Modal propagation characteristics of EM waves in ternary one-dimensional plasma photonic crystals

We have theoretically studied the modal dispersion characteristics, group velocity, and effective group as well as phase index of refraction of ternary one-dimensional (1D) plasma photonic band gap (PBG) structure having periodic multilayers of three different materials in one unit cell. The dispersion characteristics related for such structure is derived by solving Maxwell wave equation based on principle of Kronig-Penny model. From the computed results we observe that the dispersion characteristics of such structure also show the frequency gap and cutoffs as found in (binary) one-dimensional plasma photonic crystal. The frequency gap is shown to become larger with the increase of plasma frequency as well as plasma width. It is seen that such structure provide additional degree of freedom to control dispersion characteristic, group velocity and effective index of refraction compared to conventional one-dimensional plasma photonic crystal.     

Nonreciprocity of waves in 1D photonic quasiperiodic crystals

Optical properties of one-dimensional quasiperiodic crystals with a linear profile of the modulation parameters are studied. It is shown that such systems possess a wider photonic forbidden band than the ideally periodic systems. The asymmetric profile of variation of the system parameters leads to nonreciprocity, which allows one to use these systems as optical diodes.     

Wave propagation inside one-dimensional photonic crystals with single-negative materials

The propagation of light waves in one-dimensional photonic crystals (1DPCs) composed of alternating layers of two kinds of single-negative materials is investigated theoretically. The phase velocity is negative when the frequency of the light wave is smaller than the certain critical frequency ω_cr, while the Poynting vector is always positive. At normal incidence, such 1DPCs may act as equivalent left-handed materials. At the inclined incidence, the effective wave vectors inside such 1DPCs do refract negatively, while the effective energy flows do not refract negatively. Therefore, at the inclined incidence, the 1DPCs are not equivalent to the left-handed materials.     

Tunable photonic Bloch oscillations in electrically modulated photonic crystals

We exploit theoretically the occurrence and tunability of photonic Bloch oscillations (PBOs) in one-dimensional photonic crystals (PCs) containing nonlinear composites. Because of the enhanced third-order nonlinearity (Kerr-type nonlinearity) of composites, photons undergo oscillations inside tilted photonic bands, which are achieved by the application of graded external-pump electric fields on such PCs, varying along the direction perpendicular to the surface of layers. The tunability of PBOs (including amplitude and period) is readily achieved by changing the field gradient. With an appropriate graded pump ac or dc electric field, terahertz PBOs can appear and cover a terahertz band in an electromagnetic spectrum.     

Role of confined Bloch waves in the near field heat transfer between two photonic crystals

The near field heat transfer between two finite size one-dimensional photonic crystals separated by a small vacuum gap and maintained in nonequilibrium thermal situation is theoretically investigated. The main features of this electromagnetic transfer are discussed and compared with what is generally observed with media that support surface polaritons. It is shown that the presence of surface Bloch waves can significantly enhance heat transfers beyond the far field limit for both polarization states of electromagnetic field at subwavelength separation distances. A specific attention is addressed to the consequence of the slopes of surface Bloch waves dispersion curves on the heat transfer. In particular, it is shown that the localization of surface Bloch waves close to the light line allows to observe a transfer exaltaion at larger separation distances than the Wien wavelength. These results could open new possibilities for the development of innovative near-field technologies such as near-field thermophotovoltaic conversion, plasmon assisted nanophotolitography or near-field spectroscopy.     

Correlation between helical surface waves and guided modes of an infinite immersed elastic cylinder

Scattering of obliquely incident plane acoustic waves from immersed infinite solid elastic cylinders is a complex phenomenon that involves generation of various types of surface waves on the body of the cylinder. Mitri [F.G. Mitri, Acoustic backscattering enhancement resulting from the interaction of an obliquely incident plane wave with an infinite cylinder, Ultrasonics 50 (2010) 675-682] recently showed that for a solid aluminum cylinder, there exist acoustic backscattering enhancements at a normalized frequency of ka?0.1. The incidence angle α_c at which these enhancements are observed lies between the first (longitudinal) and second (shear) coupling angles of the cylinder. He also confirmed the observations previously reported by the authors that there exist backscattering enhancements of the dipole mode at large angles of incidence where no wave penetration into the cylinder is expected. In this paper, physical explanations are provided for the aforementioned observations by establishing a correlation between helical surface waves generated by oblique insonification of an immersed infinite solid elastic cylinder and the longitudinal and flexural guided modes that can propagate along the cylinder. In particular, it is shown that the backscattering enhancement observed at ka?0.1 is due to the excitation of the first longitudinal guided mode travelling at the bar velocity along the cylinder. It is also demonstrated that the dipole resonance mode observed at incidence angles larger than the Rayleigh coupling angle is associated with the first flexural guided mode of the cylinder. The correlation established between the scattering and propagation problems can be used in both numerical and experimental studies of interaction of mechanical waves with cylinders.     

Electromagnetic modes in semi-infinite photonic crystals

In a real photonic crystal, there exist three modes: propagation mode, evanescence mode and surface mode. Using ideal modal, semi-infinite photonic crystals, we study their effects on the transmission spectrum of photonic crystals, respectively. Because there exists only one air–crystal interface in a semi-infinite photonic crystal, no multiple reflection occurs and no evanescent modes and backward-propagating modes exist in this structure. The effects of the evanescence modes are studied by comparing the transmission spectrum of a finite-thickness photonic crystal slab and that of a semi-infinite photonic crystal. In addition, the effects of the backward-propagating modes are investigated using a coated semi-infinite photonic crystal structure. Finally, we study the effects of the surface modes, and find that the transmission spectrum of a semi-infinite photonic crystal is strongly dependent on its termination.     

Analytical study of the propagation of acoustic waves in a 1D weakly disordered lattice

This paper presents an analytical approach of the propagation of an acoustic wave through a normally distributed disordered lattice made up of Helmholtz resonators connected to a cylindrical duct. This approach allows to determine analytically the exact transmission coefficient of a weakly disordered lattice. Analytical results are compared to a well-known numerical method based on a matrix product. Furthermore, this approach gives an analytical expression of the localization length apart from the Bragg stopband which depends only on the standard deviation of the normal distribution disorder. This expression permits to study on one hand the localization length as a function of both disorder strength and frequency, and on the other hand, the propagation characteristics on the edges of two sorts of stopbands (Bragg and Helmholtz stopbands). Lastly, the value of the localization length inside the Helmholtz stopband is compared to the localization length in the Bragg stopband.     

Tunable self-shifting Bloch modes in anisotropic hexagonal photonic lattices

We study controllable self-shifting Bloch modes in anisotropic hexagonal photonic lattices. The shifting results from a deformed band structure due to deformation of the index distribution in each unit cell. By reconfiguration of the index profile of the unit cell, the direction in which the Bloch modes move can be controlled. Our theoretical predictions are experimentally demonstrated in hexagonal lattices optically induced in an anisotropic nonlinear crystal.     

Optical waves in photonic crystals and the photonic flame effect

We present the coupled-mode equations for inclined waves in photonic crystals. Among the eigenmodes, we focus on the evanescent modes. We consider the conjugation of the waves at the interface of the crystal and its metallic substrate. We underscore the role of resonant coupling of the fields at this interface and briefly discuss the field structure in the open space.     

Spin wave vortex from the scattering on Bloch point solitons

The interaction of a spin wave with a stationary Bloch point is studied. The topological non-trivial structure of the Bloch point manifests in the propagation of spin waves endowing them with a gauge potential that resembles the one associated with the interaction of a magnetic monopole and an electron. By pursuing this analogy, we are led to the conclusion that the scattering of spin waves and Bloch points is accompanied by the creation of a magnon vortex. Interference between such a vortex and a plane wave leads to dislocations in the interference pattern that can be measurable by means of magnon holography.     

Optical edge modes in photonic liquid crystals

An analytic theory of localized edge modes in chiral liquid crystals (CLCs) is developed. Equations determining the edge-mode frequencies are found and analytically solved in the case of low decaying modes and are solved numerically for the problem parameter values typical for the experiment. The discrete edge-mode frequencies specified by the integer numbers n are located close to the stop-band edge frequencies outside the band. The expressions for the spatial distribution of the n’s mode field in a CLC layer and for its temporal decay are presented. The possibilities of a reduction of the lasing threshold due to the anomalously strong absorption effect are theoretically investigated for a distributed feedback lasing in CLCs. It is shown that a minimum of the threshold pumping wave intensity may be reached, generally, for the pumping wave propagating at an angle to the helical axis. However, for lucky values of the related parameters, it may be reached for the pumping wave propagating along the helical axis. The lowest threshold pumping wave intensity occurs for the lasing at the first low-frequency band-edge lasing mode and the pumping wave propagating at an angle to the spiral axis corresponding to the first angular absorption maximum of the anomalously strong absorption effect at the high-frequency edge of the stop band. The study is performed in the case of the average dielectric constant of the liquid crystal coinciding with the dielectric constant of the ambient material. Numerical calculations of the distributed feedback lasing threshold at the edge-mode frequencies are performed for typical values of the relevant parameters.     

The parity function in optical waves propagation

We propose a generalization of the concept of parity as a continuous function and show that it is conserved in optical waves free propagation. Some properties are commented and an experimental implementation to optically generate a representation is suggested.     

Group velocity of gravitational waves in an expanding universe

The group velocity of gravitational waves in a flat Friedman–Robertson–Walker universe is investigated. For plane waves with wavelength well inside the horizon, and a universe filled with an ideal fluid with the pressure to density ratio less than 1/3, the group velocity is greater than the velocity of light. As a result, a planar pulse of gravitational waves propagating through the universe during the matter/dark energy dominated era arrives to the observer with the peak shifted towards the forefront. For gravitational waves emitted by inspiralling supermassive black holes at the edge of the observable universe, the typical shift that remains after the effects of nonplanarity are suppressed is of order of 10 ps.     

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.     

Investigation of magnetostatic waves in photonic crystals

The frequency dependence of the Lyapunov index in the bandgap of a magnetic photonic (spin) crystal has been experimentally determined for the first time.     

Bloch cavity solitons in nonlinear resonators with intracavity photonic crystals

We predict a novel type of cavity solitons, Bloch cavity solitons, existing in nonlinear resonators with the refractive index modulated in both longitudinal and transverse directions and for both focusing (at normal diffraction) and defocusing (at anomalous diffraction) nonlinearities. We develop a modified mean-field theory and analyze the properties of these novel cavity solitons demonstrating, in particular, their substantial narrowing in the zero-diffraction regime.     

Color of shock waves in photonic crystals

Unexpected and stunning new physical phenomena result when light interacts with a shock wave or shocklike dielectric modulation propagating through a photonic crystal. These new phenomena include the capture of light at the shock wave front and reemission at a tunable pulse rate and carrier frequency across the band gap, and bandwidth narrowing as opposed to the ubiquitous bandwidth broadening. To our knowledge, these effects do not occur in any other physical system and are all realizable under experimentally accessible conditions. Furthermore, their generality make them amenable to observation in a variety of time-dependent photonic crystal systems, which has significant technological implications.     

能谷光子晶体与拓扑光传输

在传统光学原理框架下,高效光传输问题在集成光电子领域的发展受到了制约。人们希望从物理源头出发,提出新型原理机制或设计方法,来获得整体上的高保真光传输性能。这正好与近年兴起的拓扑光子学内涵相吻合。近年来,光子晶体和超构材料等多种电磁系统都被用于拓扑光子学的研究中,并受到了广泛关注。文章简要回顾拓扑光子学的发展历程,重点介绍能谷光子晶体的物理特性和最新研究进展,集中论述了电磁对偶能谷光子晶体的理论提出、能谷光子晶体分类与微波实验观测、硅基能谷光子晶体与光波段传输实现等方面。最后,将讨论该领域的未来,并展望其在微纳集成光子学领域的可能发展方向。