Metamaterials and metasurfaces for wavefront shaping and dispersion management

• Autor(a) principal: Pepino, Vinicius Marrara
• Data de Publicação: 2023
• Tipo de documento: Tese
• Idioma: eng
• Título da fonte: Biblioteca Digital de Teses e Dissertações da USP
• Texto Completo: https://www.teses.usp.br/teses/disponiveis/18/18155/tde-06112023-171908/
• topic: amplificação passiva; dispersion management; efeito Talbot; Fano resonances; feixes não difrativos; gerenciamento de dispersão; metalens; metalentes; metamateriais; metamaterials; metassuperfícies; metasurfaces; modulação de frente de onda; non-diffractive beams; passive amplification; ressonâncias Fano; Talbot effect; wavefront shaping

Metamaterials and metasurfaces, cutting-edge technologies, have recently garnered significant attention. They provide unprecedented control over electromagnetic wave behavior, enabling the manipulation of light, sound, and other waveforms in unprecedented ways. Engineered at a sub-wavelength scale, these materials possess unique properties not found in natural substances. The concept of metamaterials arose from the notion of crafting artificial structures with distinctive electromagnetic characteristics through precise internal structure manipulation, yielding materials with extraordinary traits like negative and near-zero refractive indices, perfect absorption or reflection, enhanced polarization, chirality effects, and dispersion management. Within this thesis, four primary contributions are outlined. Initially, a three-dimensional, all-dielectric, planar metalens, fabricated through 3D printing, enhances microwave focusing into a receiving antenna. This structure elevates antenna gain by 7.5 dB at 32.5 GHz within a 2.4 GHz bandwidth. The metalens achieves a focus with a full-width at half-maximum of approximately 0.85λ and a 3 dB depth-of-focus of around 5 cm. In azimuthal and elevation planes, the antenna\'s half-power beamwidth is reduced from 36° to 3° and from 4.5° to 3°, respectively, with the assistance of the metalens. Notably, the metalens performs effectively under oblique incidence, spanning 50° in the azimuthal plane and 40° in the elevation plane. Next, a tunable terahertz Bessel beam with variable depth of focus (ranging from 22 cm to 40 cm) and adjustable beam width (from 3.7 mm to 6 mm) is designed for imaging and communication applications. Silicon microholed metasurfaces are organized in an Alvarez-type configuration. The meta axicon operates at 850 GHz and exhibits self-healing capabilities against obstructions considerably larger than the operating wavelength. Subsequently, a fully passive terahertz pulse amplification device harnesses the temporal Talbot effect within a highly dispersive silicon-based metamaterial Bragg fiber. Three distinct strategies, identified as coherent pulse addition, forward Talbot illuminator, and backward Talbot illuminator, are introduced and explored to maximize passive Talbot effect gain. These approaches accommodate a wide range of output pulse shapes and yield gain factors of 5.8 dB (coherent pulse addition), 9.9 dB (forward Talbot illuminator), and 8.8 dB (backward Talbot illuminator). Numerical simulations indicate the potential of these methods for developing high-gain passive amplification terahertz devices. The temporal Talbot effect practical observation in the microwave realm has been hindered by the requirement for controlled propagation through a highly dispersive waveguide. Overcoming this challenge, we implemented an ultra-wideband, linearly chirped Bragg grating within a standard microwave X-Band waveguide. Utilizing backwards Talbot array illuminators with particle swarm optimization, we achieved passive amplification with gains of 3.45 dB (for Gaussian pulses) and 4.03 dB (for raised cosine pulses). Moreover, numerical assessments indicate that the gain can theoretically exceed 8 dB with higher quality dielectrics. This breakthrough opens doors to various microwave applications of the Talbot effect, including temporal cloaking, sub-noise microwave signal detection, microwave pulse shaping, and microwave noise reduction.