Sep 2010, Volume 5 Issue 3

Cover illustration

  • In recent years, metamaterials has stimulated the interest of many researchers due to their many important applications, such as negative refraction, super-imaging, and invisible cloak. According to the well known effective-media model, the coupling interactions between the elements in metamaterials are somewhat ignored; therefore, the effective properties of metamaterials can be viewed as the "averaged effect' of the resonance property of the individual elements. Howeve [Detail] ...

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  • Research articles
  • Research articles
    Ye LIU(刘晔), Fei QIN(秦飞), Fei ZHOU(周飞), Qing-bo MENG(孟庆波), Dao-zhong ZHANG (张道中), Zhi-yuan LI (李志远),
    Nonlinear photonic crystals made from polystyrene materials that have Kerr nonlinearity can exhibit ultrafast optical switching when the samples are pumped by ultrashort optical pulses with high intensity due to the change of the refractive index of polystyrene and subsequent shift of the band gap edge or defect state resonant frequency. Polystyrene has a large Kerr nonlinear susceptibility and almost instantaneous response to pump light, making it suitable for the realization of ultrafast optical switching with a response time as short as a few femtoseconds. In this paper, we review our experimental progress on the continual improvement of all-optical switching speed in two-dimensional and three-dimensional polystyrene nonlinear photonic crystals in the past years. Several relevant issues are discussed and analyzed, including different mechanisms for all-optical switching, preparation of nonlinear photonic crystal samples by means of microfabrication and self-assembly techniques, characterization of optical switching performance by means of femtosecond pump-probe technique, and different ways to lower the pump power of optical switching to facilitate practical applications in optical information processing. Finally, a brief summary and a perspective of future work are provided.
  • Research articles
    Jing-feng LIU(刘景锋), Xue-hua WANG(王雪华),
    Spontaneous emission of emitters governing the performance of optoelectronic devices is a fundamental phenomenon, and it has strong environment-dependent characteristics. In this article, we mainly review the experimental and theoretical progresses in the control of spontaneous emission by manipulating optical modes with photonic crystals, optical microcavities and metallic nanostructures. The spontaneous emission from emitters in photonic crystals can be modified by the local density of states, and by employing photonic crystals, the devices’ efficiency is enhanced, the angular radiation pattern can be engineered, and highly efficient optoelectronic devices are achieved through decreasing the radiative lifetime. In quantum optical devices, microcavities would alter the lifetime of an excited state through tuning the resonance in the frequency and positioning between the emitters and cavity field, and inducing the emitters to emit spontaneous photons in a desired direction. The emerging enhanced electromagnetic field near metallic nanostructures can help to control and manipulate the spontaneous emission of an emitter. The use of micro- and nano-structures to manipulate spontaneous emission will open unprecedented opportunities for realizing functional photonic devices.
  • Research articles
    Jing WANG(王静), Min YAN(严敏), Min QIU(仇旻),
    Our recent research on surface mode optical microcavities based on two-dimensional photonic crystals (PhCs) was reviewed in this paper. We presented the design, fabrication and characterization of high quality (Q) factor surface mode microcavities. Realizations of these PhCs were based on both amorphous silicon-on-insulator (SOI) structures and crystalline SOI structures.
  • Research articles
    Tian-rui ZHAI(翟天瑞), Da-he LIU(刘大禾), Xiang-dong ZHANG(张向东),
    Although the investigation on photonic band gap materials has been done more than two decades, it is still a big challenge to fabricate three-dimensional photonic crystal (PC) possessing wide band gaps in visible range. In this article, we have reviewed recent progresses on fabricating the PC with low refractive index material in visible range. In contrast to the material with large refractive index, it is cheap to use low refractive index material in fabricating the PC and will be greatly beneficial for future industrial productions. The holographic method to fabricate such a PC has been introduced, applying it to the design of the microlaser has also been discussed.
  • Research articles
    Hui LIU(刘辉), Tao LI(李涛), Shu-ming WANG(王漱明), Shi-ning ZHU(祝世宁),
    Although the invention of the metamaterials has stimulated the interest of many researchers and possesses many important applications, the basic design idea is very simple: composing effective media from many small structured elements and controlling its artificial EM properties. According to the effective-media model, the coupling interactions between the elements in metamaterials are somewhat ignored; therefore, the effective properties of metamaterials can be viewed as the “averaged effect” of the resonance property of the individual elements. However, the coupling interaction between elements should always exist when they are arranged into metamaterials. Sometimes, especially when the elements are very close, this coupling effect is not negligible and will have a substantial effect on the metamaterials’ properties. In recent years, it has been shown that the interaction between resonance elements in metamaterials could lead to some novel phenomena and interesting applications that do not exist in conventional uncoupled metamaterials. In this paper, we will give a review of these recent developments in coupled metamaterials. For the “metamolecule” composed of several identical resonators, the coupling between these units produces multiple discrete resonance modes due to hybridization. In the case of a “metacrystal” comprising an infinite number of resonators, these multiple discrete resonances can be extended to form a continuous frequency band by strong coupling. This kind of broadband and tunable coupled metamaterial may have interesting applications. Many novel metamaterials and nanophotonic devices could be developed from coupled resonator systems in the future.
  • Research articles
    Jia-ming HAO(郝加明), Min QIU(仇旻), Lei ZHOU(周磊),
    Polarization is an important characteristic of electromagnetic (EM) waves, and efficient manipulations over EM wave polarizations are always desirable in practical applications. Here, we review the recent efforts in controlling light polarizations with metamaterials, at frequencies ranged from microwave to visible. We first presented a 4 × 4 version transfer matrix method (TMM) to study the scatterings by an anisotropic metamaterial of EM waves with arbitrary propagating directions and polarizations. With the 4 × 4 TMM, we discovered several amazing polarization manipulation phenomena based on the reflection geometry and proposed corresponding model metamaterial systems to realize such effects. Metamaterial samples were fabricated with the help of finite-difference-time-domain (FDTD) simulations, and experiments were performed to successfully realize these ideas at both microwave and visible frequencies. Efforts in employing metamaterials to manipulate light polarizations based on the transmission geometry are also reviewed.
  • Research articles
    Yun LAI(赖耘), Jack NG(吴紫辉), Huan-yang CHEN(陈焕阳), Zhao-qing ZHANG(张昭庆), C. T. CHAN(陈子亭),
    The technique of “transformation optics” establishes a correspondence between coordinate transformation and material constitutive parameters. Most of the transformation optics mappings give metamaterials that have graded positive refractive indices that can steer light in curves defined by the coordinate transformation. We will focus on those “folded-geometry mappings” that give negative refractive index materials that have special wave scattering properties. One interesting example is a kind of remote illusion device that can transform the stereoscopic image of an object into the illusion of some other object of our choice. The conceptual device can create the illusion without touching or encircling the object. For any incident wave, the device transforms the scattered waves of the original object into that of the object chosen for illusion outside a virtual boundary. We will illustrate some possible applications of this type of metamaterial remote device, including “cloaking at a distance,” partial cloaking, cloaking from an embedded device, revealing a hidden object inside a container, turning the image of one object into that of another object, and seeing through a wall. The feasibility of building this remote illusion device by metamaterials will also be discussed.
  • Research articles
    Di BAO(鲍迪), Efthymios KALLOS, Wen-xuan TANG(汤文轩), Christos ARGYROPOULOS, Yang HAO(郝阳), Tie-jun CUI(崔铁军),
    In this paper, the properties of cylindrical high permittivity dielectric particles are studied. A design for broadband reduction of the scattering signature of metallic objects is proposed by implementing simplified ground-plane cloaking schemes. The devices are functional in the presence of a ground plane as well as in free space ranging from 4 GHz to 10 GHz. The required dielectric map for the cloak is achieved by means of manipulating the dimensions of the periodically distributed dielectric cylinders embedded in a host medium with a permittivity close to one. The scattering reduction effects are verified through simulation results. The proposed all dielectric cloaks are advantageous over other schemes due to their non-dispersive nature, the broad bandwidth, the low loss, and the ease of fabrication.
  • Research articles
    Pratik CHATURVEDI, Nicholas X. FANG,
    We investigated a far-field superlens operating at mid-infrared wavelength that allows resolving subwavelength features in the far-field. By utilizing evanescent enhancement provided by surface plasmon excitation of silver nanorods and Moiré effect, we numerically demonstrated that subwavelength information of an object can be converted to propagating information. This information can then be captured by conventional optical components. A simple image reconstruction algorithm can restore the subwavelength object. A sub-diffraction-limited resolution of 2.5 μm at 6-μm wavelength is demonstrated.
  • Research articles
    We report the synthesis, characterization and modellization of optical anion sensors based on gold nanoparticles (Au NPs) stabilized by amino-functional imidazolium ionic liquids (AFIL). The addition of different salts results in anion exchange of the imidazolium ionic liquid stabilizer leading to a change in the optical response of the original nanoparticle aqueous solution. In all cases except with dodecylbenzenesulfonic acid sodium salt, a sufficient amount of salt concentration (5 times larger than equimolar) leads to the appearance of an absorption band between 600 and 700 nm in the ultravioletvisible (UV-vis) spectrum. The presence of the salt produces aggregation of the particles that localise the optical response and produce a large spectral red shift. Transmission electron microscopy images demonstrated that this optical change was due to the aggregation of the nanoparticles. We simulate the optical response of both situations, before and after salt addition, and interpret the experimental observations in terms of the different response of metallic single nanoparticles and nanoparticle aggregates. Theoretical calculations for single nanoparticle and single nanoparticle dimers demonstrate that the colour change is not due to the enlargement or structural changes of the Au NPs, but due to the formation of NP aggregation. These results show the potential of nanoparticle plasmonics to perform effective chemical sensing.
    Xin-huaPENG(彭新华), Dieter SUTER,