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UBC Theses and Dissertations

Photonic architectures for ultrafast all-optical switching and retro-modulation Born, Brandon


Optical communications is the backbone of the modern internet. However, the true potential of the deployed optical networks has not been reached due to a reliance on far slower electronic processing. The ultimate objective is a fully all-optical network, to circumvent electronic bottlenecks and allow for network transparency, but there are challenges to the realization of all-optical implementations in current fibre optic and emerging free-space optical (FSO) communication networks. This thesis introduces two photonic architectures to address these challenges. First, an all-optical switch (AOS) architecture is developed for implementation in fibre optic front-end systems, where all-optical switching is the fundamental building block of all-optical processing. The AOS architecture applies a nanophotonic superlens, in the form of a dielectric sphere, to form an intense non-evanescent near-subwavelength focus called a photonic nanojet. The photonic nanojet forms at the back surface of the sphere in a coating of semiconductor nanoparticles. The AOS architecture is refined using Drude theory to study the free-carrier dynamics within the semiconductor nanoparticles, as well as Mie theory and ray theory to optimize the photonic nanojet’s intensity. Experiments are conducted with both milli- and micro-scale spheres coated by Si, SiC, CdTe, InP, and CuO nanoparticles. The realized AOS architecture meets the ultimate goals of femtojoule switching energies and femtosecond switching times. Second, an all-optical retro-modulation (AORM) architecture is developed for implementation in FSO communication systems, for which there is keen interest to establish high-bandwidth aerial-ground links. All-optical retro-modulation, a novel method for passive FSO aerial-ground communication, is proposed for future laser-based links with satellites, unmanned aerial vehicles, and high-altitude platforms. The AORM architecture is implemented with high-refractive-index S-LAH79 hemispheres to realize effective retroreflection and an interior semiconductor thin film of CuO nanocrystals to realize ultrafast all-optical modulation. A detailed investigation is carried out on the bandstructure and ultrafast free-carrier dynamics of the CuO nanocrystals. The AORM architecture is fabricated and shown to meet the ultimate goal of multidirectional FSO communication at terabit-per-second data rates. Overall, the introduced AOS and AORM photonic architectures can lay the foundation for future all-optical networks.

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