波状结构二维光子晶体的自准直特性及亚波长成像的研究

利用平面波展开方法计算了波状结构二维光子晶体(2DPC)的等频面，对等频面内矩形轮廓的等频线进行研究，提出了波状结构2DPC的自准直特性，运用时域有限差分(FDTD)方法模拟了波状结构2DPC在不同入射角情况下对所入射高斯光束的自准直作用.将波状结构2DPC的自准直特性运用到近场亚波长成像，模拟了波状结构2DPC的自准直亚波长成像效果，单光源的成像分辨率达到0.28λ，且随着光源逐渐远离近场范围而降低. 关键词： 光子晶体 自准直 等频面 亚波长成像     

Spiral three-dimensional photonic crystals for telecommunications spectral range

Three-dimensional photonic crystals consisting of periodic arrays of spiral columns were fabricated in a commercially available photoresist (SU-8) by a direct laser writing technique. Tailoring the pre- and post-processing conditions for the photoresist has enabled the recording of extended, self-supporting periodic structures with sub-diffraction resolution. Pronounced photonic stop gaps were observed at wavelengths between 1.5 and 1.8 μm, close to the telecommunications region. These structures can be used as accurate and robust templates for subsequent infiltration by materials with higher refractive index. PACS 42.65.Re; 42.70.-a; 42.70.Qs     

光子晶体对太赫兹波的调制特性研究

利用传输矩阵方法研究了掺杂半导体n-GaAs/聚碳酸脂一维光子晶体的太赫兹波透射谱.研究结果发现,与一般由两种介电材料组成的一维光子晶体不同,由于掺杂半导体中自由载流子对太赫兹波存在较强的吸收,所以这种材料组成的一维光子晶体除可形成光子带隙外,还可以增强n-GaAs对太赫兹波的透射.同时还提出了一种基于这种一维光子晶体的太赫兹波调制器,通过外加电压控制半导体中电子浓度的大小可实现对太赫兹透射波幅度的调制. 关键词： 掺杂半导体光子晶体 太赫兹波 太赫兹波的调制     

Structural characterization of opal-based photonic crystals in the visible range

For structural characterization of periodic three-dimensional systems with submicron-scale lattice parameters (optical photonic crystals), is analogous to the use of visible light of x-rays. It is shown that specular reflectance and transmittance spectra of opal do indeed yield information on the lattice period and structural perfection of photonic crystals. Fiz. Tverd. Tela (St. Petersburg) 40, 648–650 (April 1998)     

Propagation characteristics of two-dimensional photonic crystals in the terahertz range

Based on the plane wave expansion method, the complete band gaps of two-dimensional terahertz photonic crystals with typical structures are optimized through varying structural parameters. During our calculation, two kinds of lattice structures that are very promising for the materials of terahertz components are found and some interesting phenomena that were not reported in the former papers are also presented. Using the finite difference time domain method, we simulated the electromagnetic field distribution of THz waves in a PC splitter. And by the plane wave expansion method, we achieved the dispersion relation and defect modes in a rotated PC waveguide. These results provide a useful guide and a theoretical basis for the developments of THz functional components. PACS 42.72.Ai; 42.70.Qs     

Diverging rabi oscillations in subwavelength photonic lattices

We show that Rabi oscillations between Bloch modes of an optical waveguide array with subwavelength periodicity diverge, both in frequency and in field amplitude, when the optical wavelength approaches a mathematical exceptional point at which the Bloch mode becomes self-orthogonal.     

Self-imaging effect in photonic crystal multimode waveguides exhibiting no band gaps

The properties of the propagating field in multimode photonic crystal waveguides (PCWs) exhibiting no photonic band gaps (PBGs) are investigated. The transmission spectrum shows that the input field can be guided with high efficiency, and resemble index-guided modes owing to the combination of total internal reflection (TIR) and distributed Bragg reflection (DBR). Self-imaging effect happens and the filling fraction determines the beating lengths. The rows of air holes decide DBR coming from the mirrors on both sides of the guiding region, which governs the transmission spectrum. It provides a new way to realize the components for both polarizations by combining PBG and TIR effects in PCWs.     

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.     

Metallic photonic crystals

Metallic photonic crystals (PC), also originally called artificial dielectrics, have properties different from those of their dielectric homologues. They are of strategic interest for the microwave domain where they exhibit sufficiently weak loss in addition to their robustness, conformability and low-cost fabrication. In this paper, we review some recent results on metallic photonic crystals and their potential applications to microwave circuits and antennas. After recalling spectral properties of metallic PC, we successively address ultra-compact structures such as high-impedance surfaces, electrically controllable photonic band gaps and left-handed materials. Finally, we discuss new opportunities offered by metallic PCs in the optical domain. To cite this article: J.-M. Lourtioz, A. de Lustrac, C. R. Physique 3 (2002) 79–88     

Natural photonic crystals

Photonic structures appeared in nature several hundred millions years ago. In the living world, color is used for communication and this important function strongly impacts the individual chances of survival as well as the chances to reproduce. This has a statistical influence on species populations. Therefore, because they are involved in evolution, natural color-generating structures are – from some point of view – highly optimized. In this short review, a survey is presented of the development of natural photonic crystal-type structures occurring in insects, spiders, birds, fishes and other marine animals, in plants and more, from the standpoint of light-waves propagation. One-, two-, and three-dimensional structures will be reviewed with selected examples.     

Graded photonic crystals

We present a concept of graded photonic crystals used to enhance the control of light propagation. Gradual modifications of the lattice periodicity make it possible to bend the light at the micrometer scale. This effect is tailored by parametric studies of the isofrequency curves. As a demonstration, we propose a two-dimensional graded photonic crystal that could provide frequency-selective tunable bending.     

Near-field observation of subwavelength confinement of photoluminescence by a photonic crystal microcavity

We present a direct, room-temperature near-field optical study of light confinement by a subwavelength defect microcavity in a photonic crystal slab containing quantum-well sources. The observations are compared with three-dimensional finite-difference time-domain calculations, and excellent agreement is found. Moreover, we use a subwavelength cavity to study the influence of a near-field probe on the imaging of localized optical modes.     

Optical echo in photonic crystals

The dynamics of a photonic wavepacket in the effective oscillator potential is studied. The oscillator potential is constructed on the base of one-dimensional photonic crystal with a period of unit cell adiabatically varied in space. The structure has a locally equidistant discrete spectrum. This leads to an echo effect, i.e., the periodical reconstruction of the packet shape. The effect can be observed in the nonlinear response of the system. Numerical estimations for porous-silicon based structures are presented for a femtosecond Ti:sapphire laser pump. The text was submitted by the authors in English.     

Entangling atoms in photonic crystals

We propose a method for entangling a system of two-level atoms in photonic crystals. The atoms are assumed to move in void regions of a photonic crystal. The interaction between the atoms is mediated either via a defect mode or via a resonant dipole-dipole interaction. We show that these interactions can produce pure entangled atomic states. We analyze the problem with parameters typical for currently existing photonic crystals and Rydberg atoms and we show that the atoms can emerge from photonic crystals in entangled states. Depending on the linear dimensions of the crystal we estimate that a pair of atoms entangled in a photonic crystal can be separated by tens of centimeters. Receive 11 June 1999 and Received in final form 4 October 1999     

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.     

Modeling of the optical properties of porous silicon photonic crystals in the visible spectral range

Optical devices based on photonic crystals are of great interest because they can be efficiently used in laser physics and biosensing. Photonic crystals allow one to control the propagation of electromagnetic waves and to change the emission characteristics of luminophores embedded into photonic structures. One of the most interesting materials for developing one-dimensional photonic crystals is porous silicon. However, an important problem in application of this material is the control of the refractive index of layers by changing their porosity, as well as the refractive index dispersion. In addition, it is important to have the possibility of modeling the optical properties of structures to choose precisely select the fabrication parameters and produce one-dimensional photonic crystals with prescribed properties. In order to solve these problems, we used a mathematical model based on the transfer matrix method, using the Bruggeman model, and on the dispersion of silicon refractive index. We fabricated microcavities by electrochemical etching of silicon, with parameters determined by the proposed model, and measured their reflection spectra. The calculated results showed good agreement with experimental data. The model proposed allowed us to achieve a microcavity Q-factor of 160 in the visible region.     

光子晶体器件进展

光子晶体对光具有独特的局域、反射、传导、分束、耦合、调制、慢光等操纵能力,使其成为微/纳光电集成的重要材料之一。介绍了光子晶体的几种重要物理特性——带隙特性、慢光特性、自准直和负折射特性,叙述了光子晶体集成器件方面所取得的最新进展,对光子晶体器件的发展动向做了展望。     

Transient gain in photonic crystals

Using the optical response formula for photonic crystals and the Bloch equations, we analyze coherent emission in arbitrary two-dimensional photonic crystals. The transient emission depends not only on the photon density of the states, but also on the intensity and duration of the pump laser pulses. A transient gain exists if the pump pulse area is a certain value and the transition frequency is tuned to the band edge. The sharp structure of the density of states near the band edge leads to a dramatic enhancement of the transient emission intensity and an abrupt change in the oscillation of the emission field. PACS 42.70.Qs; 32.80.-t; 42.25.Bs     

Negative refraction in photonic crystals

We demonstrate that light propagation in strongly modulated 2D/3D photonic crystals (PhCs) becomes refraction-like in the vicinity of the photonic bandgap, which is contrary to the fact that light propagation in weakly modulated PhCs is very different from refraction and thus the definition of refraction index becomes meaningless. Such a crystal behaves like a material having an effective refractive index controllable by the band structure. This situation is analogous to the effective-mass approximation in electron-band theory. The propagation states having a negative effective index exhibit unusual properties, such as mirror-like imaging effect, image-transfer effect. These properties are confirmed by finite-difference time-domain simulations.     

Extension of photonic band gaps in one-dimensional photonic crystals

A method is proposed for extending photonic band gaps by constructing periodic structures from two or more consecutively located photonic crystals with different lattice constants or filling factors. The photonic band gaps with a maximum extension are predicted by superposing the photonic band gap maps on one another. It is demonstrated that both the lowest and higher order band gaps can be merged in photonic crystals with a high refractive index contrast.