THz light has important applications in medical imaging, chemical sensing, industrial quality control, and future wireless communications. However, the widespread adoption of these applications is currently limited by the lack of practical sources of THz radiation that can operate at or near room temperature. Graphene is a promising materials system for basic studies and device applications in THz optoelectronics, with several key functionalities, including photodetection and optical modulation, already demonstrated in recent years. This thesis work is focused on the use of graphene for the THz light emission. In particular, I have demonstrated for the first time the generation of gate-tunable THz radiation from graphene nanoribbons under current injection. The underlying radiation mechanism involves the excitation of graphene plasmonic oscillations by the injected hot carriers and their subsequent radiative decay at the nanoribbon resonance frequency. Combined with suitably designed optical elements, this approach is promising for the development of compact THz sources for imaging and sensing applications. In addition, I have also investigated alternative radiation mechanisms that can provide higher efficiencies but require more complex ultra-high-mobility graphene samples. These mechanisms include Smith-Purcell emission by the graphene electron gas in the vicinity of a periodic grating and interminiband transitions in graphene superlattices produced with a periodic external potential. Finally, I have designed and investigated numerically a graphene-nanoribbon metasurface platform that can provide arbitrary wavefront shaping functionalities for incident THz light, such as beam steering and focusing. Importantly, this device can be actively reconfigured by varying the nanoribbon gate voltages, which makes it particularly attractive for applications in wireless communications beyond 5G.
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/45055 |
| Date | 26 August 2022 |
| Creators | Li, Yuyu |
| Contributors | Paiella, Roberto |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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