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Enhanced Optical Nonlinearity Based on Metamaterials and Its Applications in Self-Induced Nonreciprocal Devices
Optical nonlinearity is the change in the optical properties of an arbitrary medium excited by electromagnetic waves. Optical nonlinear effects have wide applications in information storage, processing, and computing. However, their extremely weak nature and very poor efficiencies requires very high input intensities. This detrimental issue directly limits their practical applications. With the rapid progress in nanofabrication techniques, optical materials can be designed and implemented with subwavelength dimensions unit cells. Metamaterials and their two-dimensional (2D) counterparts known as metasurfaces can exhibit strong nonlinear optical responses. Not only can the electric field be dramatically enhanced by the localized plasmon or Mie resonances, but also the phase-matching requirement is relaxed in these ultrathin materials. Nonreciprocal transmission is the basic effect of various essential photonic devices, such as isolators and circulators. Systems with highly spatial asymmetry that operate in the nonlinear regime can break the time-reversal symmetry and thus exhibit nonreciprocity. Due to the absence of an external bias, nonlinearity-based nonreciprocal devices can be realized by thin metamaterials or metasurfaces, which can be used as new free-standing devices with a notable example of protective ultrathin layers to decrease the damage of sensitive optical components. In this thesis, we present several new designs of metamaterials and metasurfaces to enhance the typically weak nonlinear effects. By carrying out theoretical studies and simulations, two plasmonic metasurfaces are designed consisting of noble metals or graphene to improve the conversion efficiency of four-wave mixing (FWM) and third-harmonic generation (THG) at optical and terahertz (THz) frequencies, respectively. By using patterned graphene, which is the most widely employed one-atom-thick 2D material, the nonlinear metasurfaces become highly tunable. Then, all-dielectric metamaterials and metasurfaces are designed exhibiting dramatically enhanced Kerr effect leading to strong passive and self-induced nonreciprocal transmission. These studies on nonlinear metamaterials and metasurfaces are expected to lead to several potential applications in wavelength conversion, THz optical sources, optical isolators, and other emerging photonic devices that can be used in classical or quantum optical systems.
Jin, Boyuan, "Enhanced Optical Nonlinearity Based on Metamaterials and Its Applications in Self-Induced Nonreciprocal Devices" (2021). ETD collection for University of Nebraska - Lincoln. AAI28652764.