Elucidating the effects of radiant and sub-radiant interactions in terahertz metamaterials

• Main Author: Manjappa, Manukumara
• Other Authors: Singh Ranjan
• Format: Theses and Dissertations
• Language: English
• Published: 2019
• Subjects: DRNTU::Science::Physics::Optics and light
• Online Access: https://hdl.handle.net/10356/90197; http://hdl.handle.net/10220/47314
• Institution: Nanyang Technological University

This thesis discusses the study and implications of near- field interactions mediated by radiant and sub-radiant resonant modes in passive metamaterials (MMs), MEMS actuated active MMs and semiconductor-metamaterial heterostructures at terahertz frequencies. The thesis is divided into two parts, where the fi rst part of the thesis includes fi rst three chapters (Chaps. 2, 3 and 4) that discusses on the phenomena of metamaterial induced transparency and lattice induced transparency in the metamaterial structures at terahertz frequencies. Theoretical analysis using classical coupled oscillators model is proposed to unravel the interaction mechanisms that reveals the radiant and subradiant type of Fano interference effects in the system. These systems show strong slow light effects with large enhancement in the group delay of the pulse through the medium. Further, the implications of the competing electric and magnetic near- field interactions on the transmission characteristics of the medium have shown to exhibit resonant invisibility effects showing an active control of effective permittivity and permeability of the medium. Second part of the thesis (Chap. 5 and Chap. 6) focuses on the demonstration of excitation and active modulation of sharp Fano resonances in a MEMS metamaterial and semiconductor-metamaterial hybrid heterostructure systems. Excitation of Fano resonance in MEMS metamaterial by introducing out-of plane structural asymmetry exhibits anisotropic coupling that results in the multiple-input-output (metahysteresis) characteristics in its near- and far-fi eld optical properties. This exhibits exciting features such as NAND and XOR logical operations, where XOR function can show direct implications in the one-time pad (OTP) secured cryptographic channel for sub-terahertz wireless communications. Further, an active control of Fano resonance in a heterostructure consisting of solution processed CH3NH3PbI3/PbI2 semiconductors spin coated on a metamaterial structure is discussed that exhibits ultrasensitive and ultrafast modulation of Fano resonance in the metamaterial structure, respectively (Chap. 6). Additionally, a new signature of localized plasmon-phonon quasiparticles sensing and interference effects are observed and elucidated using the coupled oscillator model. This phenomenon reveals a strong resonant interactions between the elementary excitations that can be actively controlled by optically pumping the sample using a femtosecond pulse. The thesis concludes by discussing the importance and the future prospectives of the conducted studies.