-distributed refractive indices are calculated with the use of the transfer-matrix method. The transmission spectrum of this kind of structures exhibits flatted pass-bands. The resonant peaks in the transmission spectrum of the conventional 1D PCs have been significantly suppressed. It is expected that this kind of structures may favor the fabrication of optical filters in applications to micro-optical devices.

Fluorescence of a two-level atom in a two-dimensional photonic crystal in the vicinity of the saddle point of the photonic band spectrum

The fluorescence of a two-level atom embedded into a two-dimensional photonic crystal is considered under the assumption that the electronic transition frequency ω10 is close to the photonic mode frequency ω0 in the saddle critical point of the photonic spectrum. In this case, the density of photonic states has a logarithmic peak, which manifests itself in a considerable rearrangement of the fluorescence spectrum. The Green’s function of the electron-photon system, which contains the description of the dynamics of spectroscopic transitions and the shape of fluorescence spectra, is obtained in the rotating field approximation. Using the Green’s function, the frequency-dependent Lamb shift and the broadening of the atomic transition are calculated. The shape of the fluorescence spectra is studied. At a large oscillator strength of the atomic transition, the fluorescence line splits into two components in the vicinity of the singularity caused by the saddle critical point. This splitting is associated with a specific Fano-type resonance between the discrete spectrum (the atomic states) and the continuum (the dispersion of photons with a saddle critical point). At small detunings δ = ω10-ω0, the components of the fluorescence line have considerably different intensities. As δ increases, the spectral positions of the strong and weak components tend to the frequencies of the atomic transition and the saddle point, respectively. The results obtained show that two-level atoms (or quantum dots) can be used as specific probes of the band spectra of photonic crystals.

Characterization of Photonic Crystals Based on Opal–Semiconductor Composites by Bragg Reflection Spectroscopy

The Bragg reflection spectra of photonic crystals based on the opal-semiconductor (GaP, GaN) composites are studied. An approach is developed which provides a means for characterizing the opal-like structures. The approach is based on examination of the Bragg reflection spectral features and of the conditions for multiwave Bragg diffraction. The shape of the Bragg spectra is analyzed in the context of the approximation of a periodic planar-layered medium taking into account sintering and axial compression of the a-SiO2 spheres that constitute the three-dimensional opal lattice. The diameters and the coefficient of compression of the spheres are determined with regard to the spectroscopic structural invariant suggested in the study for defining the conditions for observation of multiwave Bragg diffraction at the system of the {111} planes.

Isotropic photonic band gap and anisotropic structures in transmission spectra of two-dimensional fivefold and eightfold symmetric quasiperiodic photonic crystals

We measured and calculated transmission spectra of two-dimensional quasiperiodic photonic crystals (PCs) based on a 5-fold (Penrose) or 8-fold (octagonal) symmetric quasiperiodic pattern. The photonic crystal consisted of dielectric cylindrical rods in air placed normal to the basal plane on vertices of tiles composing the quasiperiodic pattern. An isotropic photonic band gap (PBG) appeared in the TM mode, where electric fields were parallel to the rods, even when the real part of a dielectric constant of the rod was as small as 2.4. An isotropic PBG-like dip was seen in tiny Penrose and octagonal PCs with only 6 and 9 rods, respectively. These results indicate that local multiple light scattering within the tiny PC plays an important role in the PBG formation. Besides the isotropic PBG, we found dips depending on the incident angle of the light. This is the first report of anisotropic structures clearly observed in transmission spectra of quasiperiodic PCs. Based on rod-number and rod-arrangement dependence, it is thought that the shapes and positions of the anisotropic dips are determined by global multiple light scattering covering the whole system. In contrast to the isotropic PBG due to local light scattering, we could not find any PBGs due to global light scattering even though we studied transmission spectra of a huge Penrose PC with 466 rods.