Surface Plasmon Optical Modulator

A high-speed optical modulator based on Surface Plasmon-Polariton (SPP) at the hetero-junction of a metal-insulator-semiconductor (MIS) tunneling diode and including a phase-matching optical element, such as a prism or gold-lattice structure, is described. An investigation using the coupled mode theory shows that the applied bias across the hetero-junction changes the optical reflectance of an optically coupled MIS tunneling diode, such as a prism-coupled MIS tunneling diode or a gold lattice-coupled MIS tunneling diode, while the modulation efficiency achievable of the device depends on the thickness of the metal film used to construct the tunneling diode

Chiral Plasmonic DNA Nanostructures with Switchable Circular Dichroism

Circular dichroism spectra of naturally occurring molecules and also of synthetic chiral arrangements of plasmonic particles often exhibit characteristic bisignate shapes. Such spectra consist of peaks next to dips (or vice versa) and result from the superposition of signals originating from many individual chiral objects oriented randomly in solution. Here we show that by first aligning and then toggling the orientation of DNA-origami-scaffolded nanoparticle helices attached to a substrate, we are able to reversibly switch the optical response between two distinct circular dichroism spectra corresponding to either perpendicular or parallel helix orientation with respect to the light beam. The observed directional circular dichroism of our switchable plasmonic material is in good agreement with predictions based on dipole approximation theory. Such dynamic metamaterials introduce functionality into soft matter-based optical devices and may enable novel data storage schemes or signal modulators

Compact Verilog-A Modeling of Silicon Traveling-Wave Modulator for Hybrid CMOS Photonic Circuit Design

A compact Verilog-A model of silicon-based junction traveling-wave Mach-Zehnder modulator (MZM) is developed for hybrid CMOS and photonic system-level simulation in Cadence environment. Critical device functions such as the voltage dependent change of refractive index, small-signal RLGC parameters for the MZM arms are extracted from the photonic device characterization from OpSIS foundry. Thermo-optical coefficient is also considered in the model. Simulation results including electro-optic S21 is characterized for the phase modulator\u27s bandwidth. Also, transient MZM operation with non-return to zero (NRZ) data transmission at 10 Gb/s and 20 Gb/s rates are demonstrated

Design Considerations for Traveling-Wave Modulator-Based CMOS Photonic Transmitters

Systematic design and simulation methodology for hybrid optical transmitters that combine CMOS circuits in a 130 nm process, and a traveling-wave Mach-Zehnder modulator (TWMZM) in 130 nm SOI CMOS process, is presented. A compact Verilog-A model for the TWMZM is adopted for the electrooptical simulation. A bond wire model using a high-frequency solver is included for accurate package simulation. Transmitter post-layout simulation result exhibits 5.48 dB extinction ratio, 9.6 ps peak-to-peak jitter, and the best power efficiency of 5.81 pJ/bit when operating up to 12.5 Gb/s non-return-to-zero data. A pulse amplitude modulation 4-level transmitter with detailed linearity design procedure is presented which has horizontal and vertical eye opening of 49 ps and 203 μW when operating at 25 Gb/s, and the power efficiency is 5.09 pJ/bit

Emulsion Properties of Mixed Tween20-Span20 in Non-Aqueous System

Oil-in-glycerol (O/G) emulsion was prepared in the presence of different weight ratios of mixed Tween20-Span20 surfactants. O/G emulsion was observed to form below 50 wt% of oil content at 3 wt% of mixed Tween20Span20 surfactants. Physical properties of the emulsion were determined by using a microscope, particle counting and rheological measurement. An attempt to correlate HLB values of mixed Tween20-Span20 with emulsion stability was also carried out

Finite-Difference Time Domain Method for Nonorthogonal Unit-Cell Two-Dimensional Photonic Crystals

A finite-difference time-domain (FDTD) method based on a regular Cartesian Yee’s lattice is developed for calculating the dispersion band diagram of a 2-D photonic crystal. Unlike methods that require auxiliary difference equations or nonorthogonal grid schemes, our method uses the standard centraldifference equations and can be easily implemented in a parallel computing environment. The application of the periodic boundary condition on an angled boundary involves a split-field formulation of Maxwell’s equations. We show that the method can be applied for photonic crystals of both orthogonal and nonorthogonal unit cells. Complete and accurate bandgap information is obtained by using this FDTD approach. Numerical results for 2-D TE/TM modes in triangular lattice photonic crystals are in excellent agreement with the results from 2-D plane wave expansion method. For a triangular lattice photonic crystal slab, the dispersion relation is calculated by a 3-D FDTD method similarly formulated. The result agrees well with the 3-D finite-element method solution. The calculations also show that the 2-D simulation using an effective index approximation can result in considerable error for higher bands

Propagation Loss of Line-Defect Photonic Crystal Slab Waveguides

Photonic crystal slab waveguides are created by inserting a linear defect in two-dimensional (2-D) periodic dielectric structures of finite height. Photonic crystals provide 2-D in-plane bandgaps through which light cannot propagate, however, the fact that the waveguide modes must be index-confined in the vertical direction implies that the propagation loss is strongly dependent on the out-of-plane radiation loss. We present a fully three-dimensional finite-difference time-domain numerical model for calculating the out-of-plane radiation loss in photonic crystal slab waveguides. The propagation loss of the single-line defect waveguide in 2-D triangular lattice photonic crystals is calculated for suspended membranes, oxidized lower claddings, and deeply etched structures. The results show that low-loss waveguides are achievable for sufficiently suspended membranes and oxidized lower cladding structures. The roles of the photonic crystal in out-of-plane loss of the waveguide modes are further analyzed. It is predicted that the out-of-plane radiation loss can be reduced by shifting one side of the photonic crystal cladding by one-half period with respect to the other sides along the propagation direction

Phase Matching for Surface Plasmon Enhanced Second Harmonic Generation in a Gold Grating Slab

Surface plasmon enhanced second harmonic generation in gold grating slabs was investigated. The efficiency is analyzed with respect to the phase matching at the fundamental and the second harmonic frequencies. A classical electromagnetic model was developed under the weak nonlinearity approximation and solved by the finite element method. The measured zeroth order transmitted second harmonic intensity was found to be in quantitative agreement with numerical results. It is shown experimentally and numerically that proper phase matching at both frequencies improves the second harmonic efficiency

Air and water flows in a vertical sand column

The unsteady state drainage of water from a vertical sand column with and without a finer layer on the top was studied theoretically and experimentally to investigate the airflow generated by the finer layer. The sand column, saturated at its lower portion and initially in the condition of hydrostatic equilibrium, is drained at its bottom at constant head. The results show that significant vacuum can be generated in the vadose zone of the column with a finer layer on the top. The vacuum increases quickly in the earlier stage of the drainage, reaches a maximum, and gradually becomes zero. Because of the effect of the vacuum in the vadose zone, water is held in and the cumulative outflow from the column with the finer layer is much smaller than without the layer during most of the drainage process. Ordinary differential equations (ODE), which require only saturated hydraulic properties of the porous media, are derived to predict the location of the surface of saturation and vacuum in the vadose zone in air-water two-phase flow. The solutions of ODE match very satisfactorily with the experimental data and give better results than TOUGH2. Copyright 2011 by the American Geophysical Union.published_or_final_versio