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Title: Dynamic modulation of plasmon excitations in monolayer graphene
Author: Matthaiakakis, Nikolaos
ISNI:       0000 0004 7225 2610
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2017
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Plasmonic devices based on noble metals have offered solutions in numerous scientific and commercial fields over the past decades. Nevertheless the optical properties of noble metals are hardly tuneable thus not allowing for dynamic control of device properties. Offering a solution for achieving efficient dynamically tuneable plasmonic devices is a crucial since it would significantly widen the range of plasmonic applications and open the way for on-chip photonic logic systems. Graphene has demonstrated high quantum efficiency for light matter interactions, strong optical nonlinearity, high optical damage threshold, and plasmons with high confinement and long propagation distances. Having a linear dispersion, zero bandgap, as well as very few free electrons available under zero doping conditions, has made this material a strong candidate for realising dynamic and highly tuneable photonic and plasmonic devices. The interest of graphene as a platform for photonic applications is enormous with numerous publications focusing on the realisation of electrostatically controlled optical devices utilizing novel properties offered by this material. Graphene plasmonics in particular have great promise in realising highly efficient on-chip modulators, optical interconnects, waveguides, sensors, and even photonic logic gates. Naturally, several issues need to be overcome in order for such devices to reach commercialization. Obtaining strong coupling of light with plasmons in graphene while also providing efficient long range frequency and intensity modulation of the plasmon absorption is a crucial and highly anticipated goal for graphene based plasmonic devices. This work overcomes these issues by utilizing a novel diffraction grating/gold-insulator-graphene combined structure to dynamically couple, enhance, and manipulate plasmons in a graphene monolayer. The proposed structure consists of a two-dimensional inverted pyramid grating on a Si wafer, which acts as a phase matching component, and utilizes a gold back reflector and a transparent spacer in order to enhance coupling of plasmons on the graphene layer that lies above. An extra ionic gel layer above the monolayer of graphene is used to achieve efficient electrostatic control of the plasmon frequency and absorption efficiency. The pyramid grating structure properties were studied experimentally. Theoretical calculations as well as Rigorous Coupling Wave Analysis simulations of the final device setup provide evidence of extremely efficient plasmon modulation both in terms of frequency and absorption efficiency, reaching even total optical absorption under certain conditions. Furthermore the device configuration allows for dynamic switching of plasmon excitations thus providing a possible solution for photonic switching applications. Finally, alternative materials for achieving tuneable plasmonic devices are also discussed.
Supervisor: Charlton, Martin Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available