Design of a High-performance Flat Reflector Antenna Based on Conformal Transformation Optics

In this paper, we design an implementable high-performance flat reflector based on conformal transformation optics. In the proposed 2-dimensional device, the rescaling refractive index approach is applied to overcome the sub-unit refractive index issue, resulting in an all-dielectric isotropic graded-index medium that is physically implementable. Rotating the permeability profile around the antenna axis yields the 3-dimensional profile of the flat reflector construction. The dielectric with continuous refractive index profile is split into eleven layers with a constant refractive index. The proposed antenna requires only dielectric layers with the permittivity of 1.1 to 3.8, making it realizable. Simulation results show that the proposed flat reflector can operate in wide frequency bandwidth. The simulated antenna gain is about 25.27 to 29.55 dBi in the 13-30 GHz frequency range with the side-lobe level below -15 dB. Design and simulation of the proposed antenna are done using COMSOL Multiphysics, and simulation results are validated with CST Studio Suite.

Comparison of Several Characteristics of Single Mode Step-Index (SMSI), Multimode Step-Index (MMSI), and Multimode Graded-Index (MMGI) Fibers for Optical Communication Systems

Optical fiber is a medium that made by silica or plastic, and widely used in transmitting information over longer distance especially in communication system. There are three types of fiber optic used in this project which are single mode stepindex (SMSI), multimode step-index (MMSI), and multimode graded-index (MMGI) in optical communication system. There are three objectives in this project in order to get the suitable optical fibers in the communication system. First objective is to simulate the result by using Excel and Origin software. The data and the formula of fiber optics will be key in through Excel software while the graph will be analyzed by using Origin software. The second objective is to compare the different types of fiber optics in communication system by comparing the several of their characteristics such as numerical aperture (NA), acceptance angle (θ(a)) and propagation constant (β). The performance of all types fiber optics are analyzed from the result using the standard communication wavelength of 1550 nm. The core diameter for SMSI, MMSI, and MMGI are 9, 200 and 50 μm respectively while the cladding diameter for SMSI and MMGI is 125 μm and 240 μm for MMSI. This diameter also been analyzed by using the standard value for optical communication system. Then, the comparison between SMSI, MMSI and MMGI will be made to choose the more suitable for optical communication system based on their characteristics. From the results, MMSI and MMGI give best performance compared to SMSI. After that, the third objective is to make the comparison between MMSI and MMGI in term of intermodal dispersion to compare the efficiencies of fiber optics. MMGI give the better result in terms of efficiencies for communication system compared to MMSI. Keyword: Single Mode Step-Index (SMSI), Multimode Step-Index (MMSI), Multimode Graded-Index (MMGI), Communication System, Excel and Origin Software

Super-resolution imaging of negative-refractive graded-index photonic crystal flat lens

Photonic crystal (PC) not only breaks through the diffraction limit of traditional lenses but also can realize super-resolution imaging. Improving the resolution is the key task of PC imaging. The main work of this paper is to use a graded-index Photonic crystal (GPC) flat lens to improve the image resolution. An air-hole type two-dimensional (2D) GPC structure based on silicon medium is proposed in this paper. Numerical simulations through RSoft reveal that when the medium in the imaging area is air, the full width at half maximum (FWHM) value of a single image reaches 0.362λ. According to the Rayleigh criterion, the images of two point sources 0.57λ apart can also be distinguished. In the imaging system composed of cedar oil and GPC flat lens, the FWHM value of a single image reaches 0.34λ. In addition, the images of multiple point sources 0.49λ apart can still be distinguished.

Effect of optical fiber core diameter on Brillouin scattering loss

This paper reports the effect of core diameter of optical fiber cables on stimulated Brillouin scattering loss, which is one of the major loss characteristics of an optical fiber communication system. Analysis of this loss characteristic at three windows of the operating wavelength of a laser has been carried out through a numerical approach. Among different types of optical fiber cables, multi-mode step index silica fiber, multi-mode graded index silica fiber and plastic fibers have been considered for the numerical analysis. The numerical analysis has been performed using MATLAB in this research work. Through the comparative analysis, it has been ascertained that the Brillouin scattering loss is not only affected by the operating wavelength, but also by the core diameter of the different type of the cable. From the investigation of the comparative analysis, it is revealed that Brillouin scattering loss declines with the application of multi-mode graded index silica fiber. However, in the plastic fiber category, plastic step index fiber offers better performance.