Browsing by Author "Kananen, Thomas"
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Item Controlling Microring Resonator Extinction Ratio via Metal-Halide Perovskite Nonlinearity(Advanced Optical Materials, 2021-09-09) Wang, Feifan; Zhao, Lianfeng; Xiao, Yahui; Li, Tiantian; Wang, Yixiu; Soman, Anishkumar; Lee, Hwaseob; Kananen, Thomas; Hu, Xiaoyong; Rand, Barry P.; Gu, TingyiThe exceptionally high optical nonlinearities, wide bandgap, and homogeneity in solution-processed metal-halide perovskite media are utilized as optical nonlinear elements on a silicon photonic platform for low-power-active components, such as all-optical switches, modulators, and lasers. With room temperature back-end-of-line compatible processing, a hybrid metal-halide perovskite (CH3NH3PbI3) microring resonator (MRR) structure is fabricated on a foundry-processed low-loss silicon photonic platform. With in-plane exci-tation near the light intensity of 110 W m−2, strong two-photon absorption and free-carrier absorption saturation are observed. With 103 field enhancements by MRRs, the photorefractive effect in the metal-halide perovskite reduces linear absorption, represented by 102 improvement of the MRR’s intrinsic quality factor and 20 dB enhancement of the extinction ratio.Item Far-infrared photonic-plasmonic phase matching enhanced graphene absorption(University of Delaware, 2019) Kananen, ThomasIn this thesis, we investigate a novel device architecture for sensing applications in the far-infrared region. This region is relatively unexplored due to a fundamental problem surrounding the optical spacer which separates the front side planar geometry from the substrate. SiO2 is commonly used but suffers from immense absorptions at wavelengths below 1000 cm-1. To overcome this problem, we use an optically transparent spacer, zinc selenide, which exhibits high transmission well into the far infrared region. We implement a monolayer of graphene that serves to broaden the plasmonic mode and increase the optical absorption through phase and momentum matching of the plasmons. Optimization of the optical spacer thickness, rod length, rod width, and periodicity allow for our device to have plasmonic resonances from 950 cm-1 to below 600 cm-1 with an extinction ratio of more than 28%. This allows for on-chip sensing through geometric tuning. ☐ Photonic crystal waveguides are a fundamental building block for all-optical communications in the chip-scale. By optimizing the radius, lattice constant, and spacing between the photonic crystal arrays, it is possible to place the high-transmission regions or band edge in the wavelength of choosing. The telecommunication bands are the target wavelengths for our project. ☐ This thesis will be broken up into six different chapters. The first four chapters will discuss in detail our graphene modified plasmonic structure starting with a chapter on the introduction to the field of plasmonics, graphene, graphene plasmons, and motivation about current works in the field of graphene-based sensors. The second chapter will discuss design principles and simulations. The third chapter will discuss fabrication and characterization of the device. The fourth chapter will discuss the experimental results. The fifth chapter will briefly discuss our results from the AIM foundry run for our photonic crystal waveguide structures alongside the simulated work and experimental setup. The final chapter will discuss the future directions for both projects.Item Graphene Absorption Enhanced by Quasi-Bound-State-in-Continuum in Long-Wavelength Plasmonic–Photonic System(Advanced Optical Materials, 2022-09-07) Kananen, Thomas; Wiggins, Marcie; Wang, Zi; Wang, Feifan; Soman, Anishkumar; Booksh, Karl; Alù, Andrea; Gu, TingyiGraphene plasmonic structures can support enhanced and localized light–mater interactions within extremely small mode volumes. However, the external quantum efficiency of the resulting devices is fundamentally limited by material scattering and radiation loss. Here, such radiation loss channels are suppressed by tailoring the structure to support a symmetry-protected bound-state-in-the-continuum (BIC) system. With practical loss rates and doping level in graphene, over 90% absorption near critical coupling is expected from numerical simulation. Experimentally measured peak absorption of 68% is achieved in such a tailored graphene photonic–plasmonic system, with maximum 50% contrast to the control sample without graphene. Significant reduction of the plasmon absorption for a different spacer thickness verifies the sensitivity of the system to the quasi-BIC condition.