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Journal of Microwaves, Optoelectronics and Electromagnetic Applications, Volume: 9, Número: 2, Publicado: 2010
  • Flexible tunable spectrum sliced microwave photonic filter using parallel Fabry-Pérot filters and Fiber Bragg Grating

    Jeyachitra, R.K.; Sukanesh, R.

    Resumo em Inglês:

    A simple and low-cost spectrum sliced microwave photonic filter with high tunability has been implemented. This is based on use of two Fabry-Pérot filters with same free spectral range connected in parallel but one filter with an external fiber delay. An extension of this configuration with Fiber Bragg Grating (FBG) as delay element is also demonstrated. This architecture overcomes the tuning difficulties of a single Fabry-Pérot filter employed as a slicing element. Flexible tunability, large overall free spectral range and high quality factor have been obtained with the proposed configuration owing to the use of fiber delay/FBG. Wide and step tuning has been achieved in the frequency range of 41.1GHz to 50.23GHz in steps of 2.28GHz. The additional components are another Fabry-Pérot filter and fiber delay/FBG which makes the proposed architecture highly compact and cost-effective. Most of the practical difficulties faced in use of optical fiber are eliminated using FBGs. The characteristics of proposed configuration with different applied delays using fiber and FBG were tabulated. An analysis of flexible tunable property of the filter was made in terms of length of fiber delay and grating length of FBG and the results were plotted. Also quality factor calculation of the proposed filter was discussed.
  • An efficient two-level preconditioner based on lifting for FEM-BEM equations

    Pereira, Fabio Henrique; Afonso, Marcio Matias; Vasconcelos, João Antônio de; Nabeta, Silvio Ikuyo

    Resumo em Inglês:

    The system resulting from the coupled Finite Element Method and Boundary Element Method formulations inherits all characteristics of both finite element and boundary element equation system, i. e., the system is partially sparse and symmetric and partially full and nonsymmetric. Consequently, to solve the resulting coupled equation system is not a trivial task. This paper proposes a new efficient lifting-based two level preconditioner for the coupled global system. The proposed approach is applied to solve the coupled systems resulting from the electromagnetic scattering problem and its performance is evaluated based on the number of iterations and the computational time. Traditional methods based on incomplete and complete LU decompositions are used for comparison.
  • Wideband dual-layer patch antenna fed by a modified L-strip

    Wang, Zhongbao; Fang, Shaojun; Fu, Shiqiang

    Resumo em Inglês:

    A wideband patch antenna is proposed. By using the dual-layer patch configuration and modified L-strip feed technique, the impedance bandwidth of the patch antenna for VSWR<1.2 is broadened to 22% with respect to 900 MHz, which is superior to the other available patch antennas. In addition, by means of the modified L-shaped strip, the high cross polarization levels of the proposed antenna are suppressed effectively. Simulation results are compared with the measurements, and a good agreement is obtained. The measurements show that the antenna has a low cross-polarization level (<-20dB) and an acceptable gain level (~9dBi) across the operating bandwidth. At last, a parametric study and a design guideline of the proposed antenna are also presented to facilitate the design and optimization processes for engineers.
  • Gain profile optimization for Raman+EDFA hybrid amplifiers with recycled pumps for WDM systems

    Martini, Márcia M. Jardim; Castellani, Carlos Eduardo S.; Pontes, Maria José; Ribeiro, Moisés R. N.; Kalinowski, Hypolito José

    Resumo em Inglês:

    An approximated technique to quickly optimize the gain profile of multi-pump broadband hybrid amplifiers under residual pump recycling in WDM systems is proposed. It is based on the amplifier spectral equalization by adjusting the flexible gain profile of a multi-pump Raman amplification stage to compensate the Erbium-doped stage gain variation within the C-band. In order to increase the pump power efficiency, the Erbium-doped fiber section recycles the residual Raman pump. Three different cases considering, respectively, one, two, and three pumps are analyzed to demonstrate the effectiveness of the proposed technique. The characterization of the Raman+EDFA hybrid amplifier has been performed in terms of global gain, ripple, and noise figure. The proposed optimization method for the Raman pump sets allows ripple figures to be reduced by half of their original values in single pumped configurations. Our results also suggest that two pump lasers is the best configuration when the maximum gain, minimum ripple, and pump power efficiency are simultaneously considered.
  • An efficient routing scheme to reduce packet loss in all optical networks

    Garg, Amit Kumar; Kaler, R S

    Resumo em Inglês:

    Optical burst switching (OBS) is a promising technology for the next generation optical Internet. A buffer-less OBS network can be implemented using ordinary optical communication equipment without the need for either wavelength converters or optical memories. However, OBS networks suffer from a relatively high blocking probability, a primary metric of interest, because of contention. In this paper, an efficient deflection routing scheme for buffer-less OBS networks has been proposed in order to reduce blocking probability (Packet loss) caused by Offset Time (OT) and burst contention. Simulation results have shown that the proposed scheme reduces blocking probability effectively and also it maintains a reasonable end-to-end delay for each burst. Thus, it improves the overall network performance by reducing the burst blocking probability effectively.
  • Comparative analysis of circular and triangular gold nanodisks for field enhancement applications

    Costa, Karlo Q. da; Dmitriev, Victor

    Resumo em Inglês:

    In this paper, we present a quantitative comparison of circular and triangular gold nanodisks with the same length and thickness. The method of moments is used to solve numerically the scattering problem. With this model, we investigate the spatial near field distribution, spectral response, far field diagrams, and bandwidth wavelength of these particles. Our results show that the resonant wavelength and the near field enhancement and confinement of the triangular particle are larger than those for the circular particle, but the resonance bandwidth and scattering cross section of the triangular particle are smaller.
  • Etched fiber bragg gratings sensors for water-ethanol mixtures: a comparative study

    Coradin, Francelli K.; Possetti, Gustavo R. C.; Kamikawachi, Ricardo C.; Muller, Marcia; Fabris, José L.

    Resumo em Inglês:

    In this work is evaluated the performance of etched fiber Bragg gratings, assembled in different configurations to operate as a refractometric sensor, in the analysis of water-ethanol mixtures. Two fiber Bragg gratings operating close to 1300 nm and 1500 nm were wet-etched and employed in the sensor design. Four configurations for the refractometric sensor were studied, in dual-wavelength and single-wavelength operation modes, and at two sample temperatures. Calibration curves were determined for the range between 0.0 and 100.0 % v/v of water in ethanol, and the sensor performance for each configuration was analyzed by comparing its sensitivity, conformity, repeatability and combined uncertainty. The best results showed that the sensor can be used to measure the ethanol-water concentration with combined uncertainty of 2.8 % v/v for the range up to 80.0 % v/v of ethanol concentration and 7.0 % v/v of uncertainty for the range above 80.0 % v/v of ethanol concentration for the single-wavelength operation mode at two temperatures.
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