Laser & Photonics Reviews

Cover image for Vol. 8 Issue 6

Editor: Katja Paff

Impact Factor: 9.313

ISI Journal Citation Reports © Ranking: 2013: 3/83 (Optics); 9/67 (Physics Condensed Matter); 10/136 (Physics Applied)

Online ISSN: 1863-8899

Associated Title(s): Advanced Optical Materials, Journal of Biophotonics

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July 28, 2014

From Narrow to Broad

From Narrow to Broad

Electromagnetic absorbers based on plasmonic and metamaterial structures are of great interest for many areas as narrowband absorbers. A variety of approaches have been proposed to achieve broadband absorption, which is needed for applications such as solar energy harvesting.

Hangzhou (China) – Early research on electromagnetic (EM) absorbers dates back to 1902 when Wood observed the anomalous dips in the reflection spectra of metallic gratings under illumination of a white-light source. EM wave absorbers are devices in which the incident radiation at the operating wavelengths can be efficiently absorbed, and then transformed into ohmic heat or other forms of energy. Thereby, neither transmission nor reflection is produced when a wave passes through a perfect absorber.
There are various types of configurations being used as EM absorbers, such as lamellar gratings, convex grooves, spherical voids, and hole arrays. These absorbers are made of noble metals, and associated with plasmonics that contains interesting physical phenomena associated with planar or localized due to the excitation of surface plasmon polaritons (SPPs). Metamaterials are artificial assemblies of structured elements of subwavelength size, i.e. much smaller than the wavelength of the incident waves. The effective permittivity and permeability can be designated from zero to infinity, and as a result, various unique properties that are not available in nature can be finally achieved.
In a review article, scientists from Zhejiang University in Hangzhou and the Taiyuan University of Technology in China give an overview on the principle of different types of narrowband EM absorbers as well as the various approaches to achieve broadband/multiband absorbers. Many mechanisms of EM absorption based on metallic structures as well as metamaterial-based schemes are described and the authors discuss how to improve the performance of the absorption band.
A series of plasmonic and metamaterial structures can work as efficient narrowband absorbers due to the excitation of plasmonic or photonic resonances, providing a great potential for selective thermal emitters, biosensing, etc. In other applications such as solar-energy harvesting and photonic detection, the bandwidth of light absorbers is required to be quite broad. A variety of mechanisms of broadband/multiband absorption have been proposed, such as mixing multiple resonances together, exciting phase resonances, slowing down light by anisotropic metamaterials, employing high loss materials.
The most profound application area of EM absorbers is solar-energy harvesting. Every improvement is of great significance to society, bringing both economic and environmental benefits. In the future, low-cost, easily fabricated, and high-performance solar absorbers will be in high demand for building economic solar plants. Despite the progress made in producing high-performance EM absorbers, their industrial realization still remains a challenge. (Text contributed by K. Maedefessel-Herrmann)

See the original publication: Yanxia Cui, Yingran He, Yi Jin, Fei Ding, Liu Yang, Yuqian Ye, Shoumin Zhong, Yinyue Lin, and Sailing He, Plasmonic and metamaterial structures as electromagnetic absorbers, Laser Photonics Rev., 8, 495-520 (2014)

July 28, 2014

Lasing with Zinc Oxide

Lasing with Zinc Oxide

Zinc oxide (ZnO) is considered as an ideal candidate for ultraviolet (UV) lasers. A review article summarizes recent progress in optically and electrically pumped whispering-gallery mode lasing from ZnO microcavities.

Shanghai (China) – From microlight sources to photoswitches and frequency converters: ultraviolet (UV) semiconductor microlasers open up a broad range of potential applications in photonics and optoelectronics. In addition, microcavity lasers also provide a platform for fundamental scientific research on cavity quantum electrodynamics, photon statistics and some other physical problems. Although the typical wide-bandgap semiconductor gallium nitride (GaN) has been used for the production of violet and ultraviolet light-emitting diodes and laser diodes, highly efficient GaN-based UV lasers have not really been realized. Zinc oxide (ZnO) opens up an attractive alternative, in fact, it seems to be an ideal material for UV lasers: It features a wide direct bandgap of 3.37 eV) as well as a strong exciton binding energy of 60 meV. Such unique properties are beneficial for achieving exciton lasing at room temperature and even high temperatures.
To improve the lasing performance, a tremendous endeavor has been focused on the whispering-gallery mode (WGM) lasing in microdisk cavities in the past decade. A micro/nanostructured ZnO crystal generally has a wurtzite structure and usually presents a natural hexagonal cross section, which naturally serves as a WGM lasing microcavity owing to its high reflective index.
In a review article, researchers led by Chunxiang Xu from Fudan University, Shanghai and City University of Hong Kong, China give an overview on WGM lasing in ZnO microcavities. They systematically report on WGM microcavity construction, optically pumped lasing, and laser device fabrication. Growth methods for typical WGM microcavities, such as ZnO micro/nanostructured wires, rods, disks, and nails with hexagonal or dodecagonal cross sections are treated.
The authors describe the characteristics of single-photon and multiphoton pumped WGM lasing and review the lasing mechanisms on excitonic, electron–hole plasma and exciton–polariton lasing. In addition, recent advances in ZnO-based microlaser devices such as heterojunction laser diodes are presented. A novel method for the fabrication of heterostructured ZnO WGM microlaser devices is described. The scientists expect that highly efficient ZnO WGM laser diodes will be fabricated with the progress in p-type ZnO. (Text contributed by K. Maedefessel-Herrmann)

See the original publication: Chunxiang Xu, Jun Dai, Guangping Zhu, Gangyi Zhu, Yi Lin, Jitao Li, and Zengliang Shi, Whispering-gallery mode lasing in ZnO microcavities, Laser Photonics Rev., 8, 469-494 (2014)

July 28, 2014

Chinese Whispers

Chinese Whispers

Optical mcirocavities with whispering-gallery modes have large potential. In particular, those with a tubular geometry enable researchers to explore and construct novel optical microdevices for a wide range of potential applications.

Shanghai (China) – Whispered communication is possible from any part of the internal side of the circumference to any other part of a so called whispering gallery. The sound is carried by waves that travel around the circumference clinging to the walls. The phenomenon was first discovered in the whispering gallery of St Paul's Cathedral in London. Just as an acoustical wave travels along the surface of a wall, a light wave as well can undergo reflection, refraction, and diffraction. If the light path is curved below a certain minimum radius, as in a whispering gallery, the normal optical mode becomes whispering gallery mode (WGM). In contrast to an optical fiber, in a whispering-gallery waveguide light requires reflection from the curved outer surface only. In WGM resonators, light waves are confined by continuous total internal reflections. Compared to other types of optical resonators, WGM resonators exhibit superior properties such as ultrahigh Q-factor and tunable size. The resonators can exhibit different shapes, such as spherical, microtoroid, microring, and tubular geometries.
The advent of tubular optical microcavities has led to new generations of integrated devices and sensors. Various dye-doped and undoped transparent materials were chosen to prepare tubular microcavity structures by depositing thin films such as polyurethane, epoxy, lead-silica, gelatin, and polymethylmethacrylate (PMMA) on glass fibers. In a review article, scientists from the Fudan University, Shanghai, and the City University of Hong Kong (China) give an overview on tubular optical microcavities from the perspectives of theoretical consideration, optical characterization, and potential applications. The authors describe possible fabrication methods including fiber-drawing, rolled-up nanotechnology, electrospin techniques, and template-assistant methods.
Tubular optical microcavities enable researchers to explore and construct novel optical microdevices for a wide range of potential applications. They feature many interesting properties, such as trimmed resonant modes, simplicity as fluidic channels, three-dimensionally (3D) mode confinement, and unique evanescent waves. They open up the possibility to assemble conductive, semiconductive and insulating materials into a tubular geometry, thus spurring multifunctional applications to optofluidic devices, optical microdevices like microlasers, and bio/chemical sensors.
The authors are convinced that future research will produce more sophisticated functionalities such as truly multifunctional fabrics. They propose not to ignore the evanescent-wave effect and interactions with materials with special functions. A better understanding might lead to improved tubular optical microcavities in complex systems with integrated functions such as multimaterials multifunctional fibers that can see, hear, sense, and communicate, as well as lab-in-a-tube microsystems. (Text contributed by K. Maedefessel-Herrmann)

See the original publication: Jiao Wang, Tianrong Zhan, Gaoshan Huang, Paul K. Chu, and Yongfeng Mei, Optical microcavities with tubular geometry: properties and applications, Laser Photonics Rev., 8:4, 521-547 (2014)

July 28, 2014
From Narrow to Broad

July 28, 2014
Lasing with Zinc Oxide

July 28, 2014
Chinese Whispers

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