Sajid Muhaimin Choudhury

Controlling the Polarization State of Light with Plasmonic Metal Oxide Metasurface

Conventional plasmonic materials, namely, noble metals, hamper the realization of practical plasmonic devices due to their intrinsic limitations, such as lack of capabilities to tune in real-time their optical properties, failure to assimilate with CMOS standards, and severe degradation at increased temperatures. Transparent conducting oxide (TCO) is a promising alternative plasmonic material throughout the near- and mid-infrared wavelengths. In addition to compatibility with established silicon-based fabrication procedures, TCOs provide great flexibility in the design and optimization of plasmonic devices because their intrinsic optical properties can be tailored and dynamically tuned. In this work, we experimentally demonstrate metal oxide metasurfaces operating as quarter-waveplates (QWPs) over a broad near-infrared (NIR) range from 1.75 to 2.5 μm. We employ zinc oxide highly doped with gallium (Ga:ZnO) as the plasmonic constituent material of the metasurfaces and fabricate arrays of orthogonal nanorod pairs. Our Ga:ZnO metasurfaces provide a high degree of circular polarization across a broad range of two distinct optical bands in the NIR. Flexible broad-band tunability of the QWP metasurfaces is achieved by the significant shifts of their optical bands and without any degradation in their performance after a post-annealing process up to 450 °C.

Modeling the illumination function of a cassegrain reflector for a corrugated horn feed and calculation of the far field pattern

A model of the illumination function of cassegrain reflector for a corrugated horn feed is presented here. A conical corrugated feed horn designed for a Ku band cassegrain reflector is simulated. The simulation data is compared to the illumination function. Comparison between the developed illumination function and the widely used quadratic on a pedestal function is also presented. Finally, the developed illumination function is used to calculate the radiation pattern of the cassegrain reflector by evaluating the aperture field integration.

Design and implementation of a low cost Power Factor Improvement device

A low cost single phase power factor improvement (PFI) device was designed and implemented for small signal low power loads. The designed PFI keeps the power factor of a load within a specified but adjustable range (0.85-0.90) if the load is within its capacity. The design involved designing of a small signal model load, selecting appropriate capacitors, and designing appropriate switching circuits to select proper combination of capacitors. The power factor improvement device was simple, low cost and it is an innovative way to demonstrate the logic of switching the capacitors. The components used were standard logic chips and no microcontroller or application specific integrated circuit (ASIC) was used.

Hybrid plasmonic waveguides formed by metal coating of dielectric ridges

Bound hybrid plasmon-polariton modes supported by waveguides, which are formed by gold coating of ridges etched into a silica substrate, are analyzed using numerical simulations and investigated experimentally using near-field microscopy at telecom wavelengths (1425-1625 nm). Drastic modifications of the fundamental mode profile along with changes in the mode confinement and propagation loss are found when varying the ridge height. The main mode characteristics (effective mode index, propagation length, and mode profile) are determined from the experimental amplitude- and phase-resolved near-field images and compared with the simulations. The possibility of strongly influencing the mode properties along with subwavelength confinement found simultaneously with relatively long propagation can further be exploited in mode shaping and sensing applications.

Nanostructured Transparent Conducting Oxide Films for Polarization Control with Plasmonic Metasurfaces

Transparent Conducting Oxides (TCOs) enable the realization of practical plasmonic and metamaterial devices at the telecommunication frequency due to their low optical loss and CMOS compatibility. By employing a conventional dry-etching process, we have fabricated GZO plasmonic waveplates, which convert linearly polarized light into circularly polarized light.

Optimization and analysis of a Ka band Pickett Potter horn antenna with low cross polarization

In this paper, a Pickett Potter horn antenna is designed and analyzed for Ka band operation. The dimensions of horn are optimized so that the cross polarization level is minimized for the operating frequency range. The design and optimization is done based on theoretical analysis of dual mode horn antennas and computer simulation. The copolarization and the cross polarization radiation pattern of the designed horn are analyzed at 32 GHz. The S11 parameter of the horn antenna for operating frequency range is obtained from simulation. Finally, maximum cross polarization level of the designed horn for Ka band frequencies is analyzed using theoretical analysis and simulation.

Experimental realization of color hologram using pancharatnam-berry phase manipulating metasurface

We design and fabricate a Pancharatnam-Berry phase manipulating metasurface to experimentally demonstrate a three-color RGB pattern. The color pattern is produced by illuminating a nanostructured silver metasurface hologram with a white light source.

GZO/ZnO Multilayered nanodisk metasurface to engineer the plasma frequency

A metal/dielectric multilayered metasurface can be used to engineer the plasma frequency by controlling the ratio between the metal and dielectric layers. In this work, we demonstrate that a multilayered nanodisk metasurface based on semiconductor materials offers the design flexibility for tuning the plasmonic resonance.

Effect of FSS ground plane on second iteration of hexaflake fractal patch antenna

Frequency Selective Surface (FSS) can be used as a surface frequency dependant translucency - thereby reflecting a particular frequency while allowing other frequencies to pass. In this paper, FSS is used as the ground plane of a Hexaflake fractal patch antenna structure. FSS selectively forms cavity along with the hexaflake patch structure, which can be exploited to enhance performance of patch antenna. Effect of altering width of FSS elements on antenna performance is studied. Simulations are performed using Finite Element Method. The designed fractal patch antenna structure shows 19.9% improvement of bandwidth over a second iteration of hexaflake fractal patch antenna with PEC ground plane.

Sensitivity analysis of a circularly polarized U-slot microstrip antenna

In this paper, sensitivity models for centre frequency and maximum radiated power of a rectangular microstrip antenna at ϕ = 0 plane using Effective Length Theory have been developed. A wide operating bandwidth for a single-layer coaxially fed microstrip antenna is obtained by cutting a U shaped slot on the metal patch. The sensitivity of perturbation of different truncated slot and feed position for a microstrip antenna is a novel concept. An approximate sensitivity model is derived here using perturbation and variational method and confirmed by modified Haneishi model and hybrid FEM/MoM solver. The proposed sensitivity models provide better approximations for calculating shift of centre frequency and maximum radiated power of the microstrip antenna.