Mohamed A. Swillam

Hybrid orthogonal junctions: wideband plasmonic slot-silicon waveguide couplers

In this paper, novel ultra compact and ultra wide band couplers between silicon and plasmonic slot waveguides are analyzed, characterized, and fabricated. This novel coupling scheme is fabricated using silicon on insulator platform. An orthogonal junction configuration is designed to provide non-resonate wideband coupling from a 400 nm silicon waveguide to 50-nm wide air-filled plasmonic slot. The 1 μm wide full-width half-max coupling spectrum can theoretically reach high peak of 70% coupling to the plasmonic slot centered around the 1550 nm wavelength. This center wavelength can be controlled by varying the silicon waveguide width. Theoretical analysis is in good agreement with FDTD simulated results, and experimental results. The fabrication procedure is also presented and discussed.

Feedback Effects in Plasmonic Slot Waveguides Examined Using a Closed Form Model

Analysis of the feedback effects in plasmonic waveguides is carried out using an analytical model. The closed-form model is extracted from the waveguide physical parameters is simple, accurate, and provides insight into understanding the feedback effects in plasmonic waveguide structures. These feedback effects are utilized to obtain various filter functions using the same base structures, with exceptional tolerance to fabrication imperfections in comparison to its plasmonic and dielectric counterparts.

Analytical model for metal-insulator-metal mesh waveguide architectures

Metal–insulator–metal (MIM) waveguide mesh structures utilize X-junctions as power distribution elements to create interference and feedback effects, thereby providing rich device functionality. We present a generalized analytical model for MIM mesh structures by incorporating a modified characteristic impedance model for MIM junctions into the scattering matrix formalism. The modified impedance model accounts for metal absorption and provides accurate prediction of plasmonic field distribution at X-junctions in terms of both magnitude and phase. Closed-form expressions for 2×1 and 2×2 MIM mesh architectures as well as MIM stub structures are then obtained and are dependent only on waveguide geometry and junction configuration. The model does not require numerically extracted parameters, and results agree, within a few percent, with those obtained from finite-difference time-domain method for both two-dimensional and three-dimensional waveguide geometries. The capability of the model for efficient design and optimization of junction-based MIM devices is demonstrated through the development of various filter and resonant devices.

Adjoint Sensitivity Analysis of Dielectric Discontinuities Using FDTD

Abstract We propose an accurate central adjoint variable method (CAVM) for estimating objective function sensitivities related to dielectric discontinuities with structured-grid finite difference time domain (FDTD). Our novel approach features accuracy comparable to that of the central finite difference approximation at the response level. Using only two simulations, of the original and the adjoint EM structures, the sensitivities with respect to all the designable parameters are obtained regardless of their number. Our approach uses the same update equations of the conventional FDTD for the adjoint problem which simplifies the implementation. The proposed technique is extended to evaluate the sensitivities of the S-parameters of multi-port electromagnetic structures. Very good agreement is obtained between our approach and the expensive finite difference approximations.

Integrated Metal-Insulator-Metal Plasmonic Nano Resonator: an Analytical Approach

A novel structure is proposed as an inline resonator. The resonator has low loss, compact size and good sensing characteristics. A simple analytical form to the plasmonic waveguide discontinuity, fllter resonance response and cascaded fllters behavior is proposed. The model is extracted from the waveguide physical parameters and provides a physical insight into the structure of the fllter. This model is simple, accurate, and shows a good agreement with FDTD simulations. The ability of the model to provide a good methodology to obtain high quality fllters using cascaded inline flltering is verifled using FDTD. The proposed nanofllter can be used in various plasmonic applications such as sensing, biomedical diagnostics and on-chip interconnects. Using cascaded fllters, a higher quality fllter is achieved.

Efficient broadband energy transfer via momentum matching at hybrid junctions of guided-waves

Momentum matching at hybrid junctions is examined for efficient broadband energy transfer between internal reflection guided waves and evanescence-based plasmonic-gap guided waves. We demonstrate a nanoscale orthogonal junction coupler between 50 nm air-filled plasmonic slot waveguides (PSWs) and 450 nm silicon rib waveguides. Non-resonant junction coupling efficiency of 50 ± 2 % between 1450 nm and 1650 nm is achieved experimentally and PSW propagation loss is directly measured to be only 2.5 dB/μm. This taperless hybrid junction reduces PSW-based device footprint and enhances device tolerance to temperature and fabrication process variations, serving as a potential platform for hybrid silicon-plasmonic interconnects.

Analysis and applications of 3D rectangular metallic waveguides

Plasmonic modes in rectangular metallic waveguides are analyzed in depth and are demonstrated to possess attractive properties for different applications. Their dispersion characteristics allow for wide range of applications including slow and fast light, metamaterial, low loss energy transmission, and opportunities for sensing devices. The sensitivity of this waveguide configuration is higher than its counterparts and can reach four times the sensitivity of the MIM structures. The characteristics of the TM(10) mode are demonstrated. Its applications for sensing, low propagation loss with relaxed practical dimension are also highlighted. A high effective index of more than 30 is also obtainable for the TE(01) mode for slow light operation. A non resonant negative index material with isotropic polarization in the visible region is also proposed using this waveguide structure.

Efficient Approach for Sensitivity Analysis of Lossy and Leaky Structures Using FDTD

An e-cient approach is utilized for extracting the modal parameters of high frequency structures and their sensitivities with respect to all the design parameters. Using one FDTD simulation, the modal parameters of all the guided and leaky modes are extracted over the frequency band of interest. An adapted version of the matrix pencil method is utilized for e-cient extraction of the modal parameters. In addition, using no extra simulations, the sensitivities of the propagation constants with respect to all the design parameters of the structure are extracted regardless of their number. The computational time is a small fraction of the cost of similar approaches.

Full Wave Sensitivity Analysis of Guided Wave Structures Using FDTD

A simple and efficient approach is utilized to extract the propagation constants of any guided structures and their sensitivities using FDTD. Using our approach, the propagation constants of all the guided modes are obtained at all the desired frequencies using only one simulation. It is also capable of extracting the sensitivities of the propagation constants with respect to all the design parameters, regardless of their number, without any additional simulation. Results show good agreement between our approach and existing analytical approaches.

Plasmonic silicon solar cells using titanium nitride: a comparative study

Abstract. Plasmonic materials, especially silver, are widely used to increase efficiency of solar cells due to their ability to localize the light in nanoscale. This tight confinement increases the absorption of a thin film solar cell. However, these materials are expensive and increase the cost/watt of the solar cell. Thus, finding an abundant and cheap material with a comparable plasmonic effect can dramatically reduce solar cell cost by enabling the use of ultrathin active layers. In this work, we investigate TiN as an alternative cheap and abundant plasmonic material. TiN is also more CMOS compatible. Several TiN plasmonic solar cell configurations are studied and analyzed. These studies show that the TiN plasmonic solar cell has a comparable performance for back side plasmonic configuration.