Anisotropic Defect Layer Research Articles

An ultracompact optical polarizer based on the one-dimensional photonic crystals containing anisotropic layers

The linear birefringence effect of the uniaxial anisotropic materials is utilized to design an optical polarizer in this paper. We propose a one-dimensional photonic crystal structure with an anisotropic defect layer to break the degeneracy of the TE and TM mode resonances. The band structures of the TE and TM mode polarizations are calculated using the plane wave expansion method, which has been generalized for the structures containing anisotropic materials. By increasing the refractive index contrast ratio of the HL pair layers of the crystal, we present an ultracompact structure with significant performance of a very high polarization extinction ratio (PER) and a very low insertion loss (IL). The presented polarizer, which operates at the near-infrared region centered at the wavelength of 1550 nm, is 2.67 μm long. It is obvious that the structure is considerably compact for the long wavelength of the third communication window. The polarizer can be designed in such a way that only the fields with a specific polarization direction (TM, TE, or any other direction) are transmitted.

Bound state in the continuum in an anisotropic photonic crystal supported by a full-wave phase plate

We consider bound states in the continuum (BICs) in a 1D multilayered system of an anisotropic defect layer embedded into an anisotropic photonic crystal. We analytically demonstrate that an anisotropic defect layer embedded into anisotropic photonic crystal supports accidental BICs. These BICs can be transformed to high-Q resonances by variation of one of the system’s parameters. At the same time, the BICs are remarkably robust in the sense that a true BIC can be recovered by further tuning any of the system’s other parameters, leading to tunability of the resonance position.

Spectral statistics of a 1D photonic crystal containing an anisotropic graphene-based hyperbolic metamaterial defect layer

A simple photonic crystal is a periodic and regular nanostructure. Breaking the periodicity of a photonic crystal by a defect layer can be an interesting pattern. We study the spectral statistics of eigenfrequency spacings (the so-called level spacing statistics) for TM-polarized waves in the one-dimensional (1D) defective photonic crystal containing graphene-based hyperbolic metamaterial as a defect layer. The localization of light in the proposed structure has been investigated using the transfer matrix method. Moreover, the effects of different parameters, such as the number of graphene cells and the defect layer's optical axis orientation, are discussed. The performance of the ratios of nearest neighbor level spacings has become a Wigner distribution at the localized phases which are introduced by inserting a defect layer. The spectral statistics are found to approach the Wigner distribution for different repeat numbers of graphene layers. In contrast, in the absence of graphene layers, the level spacing statistics follow the Poisson distribution.

Magneto-sensitive photonic crystal optical filter with tunable response in 12–19 GHz; cross over from design to prediction of performance using machine learning

Photonic crystal structure made of Si, SiO2 and a plasma defect layer is suggested for optical filter applications. Generation of stop band and resonant modes localizations at transmittance spectrum of the structure are studied by exploring the dependences of the response on the period number of the layers and the electron density of the plasma slab. Also, the role of the magnetically induced birefringence in the anisotropic defect layer and the light incident angle on the optical features of crystal are studied. Results show that the response of the proposed structure could be tuned remarkably in practice by the selected structural as well as external parameters. Furthermore, an artificial intelligence (AI) approach is proposed to predict the final response of the suggested crystal in various input circumstances. Very significant concordance between results of the AI and transfer matrix method (TMM) approaches is observed.

Photonic band gap properties of one-dimensional photonic quasicrystals containing Nematic liquid crystals

Reflectance spectra of one-dimensional periodic multilayered stacks with anisotropic defect layer built according to the Generalized Thue Morse sequence is investigated bythe theoretical transfer matrix method for both polarized waves. The main hetero-layers of the structure are made up using SiO2 and Bi4Ge3O12 materials. The photonic quasicrystal reveal an interesting reflectance spectra for specific generation (m = n, n) of the Generalized Thue Morse sequence and layers thicknesses. Upon increasing the deformed thicknesses a significant enhance of the photonic band gap is shown and an improvement of the optical properties of the photonic crystal slab is observed. By applying homogeneously Nematic Liquid Crystal as defects into the photonic quasicrystals, a tunable resonant transmission can be notably opened and it is very sensitive to the thicknesses of incorporated Nematic Liquid Crystal. These results may be useful for tunable quasi-photonic Bragg reflectors.

Fano feature induced by a bound state in the continuum via resonant state expansion

We consider light scattering by an anisotropic defect layer embedded into anisotropic photonic crystal in the spectral vicinity of an optical bound state in the continuum (BIC). Using a resonant state expansion method we derive an analytic solution for reflection and transmission amplitudes. The analytic solution is constructed via a perturbative approach with the BIC as the zeroth order approximation. The solution is found to describe the collapsing Fano feature in the spectral vicinity of the BIC. The findings are confirmed via comparison against direct numerical simulations with the Berreman transfer matrix method.

Reflectivity of Cholesteric Liquid Crystals with an Anisotropic Defect Layer Inside

In this study, first, we numerically investigated the reflectivity of a cholesteric liquid crystal with an anisotropic defect layer inside. To model optical phenomena in the examined system, a 4 × 4 matrix method was employed. The tests were carried out for different thicknesses of the whole system, different thicknesses of the defect layer, as well as different defect layer locations inside the cell. Next, a cholesteric liquid crystal comprising a defect layer and held between two parallel electrical conductors was also considered. In this case, the optical properties of the system could also be adjusted by an external applied electric field. Some interesting simulation results of the reflection coefficient (i.e., the fraction of electromagnetic energy reflected) were obtained, illustrated, and discussed. The simulation results showed a significant influence of both the defect and the external electric field on the selective reflection phenomenon, and the possibility of controlling the shape of the reflection spectrum. Finally, some potential applications of the analyzed optical system were discussed.

One-dimensional photonic bound states in the continuum

In 1985 Fridriech and Wintgen proposed a mechanism for bound states in the continuum based on full destructive interference of two resonances which can be easily applied to the two- and three-dimensional wave systems. Here we explicitly show that this mechanism can be realized in one-dimensional quantum potential well, owing to destructive interference of electron paths with different spin in tilted magnetic field. Due to one-by-one correspondence between the spin of the electron and the polarization state of light, we have found numerous bound states in the continuum in the one-dimensional photonic system and experimentally confirmed them. The experimental set-up consists of the one-dimensional photonic crystal conjugated with a liquid-crystalline anisotropic defect layer and covered by metal film.

Study of transmission property of periodic layer consisting of SiO2 and TiO2 layers with anisotropic liquid crystal (LC) and LiNbO3 as defect layers for optical switching

Abstract This paper reports the theoretical investigation of transmission properties of a one-dimensional periodic layer consisting of SiO2 and TiO2 layers with anisotropic liquid crystal (LC) and LiNbO3as defect layers with the variation of incident angle, temperature and applied a voltage across the crystal. The optical transmission properties of the considered structure have been calculated by using a 4 × 4 transfer matrix method (TMM). The transmittance of the considered structure with LC and LiNbO3as defects gives rise to defect mode wavelength peak inside the bandgap region. The transmittance peak of the defect mode shows the blue shift in the transmission of periodic structure for TE and TM polarizations with incident angle, applied voltage, and temperature. Further, the transmission behavior of defect modes and terminal wavelengths are analyzed with the variation of incident angle and temperature. The transmission of the considered structure has found the tunable characteristics due to the presence of anisotropic defect layer LC and LiNbO3. The one-dimensional periodic layer consisting of SiO2 and TiO2 layers with the defect layers of anisotropic materials, liquid crystal (LC) and LiNbO3, as may be used to design optical switching devices.

Optical defect mode with tunableQfactor in a one-dimensional anisotropic photonic crystal

We consider a one-dimensional photonic crystal composed of alternating layers of isotropic and anisotropic dielectric materials. Such a system has different band structures for different polarizations of light. We demonstrate that if an anisotropic defect layer is inserted into the structure, the crystal can support an optical bound state in the continuum. By tilting the principle dielectric axes of the defect layer relative to those of the photonic crystal we observe a long-lived resonance in the transmission spectrum. We derive an analytical expression for the decay rate of the resonance that agrees well with the numerical data by the Berreman anisotropic transfer matrix approach. An experimental set-up with a liquid crystal defect layer is proposed to tune the Q-factor of the resonance through applying an external electric field. We speculate that the set-up provides a simple and robust platform for observing optical bound states in the continuum in the form of resonances with tunable Q-factor.

Optical transmission properties of an anisotropic defect cavity in one-dimensional photonic crystal

We investigate theoretically the possibility to control the optical transmission in the visible and infrared regions by a defective one dimensional photonic crystal formed by a combination of a finite isotropic superlattice and an anisotropic defect layer. The Green's function approach has been used to derive the reflection and the transmission coefficients, as well as the densities of states of the optical modes. We evaluate the delay times of the localized modes and we compare their behavior with the total densities of states. We show that the birefringence of an anisotropic defect layer has a significant impact on the behavior of the optical modes in the electromagnetic forbidden bands of the structure. The amplitudes of the defect modes in the transmission and the delay time spectrum, depend strongly on the position of the cavity layer within the photonic crystal. The anisotropic defect layer induces transmission zeros in one of the two components of the transmission as a consequence of a destructive interference of the two polarized waves within this layer, giving rise to negative delay times for some wavelengths in the visible and infrared light ranges. This property is a typical characteristic of the anisotropic photonic layer and is without analogue in their counterpart isotropic defect layers. This structure offers several possibilities for controlling the frequencies, transmitted intensities and the delay times of the optical modes in the visible and infrared regions. It can be a good candidate for realizing high-precision optical filters.

About defect mode peculiarities in cholesteric liquid crystals with anisotropic defect layer inside

The effect of anisotropy on defect mode features in cholesteric liquid crystals was investigated. The problem is solved by Ambartsumian's layer addition modified method. Two cases are considered. In the first case, it is assumed that the defect layer is not absorbing and the effect of the refractive index anisotropy on the reflection, the polarization plane rotation, polarization ellipticity, eigen polarizations, and the total field intensity in the defect layer is investigated. In the second case, it is considered that the defect layer has the properties of the isotropy of refraction and absorption anisotropy, and the influence of the anisotropy of the absorption of the defect layer on the polarization plane rotation, the polarization ellipticity, and the eigen polarizations is investigated.

Transmittance properties of tunable filter in a 1D photonic crystal doped by an anisotropic metamaterial

The influence of the variation in the optical axis and the incidence angle a the P and the S polarizations on the transmittance properties of the tunable filter in a 1D photonic crystal (1DPC) with an anisotropic metamaterial defect layer is theoretically investigated. By using the 4 × 4 transfer matrix method, the pronounced contrast in the behavior of the P-and the S-polarized modes were demonstrated. The results indicate that, the intensity and the peak wavelength of the defect mode under the P –polarized wave can be tuned by a variation of the optical axis of the anisotropic layer, whereas the intensity and the peak wavelength of the defect mode under the S polarized wave remains unchanged. In addition, we show that the peak wavelength and the intensity of the tunable filter can be tailored by varying the incidence angle of light. The results, therefore, illustrate that the peak wavelength of the defect mode shifts towards blue as the angle of incidence increases for both polarizations. These results lead to certain new findings concerning the design of new types of tunable narrowband filters.

Electrically tunable polarization splitting and conversion based on 1DPC structure with anisotropic defect layer

The present study examined the tunability of wave polarization splitting and conversion in a one-dimensional photonic crystal (1DPC) structure containing anisotropic electro-optical material. The 4 × 4 transfer matrix method was used to study the transmission properties of the structure. The incident light was assumed to be perpendicular to the optical axes of the anisotropic defect layer. The results indicate that, in the absence of an applied external electric field, for an incident plane wave with P- or S-polarization, a single P- or S-polarized defect mode, respectively, appears with the photonic band gap. Application of the external electric field create two P-polarized and two S-polarized defect modes of equal intensity. As the applied field increased, the splitting mode increased. The photonic band edges of the induced P(S)-polarized mode decreased (increased) as the field increased. The results of this communication can be useful in the design of tunable mode-selecting optical filters.

Effect of incident angle and polarization on electrically-tunable defect mode in anisotropic photonic crystals.

In this study, the effects of incident angle and state of wave polarization on electrically-tunable defect mode in a one-dimensional photonic crystal (1DPC) structure with an anisotropic defect layer is theoretically investigated. A 4×4 transfer matrix method is employed to calculate the transmittance spectrum of the structure with biased defect layer at different incident angles for TE and TM polarizations. The results indicate that at both polarizations, the peak wavelength of the defect mode shifts toward blue as the angle of incidence increases. Also, blue and red shifts can be observed in the defect mode for positive and negative biases, respectively. In addition, the defect mode compresses at TE (TM) polarization at negative (positive) biases and broadens for positive (negative) biases. A tunability defect mode may have potential application in the design of controllable optical filters in all optoelectronic devices.

Experimental investigation of polarization plane rotation of light in nanoparticle-enriched cholesteric liquid crystal cell with an anisotropic defect layer

The possibility of defect induction controlled by external electric field in nanoparticle-enriched cholesteric liquid-crystalline cells with selective reflection in visible range of light and control the rotation of polarization plane of light by induced defect was experimentally demonstrated. The main result of the experiment is the fact that the rotation of the polarization plane of light occurs at lower voltages when the cholesteric liquid crystal is enriched by nanoparticles. A new configuration of liquid crystal device that performs as a tunable linear polarizer for both polarized and unpolarized lights is presented.

Spectral properties of one-dimensional photonic crystal with anisotropic defect layer of nanocomposite

The spectral properties of a one-dimensional photonic crystal with a structure defect—anisotropic nanocomposite layer incorporated between two multilayer dielectric mirrors—have been theoretically investigated. Some specific features are revealed in the transmission spectrum of a photonic crystal. They are primarily due to the resonant behavior of the effective permittivity of nanocomposite and the strong dependence of this parameter on the volume fraction of nanoparticles in the composite.

Peculiarities of spectral properties of a one-dimensional photonic crystal with an anisotropic defect layer of the nanocomposite with resonant dispersion

We have studied the spectral properties of a one-dimensional photonic crystal with a structure defect that represents an anisotropic nanocomposite layer sandwiched between two multilayer dielectric mirrors. The nanocomposite consists of metallic nanoscale inclusions of orientationally ordered spheroidal shape, dispersed in a transparent matrix, and is characterised by an effective resonant permittivity. Each of the two orthogonal polarisations of probe radiation corresponds to a particular plasmon resonant frequency of the nanocomposite. The problem of calculating the transmittance spectrum of the waves with s- and p-polarisations for such structures is solved. Spectral manifestation of splitting of the defect mode depending on the structure parameters and volumetric fraction of the nanospheroids is studied. The essential dependence of the position of maxima of the defect modes in the bandgap of the photonic crystal and their splitting on the incidence angle, polarisation, and the ratio of lengths of the polar and equatorial semi-axes of the spheroidal nanoparticles is shown.

Temperature dependent transmission and optical bistability in a 1D photonic crystal with a liquid crystal defect layer

The transmission properties of a one-dimensional periodic structure with anisotropic defect layer is investigated using a transfer matrix method. A layer of homogeneously aligned nematic liquid crystal is taken as a defect. We show that the frequency and polarization of the defect mode is modified by changing the operating temperature and liquid crystal orientation. Also the temperature dependent nonlinear response of the defect structure is investigated. It is shown that the threshold intensity needed to achieve the bistability depends on the operating temperature. So, the structure can be used as a thermal switch at the frequency near the defect mode.

Experimental Investigation of the Polarization Plane Rotation of Light in Cholesteric Liquid-Crystalline Film with an Anisotropic Defect Layer

This paper experimentally demonstrated that in the cholesteric liquid-crystalline films it is possible to induce defect, which can be controlled by external electric field. Three cases of induced defects were examined and the main result of the experiment is that the rotation of polarization plane has maximum value when light first propagates through chiral liquid-crystalline photonic structure and then falls to the anisotropic layer. We have also supporting calculations, showing an agreement between experimental results and theoretical calculations. We present a new liquid crystal device configuration that performs as a tunable linear polarizer for both polarized and unpolarized lights.