The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

http://ieeexplore.ieee.org/iel5/6354/16969/00781867.pdf

Photonic crystals

Manipulation of light is in strong demand in information technologies. Among the wide range of linear and nonlinear optical devices that have been used, growing attention has been paid to photonic crystals that possess a periodic modulation of dielectric function. Among many photonic bandgap (PBG) structures, liquid crystals with periodic structures are very attractive as self-assembled photonic crystals, leading to optical devices such as dye lasers. Here we report a new hetero-PBG structure consisting of an anisotropic nematic layer sandwiched between two cholesteric liquid-crystal layers with different helical pitches. We optically visualized the dispersion relation of this structure, displaying the optical diode performance: that is, the non-reciprocal transmission of circular polarized light at the photonic-bandgap regions. Transmittance spectra with circularly polarized light also reveal the diode performance, which is well simulated in calculations that include an electro-tunable diode effect. Lasing action was also confirmed to show the diode effect with a particular directionality.

Electro-tunable optical diode based on photonic bandgap liquid-crystal heterojunctions.

Accumulation and transmission of the light energy in nonreciprocal multilayer systems

Chiral photonic crystals with an anisotropic defect layer : Oblique incidence

A liquid crystal (LC) photonic device with an anisotropic optical heterojunction structure has been fabricated. The device has a phase-retarding nematic LC (NLC) layer sandwiched between two polymer cholesteric LC films with right-handed helices of different pitches. Electrotunable non-reciprocal light transmittance and unidirectional circularly polarized (CP) lasing emission have been successfully demonstrated for this device structure. Two left CP (LCP) lasing emission peaks are observed at the edges of the overlapping region between the two photonic bands in the structure and are shifted upon the application of a voltage. In contrast, a non-reciprocal right CP (RCP) lasing emission peak emerges at one of the band edges and diminishes upon the application of a voltage. These phenomena are interpreted based on the selective reflection of RCP light and the reorientation of the NLC molecules by the application of a voltage.

Electrotunable Non-reciprocal Laser Emission from a Liquid-Crystal Photonic Device†

The propagation of naturally polarized light through a Fabry-Perot resonator with a layer of cholesteric liquid crystal is considered. In the presence of absorption, this system exhibits nonreciprocity even for naturally polarized light, which implies the existence of a new type of nonreciprocal reflection. An analysis of the peculiarities of this nonreciprocity shows that strongly nonreciprocal multilayer systems can be used as optical diodes or optical insulators (transmitting signals via an optical communication channel in one direction and blocking signals propagating in the opposite direction) or as systems for the accumulation of light energy.

Nonreciprocal waves in absorbing multilayer systems

The optical properties of one-dimensional quasiperiodic photonic crystals with linear profiles of modulation parameters are considered. It is shown that such systems possess a wider photonic band gap as compared to the ideal periodic system and can be used as omnidirectional reflectors. The asymmetric profiles of parameters in these systems results in the appearance of nonreciprocity of a new type that makes possible their use as the ideal, purely optical diodes.

Optical diodes and omnidirectional reflectors based on one-dimensional quasiperiodic photonic crystals

The properties of defect modes in chiral photonic crystals with anisotropic defects are considered. The problem has been solved using the modified method of Ambartsumyan layer addition. The influence of the defect layer thickness and the optical axis orientation on the properties of defect modes is analyzed. At a certain thickness of the defect layer, the medium loses its main property, namely, the polarization dependence of diffraction reflection.

The loss of the polarization dependence of diffraction reflection in chiral photonic crystals in the presence of anisotropic defects

The properties of defect modes in chiral photonic crystals with anisotropic defects are considered, and changes in these properties caused by variations of the position of a defect layer in the system are analyzed. It is shown that, for certain thicknesses of a defect layer, a change in its position leads to a change in the ellipticity of the transmitted (reflected) light. This phenomenon can be used to create a device capable of selecting the polarization of light by changing the position of a defect layer. Such a device can also operate as a light modulator, a purely optical diode, or a bidirectional asymmetric switch. In a certain wavelength range, this light polarization selector can produce controlled rotation of the polarization plane.

A. H. Gevorgyan

Papers

Nonreciprocal waves in absorbing multilayer systems

Optical diodes and omnidirectional reflectors based on one-dimensional quasiperiodic photonic crystals

The loss of the polarization dependence of diffraction reflection in chiral photonic crystals in the presence of anisotropic defects

A device for the light polarization selection