Nanophotonic control of optical emission, propagation, and all-optical modulation

Research output: ThesisDoctoral ThesisCollection of Articles

Abstract

The field of nanophotonics is concerned with the use of nanoscale structures and systems to control light for purposes such as miniaturization of optical components and control over the emission of light by quantum emitters. The research compiled in this dissertation focuses on artificial optical nanomaterials, generation of light, and all-optical modulation. Most of the artificial optical materials examined in this dissertation are metamaterials. These consist of scatterers, such as nanorods, in a lattice with a sub-wavelength period. For light passing through a metamaterial, the material appears as a homogeneous medium but with extraordinary optical properties. Typically, the optical properties also vary depending on the direction of light propagation; this effect is known as spatial dispersion. To analyze and design spatially dispersive metamaterials for different purposes, this dissertation adopts a wave parameter-based approach where a refractive index and wave impedance is assigned to each plane wave propagating in the metamaterial. We refine the previously-developed wave parameter theory to describe the movement of optical energy inside nanomaterials. We then develop a Fourier transform-based method to analyze optical emission inside spatially dispersive materials. We also discuss the outcoupling of light from inside nanomaterials, and show how emitted light can efficiently escape even from inside materials that exhibit strong attenuation. We then design and experimentally demonstrate nanostructures that drastically increase the brightness of a fluorescent film by combining the enhancements of radiation directivity and pump light absorption. The methods and ideas put forward in this part are useful for understanding and designing nanomaterials and structures for the purpose of controlling optical emission, with an eye on applications such as sensors and light sources. The dissertation also discusses nanomaterials for controlling the polarization of light. We theoretically and experimentally demonstrate a wave plate that relies on the strong birefringence of a sub-wavelength metal-dielectric structure. The wave plate combines low loss, broad bandwidth, and operation in the transmission mode, and we also discuss how it can be fabricated on large areas, making mass production feasible. Finally, we present a method of ultrafast all-optical modulation, as well as a method of ultrafast detection. Both methods rely on an optical gain medium and a Fourier transform pulse shaper. The on-resonance gain medium facilitates strong nonlinear interaction of two optical signals. The pulse shaper is used as a wavelength splitter and recombiner (in all-optical modulation) and a time-to-space mapper (in detection). In our experiments, modulation and detection reach sub-picosecond speed and resolution, respectively, despite the overall nanosecond-scale response of the gain medium.
Translated title of the contributionValon emission, etenemisen ja moduloinnin hallinta nanofotoniikan avulla
Original languageEnglish
QualificationDoctor's degree
Awarding Institution
  • Aalto University
Supervisors/Advisors
  • Kaivola, Matti, Supervising Professor
  • Shevchenko, Andriy, Thesis Advisor
Publisher
Print ISBNs978-952-64-0288-8
Electronic ISBNs978-952-64-0289-5
Publication statusPublished - 2021
MoE publication typeG5 Doctoral dissertation (article)

Keywords

  • optical nanomaterials
  • metamaterials
  • spontaneous emission
  • modulation

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