Photonic Gap Research Articles

Spectral and Polarization Characteristics of the Light Passing through a Cholesteric Photonic Crystal

Combined optical studies of a cholesteric photonic crystal are performed: the transmission spectra and the rotation of the plane of polarization of light (RPPL) spectra of the crystal are recorded, and the polarization characteristics of the light having passed through the photonic crystal are measured. The RPPL spectra have specific features related to the presence of a photonic quasi-band gap. The photonic density of states and its transformation with the photonic crystal temperature and thickness are determined. The ellipticity (ratio of the minor to the major axis of ellipse) of the light having passed through the sample is maximal at the center of the band gap and decreases when the distance from the band gap increases. At the center of the photonic quasi-band gap, the ellipticity increases with increasing photonic crystal thickness L and decreasing temperature, and it is close to a circular one in samples with L > 5 μm. The results obtained are compared with the existing theories, the analytical expressions derived from the Maxwell equations, and the results of numerical calculations performed by the 4 × 4 Berreman matrix method

Impact of the tilted magnetic field on the propagation of oblique waves in the plasma superlattice

In its most general statement, we consider the problem of the impact of the external magnetic field on photonic properties of the superlattice comprising dielectric and conducting layers: the direction of the wave propagation as well as the direction of the external magnetic field are assumed to be arbitrary. We show that even a relatively weak external magnetic field can drastically alter the photonic spectrum of the superlattice, since within the photonic gaps there emerge photonic bands making the superlattice transparent for incident radiation. We demonstrate that the spectral width of photonic bands can be effectively controlled by rotation of the static external magnetic field.

Meron Spin Textures in Momentum Space.

We show that a momentum-space meron spin texture for electromagnetic fields in free space can be generated by controlling the interaction of light with a photonic crystal slab having a nonzero Berry curvature. These spin textures in momentum space have not been previously noted either in electronic or photonic systems. Breaking the inversion symmetry of a honeycomb photonic crystal gaps out the Dirac cones at the corners of Brillouin zone. The pseudospin textures of photonic bands near the gaps exhibit a meron or antimeron. Unlike the electronic systems, the pseudospin texture of the photonic modes manifests directly in the spin (polarization) texture of the leakage radiation, as the Dirac points can be above the light line. Such a spin texture provides a direct approach to visualize the local Berry curvature. Our work highlights the significant opportunities of using photonic structures for the exploration of topological spin textures, with potential applications towards topologically robust ways to manipulate polarizations and other modal characteristics of light.

Controlling the null photonic gap and zero refractive index in photonic superlattices with temperature-controllable-refractive-index materials

Temperature-adjustable optical properties of two types of one-dimensional photonic superlattices made from lithium niobate or liquid crystal are theoretically investigated. The control of band structures and density of states is achieved through the temperature with various values of refractive index, layer width, and propagation wavelength. It is presented that a null photonic gap appears at certain temperature points, which are decided by the ratio of layer width and the refractive index. It is shown that the spatial average of the wave vector ⟨ k ⟩ vanishes at a specific temperature as functions of the layer thickness and refractive index. The values of the temperature corresponding to zero-refractive-index (zero- ⟨ n ⟩ ) are demonstrated to be suppressed when the refractive index or the ratio of the layer width is enhanced. Null photonic gap and zero- ⟨ n ⟩ can appear simultaneously at certain wavelengths in the range of visible light, which can be modulated by the temperature. This implies the importance of one-dimensional photonic superlattices made from temperature-controllable-refractive-index materials for many important practical applications.

Effects of hydrostatic pressure on an L1 and L3 cavity of a photonic slab

In this work, we used the guided-mode expansion method to calculate the photonic band dispersion in two-dimensional photonic crystal slabs. The photonic lattice is hexagonal, composed of air holes with a circular cross-section. The slab is made of a semiconductor material (GaAs) with a dielectric function dependent on pressure and temperature. By maintaining the constant temperature, we found a shift in the photonic band dispersion towards regions of larger frequencies when the hydrostatic pressure increased. Moreover, we consider the effects of pressure on defective modes in cavities L1 and L3. The results reveal that by increasing the pressure, the position of the defective modes manages to tune for the photonic gap. Additionally, we found a decrease in the Q-factor for the L1 cavity when the pressure increases. However, for the L3 cavity, the Q-factor exhibits a non-monotonous behavior by increasing the pressure.

The guided-mode expansion method in the calculate of dispersion of photonic band in symmetrical slabs composed by square lattices

In this paper, we calculate the photonic band dispersion in two-dimensional photonic crystal slabs using the guided-mode expansion method. We consider that the two-dimensional photonic crystal comprises air holes with circular cross-sections distributed in a square lattice. We report an increase in the width of the photonic gap for TE-like modes when we increase the radius of the holes while holding slab thickness constant. Considering the dependence of the dielectric function of the slab on pressure and temperature, as the pressure increases at a fixed temperature, a shift to higher frequencies is observed for the photonic band dispersion in TE-like and TM-like modes.

Stochastic analysis for one dimensional photonic crystals

Tolerance variations of the design parameters of the photonic crystals due to fabrication processes have a strong effect on the performance of the photonic crystals and their operating wavelengths. In this work, the uncertainties of the design parameters of one-dimensional photonic crystals (1D-PCs) and their impacts on the PCs optical properties and the operating performance are investigated. The effects of these uncertainties for different tolerances are studied for both defect-free PCs and PCs with a defect air layer. The probability distribution function and the standard deviations of the photonic gap bandwidth, the defect mode wavelength and the trust gap width are studied. These stochastic analyses and modeling are based on the transfer matrix and Monte Carlo simulations.

One-dimensional photonic crystal with coupled InSb defects

In this work, we estimate the transmittance spectrum in a one-dimensional photonic crystal with two coupled defects of an extrinsic semiconductor of n-type InSb. By applying the transfer matrix method, we detected two defective modes in the photonic gap. These defective modes are sensitive to increases in both temperature and doping concentration. A blue-shift is produced along with a decrease in the transmittance value. We also estimated the effect on defective modes when increasing the separation between defects; when the number of layers increased, the separation among the defective modes decreased.

X-ray Imaging of Functional Three-Dimensional Nanostructures on Massive Substrates.

To investigate the performance of three-dimensional (3D) nanostructures, it is vital to study their internal structure with a methodology that keeps the device fully functional and ready for further integration. To this aim, we introduce here traceless X-ray tomography (TXT) that combines synchrotron X-ray holographic tomography with high X-ray photon energies (17 keV) in order to study nanostructures “as is” on massive silicon substrates. The combined strengths of TXT are a large total sample size to field-of-view ratio and a large penetration depth. We study exemplary 3D photonic band gap crystals made by CMOS-compatible means and obtain real space 3D density distributions with 55 nm spatial resolution. TXT identifies why nanostructures that look similar in electron microscopy have vastly different nanophotonic functionality: one “good” crystal with a broad photonic gap reveals 3D periodicity as designed; a second “bad” structure without a gap reveals a buried void, and a third “ugly” one without gap is shallow due to fabrication errors. Thus, TXT serves to nondestructively differentiate between the possible reasons of not finding the designed and expected performance and is therefore a powerful tool to critically assess 3D functional nanostructures.

Tunable band structure in 2D Bravais–Moiré photonic crystal lattices

This work introduces the recent so called Bravais–Moiré theory in the context of two dimensional photonic crystals. In particular, new periodic cells involving commensurable bilayer rotated square alignments of photonic crystals with different permittivity constants are considered. The corresponding band gaps are wider than those usually reported in literature for square lattice dielectric structures, and a practical comparison is carried out in the calculation in order to verify such assert. These photonic gaps can be adjusted by changing different lattice parameters, such as the commensurable angle, and the permittivities involved.

Analysis of Temperature Sensors Based on Ternary One Dimensional Photonic Crystals with Double Defects

Based on the transfer matrix method (TMM), the interaction of electromagnetic waves in ultraviolet (Uv), visible and Infrared (IR) spectra with ternary one-dimensional photonic crystals with different double defects, has been theoretically studied. The multilayer system has been taken as temperature dependent. The numerical results showed that the number of photonic band gap (PBG) was increased by increasing the degree of temperature. The variation of temperature, the thickness of the second layer and both the type and the thickness of the second defect caused shifting of the photonic ban gaps to higher wavelengths which can be exploited in the design of temperature sensors.

The interaction between optical Tamm state and microcavity mode in a planar hybrid plasmonic-photonic structure

We have studied the mode hybridization between the optical Tamm state and a microcavity mode in a planar hybrid plasmonic-photonic crystal structure. The optical Tamm state appears as an allowed mode within the photonic stop gap of the photonic crystal structure. Unlike the conventional microcavity mode which localizes its energy inside the structure, the Tamm mode localizes its optical energy at the interface between the plasmonic layer and photonic crystal structure. The strong coupling between the Tamm and microcavity mode is achieved through evoking the Tamm mode dependence of the top layer thickness of the hybrid structure. The Tamm and microcavity mode exhibit an avoided crossing characteristics in the strong coupling regime with a Rabi splitting of 4.3 meV. The electric field intensity is calculated to confirm the indistinguishability of individual modes in the exact coupling regime. The electric field intensity is spatially localized both at the interface and deep within the photonic crystal structure. The structural parameters that would influence the strong coupling between the modes are also discussed.

New dynamic mechanism of interplay between nonlinearity and Bragg scattering in a femtosecond all-optical photonic crystal switch

We have studied a femtosecond (fs) ultrafast all-optical photonic crystal (PhC) switch, and a new dynamic mechanism of the interplay between nonlinearity and Bragg scattering is revealed. Almost all phenomena observed in the experiments are reproduced in our numerical simulations. Completely different from the traditional band-gap shift mechanism, we propose a new dynamic mechanism that can explain the considerable increase of transmission and almost all other complex transmission behaviors of the switch. First, the fs-level ultrashort-lifetime nonlinearity generated by the fs pumping pulse, which cannot generate a band-gap shift, only causes a sudden phase change on the signal field that is still inside the PhC. Second, such a phase change can partially destroy the destructive interference of Bragg scattering, which is the physical reason for the low transmission in the photonic gap of the PhC. The study by Fourier transform of the temporally transmitted field can clearly support our new explanation. New phenomena, such as the larger than unity sum of transmission and reflection, are predicted. The new dynamic mechanism could be widely used in other systems as a new method to amplify nonlinear effects, or as a detector for ultrafast (femto- or attosecond) electronic processes.

Proof of the Bulk-Edge Correspondence through a Link between Topological Photonics and Fluctuation-Electrodynamics

The bulk-edge correspondence links the Chern-topological numbers with the net number of unidirectional states supported at an interface of the relevant materials. This fundamental principle is perhaps the most consequential result of topological photonics, as it determines the precise physical manifestations of nontrivial topological features. Even though the bulk-edge correspondence has been extensively discussed and used in the literature, it seems that in the general photonic case with dispersive materials it has no solid mathematical foundation and is essentially a conjecture. Here, I present a rigorous demonstration of this fundamental principle by showing that the thermal fluctuation-induced light-angular momentum spectral density in a closed cavity can be expressed in terms of the photonic gap Chern number, as well as in terms of the net number of unidirectional edge states. In particular, I highlight the rather fundamental connections between topological numbers in Chern-type photonic insulators and the fluctuation-induced light-momentum

Can a photonic thermalization gap arise in disordered non-Hermitian Hamiltonian systems?

The phenomenon of a chiral-symmetry protected thermalization gap in Hermitian photonic systems is counterintuitive as it implies that the photon coherence can be continuously improved by disorders towards an asymptotic limit. We show that the phenomenon disappears in time-independent, non-Hermitian photonic systems even when the chiral symmetry is well preserved. In fact, the degree of thermalization generally increases with the disorder strength, in agreement with intuition. As non-Hermitian characteristics (e.g., weak gain and loss) can be expected in realistic physical situations, the phenomenon of a thermalization gap may be observed but only in well-controlled experiments with high-quality materials.

Effect of segment length modification on localized modes in Cantor bar microstrip lines

We investigated the impurity modes in a one-dimensional fractal called Cantor bar by modifying the central and side segment lengths of the microstrip lines to control the propagation properties of the microwaves. It was confirmed, using a vector network analyzer, that there exists several localized modes in the photonic gap regions in the third-stage Cantor bar with self-similar patterns. By simulating the electrical current using the method of moments, the microwaves were found to localize in either the central segment area or in both the end areas of the fractal pattern. The length modification of the segment where the microwave is localized led to large frequency shifts of the localized modes and hardly influenced the gap region. The quality factors of the modes localized in the central area are quite affected by the length modifications of both the first and second segments.

CAVITY MODES IN DUAL PHONONIC AND PHOTONIC CRYSTAL WITH WIDE ABSOLUTE BANDGAP

In this paper, we discuss theoretically the simultaneous existence of dual phononic and photonic band gaps and cavity modes in a PhoXonic crystal. The cavity is created in the center of a square lattice PhoXonic crystal made from silicon using the one-missing-holes point defect (L1). Following the design, dispersion diagrams and the resonant frequency are numerically analyzed by the finite elements method (FEM). Optimization of the PhoXonic crystal design by modulating the structure parameter yields a complete phononic gap together with a photonic gap. Furthermore, we demonstrate the existence of the largest number of cavity modes with a high quality factor of 10 5 . This structure configuration design shows considerable promise as regards the simultaneous confinement of acoustic and optical waves and thus more attractive for experimental observation of optomechanical coupling.

Nanophotonic control of the color center emission from nanodiamonds.

Recently, the nitrogen vacancy (NV) center has emerged as a deterministic single-photon source at room temperature. However, the presence of phonon sideband emission limits the use of NV centers in various quantum optical applications. Here we report a novel way to suppress the phonon sideband emission of NV centers aided with the enhancement of zero phonon line intensity using photonic crystals at room temperature. We study the photonic stop gap mediated charge state conversion in NV centers. The enhancement of phonon sideband emission from the same structures by implementing a different measurement geometry is also discussed. The studies open new avenues in studying the NV center-based quantum nanophotonics and biophotonics.

Effect of Annealing Temperature in ZnO For Photonic Applications

ZnO nanorods were synthesized on glass substrate by two step chemical bath deposition (CBD) method and annealed at different temperatures in argon environment for 1 hour. The structural and optical properties of the as-grown and annealed samples were investigated using X-ray diffractometer (XRD), UV-Visible-NIR spectroscopy, Raman spectroscopy and photoluminescence (PL) measurement. As grown sample has the largest crystallite size with a photonic gap of 90 nm whilst. Raman measurement shows sharp E2 (H) peak typical for the wurtzite ZnO structure and PL spectra exhibit a strong UV emission peak at 380 nm for all samples. The ratio of UV to visible peak in the PL spectrum for as grown sample was the highest indicating lowest level of defects for these set of samples. This is consistent with the crystallinity of the samples. Results suggest potential of using CBD as a method of growth for synthesizing ZnO nanorods for nanophotonic devices.

A multichannel filter based on ternary nano metallo-dielectric photonic crystal with Thue-Morse defect layer structure

In this paper, we have investigated a multichannel filter by using one dimensional ternary photonic crystal (1DTPC). We have used Thue-Morse sequence (TMS) for defect layer. To model the multichannel filter, we have checked the effect of different number of unit cells (N) and TMS in defect layer (m). First, we have plotted transmission in terms of wavelength with different N in TPC. Then, we have shown transmission in terms of wavelength for different m in normal incidence. The analysis shows that there are three photonic bang gaps (PBG) with three channels in visible and two PBG with three channels in infrared regions in transverse electric (TE) polarizations. As we have shown the transmission value decreased by increasing N. Moreover, the number of channels increased by increasing m in both visible and infrared regions. So, by tuning them, this structure can use as multichannel filter within an optical wavelength range.