Islam Ashry

All-optical variable delay buffer for next generation optical networks

A novel all-optical delay buffer based on fiber Bragg gratings (FBGs) is proposed. This buffer has the ability to provide variable delay times and can store the contenting packets for a relatively long time.

Mode-division-multiplexing of absorption-based fiber optical sensors

We theoretically consider the possibility of using a few-mode fiber (FMF) and mode-division-multiplexing (MDM) to construct a quasi-distributed network of absorption-based fiber optical sensors. In this design, we utilize the low-attenuation fundamental linearly polarized (LP) mode for signal transmission, and a high-attenuation LP mode for absorption-based sensing. We develop a matrix formalism and use it to analyze the performance of such a MDM sensor network. We demonstrate that such a sensor network can indeed combine high sensitivity with large scale multiplexing, which is very difficult to achieve in traditional single-mode-fiber-based sensor networks.

High quality factor silica microspheres functionalized with self-assembled nanomaterials

With extremely low material absorption and exceptional surface smoothness, silica-based optical resonators can achieve extremely high cavity quality (Q) factors. However, the intrinsic material limitations of silica (e.g., lack of second order nonlinearity) may limit the potential applications of silica-based high Q resonators. Here we report some results in utilizing layer-by-layer self-assembly to functionalize silica microspheres with nonlinear and plasmonic nanomaterials while maintaining Q factors as high as 10(7). We compare experimentally measured Q factors with theoretical estimates, and find good agreement.

Tunable Fabry-Perot interferometer based on fiber Bragg gratings

In this paper, we propose a new architecture for tunable Fabry-Perot (FP) interferometer using fiber Bragg gratings (FBGs). The main feature of the architecture is its ability to increase the finesse using a potentially low cost technique. Furthermore, it decreases the power loss of the filtered channel and can be implemented easily in practice.

Analysis of Different Fiber Bragg Gratings for Use in a Multi-wavelength Erbium Doped Fiber Laser

A simple multi-wavelength laser source using, an erbium doped fiber (EDF) as a gain medium is proposed. The source is terminated by a chirped fiber Bragg grating (CFBG) on one side and cascaded FBGs on the other side. Different apodization profiles for the FBG are analyzed to improve the lasing wavelengths selectivity. The Blackman profile is found to be the best to reduce the reflection spectrum sidelobes with a maximum reflectivity of 99%.

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.

Fabrication and characterization of periodically patterned silica fiber structures for enhanced second-order nonlinearity.

We develop and characterize a UV ablation technique that can be used to pattern soft materials such as polymers and nonlinear molecules self-assembled over silica microstructures. Using this method, we fabricate a spatially periodic coating of nonlinear film over a thin silica fiber taper for second harmonic generation (SHG). Experimentally, we find that the second harmonic signal produced by the taper with periodic nonlinear coating is 15 times stronger than the same taper with uniform nonlinear coating, which suggests that quasi-phase-matching is at least partially achieved in the patterned nonlinear silica taper. The same technique can also be used to spatially pattern other types of functional nanomaterials over silica microstructures with curved surfaces, as demonstrated by deposition of gold nanoparticles in patterned structures.

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.

Adaptive Mode Control for Few-Mode Fiber Based Sensors and Sensor Networks

The development of mode division multiplexing has found numerous interesting applications in optical sensing. A major challenge has been how to control the mode composition of the interrogation signals. In this work, we presented a time-domain method that can adaptively control the form of optical signals at multiple locations in a two-mode-fiber. We also carry out a preliminary study that suggests the method of adaptive mode control is compatible with the requirements of optical sensing.

The Effect of Mutual Coupling on a Microstrip Printed Antenna Array Operates at 5 GHz Using Three Different Substrates

Curvature has a great effect on fringing field of a microstrip antenna. Consequently, the fringing field affects the effective dielectric constant and then all antenna parameters. A new mathematical model for return loss mutual coupling coefficient as a function of curvature for two element array antenna is introduced in this paper. These parameters are given for TM10 mode and using three different substrate materials RT/duroid-5880 PTFE, K-6098 Teflon/Glass and Epsilam-10 ceramic-filled Teflon.