International Journal of

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In this paper, we present a comparative numerical analysis to determine the refractive index of photonic crystal fibers (PCFs) by using FDFD method and used the results to evaluate the confinement losses of PCFs by considering the effects of air-hole rings in the cladding. It is shown that by increasing the wavelength, the imaginary part of refraction index rises, resulting in increase of confinement losses nearly by order of 10. In lower wavelengths over the range of 0.2 to 1 μm, these losses were shown to be negligible. The obtained results show that as the number of air-hole ring in the cladding increases, the confinement losses over wavelengths would reduce. To show the effect of air-hole rings on confinement losses in PCFs, the FDFD method yielded accurate results that agree well with results of FEM method and source–model technique reported by others.

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The refraction phenomenon at the interface of an ordinary material and a lossy metamaterial has been investigated. For oblique incidence on the lossy metamaterial, the planes of constant amplitude of the refracted wave are parallel to the interface and the plane of constant phases make a real angle with the interface (real refraction angle). The real refraction angle and hence, the real refraction index corresponds to the real refraction angle which satisfies the real version of Snell's law are negative in two different regimes. In one regime, the metamaterial is double-negative, while in the other one it is single-negative. Moreover, we show that the plane wave solution for the refracted wave is causal in both double-negative and single-negative regimes

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We perform a theoretical investigation on the Goos-Häenchen shift (the lateral shift) in one-dimensional photonic crystals (1DPCs) containing left-handed (LH) metamaterials. The effect was studied by use of a Gaussian beam. We show that the giant lateral displacement is due to the localization of the electromagnetic wave which can be both positive and negative depending on the incidence angle of Gaussian beam that can be excited the forward and backward surface states, respectively. Dependence of beam width on the incidence angle of beam and thickness of air layer for both backward and forward surface states are studied in this paper. We also find that the weak lossy in LH layers of 1DPCs may affect these shifts. These giant negative and positive lateral shifts are smaller than that of the lossless structure.

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A novel design of Dual-Core Photonic Crystal Fiber (DC-PCF) with silica-air microstructures is proposed in this paper. Nonlinearity and confinement loss of DC-PCF are evaluated by using a Full-Vectorial Finite Element Method (FV-FEM) successfully. By optimizing the geometry of three ring DC-PCFs, a high nonlinearity (52w-1km-1) and low confinement loss (0.001dB/km) can be achieved at 1.55μm wavelength when diameter to pitch ratio (d/Λ) is 0.70.

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Laser diode beam divergence is the main parameter for beam shaping and fiber optic coupling. Increasing the waveguide layer thickness is the conventional method to decrease the beam divergence. In this paper, the broadened asymmetric waveguide is introduced to decrease the divergence without increasing the optical power. The asymmetric waveguide was used to shift the vertical optical field to n-section, which has lower free carrier loss. The main target in this research is to minimize the internal loss to avoid the disadvantage of the broadened waveguide. Finally the beam divergence was decreased to 35 degrees that is very suitable for the conventional multi-mode optical fiber coupling and the optical power was increased to 2400mW in the laser diode with 100μm stripe width and 1mm cavity length. In addition to the fiber coupling, this improvement can be used for other direct applications that need beam shaping. 
 

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Using terahertz waves for intra-body communications between nanomachines is associated with dissipation during propagation, of which scattering is one of the most important effects. In this paper, scattering path loss with two different assumptions of air-enclosed and tissue-enclosed in subcutaneous fat is calculated and compared. The results show that for TM polarization, air-enclosed assumption gives smaller and greater scattering loss for frequencies less and bigger than 0.26 THz. The greatest difference between air-enclosed and tissue-enclosed results is observed for TE polarization at the approximate frequency of 0.4 THz.