Marwa M. Tharwat

Investigating the Optical Transmission Spectra of Plasmonic Spherical Nano-Hole Arrays

Plasmonic nano-structures are important for many photonic devices and applications. The optical transmission spectra of such structures are extraordinary. In this paper, we investigate the optical transmission spectra of thin gold films perforated with imperfect circular nano-hole arrays using the finite difference time domain (FDTD). It is observed that both of the intensity and resonance positions of the transmission spectra of perfect plasmonic circular nano-hole arrays are strongly modified due to nano-holes imperfection. Furthermore, we comprehensively study the transmission spectrum of plasmonic spherical nano-hole arrays as a simple example for hole imperfection.

Investigating the characteristics of TM-pass/TE-stop polarizer designed using plasmonic nanostructures

Plasmonics-based polarizers are important for many photonic devices and applications. In this paper, we design and investigate the characteristics of a new TM-pass/TE-stop polarizer using silver nanograting of exponentially tapered slit sidewalls. Performance of the designed polarizer is determined through monitoring the modification of its insertion loss, return loss, extinction ratio, and far-field transform due to changing its structural parameters. We find that the structural parameters of the reported polarizer such as a slit sidewall tapering coefficient and slit opening widths have a significant impact on tuning the polarizer characteristics.

Investigating the fabrication imperfections of plasmonic nanohole arrays and its effect on the optical transmission spectra

We investigate the extraordinary optical transmission spectra of thin gold films perforated with imperfect nanohole arrays using the finite difference time domain (FDTD) method. Exponential shapes for the nanohole sidewalls are used. To the best of our knowledge, such investigation of transmission spectra of imperfect nanohole arrays has not previously been demonstrated. It was found that the asymmetry between the two openings of the circular nanoholes or bending to their sidewalls strongly modifies both the intensity and resonance positions of the transmission spectra. Furthermore, the results of this study assist in explaining the technicality of extraordinary optical transmission phenomenon and why some experimental results on transmission differ from those expected.

Design of an optical sensor based on plasmonic nanostructures

Plasmonic nano-structured array sensors have been highlighted by their tremendously promising applications, such as the surface plasmon resonance (SPR) optical biosensors. In this paper, within the visible spectrum region, the optical transmission properties of a metallic thin film deposited over dielectric films of various refraction indices are investigated. With finite difference time domain (FDTD) method, we investigate the optical transmission spectra of such plasmonic structures based on both nano-holes and nano-disc arrays. This investigation includes monitoring the modification in both the transmission resonance wavelengths and peak transmittance. The results of this study provide a better understanding of the interaction between light and plasmonic nano-hole and nano-disc arrays. It shows that the changing the shapes of the nano-holes can affect the resonance wavelengths and the intensity of transmitted spectra and alter its resonance peak transmittance values. We found that the interaction coupling between the localized plasmons (LSP) and the propagating surface plasmons (PSP) can be tuned to boost the performance of the optical sensor.

A Novel Performance Analysis of the Microstrip Antenna Printed on a Cylindrical Body

Performance of a circular patch microstrip antenna is highly affected by the effective dielectric constant of a used substrate material. When the circular patch is conformed on a cylindrical body, the effective dielectric constant is changing with curvature due to the changing in the fringing field. Consequently, some of antenna parameters such as resonance frequency, input impedance, voltage standing wave ratio, return loss, quality factor, and antenna bandwidth are functions of curvature. In this work, we study the effect of curvature on the performance of circular patch microstrip antenna. A mathematical model for the antenna parameters as functions of curvature is also introduced. The model is applied in case of using two substrates of different refractive index values. By extension, the antenna performance was studied through simulation by using method of moments (MoM) which is reliable in solving Maxwell’s integral equations in the frequency domain. The results from simulation compare very favorably with the described analytical results.