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Frontiers of Optoelectronics

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, Volume 11 Issue 1 Previous Issue   
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PREFACE
REVIEW ARTICLE
Two-dimensional material functional devices enabled by direct laser fabrication
Tieshan YANG, Han LIN, Baohua JIA
Front. Optoelectron.. 2018, 11 (1): 2-22.  https://doi.org/10.1007/s12200-017-0753-1
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During the past decades, atomically thin, two-dimensional (2D) layered materials have attracted tremendous research interest on both fundamental properties and practical applications because of their extraordinary mechanical, thermal, electrical and optical properties, which are distinct from their counterparts in the bulk format. Various fabrication methods, such as soft-lithography, screen-printing, colloidal-templating and chemical/dry etching have been developed to fabricate micro/nanostructures in 2D materials. Direct laser fabrication with the advantages of unique three-dimensional (3D) processing capability, arbitrary-shape designability and high fabrication accuracy up to tens of nanometers, which is far beyond the optical diffraction limit, has been widely studied and applied in the fabrication of various micro/nanostructures of 2D materials for functional devices. This timely review summarizes the laser-matter interaction on 2D materials and the significant advances on laser-assisted 2D materials fabrication toward diverse functional photonics, optoelectronics, and electrochemical energy storage devices. The perspectives and challenges in designing and improving laser fabricated 2D materials devices are discussed as well.

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Recent advances in photonic dosimeters for medical radiation therapy
James ARCHER, Enbang LI
Front. Optoelectron.. 2018, 11 (1): 23-29.  https://doi.org/10.1007/s12200-018-0759-3
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Radiation therapy, which uses X-rays to destroy or injure cancer cells, has become one of the most important modalities to treat the primary cancer or advanced cancer. High resolution, water equivalent and passive X-ray dosimeters are highly desirable for developing quality assurance (QA) systems for novel cancer therapy like microbeam radiation therapy (MRT) which is currently under development. Here we present the latest developments of high spatial resolution scintillator based photonic dosimeters, and their applications to clinical external radiation beam therapies: specifically high energy linear accelerator (LINAC) photon beams and low energy synchrotron photon beams. We have developed optical fiber dosimeters with spatial resolutions ranging from 50 to 500 mm and tested them with LINAC beams and synchrotron microbeams. For LINAC beams, the fiber-optic probes were exposed to a 6 MV, 10 cm by 10 cm X-ray field and, the beam profiles as well as the depth dose profiles were measured at a source-to-surface distance (SSD) of 100 cm. We have also demonstrated the possibility for temporally separating Cherenkov light from the pulsed LINAC scintillation signals. Using the 50 mm fiber probes, we have successfully resolved the microstructures of the microbeams generated by the imaging and medical beamline (IMBL) at the Australian Synchrotron and measured the peak-to-valley dose ratios (PVDRs). In this paper, we summarize the results we have achieved so far, and discuss the possible solutions to the issues and challenges we have faced, also highlight the future work to further enhance the performances of the photonic dosimeters.

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Dipole-fiber system: from single photon source to metadevices
Shaghik ATAKARAMIANS, Tanya M. MONRO, Shahraam AFSHAR V.
Front. Optoelectron.. 2018, 11 (1): 30-36.  https://doi.org/10.1007/s12200-018-0762-8
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Radiation of an electric dipole (quantum emitter) in vicinity of optical structures still attracts great interest due to emerging of novel application and technological advances. Here we review our recent work on guided and radiation modes of electric dipole and optical fiber system and its applications from single photon source to metadevices. We demonstrate that the relative position and orientation of the dipole and the core diameter of the optical fiber are the two key defining factors of the coupled system application. We demonstrate that such a coupled system has a vast span of applications in nanophotonics; a single photon source, a high-quality factor sensor and the building block of metadevices.

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Development of Bi/Er co-doped optical fibers for ultra-broadband photonic applications
Yanhua LUO, Binbin YAN, Jianzhong ZHANG, Jianxiang WEN, Jun HE, Gang-Ding PENG
Front. Optoelectron.. 2018, 11 (1): 37-52.  https://doi.org/10.1007/s12200-017-0764-y
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Targeting the huge unused bandwidth (BW) of modern telecommunication networks, Bi/Er co-doped silica optical fibers (BEDFs) have been proposed and developed for ultra-broadband, high-gain optical amplifiers covering the 1150–1700 nm wavelength range. Ultra-broadband luminescence has been demonstrated in both BEDFs and bismuth/erbium/ytterbium co-doped optical fibers (BEYDFs) fabricated with the modified chemical vapor deposition (MCVD) and in situ doping techniques. Several novel and sophisticated techniques have been developed for the fabrication and characterization of the new active fibers. For controlling the performance of the active fibers, post-treatment processes using high temperature, g-radiation, and laser light have been introduced. Although many fundamental scientific and technological issues and challenges still remain, several photonic applications, such as fiber sensing, fiber gratings, fiber amplification, fiber lasers, etc., have already been demonstrated.

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Silicon waveguide cantilever displacement sensor for potential application for on-chip high speed AFM
Peng WANG, Aron MICHAEL, Chee Yee KWOK
Front. Optoelectron.. 2018, 11 (1): 53-59.  https://doi.org/10.1007/s12200-018-0774-4
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This paper reviews an initial achievement of our group toward the development of on-chip parallel high-speed atomic force microscopy (HS-AFM). A novel AFM approach based on silicon waveguide cantilever displacement sensor is proposed. The displacement sensing approach uniquely allows the use of nano-scale wide cantilever that has a high resonance frequency and low spring constant desired for on-chip parallel HS-AFM. The approach consists of low loss silicon waveguide with nano-gap, highly efficient misalignment tolerant coupler, novel high aspect ratio (HAR) sharp nano-tips that can be integrated with nano-scale wide cantilevers and electrostatically driven nano-cantilever actuators. The simulation results show that the displacement sensor with optical power responsivity of 0.31%/nm and AFM cantilever with resonance frequency of 5.4 MHz and spring constant of 0.21 N/m are achievable with the proposed approach. The developed silicon waveguide fabrication method enables silicon waveguide with 6 and 7.5 dB/cm transmission loss for TE and TM modes, respectively, and formation of 13 nm wide nano-gaps between silicon waveguides. The coupler demonstrates misalignment tolerance of ±1.8 µm for 5 µm spot size lensed fiber and coupling loss of 2.12 dB/facet for standard cleaved single mode fiber without compromising other performance. The nano-tips with apex radius as small as 2.5 nm and aspect ratio of more than 50 has been enabled by the development of novel HAR nano-tip fabrication technique. Integration of the HAR tips onto an array of 460 nm wide cantilever beam has also been demonstrated.

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RESEARCH ARTICLE
Use of fiber Bragg grating sensors for monitoring delamination damage propagation in glass-fiber reinforced composite structures
Ayad KAKEI, Jayantha A. EPAARACHCHI
Front. Optoelectron.. 2018, 11 (1): 60-68.  https://doi.org/10.1007/s12200-018-0761-9
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Embedded fiber Bragg grating (FBG) sensors have been widely used for damage monitoring of fiber composite structures for a few decades. However, many remaining engineering challenges have delayed FBG based in situ structural health monitoring (SHM) systems. One of the major problem associated with FBG based SHM system is the unavailability of reliable data processing algorithms. The present work details a study which has been undertaken for identification of delamination crack propagation in fiber reinforced polymer (FRP) composite plate under uniaxial loading. The strain measured by embedded FBG sensors closer to the crack tip was used to qualitatively and quantitatively analyze delamination damage propagation using recently proposed elasto-plastic model. Strain energy release rate was calculated and compared with the model prediction. The study has concluded that the delamination crack propagation in a FRP composite can be monitored successfully using an integral approach of FBG sensors measurements and the predictions of proposed elasto-plastic model.

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Structure formation dynamics in drawing silica photonic crystal fibres
Wenyu WANG, Ghazal Fallah TAFTI, Mingjie DING, Yanhua LUO, Yuan TIAN, Shuai WANG, Tomasz KARPISZ, John CANNING, Kevin COOK, Gang-Ding PENG
Front. Optoelectron.. 2018, 11 (1): 69-76.  https://doi.org/10.1007/s12200-018-0775-3
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The special features of photonic crystal fibres (PCFs) are achieved by their air hole structures. PCF structure is determined and formed by its origin preform design and drawing process. Therefore, structure formation dynamics in drawing PCF is important for the fabrication of PCF achieving desirable structure and thus the intended feature. This paper will investigate structure formation dynamics of PCF drawing in relation to key parameters and conditions, such as hole dimension, temperature, pressure, etc.

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REVIEW ARTICLE
On-chip silicon polarization and mode handling devices
Yong ZHANG, Yu HE, Qingming ZHU, Xinhong JIANG, Xuhan Guo, Ciyuan QIU, Yikai SU
Front. Optoelectron.. 2018, 11 (1): 77-91.  https://doi.org/10.1007/s12200-018-0772-6
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Mode- and polarization-division multiplexing are new promising options to increase the transmission capacity of optical communications. On-chip silicon polarization and mode handling devices are key components in integrated mode- and polarization-division multiplexed photonic circuits. In this paper, we review our recent progresses on silicon-based polarization beam splitters, polarization splitters and rotators, mode (de)multiplexers, and mode and polarization selective switches. Silicon polarization beam splitters and rotators are demonstrated with high extinction ratio, compact footprint and high fabrication tolerance. For on-chip mode multiplexing, we introduce a low loss and fabrication tolerant three-mode (de)multiplexer employing sub-wavelength grating structure. In analogy to a conventional wavelength selective switch in wavelength-division multiplexing, we demonstrate a selective switch that can route mode- and polarization-multiplexed signals.

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PERSPECTIVE
Non-thermal plasma fixing of nitrogen into nitrate: solution for renewable electricity storage?
Yi HE, Zhengwu CHEN, Zha LI, Guangda NIU, Jiang TANG
Front. Optoelectron.. 2018, 11 (1): 92-96.  https://doi.org/10.1007/s12200-018-0807-z
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The rapid deployment of solar and wind technology produces significant amount of low-quality electricity that calls for a better storage or usage instead of being discarded by the grid. Instead of electrochemical CO2 reduction and/or NH3 production, here we propose that non-thermal plasma oxidation of N2 into nitrate or other valuable nitrogen containing compounds deserve more research attention because it uses free air as the reactant and avoids the solubility difficulty, and also because its energy consumption is merely 0.2 MJ/mol, even lower than the industrially very successful Haber–Bosch process (0.48 MJ/mol) for NH3 production. We advocate that researchers from the plasma community and chemistry community should work together to build energy efficient non-thermal plasma setup, identify robust, active and low-cost catalyst, and understand the catalyzing mechanism in a plasma environment. We are confident that free production of nitrate with zero CO2 emission will come true in the near future.

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