Terahertz bound states in the continuum

Localized wave confinement in electromagnetic devices is crucial in science and technology. Waves can be confined with diverse methods ranging from metallic reflectors, total internal reflection, photonic bandgap, to Anderson localization and symmetry separability, where the “resonator” is surrounde...

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Main Author: Han, Song
Other Authors: Singh Ranjan
Format: Thesis-Doctor of Philosophy
Language:English
Published: Nanyang Technological University 2020
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Online Access:https://hdl.handle.net/10356/137303
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Institution: Nanyang Technological University
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spelling sg-ntu-dr.10356-1373032023-02-28T23:54:42Z Terahertz bound states in the continuum Han, Song Singh Ranjan School of Physical and Mathematical Sciences ranjans@ntu.edu.sg Science::Physics::Optics and light Localized wave confinement in electromagnetic devices is crucial in science and technology. Waves can be confined with diverse methods ranging from metallic reflectors, total internal reflection, photonic bandgap, to Anderson localization and symmetry separability, where the “resonator” is surrounded by a medium that does not support outgoing waves, which inevitably trapping the waves in it. Recently, it has been found that waves can sometimes be perfectly trapped without leakages through symmetry separability which is known as a bound state in continuum (BIC). It has a localized eigenstate, whose frequency (or energy) lies within the continuous plane waves. In this thesis, we numerically and experimentally investigate diverse resonant all-dielectric metamaterials and photonic crystal (PhC) slabs for observation of these non-radiating BICs. A 2D dielectric metasurface is proposed to demonstrate supercavity govern by the BICs under TE-polarized excitation. With silicon as the metasurface building blocks, the supercavity enables low-fluence (10.16 µJ/cm^2) switching at nanosecond time scales. Under TM-polarized excitations, terahertz guided mode resonances (GMRs) are also discovered in the same 2D dielectric metasurfaces. It is also observed multiple BICs at terahertz regime by employing a C4v symmetric metasurface and their diverse counterparts with in-plane symmetry breaking. The BICs, demonstrated by ultra-high-Q resonances enable extremely high field localization, which are desired for low-threshold terahertz quantum cascade lasers. Finally, we investigate, for the first time, the dynamic zero-index BICs in terahertz large-scale integrated photonic devices. The zero-index is realized by constructing an accidental degeneracy dispersion, also known as photonic Dirac-like cone, which enables non-radiating BICs such that a low-loss zero-index PhC slab is achieved. The active modulation of zero-index PhC is also demonstrated. This thesis opens up bright avenues for designing low-loss, on-chip, and dynamic terahertz resonant devices. Doctor of Philosophy 2020-03-17T01:53:12Z 2020-03-17T01:53:12Z 2020 Thesis-Doctor of Philosophy Han, S. (2020). Terahertz bound states in the continuum. Doctoral thesis, Nanyang Technological University, Singapore. https://hdl.handle.net/10356/137303 10.32657/10356/137303 en This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License (CC BY-NC 4.0). application/pdf Nanyang Technological University
institution Nanyang Technological University
building NTU Library
continent Asia
country Singapore
Singapore
content_provider NTU Library
collection DR-NTU
language English
topic Science::Physics::Optics and light
spellingShingle Science::Physics::Optics and light
Han, Song
Terahertz bound states in the continuum
description Localized wave confinement in electromagnetic devices is crucial in science and technology. Waves can be confined with diverse methods ranging from metallic reflectors, total internal reflection, photonic bandgap, to Anderson localization and symmetry separability, where the “resonator” is surrounded by a medium that does not support outgoing waves, which inevitably trapping the waves in it. Recently, it has been found that waves can sometimes be perfectly trapped without leakages through symmetry separability which is known as a bound state in continuum (BIC). It has a localized eigenstate, whose frequency (or energy) lies within the continuous plane waves. In this thesis, we numerically and experimentally investigate diverse resonant all-dielectric metamaterials and photonic crystal (PhC) slabs for observation of these non-radiating BICs. A 2D dielectric metasurface is proposed to demonstrate supercavity govern by the BICs under TE-polarized excitation. With silicon as the metasurface building blocks, the supercavity enables low-fluence (10.16 µJ/cm^2) switching at nanosecond time scales. Under TM-polarized excitations, terahertz guided mode resonances (GMRs) are also discovered in the same 2D dielectric metasurfaces. It is also observed multiple BICs at terahertz regime by employing a C4v symmetric metasurface and their diverse counterparts with in-plane symmetry breaking. The BICs, demonstrated by ultra-high-Q resonances enable extremely high field localization, which are desired for low-threshold terahertz quantum cascade lasers. Finally, we investigate, for the first time, the dynamic zero-index BICs in terahertz large-scale integrated photonic devices. The zero-index is realized by constructing an accidental degeneracy dispersion, also known as photonic Dirac-like cone, which enables non-radiating BICs such that a low-loss zero-index PhC slab is achieved. The active modulation of zero-index PhC is also demonstrated. This thesis opens up bright avenues for designing low-loss, on-chip, and dynamic terahertz resonant devices.
author2 Singh Ranjan
author_facet Singh Ranjan
Han, Song
format Thesis-Doctor of Philosophy
author Han, Song
author_sort Han, Song
title Terahertz bound states in the continuum
title_short Terahertz bound states in the continuum
title_full Terahertz bound states in the continuum
title_fullStr Terahertz bound states in the continuum
title_full_unstemmed Terahertz bound states in the continuum
title_sort terahertz bound states in the continuum
publisher Nanyang Technological University
publishDate 2020
url https://hdl.handle.net/10356/137303
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