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.     

A method of suppression of diffraction oscillations near the diffraction reflection region

Light propagation through the layer of a chiral photonic crystal with graded parameters of modulation is considered in the case of oblique incidence. The problem is solved by the Ambartsumian’s layer addition method. It is shown that under certain conditions it is possible to suppress the diffraction oscillations near the diffraction reflection region.     

Features of light absorption in chiral photonic crystals with a strong local anisotropy

The interaction of light with a layer of a chiral photonic crystal is considered. Features of the Borrmann effect at a strong anisotropy are studied. The natural polarizations are considered, and it is shown that in the limit δ << 1 (δ = (?₁ ? ?₂)/(?₁ + ?₂), where ?₁ and ?₂ are the principal values of the dielectric permittivity tensor in the plane perpendicular to the medium axis) these polarizations are orthogonal and quasi-circular, while in the limit δ >> 1 they are orthogonal but linearly polarized. It is established that in the general case the chiral photonic crystals show a complete selectivity not to the circular polarizations (as at δ << 1), but to the natural polarizations.     

Optical properties of chiral photonic crystals with an anisotropic defect layer

Properties of defect modes in chiral photonic crystals with an anisotropic defect are considered. The influence of the defect layer thickness, its location in the crystal and orientation of its optical axis, as well as of the chiral photonic crystal thickness on the properties of defect modes is studied. It is shown that at certain values of the defect layer thickness the medium loses its main property, namely, the polarization dependence of the diffraction reflection. At certain thicknesses of the defect layer this system transforms from the source of the right circular polarization into the source of the left circular polarization, if the layer position in the chiral photonic crystal changes.     

Peculiarities of radiation in chiral photonic crystals without local refraction

Propagation of light through a planar layer of a chiral photonic crystal (CPC) enriched by dye molecules. The limiting case (namely, an amplifying CPC in the absence of local refraction) is considered. Peculiarities of emission spectra in the absence and in the presence of insulating boundaries are considered. Peculiarities of radiation for various thicknesses of the layer and concentrations of dye molecules are analyzed.     

Peculiarities of light beam reflection from the boundary of a 1D-photonic crystal

Typical cases of lateral shift and deformation of the profile of two-dimensional light beams reflected from the surface of a one-dimensional photonic crystal are considered. We use harmonic modulation of the spatial dependence of dielectric permeability of a crystal, which permits one to study reflectance profiles analytically. The results of numerical calculations that were performed are presented for the cases when the angular spectrum of the incident beam is split.     

Photonic density and nonreciprocal optical properties in chiral liquid crystals

Nonreciprocal optical properties of anisotropic (nano-film) heterostructures made of a cholesteric and nematic liquid crystal (CLC-NLC) layers are studied. Namely, a NLC-CLC (and CLC-NLC) structures are considered in which the NLC layer is a quarter-wave plate. The problem is exactly solvable by Ambartsumians’ modified layer addition and Mullers’ transfer-matrix methods. The peculiarities of the polarization dependent properties, such as the photonic density of states, reflection spectra, the polarization plane rotation and ellipticity spectra are investigated. It is shown that such a system canwork as a light modulator, an element for obtaining linearly polarized light with an electrically tunable polarization plane rotation, or a transformer of non-polarized source into linearly polarized light. The analysis of the optical properties in investigated structures can be used for design of perspective optical diodes, microlasers and multifunctional elements on chiral liquid crystals with electrically tunable polarization plane rotation and field controlled light polarization.     

Influence of dielectric boundaries,angle of incidence,and polarization of light on the optical properties of chiral photonic crystals

Oblique transmission of light through a planar layer of a chiral photonic crystal is considered. The problem is solved by the Ambartsumian layer addition method. The peculiarities of spectra of the polarization-plane rotation and the polarization ellipticity, as well as the features of proper polarizations are studied in the presence of dielectric boundaries.     

Polarization-independent low-pass spatial filters based on one-dimensional photonic crystals containing negative-index materials

A new application of one-dimensional photonic crystals containing negative-index materials is proposed as low-pass spatial filters. Through optimizing the parameters of defect layer, a series of polarization-independent defect modes in the zero-average-index gap of the photonic crystals are obtained with the increase of the incident angle. Based on these defect modes, polarization-independent low-pass spatial filters are designed. The spatial-frequency bandwidth of the spatial filters can be adjusted by changing the period number of the defective photonic crystal structures. In addition, the effect of the losses of negative-index materials on the spatial filters is considered.     

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.     

Broad Stopband Characteristic of Dielectric Chiral Photonic Crystals

In this paper, a novel chiral photonic crystal structure is presented. The formula of reflection coefficient of multi-layer chiral media is applied to dielectric-chiral photonic crystal structure, which is composed of thin chiral layers sandwiched by conventional media. To compare with previous literature, we consider the dielectric structure with alternate glass and GaAs layers. The power reflectance as a function of wavelength for this photonic crystal structure has been calculated. The results are in good agreement with that of Reference. However, our method is simpler. From these graphs, it is found that 100% reflectance is only in finite wavelength ranges, and reflection bandwidth is also small for conventional photonic crystal structure. For chiral photonic crystal, the results show that the chiral photonic band gap (PBG) structure gives nearly 100% reflections in the near-infrared region in addition to some parts of the visible region of the wavelengths. Therefore, it can be used as a broadband reflector and filter.     

Control of the transmission spectrum of a photonic crystal with lattice defects

The transmission spectrum of a one-dimensional photonic crystal with structural defects is investigated. An anisotropic layer of a nematic liquid crystal is considered as a defect. The possibility of effective external control of the transmission spectrum of the photonic crystal by changing either the orientational state of the defect liquid crystal layer (for example, using an electric field) or the angle of incidence of light is shown. It is established that the spectral properties of the photonic crystal change radically with a change in the optical characteristics of the defect layer in the vicinity of the temperature phase transition of the nematic liquid crystal to the isotropic state.     

Dual-frequency division de-multiplexer based on cascaded photonic crystal waveguides

A dual-frequency division de-multiplexing mechanism is demonstrated using cascaded photonic crystal waveguides with unequal waveguide widths. The de-multiplexing mechanism is based on the frequency shift of the waveguide bands for the unequal widths of the photonic crystal waveguides. The modulation in the waveguide bands is used for providing frequency selectivity to the system. The slow light regime of the waveguide bands is utilized for extracting the desired frequency bands from a wider photonic crystal waveguide that has a relatively larger group velocity than the main waveguide for the de-multiplexed frequencies. In other words, the wider spatial distribution of the electric fields in the transverse direction of the waveguide for slow light modes is utilized in order to achieve the dropping of the modes to the output channels. The spectral and spatial de-multiplexing features are numerically verified. It can be stated that the presented mechanism can be used to de-multiplex more than two frequency intervals by cascading new photonic crystal waveguides with properly selected widths.     

Computer simulation and observation of anomalous light emission from nonlinear photonic crystal with various geometry of its elements

Recently, in papers [1, 2] were described the effect of long-time emission of photonic crystal (synthetic opals) under the action of nanosecond laser pulse. The duration of the luminescence is of the order of seconds. Despite on the other phenomena, which were considered in these papers, below we focus our attention on possible explanation of long time emission from nonlinear photonic crystal. The basis of our consideration is papers [3, 4], those deal with soliton formation in several layers of 1D nonlinear photonic crystal. Because of this, the light wave can exist in photonic crystal a long time (in ideal case—infinite time interval). Taking into account a relation between soliton duration and its maximum intensity, the leaving of laser energy from the layer of photonic crystal takes place due not full reflection from boundaries of layer. The time of light emission for this case depends on nonlinear susceptibility of photonic crystal and the intensity of laser pulse. Hence, soliton formation inside the nonlinear elements of photonic crystal can be one of the reasons of long time emission. We got in computer simulation a long time emission of 1D (layered) and 2D (circular or rectangular elements) nonlinear photonic crystal under the action of laser pulse with femtosecond duration under the conditions of soliton formation in some elements of photonic crystal. Input intensity of laser pulse, at which a soliton appears in nonlinear photonic crystal, can be ten times less due to effects of enhancement of optical intensity in periodic structure [4, 5].     

Modulation bandwidth of planar waveguide laser with 1D photonic crystal mirrors

An analysis of the 3-dB modulation bandwidth in planar waveguide laser based on 1D photonic crystal structures is presented. The theoretical model takes into account the gain saturation effect, transverse and longitudinal field distribution. A small-signal perturbation solution of the coupled laser rate equation is used to obtain relations describing the dynamic operation. In paper, the distributed Bragg resonator DBR created as 1D photonic crystal is considered. The active waveguide is surrounded by 1D photonic crystal mirrors consisting of alternately placed stripes with different refractive indices. In particular, the influence of the photonic crystal parameters on the 3-dB modulation bandwidth is investigated.     

Transform-limited spectral compression by self-phase modulation of amplitude-shaped pulses with negative chirp

Spectral compression by self-phase modulation of amplitude- and phase-shaped pulses is demonstrated as superior compared to pulses that have only been phase shaped. We synthesize linearly negatively chirped parabolic pulses, which we send through a nonlinear photonic crystal fiber, in which self-phase modulation compresses the spectrum of the pulses to within 20% of the Fourier transform limit.     

Polarization characteristics of chiral photonic crystal fibers with an elliptical hollow core

The theoretical study of dielectric-chiral photonic crystal fiber(PCF)with an elliptical hollow core is presented.The band structure of chiral photonic crystal(PhC)is calculated by using a modified plane-wave expansion(PWE)method.By examining the out-of-plane photonic bandgaps(PBGs)of chiral PhC,a kind of chiral PCF with a hollow core is designed and their eigenstates are calculated.The distributions of mode field and polarization state are demonstrated,and how the structural asymmetry of the core together with the chirality in the background affects the modal polarization is discussed.The dependences of birefringence on chirality for different ellipticities of core are investigated.     

Floquet-bloch waves in bound one-dimensional photonic crystals

Floquet-Bloch waves in a bound one-dimensional photonic crystal are considered. It is shown that a single Floquet-Bloch wave can be excited in a one-dimensional photonic crystal located between two homogeneous media. An exact solution of the wave equation corresponding to this case is represented in the form of a set of heterogeneous waves. For the case of incidence of the plane wave from a homogeneous medium on a bounded one-dimensional photonic crystal, the functions for the reflection and transmission coefficients are obtained based on the exact solution of the wave equation. It is shown that the transmission function for the one-dimensional photonic crystal has a form similar to that for the traditional Fabri-Perot interferometer and is determined by the interference of the Floquet-Bloch waves excited in the crystal. The evolution of the amplitude profile of the decaying Floquet-Bloch waves and the reflection spectrum of the bounded one-dimensional photonic crystal are considered in the first-order forbidden band.     

Study on modulation of near infrared radiation based on plasma photonic crystal

In this paper, a plasma photonic crystal (PPC) for infrared radiation modulation which is composed of indium tin oxide (ITO) and plasma is proposed. The performance of plasma photonic crystal in near infrared radiation modulation is researched by transfer matrix method (TMM). The simulation results show that the near infrared radiation pass band can be adjusted by the changing of plasma frequency of plasma. The reflection to near infrared radiation by plasma photonic crystal increases with plasma frequency and that of absorption decreases. In addition, the modulation performance of the plasma photonic crystal at different incidence wave angles is also studied. The results show that the incident wave angles have little effect on the transmission of plasma photonic crystal in near infrared band. The reflection of the plasma photonic crystal to near infrared radiation decreases with increasing of the incident wave angle, but that of the absorption increases with the incident wave angle. Therefore, the proposed plasma photonic crystal has a potential application in tunable near infrared filter devices.     

一维光子晶体缺陷模激光器的放大特性

光子晶体中引入缺陷后将形成缺陷模,这些缺陷模在增益介质中将被放大形成激光。基于麦克斯韦方程和速率方程相结合的模型,用时域有限差分法(FDTD)计算和分析了一维单缺陷光子晶体激光器中缺陷模的空间分布和频谱特性,以及这些缺陷模的放大特性,主要研究了缺陷层的厚度、晶体层数对缺陷模放大特性的影响。模拟结果显示,类似于传统激光腔的腔模,这些缺陷模能够被放大,形成激光。调整缺陷层的厚度、晶体层数等结构参量,将改变缺陷模的谐振,激射频率以及空间分布,这将直接影响激射阈值和饱和特性。增加晶体的层数,激光器的阈值将降低,饱和值将增加,但晶体层数增加到一定限度时,这种增减趋势变弱。模拟结果证明了有效层数的存在。