Beaming of light and enhanced transmission via surface modes of photonic crystals

We report beaming and enhanced transmission of electromagnetic waves by use of surface corrugated photonic crystals. The modes of a finite-size photonic crystal composed of dielectric rods in free space have been analyzed by the plane-wave expansion method. We show the existence of surface propagating modes when the surface of the finite-size photonic crystal is corrugated. We theoretically and experimentally demonstrate that the transmission through photonic crystal waveguides can be substantially increased by the existence of surface propagating modes at the input surface. In addition, the power emitted from the photonic crystal waveguide is confined to a narrow angular region when an appropriate surface corrugation is added to the output surface of the photonic crystal.     

Surface wave-induced enhancement of the Goos-Hänchen effect in one-dimensional photonic crystals

The excitation conditions of surface electromagnetic waves in one-dimensional photonic crystals (Bragg reflectors) are studied. Surface electromagnetic waves are visualized by the far-field optical microscopy of the surface of the photonic crystal. The enhancement of the Goos-Hänchen effect by surface electromagnetic waves excited in one-dimensional photonic crystals has been experimentally observed. The Goos-Hänchen shift reaches 30λ for a wavelength of λ = 532 nm.     

Polariton dynamics of a one-dimensional gyrotropic magnetic photonic crystal in a dc electric field: I. Peculiarities of refraction

It is shown that both TE and TM waves incident on the surface of a semi-infinite one-dimensional thin-layer gyrotropic magnetic photonic crystal of the magnetic-nonmagnetic dielectric type can experience a number of refraction anomalies in an external electric field due to the effect of hybridization of evanescent waves in magnetic and nonmagnetic layers. These anomalies are absent under the same conditions in spatially homogeneous media consisting of the same materials as the photonic crystal.     

A scheme of plasmon excitation at the interface between metal and a photonic crystal

A one-dimensional photonic crystal and an incident light wave that is noncollinear with the permittivity gradient of the crystal are considered. On the basis of coupled-mode equations, eigensolutions for the fields are obtained; a special focus is placed on evanescent waves. Field transformation at the crystal-air and crystal-metal interfaces is analyzed. A condition for the resonance excitation of surface waves at the interface between a crystal and a metal is obtained, and an estimate is given for the efficiency of transformation of the original traveling wave into a surface wave.     

Modification of the spontaneous emission of quantum dots near the surface of a three-dimensional colloidal photonic crystal

This paper demonstrates experimentally and numerically that a significant modification of spontaneous emission rate can be achieved near the surface of a three-dimensional photonic crystal.In experiments,semiconductor core-shell quantum dots are intentionally confined in a thin polymer film on which a three-dimensional colloidal photonic crystal is fabricated.The spontaneous emission rate of quantum dots is characterised by conventional and time-resolved photoluminescence (PL) measurements.The modification of the spontaneous emission rate,which is reflected in the change of spectral shape and PL lifetime,is clearly observed.While an obvious increase in the PL lifetime is found at most wavelengths in the band gap,a significant reduction in the PL lifetime by one order of magnitude is observed at the short-wavelength band edge.Numerical simulation reveals a periodic modulation of spontaneous emission rate with decreasing modulation strength when an emitter is moved away from the surface of the photonic crystal.It is supported by the fact that the modification of spontaneous emission rate is not pronounced for quantum dots distributed in a thick polymer film where both enhancement and suppression are present simultaneously.This finding provides a simple and effective way for improving the performance of light emitting devices.     

Negative refraction in two-dimensional photonic crystals

We present some of our recent results for negative refraction in photonic crystals. The concept of negative refraction in photonic crystals is firstly introduced. Then, the propagation of electromagnetic waves in photonic crystals is systematically studied. By the layer Korringa–Kohn–Rostoker method, the coupling efficiency between external plane waves and the Bloch waves in photonic crystals is investigated. It is found that the coupling coefficient is highly angular dependent even for an interface between air with n=1 and a photonic crystal with effective index n_eff=-1. It is also shown that, for point imaging by a photonic crystal slab, owing to the negative refraction, the influence of the surface termination on the transmission and the imaging quality is significant. Finally, we present results experimentally demonstrating negative refraction in a two-dimensional photonic crystal at optical communication wavelengths. PACS 42.70.Qs; 41.85.Ct; 42.30.Va     

利用二维光子晶体提高波的耦合效率

通过多重散射方法数值模拟研究和实验测量表明利用二维光子晶体可以提高波的耦合效率.研究发现,高的波耦合效率通常发生在光子禁带的边沿和其它非禁带区的某些频率处.当光子晶体的晶格常数接近于所传输的波的波长时,会出现很高耦合效率的共振耦合现象.利用二维光子晶体的情况下的波耦合效率最高可以达到不利用二维光子晶体时的1.89倍.这种现象在光集成器件中尤其有用.     

Features of the manifestation of a stop band in the spectrum of light diffracted at a glass-opal interface

The diffraction of light passing through a glass plate coated by an artificial opal film has been analyzed. It has been shown that the stop band of a photonic crystal is manifested against the background of the unchanged spectrum of reflected and refracted Bragg waves. The position of this stop band can be changed under a small change in the concentration of a number of substances filling the photonic crystal. The application of such an optical system as an optical chemical sensor has been demonstrated.     

Vertical cavity-surface emitting photonic crystal surface-mode lasers

We present the research of a type of vertical cavity-surface emitting photonic crystal laser with a periodically modulated surface. The proper modulation to the cavity surface changes nonradiative surface modes into radiative ones and the constructive interference of the radiative waves results in the vertical surface emission. The numerical investigation of such cavities shows that, for a cavity with a definite length, resonant frequencies and their quality factors mainly depend on the magnitude of the corrugated surface. Furthermore, the simulation of the lasing processes demonstrates the features of this type of laser, such as vertical surface emitting, flat wavefront and single mode operation which is robust.     

在色散渐减光子晶体光纤中产生超连续谱的实验研究

本文利用非线性偏振锁模激光器产生的重复频率50 MHz, 脉宽为1.8 ps的脉冲分别抽运外径均匀和色散渐减两种高非线性光子晶体光纤, 在三阶非线性效应 (自相位调制、交叉相位调制、四波混频和受激拉曼散效应等) 和色散共同作用下得到扩展至蓝光部分的超连续谱. 模拟了光谱在色散渐减光纤和均匀光纤中的展宽过程, 通过对比均匀光纤发现色散渐减光纤在调控色散, 加强拉曼孤子和色散波的群速度匹配条件, 产生超带宽光谱方面具有很大优势. 实验利用20 m长的色散渐减光纤, 得到了406.1至671.8 nm的可见光波段增强的较为平坦的超连续谱. 关键词： 超连续谱 色散渐减光子晶体光纤 群速度匹配 非线性效应     

FDTD study of subwavelength imaging by a photonic crystal slab

The problem of subwavelength imaging via a photonic crystal slab lens made of two-dimensional (2D) square arrays of parallel dielectric cylinders in air is studied and discussed theoretically. The finite-difference time-domain method is employed to investigate the unique features of imaging by such lens. We confirm earlier findings that a photonic crystal slab lens can provide the imaging of a point source. By analysing the transmission properties of the proposed structure, we demonstrate that inside the all-angle negative refraction, there are some favourable directions for waves to travel. We show that the surface termination of the photonic crystal is a key parameter to obtain a good quality image. The super-resolution of two sources separated by a distance less than the wavelength is also considered. It is shown that the achievable resolution is limited by the slab length.     

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.     

Design and analysis of coherent OCDM en/decoder based on photonic crystal

The design and performance analysis of a new coherent optical en/decoder based on photonic crystal (PhC) for optical code -division -multiple (OCDM) are presented in this paper. In this scheme, the optical pulse phase and time delay can be flexibly controlled by photonic crystal phase shifter and time delayer by using the appropriate design of fabrication. According to the PhC transmission matrix theorem, combination calculation of the impurity and normal period layers is applied, and performances of the PhC-based optical en/decoder are also analyzed. The reflection, transmission, time delay characteristic and optical spectrum of pulse en/decoded are studied for the waves tuned in the photonic band-gap by numerical calculation. Theoretical analysis and numerical results indicate that the optical pulse is achieved to properly phase modulation and time delay, and an auto-correlation of about 8 dB ration and cross-correlation is gained, which demonstrates the applicability of true pulse phase modulation in a number of applications.     

Optical Tamm states at the interface between a photonic crystal and a nanocomposite with resonance dispersion

Optical Tamm states localized at the edges of a photonic crystal bounded from one or both sides by a nanocomposite have been studied. The nanocomposite consists of metallic nanoinclusions, which have a spherical or orientationally ordered spheroidal shape and are dispersed in a transparent matrix, and is characterized by the resonant effective permittivity. The transmission, reflection, and absorption spectra have been calculated for waves with longitudinal and transverse polarizations in such structures at the normal incidence of light. The spectral manifestation of Tamm states that is due to the existence of negative values of the real part of the effective permittivity has been analyzed for the visible spectral range. It has been established that the characteristics of Tamm states localized at the edge of the photonic crystal depend strongly both on the concentration of nanoballs in the nanocomposite film and on its thickness. Modes formed by two coupled Tamm plasmon polaritons localized at the edges of the photonic crystal adjacent to two nanocomposite layers have been examined. It has been shown that, in the case of the anisotropic nanocomposite layer adjacent to the photonic crystal, each of two orthogonal polarizations of the incident wave corresponds to a specific frequency of the Tamm state localized at the edge; owing to this property, the transmission spectra of such a structure are polarization sensitive.     

Microwave photonic crystal on the slot transmission line with a ferroelectric film

A microwave electrically tunable photonic crystal based on a periodically width-modulated slot transmission line with a ferroelectric film is investigated for the first time. The dispersion and transmission characteristics of electromagnetic waves propagating in such a structure are calculated. The electric control over photonic crystal characteristics is simulated.     

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.     

Magnetic-field control of the transmission of a photonic crystal with a liquid-crystal defect

The method of modulation of transmittance of a multilayer photonic crystal with a nematic liquid-crystal defect upon the orientational transition from the homeotropic to the planar state is investigated. The orientation of the director of the nematic is controlled by a magnetic field in the B-effect mode. The method of recurrent relations is used for numerical simulation of transmission spectra of the photonic crystal structure under investigation.     

光子晶体中基于有效折射率接近零的光束准直出射

利用平面波展开法(PWM)和时域有限差分法(FDTD)研究了二维正方格子光子晶体靠近禁带边沿附近频率光波的传输特性.研究发现,若有效折射率接近于零,可出现光束从晶体表面准直出射的现象,且光束的出射方向只与晶体表面的取向有关,而与晶格取向无关.这种现象与自准直现象有很大不同.     

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.     

Generation of slow intense optical solitons in a resonance photonic crystal

We demonstrate interesting and previously unforeseen properties of a pair of gap solitons in a resonant photonic crystal which are predicted and explained in a physically transparent form using both analytical and numerical methods. The most important result is the fact that an oscillating gap soliton created by the presence of a localized population inversion inside the crystal can be manipulated by means of a proper choice of bit rate, phase and amplitude modulation. Developing this idea, we are able to obtain qualitatively different regimes of a resonant photonic crystal operation. In particular, a noteworthy observation is that both the delay time and amplitude difference must exceed a certain level to ensure effective control over the soliton dynamics.