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Polarization properties in helical metamaterials
Zhenyu YANG, Peng ZHANG, Peiyuan XIE, Lin WU, Zeqin LU, Ming ZHAO
Front Optoelec. 2012, 5 (3): 248-255.
https://doi.org/10.1007/s12200-012-0267-9
In the last few years, there has been growing interest in the research of helical metamaterials due to the advantages of giant circular dichroism, broad operation bands, and compact structures. However, most of the researches were in the cases of single-, circular-helical metamaterials, and normal incidences. In this paper, we reviewed recent simulation works in the helical metamaterials with the finite-difference time-domain (FDTD) method, which mainly included the optical performances of double-, three-, four-helical metamaterials, performances of elliptical-helical metamaterials, and the polarization properties under the condition of oblique incidences. The results demonstrate that the double-helical metamaterials have operation bands more than 50%, which is broader than those of the single-helical structures. But both of them have low signal-to-noise ratios about 10 dB. The three- and four-helical metamaterials have significant improvement in overall performance. For elliptical-helixes, simulation results suggest that the transmitted light can have elliptical polarization states. On the condition of oblique incidences, the novel property of tunable polarization states occurred in the helical metamaterials, which could have much broader potential applications such as tunable optical polarizers, tunable beam splitters, and tunable optical attenuators.
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A simple infrared nanosensor array based on carbon nanoparticles
Junjie DAI, Longyan YUAN, Qize ZHONG, Fengchao ZHANG, Hongfei CHEN, Chao YOU, Xiaohong FAN, Bin HU, Jun ZHOU
Front Optoelec. 2012, 5 (3): 266-270.
https://doi.org/10.1007/s12200-012-0253-2
A simple (2×2) pixelated flexible infrared nanosensor array based on carbon nanoparticles (CNPs) was fabricated through a simple and low-cost flame method. By integrated with a micro controller unit, the sensor array could detect power density of incident infrared light in real-time. The mechanism for the superior infrared sensing property of the flexible sensor array based on CNP was also studied in detail in this work.
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Temperature effects on output characteristics of quantum dot white light emitting diode
Amin RANJBARAN
Front Optoelec. 2012, 5 (3): 284-291.
https://doi.org/10.1007/s12200-012-0275-9
In this paper, we proposed quantum dot (QD) based structure for implementation of white light emitting diode (WLED) based on InGaN/GaN. The proposed structure included three layers of InGaN QD with box shapes and GaN barriers. By using of single band effective mass method and considering strain effect, piezoelectric and spontaneous polarizations internal fields, then solving Schr?dinger and Poisson equations self consistently, we obtained electron and hole eigen energies and wave functions. By evaluating dipole moment matrix elements for interband transitions, the output intensity was calculated due to the interband transition between two energy levels with highest emission probability. We adjusted QDs dimensions and material compositions so that the output light can be close to the ideal white light in chromaticity diagrams. Finally, effects of temperature variations on output spectrum and chromaticity coordinates were studied. We demonstrated that temperature variations in the range of 100 to 400 K decrease output intensity, broaden output spectral profile and cause a red shift in three main colors spectrums. This temperature variation deviates (x, y) are coordinated in the chromaticity diagram, but the output color still remains close to white.
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A new construction method of LDPC codes for optical transmission systems
Jianguo YUAN, Yuexing JIA, Wenjuan BI, Liang XU
Front Optoelec. 2012, 5 (3): 311-316.
https://doi.org/10.1007/s12200-012-0269-7
Based on the construction method of systematically constructed Gallager (SCG)(4, k) code, a new improved construction method of low density parity check (LDPC) code is proposed. Compared with the construction method of SCG(4, k) codes improved before, the proposed construction method has some advantages, such as saving storage space and reducing computation complexity in the hardware implementation. And then LDPC(5929, 5624) code with 5.42% redundancy is constructed by the proposed method. The simulation results and analysis show that the constructed LDPC(5929, 5624) code has better error-correction performance, lower redundancy and lower decoding complexity than those of a classic Reed-Solomon (RS)(255, 239) code. Therefore, LDPC(5929, 5624) code, constructed by the proposed construction method on LDPC codes, can better suitable for optical transmission systems.
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Characteristic control of long period fiber grating (LPFG) fabricated by infrared femtosecond laser
Xiaoyan SUN, Peng HUANG, Jiefeng ZHAO, Li WEI, Nan ZHANG, Dengfeng KUANG, Xiaonong ZHU
Front Optoelec. 2012, 5 (3): 334-340.
https://doi.org/10.1007/s12200-012-0270-1
Long period fiber gratings (LPFGs) with different spectral characteristics were fabricated with 1 kHz, 50 fs laser pulses. The contrast of resonant rejection band can be significantly increased by a proper amount of axial stress along a fiber during laser writing or post-processing with lower energy density laser irradiation. Variations of focal condition, pulse energy of laser irradiation and the number of grating periods lead to the generation of resonance rejection band of LPFGs from single-peak to multi-peak plus larger out-of-band loss. The out-of-band loss is primarily caused by Mie scattering from the laser processed cites, and it can be reduced by decreasing the duty cycle of grating pitch instead of lowing down the actual power of laser irradiation.
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Local density of states in photonic crystal cavity
Peng QIU, Guanglong WANG, Jianglei LU, Hongpei WANG
Front Optoelec. 2012, 5 (3): 341-344.
https://doi.org/10.1007/s12200-012-0271-0
Local radiative density of optical states (LDOS) offers a tool to control the radiative rate of spontaneous emission from molecules, atoms, and quantum dots, which is proportional to LDOS. This paper presents that LDOS how to make the population of excited-state decay exponentially in time, and how these dynamics can be affected. By adopting the plane-wave expansion method, properties of an inverse-opal photonic crystal are studied with the help of photonic dispersion relations. Results in this paper show that the LDOS is radically modified in photonic crystal, and the rate of spontaneous emission can be described by the functions of position in the crystal and orientation of transition dipole moment.
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18 articles
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