Optical Anisotropy of Photonic Crystals of Cubic Symmetry Induced by Multiple Diffraction of Light

The optical spectra of Bragg reflection from opal-like photonic crystals under conditions of the resonant enhancement of the multiple diffraction of light have been studied experimentally and theoretically using the photonic crystal structures prepared of monodisperse polystyrene globules. It is shown that the reflection signal registered in mutually orthogonal configurations of the polarizer and analyzer is related to the intrinsic optical anisotropy of the crystals and is a specific manifestation of the multiple Bragg diffraction in three-dimensional photonic crystals.     

Polarization-dependent suppression of Bragg reflections in light reflection from photonic crystals

This paper reports on an experimental and theoretical study of the spectra of Bragg reflection of light from opal-like photonic crystals near the critical angle of incidence ? _c , at which the Bragg reflection in the p polarization of reflected light disappears The objects studied were polymer photonic-crystal structures made up of polystyrene particles. It is shown that Bragg reflection for the electromagnetic TM mode becomes totally suppressed at an angle of incidence ? _c , which depends on the geometric parameters and dielectric constants of the spatially periodic structure.     

Novel spatial solitons in light-induced photonic bandgap structures

The study of wave propagation in periodic systems is at the frontiers of physics, from fluids to condensed matter physics, and from photonic crystals to Bose-Einstein condensates. In optics, a typical example of periodic system is a closely-spaced waveguide array, in which collective behavior of wave propagation exhibits many intriguing phenomena that have no counterpart in homogeneous media. Even in a linear waveguide array, the diffraction property of a light beam changes due to evanescent coupling between nearby waveguide sites, leading to normal and anomalous discrete diffraction. In a nonlinear waveguide array, a balance between diffraction and self-action gives rise to novel localized states such as spatial “discrete solitons” in the semi-infinite (or total-internal-reflection) gap or spatial “gap solitons” in the Bragg reflection gaps. Recently, in a series of experiments, we have “fabricated” closely-spaced waveguide arrays (photonic lattices) by optical induction. Such photonic structures have attracted great interest due to their novel physics, link to photonic crystals, as well as potential applications in optical switching and navigation. In this review article, we present a brief overview on our experimental demonstrations of a number of novel spatial soliton phenomena in light-induced photonic bandgap structures, including self-trapping of fundamental discrete solitons and more sophisticated lattice gap solitons. Much of our work has direct impact on the study of similar discrete phenomena in systems beyond optics, including sound waves, water waves, and matter waves (Bose-Einstein condensates) propagating in periodic potentials.      

Novel spatial solitons in light-induced photonic bandgap structures

The study of wave propagation in periodic systems is at the frontiers of physics, from fluids to condensed matter physics, and from photonic crystals to Bose-Einstein condensates. In optics, a typical example of periodic system is a closely-spaced waveguide array, in which collective behavior of wave propagation exhibits many intriguing phenomena that have no counterpart in homogeneous media. Even in a linear waveguide array, the diffraction property of a light beam changes due to evanescent coupling between nearby waveguide sites, leading to normal and anomalous discrete diffraction. In a nonlinear waveguide array, a balance between diffraction and self-action gives rise to novel localized states such as spatial “discrete solitons” in the semi-infinite (or total-internal-reflection) gap or spatial “gap solitons” in the Bragg reflection gaps. Recently, in a series of experiments, we have “fabricated” closely-spaced waveguide arrays (photonic lattices) by optical induction. Such photonic structures have attracted great interest due to their novel physics, link to photonic crystals, as well as potential applications in optical switching and navigation. In this review article, we present a brief overview on our experimental demonstrations of a number of novel spatial soliton phenomena in light-induced photonic bandgap structures, including self-trapping of fundamental discrete solitons and more sophisticated lattice gap solitons. Much of our work has direct impact on the study of similar discrete phenomena in systems beyond optics, including sound waves, water waves, and matter waves (Bose-Einstein condensates) propagating in periodic potentials.     

Photonic Bandgap Deformation in a Nonideal Synthetic Opal Photonic Crystal

The Bragg diffraction in synthetic opal as a 3D photonic crystals has been analyzed using the weak disorder model in various approximations. For a one-domain crystal, the photonic bandgap is calculated in the regime of reflection along the 〈111〉 axis. In the multidomain case, a considerable expansion of the photonic bandgap, the emergence of asymmetry, and the photon band shift to the short-wavelength region are demonstrated. The results are compared with experimental dependences.     

Specific features of polarization anisotropy in optical reflection and transmission of colloidal photonic crystals

This paper reports on the measurements (in linearly polarized light) of the transmission and reflection spectra of colloidal photonic crystals with three-dimensional and one-two-dimensional photonic band structure, i.e., opal films and Langmuir-Blodgett crystals with a refractive index contrast of ∼1.5: 1.0. It has been shown that the polarization anisotropy is enhanced considerably in the diffraction resonance range both in transmitted and reflected light, and that the anisotropy in the resonance range can be as high as 99%. The interaction of photonic crystal eigenmodes has been found to affect the polarization anisotropy. The assumption has been made that the coincidence of the maxima in polarization anisotropy of the resonant and nonresonant light reflection in colloidal crystals originates from the disorder in their lattices. The generality of the results obtained is confirmed by the fact that the polarization anisotropy manifests itself in the same way in colloidal crystals with different lattice symmetries.     

Slow wave phenomena in photonic crystals

Slow light in photonic crystals and other periodic structures is associated with stationary points of the photonic dispersion relation, where the group velocity of light vanishes. It is shown that in certain cases, the vanishing group velocity is accompanied by the so‐called frozen mode regime, when the incident light can be completely converted into the slow mode with huge diverging amplitude. The frozen mode regime is a qualitatively new wave phenomenon – it does not reduce to any known electromagnetic resonance. Formally, the frozen mode regime is not a resonance, in a sense that it is not particularly sensitive to the size and shape of the photonic crystal. The frozen mode regime is more robust and powerful, compared to any known slow‐wave resonance. It has much higher tolerance to absorption and structural imperfections.     

Tunneling of electromagnetic waves through a barrier with a periodic structure

The propagation of an electromagnetic wave through a barrier with a periodic structure is considered. An interesting manifestation of electromagnetic wave tunneling through a barrier with a periodic structure is revealed. Specifically, it is theoretically and experimentally shown that, when an electromagnetic wave passes through a medium with a periodic structure in the diffraction mode within a photonic band gap, the field in the medium is localized near its boundaries. Theoretical calculations have been performed for a cholesteric liquid crystal layer of finite thickness and for a 1D photonic crystal. The experiment was carried out with perfect Si single crystals in reflection from the $ (2\bar 20)$ (2\bar 20) and $ (4\bar 40)$ (4\bar 40) planes using MoK _α X rays.     

Photonic band gap effect in one-dimensional plasma dielectric photonic crystals

Propagation of electromagnetic waves in one-dimensional plasma dielectric photonic crystals, the superlattice structure consisting of alternating plasma and dielectric materials, is studied theoretically using transfer matrix method. Numerical calculation is presented for plasma-air finite and infinite periodic structures. The results of photonic band gap characteristics are discussed in terms of plasma density, plasma width, and number of unit cells (N).     

磁化等离子体光子晶体的FDTD分析

磁化等离子体光子晶体是磁化等离子体和介质(真空)构成的人工周期性结构.本文用磁化等离子体的分段线形电流密度卷积(PLCDRC)时域有限差分(FDTD)算法分析了磁化等离子体光子晶体特性.分析了磁化等离子体参数对电磁带隙的影响.从时域的角度分析了高斯脉冲在磁化等离子体光子晶体中的传播过程，给出了时域反射和透射波形.从频域的角度给出了磁化等离子体光子晶体的电磁反射系数和透射系数，并对结果进行了分析. 关键词： 磁化等离子体 光子晶体 时域有限差分法     

On the theory of diffraction of light in photonic crystals with allowance for interlayer disordering

Electrodynamic Green’s functions are used to construct an analytical theory of the Bragg diffraction of polarized light in photonic crystals having a close-packed structure. For opal-based photonic crystals, the Bragg diffraction intensity is calculated with allowance for permittivity periodic modulation and for the presence of an optical crystal boundary and interlayer disordering, which usually appears during sample growth. A comprehensive study is made of the effect of the structure disorder caused by the random packing of growth layers on diffraction. For a random constructed twinned fcc structure, the average structure factor and the scattering (diffraction) cross sections (which are dependent on the linear polarization of the incident and scattered waves) are calculated. Numerical examples are used to show that the theory developed can be applied to analyze and process experimental diffraction patterns of real photonic crystals having a close-packed structure disordered in one direction.     

Multiple higher-order stop gaps in infrared polymer photonic crystals

Engineering of stop gaps between higher photonic bands provides an alternative to miniaturization of photonic crystals. Femtosecond laser microfabrication of highly correlated void channel polymer microstructures results in photonic crystals with large stop gaps and a multitude of higher-order gaps in the mid- and near-infrared spectral regions. The gap wavelengths obey Bragg's law. Consistent with theory, varying the woodpile structure unit cell allows for tuning the number of higher-order gaps, and transitions from mere resonant Bragg scattering to stop band total reflection are observed.     

Periodic thin-film interference filters as one-dimensional photonic crystals

We review the photonic band gap-related properties of a simple periodic system of thin dielectric layers. Properties associated with forbidden and allowed bands of such one-dimensional photonic crystals are presented. A revision of the properties of forbidden bands leads to an omnidirectional Bragg mirror design. The anisotropy of allowed bands suggests the formation of photon-focusing caustics in one-dimensional photonic crystals.     

Slow light in photonic crystals

The problem of slowing down light by orders of magnitude has been extensively discussed in the literature. Such a possibility can be useful in a variety of optical and microwave applications. Many qualitatively different approaches have been explored. Here we discuss how this goal can be achieved in linear dispersive media, such as photonic crystals. The existence of slowly propagating electromagnetic waves in photonic crystals is quite obvious and well known. The main problem, though, has been how to convert the input radiation into the slow mode without losing a significant portion of the incident light energy to absorption, reflection, etc. We show that the so-called frozen mode regime offers a unique solution to the above problem. Under the frozen mode regime, the incident light enters the photonic crystal with little reflection and, subsequently, is completely converted into the frozen mode with huge amplitude and almost zero group velocity. The linearity of the above effect allows the slowing of light regardless of its intensity. An additional advantage of photonic crystals over other methods of slowing down light is that photonic crystals can preserve both time and space coherence of the input electromagnetic wave.     

Band-edge-induced Bragg diffraction in two-dimensional photonic crystals

Two-dimensional photonic crystals composed of two orthogonal volume diffraction gratings have been photogenerated in photopolymers. When the read beam is set at the Bragg angle, the diffraction efficiency of the transmission grating is strongly enhanced at the band edge of the reflection grating recorded in the material. Such a device provides Bragg operation and enhancement of the diffraction efficiency of the thin diffraction grating together with good wavelength selectivity. Such advantages could be interesting for optical signal processing.     

Control of absorption spectrum of a one-dimensional resonant photonic crystal

The crystal under consideration is a layered structure consisting of alternating layers of two materials, one of which is a resonantly absorbing gas. It is shown that the combination of the dispersion of an atomic gas with the dispersion of a photonic-bandgap structures allows one to efficiently control the transmission spectra of s- and p-polarized modes in these combined systems. It is found that the spectrum is highly sensitive to the position of the gas resonance frequency with respect to the bandgap edge and to a change in the gas pressure. The transmission, reflection, and absorption spectra of the resonant photonic crystal are studied at an angle of incidence equal to the Brewster angle of a seed photonic crystal. Possible applications of the found particular features of the dispersion of resonant photonic crystals are discussed.     

Photonic crystals as metamaterials

The visionary work of Veselago had inspired intensive research efforts over the last decade, towards the realization of man-made structures with unprecedented electromagnetic (EM) properties. These structures, known as metamaterials, are typically periodic metallic-based resonant structures demonstrating effective constitutive parameters beyond the possibilities of natural material. For example they can exhibit optical magnetism or simultaneously negative effective permeability and permittivity which implies the existence of a negative refractive index. However, also periodic dielectric and polar material, known as photonic crystals, can exhibit EM capabilities beyond natural materials. This paper reviews the conditions and manifestations of metamaterial capabilities of photonic crystal systems.     

Propagating mode in the photonic gap of 1D resonant Bragg reflector

Concerning “1D resonant photonic crystals”, i.e., 1D periodic arrays of resonant layers with a spacing satisfying the Bragg condition for resonant light, recent topics are summarized together with additional new findings. The central points are about (1) the recent theoretical finding of a new branch in the middle of photonic gap, (2) an approach-dependent controversy about its existence, (3) its consequence as sharp dips in reflectance spectrum and the corresponding internal field patters, indicating its propagating mode character, (4) the comparison between macroscopic and microscopic treatment of resonance effect, and (5) corrected transfer matrix method and its analytical equivalence with nonlocal response theory.     

聚苯乙烯微粒光子晶体的反常透过特性

在实验上发现了3μm聚苯乙烯(PS)小球光子晶体在350nm至900nm波长上的透过率的周期扰动.根据透过率曲线的周期扰动的峰谷值判断，这种周期性透过率特性是基于PS小球的whispering-gallery-mode(WGM)共振，而不是源于米氏散射或布拉格衍射.实验表明，周期性排列 小球在非带隙区域对光的传输同样有一定的影响.这一结果对光子晶体薄膜的应用提供了新 的可能性. 关键词： 光子晶体 透过率 whispering-gallery-mode共振