Rami A. Wahsheh

Nanoplasmonic couplers and splitters

In this paper, we present novel designs and analysis of ultra-compact couplers and 1 x 2 splitters based on plasmonic waveguides. Numerical simulation shows coupling efficiency up to 88% for the former one and 45% for each branch for the latter one. The proposed coupler design has the advantages of improving the alignment tolerance of the plasmonic waveguide with respect to the dielectric waveguide and broadening the spectrum response of the splitter.

Efficient light coupling between dielectric slot waveguide and plasmonic slot waveguide

An efficient coupler between a dielectric waveguide and a plasmonic metal-insulator-metal (MIM) waveguide is proposed, modeled, fabricated, and characterized. Based on the platform of a silicon slot waveguide, a quasi-MIM plasmonic junction is formed via e-beam lithography and lift-off process. Coupling efficiency between the silicon slot waveguide and plasmonic waveguide up to 43% is obtained after normalizing to reference waveguides at 1550 nm. This coupling scheme can be potentially used for fast optical switching and small-footprint optical modulation.

Radii-changing effect on the coupling efficiency between a silica waveguide and a planar photonic crystal

In this paper, we designed different structures for PPC tapered waveguide to enhance the coupling between silica waveguide (SWG) and planar photonic crystal (PPC). The designed structures are based on changing the radii of the inner PPC tapered waveguides crystals before and after adding extra defects. We found that above 88% transmission efficiency is possible by using extra defects followed by radii changes. We also found that changing the operating wavelength from 1.55μm to 1.558μm increases the transmission efficiency to 90% since the field is more confined at the later wavelength.

Ultra-compact nanoplasmonic splitter

We present novel designs and fabrication of ultra-compact coupler and 1×2 splitter using plasmonic waveguides. The coupling efficiency is 88% for the former one and 45% for each branch for the latter one.

Crosstalk Reduction in Square Cavities

Theoretically and experimentally, we demonstrate that low crosstalk between two crossed line-defect waveguides formed in a square lattice photonic crystal (PC) structure can be achieved using a resonant cavity at the intersection area. The PC resonator consists of cubic air-holes in silicon air-holes. The Q-factor of the cavity can be changed by increasing the number of holes that form the cavity. The theoretical and experimental crosstalk results are about -40 dB and -20 dB, respectively.

Ultra low cross talk in crossed strip waveguides with the assistance of a photonic crystal cavity

In this paper, ultra low cross talk is achieved by using a resonant cavity at the intersection between two strip waveguides formed in a square lattice photonic crystal structure (PhC). Two PhC structures are studied: one consists of cylindrical rods and another consists of cubic rods. The Q-Factor of the cavity is changed by increasing the number of rods that form the cavity and by decreasing the spacing between the waveguide and the cavity. Our two dimensional simulation results show that the latter method resulted in cross talk reduction of more than 21 dB for both structures. The overall cross talk was -90.50 dB for the cylindrical rods structure and -105.0 dB for the cubic rods structure. The optimized PhC structures were fabricated on a silicon-on-insulator platform. The rods were buried in silicon oxide in order to maximize the photonic band gap and provide index guiding in the vertical direction.

Experimental and theoretical investigations of an air-slot coupler between dielectric and plasmonic waveguides

In this paper, we experimentally show an effective method of coupling light between dielectric waveguides and metal-dielectric-metal plasmonic waveguides using an air-slot waveguide that extends into both types of waveguides. Our experimental results validate the theoretical calculation results of the proposed coupler. In addition, we investigated the sensitivity of our design to different fabrication challenges that may result in changing the width and length of the targeted optimum values in our design. Numerical simulation results show that the cut-off wavelength can be shifted by either changing the width of the dielectric or slot waveguide. The shift occurs because, as the waveguides width changes, the mode size changes and consequently the impedance mismatch between the dielectric and slot waveguide changes. We also found that changing the position of the air-slot waveguide with respect to the center of the dielectric waveguide resulted in a reduction in the coupling efficiency due to the reduction in the overlapped area between the mode supported by the slot waveguide and that of the dielectric waveguide.

Experimental Investigation of a Nanoplasmonic Air-Slot Coupler Toward Dense Optical Integrated Circuits

Experimentally, we demonstrate that light can be coupled from a silicon waveguide into a plasmonic waveguide using an air-slot coupler. The theoretical and experimental results at 1550 nm are about 85% and 40%, respectively.

Integrated nanoplasmonic splitter

Novel design and fabrication steps of an ultracompact 1×2 plasmonic splitter are presented. The proposed splitter operates at broad frequency range. The theoretical result at 1550 nm is approximately 25% for each branch.

Compact nanoplasmonic Mach-Zehnder interferometers

We present a novel design of two nano-scale plasmonic devices: a 2×2 directional coupler switch and a Mach-Zehnder interferometer. The overall efficiency was 37% for the former one and 70% for the latter one.