A. H. Gevorgyan

Reflection and transmission of light for a layer of a naturally gyrotropic medium found in an external magnetic field

The propagation of electromagnetic waves through a layer of a naturally gyrotropic medium found in a magnetic field is studied. The problem is solved mathematically using 4×4 Berreman matrices. The Berreman Δ matrix and exact Jones reflection (R̂) and transmission (T̂) matrices are constructed. The reflectivity, the transmittance, the azimuth, and the ellipticity of polarization of the transmitted wave are calculated. Specific features of the irreversibility of waves are studied. It is shown that multiple reflections in a finite layer lead to a manifold increase in irreversibility, which makes possible the use of such systems as optical diodes working in reflection or as unidirectional reflectors. It is shown that three eigenmodes are excited in such media under certain conditions. The relation between the azimuths of transmitted and incident waves is found and specific features of the relation are analyzed.

Effects of angle of incidence and polarization in the chiral photonic crystals

Oblique propagation of light through a planar layer of a chiral photonic crystal (CPC) is considered. The problem is solved using Ambartsumyan’s layer-summation method. Specific features of the reflection (transmission) spectra in the presence of dielectric boundaries are studied. Apparent contradictions of the Belyakov-Dmitrienko theory with experiments are discussed. Possibility of the laser emission wavelength control in a CPC layer doped with a laser dye is analyzed. Characteristic features of the light absorption at oblique incidence are investigated.

Specific features of the emission of chiral photonic crystals with an anisotropic defect: I. Thickness effects

The specific features of defect modes of chiral photonic crystals with an anisotropic defect have been investigated. Peculiarities of the spectra of polarization observables of the system under consideration are analyzed at different thicknesses of the defect layer. It is shown that single refraction occurs in a defect mode, even though the system is anisotropic and inhomogeneous. We also investigated the specific features of the spectra of the photon density of states, light intensity at the defect center, and the Q factor of defect modes at different thicknesses of the defect layer and chiral photonic crystals. It is shown that the lasing wavelength of chiral photonic crystals with an anisotropic defect enriched in laser dyes (resonant atoms) can be controlled in a different way: by varying the defect layer thickness. It is shown that this system can operate as a narrow-band filter (mirror) with a controlled frequency width and location of the total transmission (reflection) range on the frequency scale.

Optical properties of a stack of right- and left-handed layers of a cholesteric liquid crystal

We have studied the optical properties of a stack that consists of right- and left-handed layers of a cholesteric liquid crystal (CLC). The problem has been solved using the modified Ambartsumyan layer-summation method. We have examined particular features of the reflection spectra of this system and have shown that, as distinct from a single CLC layer, this system has multiple photonic band gaps. Particular features of the spectra of the photonic density of states have been considered. We have shown that this system has unique polarization characteristics; thus, in particular, if the number of sublayers is even, the eigenpolarizations of the system are degenerate (both eigenpolarizations coincide) and, as distinct from ordinary gyrotropic media, the rotation of the plane of polarization can decrease with increasing thickness of the system, the sign of the rotation depends on the sign of the chirality of the first sublayer of the system, the system is very sensitive to the variation in the number of sublayers, etc. We have investigated how the sublayer thickness, the angle of incidence, the local dielectric anisotropy, and the pitch of helix of sublayers affect the reflection spectra and other optical characteristics of the system.

Anomalies of radiation absorption and superluminal propagation of light: I. An isotropic layer

The features of superluminal propagation of light through an isotropic layer are investigated and the group velocity is calculated. Multilayer systems providing superluminal propagation of light over large distances with compensation of losses upon light transmission through the system are considered. The situations in which the propagation speed of a light pulse decreases or in which it is equal to zero are also investigated. The features of radiation absorption in a thin isotropic layer are considered. The effects of anomalously high and anomalously low absorption are found. It is shown that these effects are caused by an increase (decrease) in the density of light energy in the layer and by changes in the group velocity. The possibility of experimental observation of the effects discovered is discussed.

Anomalies of Radiation Absorption and Superluminal Propagation of light: II. A Layer of a Periodic Medium with a Helical Structure

The features of superluminal propagation of light through a layer of a helical periodic medium (HPM) are investigated and the group velocity is calculated. Multilayer systems with a layer of an HPM that provide superluminal propagation of light over large distances with compensation of losses upon light transmission through the system are considered. The features of radiation absorption in a layer of an HPM are considered. Effects of anomalously high and anomalously low absorption are found. It is shown that these effects are caused by an increase (decrease) in the density of light energy in the layer and by changes in the group velocity. The possibility of experimental observation of the effects discovered is discussed.

Specific Features of Emission of Chiral Photonic Crystals with an Anisotropic Defect: II. Specific Features of Emission

Specific features of emission of chiral photonic crystals with an anisotropic defect are studied. Under certain conditions, an anomalously strong emission of defect modes is observed. A low-threshold laser generation as well as the effect of suppression of the emission of these modes is possible. Threshold values of the gain are determined numerically.

Reflection and transmission of light through a layer possessing dielectric and magnetic helicities: II. Principal axes of dielectric and magnetic helicities are rotated relative to each other

The transmission and reflection of light are considered in the case of its normal incidence on a layer of a periodically nonuniform medium possessing dielectric and magnetic helicities, with the axes of electrical and magnetic permittivities being rotated relative to each other. A simple algorithm for constructing the solution of the boundary problem for a layer of a helical periodic medium (HPM) of finite thickness is proposed. Jones matrices are constructed and natural polarizations and eigenvalues of the transfer function for the complex amplitude corresponding to natural polarizations are calculated. Numerical analysis is carried out for the case of large (and very large) local anisotropy of the medium. It is shown in particular that a domain of transmission appears between domains of diffraction and specular reflection under certain conditions.

Defect modes of chiral photonic crystals with an isotropic defect

Specific features of the defect modes of cholesteric liquid crystals (CLCs) with an isotropic defect, as well as their photonic density of states, Q factor, and emission, have been investigated. The effect of the thicknesses of the defect layer and the system as a whole, the position of the defect layer, and the dielectric boundaries on the features of the defect modes have been analyzed. It is shown that when the CLC layer is thin the density of states and emission intensity are maximum for the defect mode, whereas when the CLC layer is thick, these peaks are observed at the edges of the photonic band gap. Similarly, when the gain is low, the density of states and emission intensity are maximum for the defect mode, whereas at high gains these peaks are also observed at the edges of the photonic band gap. The possibilities of low-threshold lasing and obtaining high-Q microcavities have been investigated.

Optical properties of chiral photonic crystals with linear profiles of modulation parameters

The oblique propagation of light through a layer of chiral photonic crystal (PC) with linear profiles of modulation parameters is considered. The problem is solved by the method of Ambartsumyan layer addition. The wavelength dependences of the amplitude characteristics have been studied at different angles of incidence in two cases, i.e., in a chiral PC with a linear profile of modulation period and a chiral PC with a linear profile of modulation depth. It is shown that the photonic band gap is broadened in both cases and that omnidirectional reflection occurs under certain conditions. The nonreciprocity features are investigated for these two cases and it is shown that a chiral PC with a linear profile of modulation period can operate as an ideal optical diode in a certain frequency range. The features of the effect of change in the modulation parameters on the photon density of states, group velocity, and group velocity dispersion are analyzed. It is shown that, when the modulation parameters change in space, the photon density of states at the photonic band gap edges significantly decreases. It is proposed to use PCs with a spatially changing modulation period can be used to compress (expand) light pulses.