6 research outputs found
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Finite element characterisation of plasmonic waveguides in terahertz and optical frequencies
In recent years plasmonic devices have become an interesting area of research due to the sub-wavelength confinement and propagation of radiation, allowing the design of very compact structures. Compact structures are necessary to make smaller integrated optical circuits. Due to the use of metals, plasmonic guides usually show more losses compared to the conventional dielectric guides. Therefore, plasmonic waveguides are not normally used for long distance transmission. However, they are promising for inter-chip or intra-chip communication and also have seen a lot of sensor applications.
There has been considerable interest in exploiting the frequency bands in the terahertz regime to open up new frontiers of research across a diverse range of applications. An array of opportunities for creating novel technologies using this frequency band had remained largely unexplored and undeveloped for a considerable period of time due to the lack of suitable sources, as well as lack of guiding and detecting devices.
This thesis describes the design, analysis and optimisation of plasmonic devices in optical and terahertz frequencies. A fully vectorial H-field based finite element method has been used in the research reported in this thesis to reveal the modal characteristics of different plasmonic structures.
A six layer planar contra-directional nano-coupler has been analysed at optical frequency. Three different modes of propagation were considered to study the characteristics of different properties of the structure, including the coupling length. A design approach has been proposed to make the coupler low loss as well as smaller in length.
For the terahertz plasmonics, a rectangular metallic hollow core guide was considered at terahertz frequency. Several modes were considered for the modal analysis of the structure. Modal analysis was performed by changing metal, introducing different dielectric coating in the hollow core, changing the thickness of the metal and dielectric layers and changing the dimensions of the guide. A dispersion analysis was also performed. The criteria for designing very low loss, compact and low dispersion guide have been presented for the structure at the end of the study
Plasmonic Nanoplatforms for Biochemical Sensing and Medical Applications
Plasmonics, the science of the excitation of surface plasmon polaritons (SPP) at the metal-dielectric interface under intense beam radiation, has been studied for its immense potential for developing numerous nanophotonic devices, optical circuits and lab-on-a-chip devices. The key feature, which makes the plasmonic structures promising is the ability to support strong resonances with different behaviors and tunable localized hotspots, excitable in a wide spectral range. Therefore, the fundamental understanding of light-matter interactions at subwavelength nanostructures and use of this understanding to tailor plasmonic nanostructures with the ability to sustain high-quality tunable resonant modes are essential toward the realization of highly functional devices with a wide range of applications from sensing to switching.
We investigated the excitation of various plasmonic resonance modes (i.e. Fano resonances, and toroidal moments) using both optical and terahertz (THz) plasmonic metamolecules. By designing and fabricating various nanostructures, we successfully predicted, demonstrated and analyzed the excitation of plasmonic resonances, numerically and experimentally. A simple comparison between the sensitivity and lineshape quality of various optically driven resonances reveals that nonradiative toroidal moments are exotic plasmonic modes with strong sensitivity to environmental perturbations. Employing toroidal plasmonic metasurfaces, we demonstrated ultrafast plasmonic switches and highly sensitive sensors. Focusing on the biomedical applications of toroidal moments, we developed plasmonic metamaterials for fast and cost-effective infection diagnosis using the THz range of the spectrum. We used the exotic behavior of toroidal moments for the identification of Zika-virus (ZIKV) envelope proteins as the infectious nano-agents through two protocols: 1) direct biding of targeted biomarkers to the plasmonic metasurfaces, and 2) attaching gold nanoparticles to the plasmonic metasurfaces and binding the proteins to the particles to enhance the sensitivity. This led to developing ultrasensitive THz plasmonic metasensors for detection of nanoscale and low-molecular-weight biomarkers at the picomolar range of concentration.
In summary, by using high-quality and pronounced toroidal moments as sensitive resonances, we have successfully designed, fabricated and characterized novel plasmonic toroidal metamaterials for the detection of infectious biomarkers using different methods. The proposed approach allowed us to compare and analyze the binding properties, sensitivity, repeatability, and limit of detection of the metasensing device