Abstract

The emerging field of silicon photonics offers solutions to designing CMOScompatible optical devices. By taking advantage of the immense fabrication infrastructure offered by the silicon industry, it would be possible to design optical structures that are smaller, faster, less-power consuming and cheaper than traditional, non-silicon-based optical devices. In this dissertation, the design and performance testing of two novel silicon photonic structures are presented: 1) Silicon nanowire ridge waveguide for sensing applications at the optical transmission frequency. 2) Doped silicon plasmonic structures for negative-index, epsilon-near-zero and sensing applications at the mid-infrared. For the first design, silicon nanowires are arranged in a ridge shape to act as a sensitive medium. Most conventional optical sensors rely on evanescent field detection, where only the tail of the incident wave contributes to the sensing process. Silicon nanowires, on the other hand, allow a large portion of the light wave to be present in the low-index-region, which is comprised of the gaps between the nanowires. This feature provides an opportunity for the optical wave to be vastly affected by the refractive index of the gaps between the nanowires. Thus, by introducing materials-under-test, or analytes, to the gaps, the optical signal response is heavily altered, hence, providing a much larger sensitivity than evanescent field sensors. Previous literature has reported on rib-shaped silicon nanowire sensors. We show that the proposed design is more superior in several areas. Firstly, simulations show that ridge-shaped sensors respond slightly more strongly to refractive-index changes than rib-shaped sensors. This could be due to their slightly larger optical overlap with their surroundings, provided by the inherently larger dimensions of the ridge shape. They can also detect up to a 1e-8 refractive-index-changes in the surrounding environment. Secondly and more importantly, single-mode operation, which is usually mandatory for most optical sensor configurations, can be guaranteed using more flexible dimensions for the ridge-shaped nanowire waveguide than for its rib-shaped counterpart. This provides a fabrication convenience, since devices with larger dimensions are generally cheaper and easier to manufacture. Additionally, since the ridge waveguide sports a wide low-thickness region, it can cover the substrate and safe-guard it against erosion during the fabrication process. To further characterize our design, the ridge-shaped silicon nanowire waveguide was put in a bimodal interferometer sensor configuration. The sensitivity obtained through FDTD simulations proved to be very high; its value was comparable to recently reported sensitivities using much larger footprints. This very high sensitivity-to-footprint ratio, along with the CMOS compatibility of the proposed design, deems it as a suitable candidate for on-chip integration. In the second portion of this dissertation, we aim to model and characterize highconfinement plasmonic devices using doped silicon in the mid-infrared range. The midinfrared range is home to some important applications such as molecular sensing, environmental monitoring and security applications. Traditional plasmonic devices possess some much desired features that may be utilized in the mid-infrared. These include hosting a high surface sensitivity, and having the ability to guide and confine light through subwavelength structures, including sharp bends. However, much of these features are exclusive to the near-infrared and visible frequencies, where the plasma resonance of conventional plasmonic materials lie. This is because conventional materials tend to suffer from low confinement in the mid-infrared region, and are rendered inconvenient for applications that require high confinement such as sensing and on-chip communications. For this reason and for its CMOS compatibility, doped silicon plasmonics seems to be a viable solution. We demonstrate that plasma resonance tunability can be achieved through controlling the doping level. Moreover, the dispersion characteristics of doped silicon devices were analyzed for different applications at the mid-infrared region, and displayed valuable phenomenon such as negative dispersion, which can be utilized for slow light and metamaterial applications, and epsilon-near-zero characteristics, that can be used for extraordinary transmission. The mid-infrared dispersion was studied thoroughly for multiple structures, including the slot structure and the rectangular shell structure. The potential for biological and environmental sensing for the aforementioned structures, as well as for a doped silicon nanoparticle was investigated and very high sensitivity was achieved. In addition, the performance of the slot structure in the negative dispersion region was established through using the waveguide as a slow light medium. Moreover, plasmonic structures that can be used for on-chip light-guiding, such as bends and junctions were evaluated. FDTD simulations showed superior performance through successful lightsplitting in gaps as wide as 1μm.

School

School of Sciences and Engineering

Department

Electronics & Communications Engineering Department

Degree Name

MS in Electronics & Communication Engineering

Graduation Date

Fall 2014

Submission Date

9-2-2014

First Advisor

Swillam, Mohamed

Committee Member 1

Ismail, Yehea

Committee Member 2

Addas, Karim

Extent

98 leaves

Document Type

Master's Thesis

Institutional Review Board (IRB) Approval

Not necessary for this item

Available for download on Wednesday, May 25, 2022

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