RESUMO
The theoretical mechanism for realizing a negative refractive index material in an optical frequency range with an atomic gas system of electromagnetically induced transparency (EIT) is studied. It is shown that under certain conditions such a dense gas can exhibit simultaneously negative permittivity and negative permeability, and negligibly small loss.
Assuntos
Campos Eletromagnéticos , Modelos Teóricos , Óptica e Fotônica , Teoria Quântica , Refratometria/métodos , Impedância ElétricaRESUMO
The configuration of the novel three-stage L-band erbium-doped fiber amplifier with very large and flat gain and very low noise figure presented in this paper uses the forward ASE (amplified spontaneous emission) from the first section of the EDF (erbium-doped fiber) and the backward ASE from the third section of the EDF (both serve as the secondary pump sources of energy) to pump the second EDF. To improve the pump efficiency, the power of the pump is split into two parts (with a ratio of e.g. 2:7). The characteristics of this L-band EDFA are studied on the basis of the Giles Model with ASE.
Assuntos
Amplificadores Eletrônicos , Redes de Comunicação de Computadores/instrumentação , Desenho Assistido por Computador , Análise de Falha de Equipamento , Tecnologia de Fibra Óptica/instrumentação , Micro-Ondas , Processamento de Sinais Assistido por Computador/instrumentação , Desenho de Equipamento , Érbio , Tecnologia de Fibra Óptica/métodosRESUMO
A new photonic bandgap (PBG) cover for a patch antenna with a photonic bandgap substrate is introduced. The plane wave expansion method and the FDTD method were used to calculate such an antenna system. Numerical results for the input return loss, radiation pattern, surface wave, and the directivity of the antennas are presented. A comparison between the conventional patch antenna and the new PBG antenna is given. It is shown that the new PBG cover is very efficient for improving the radiation directivity. The physical reasons for the improvement are also given.
