Nonlinear nanophotonics in plasmonic and graphene structures

Abstract

Going beyond the diffraction limit of light, nanophotonics studies nontrivial physical phenomena involving the interaction of photons with nanostructured media. Within decades of fruitful developments, the field of nanophotonics has become a prominent area of research with applications ranging from integrated optical circuits and ultrafast photonic devices to super-imaging, nanolasing and biosensing. Nonlinear intensity-dependent optical effects, facilitated by strong light-matter interaction, are indispensable in modern photonics, enriching the beauty of physics comprised and providing novel opportunities for subwavelength light control.

To date, the possibilities of photon nanoscale confinement and operations with photonic flows are primarily associated with surface plasmons that are localized in the vicinity of metal-dielectric interfaces infrared or visible-frequency electromagnetic eigenmodes originating from coupling of the electromagnetic field to the electron oscillations in a metal plasma. Physics of light interaction with metal structures that are much smaller than the free space wavelength of light constitutes one of the most significant branches of contemporary nanophotonics – nanoplasmonics. Combining strong surface plasmon resonances and high intrinsic nonlinearities in the deep subwavelength scales, plasmonic structures offer a unique playground to develop novel concepts for light manipulation at the nanoscale. Tight field confinement in plasmonic systems can boost the efficiency of various nonlinear optical effects, the study of which can help delineate a roadmap in designing novel subwavelength nonlinear optical elements.

Recently, graphene, a single atomic layer of graphite, has emerged as a promising alternative to noble metals for applications in plasmonics. The study of plasmonic effects in doped graphene structures has attracted special interest from the nanoplasmonics research community due to novel functionalities suggested by such systems, including an extraordinary field confinement by a graphene layer, tunability of graphene properties through doping or electrostatic gating and longer lifetimes in the infrared and terahertz frequency ranges, which is extremely important for biomedical and security applications. In addition, graphene demonstrates strong and tunable optical nonlinearity and it can be incorporated into various components of nanoscale optics. However, the potential of the nonlinear response of graphene is not yet fully realized and almost not studied, especially in the resonant plasmonic geometries. It is therefore of significant interest to construct analytical models for the underlying principles and explore the viability of nonlinear optical effects in graphene-based photonic devices.

This thesis focuses on the nonlinear photonics of plasmonic and graphene-based nanostructures. Exploiting nonlinear optical response, it develops theoretical ideas for the alloptical light control at subwavelength scales and studies the advantageous possibilities of manipulating electromagnetic waves by utilizing the unique properties of graphene.

Chapter 2 presents a comprehensive study of nonlinear dynamics in arrays of optically driven plasmonic nanoparticles with a Kerr-like nonlinear response. We perform detailed modulation instability analysis and demonstrate the pattern formation and the existence of plasmonic kinks and nonlinear localized modes in the form of trapped and walking solitons in such systems under control guidance of the external driving field.

Chapters 3 and 4 include a theoretical prediction and analytical description of manifold nonlinear effects that can be actualized due to the graphene nonlinear response. Utilizing conventional concepts of photonics and metal plasmonics combined with unique electronic and optical properties of graphene, we establish a theoretical framework for designing various graphene-enhanced components of nanoscale optics and nanodevices, such as waveguides, couplers, nano-antennas and metasurfaces. These studies outline substantial features of graphene as a promising material for surface physics and plasmonics, and envision their potential applications in optical nanocircuits, optoelectronics, metamaterials, and THz technology.

Specifically, in Chapter 3 we investigate the nonlinear self-action of surface plasmons and the generation of subwavelength solitons in graphene waveguides and multilayers. Our studies elucidate the nonlinear switching of light in two coupled layers of graphene, the formation of nonlinear modes in graphene metamaterials, and the excitation of dissipative plasmon solitons coupled to the external driving source via an evanescent field.

Chapter 4 examines the harmonic generation in different geometries with graphene. We develop theoretical models for the resonant (enhanced) second-harmonic generation from a graphene-wrapped dielectric spherical nanoparticle and frequency conversion in graphene-based waveguides through the phase-matched nonlinear interaction of the plasmonic modes. We describe the second-harmonic generation from a double-layer graphene structure with modulated conductivity and nonlinear plasmon-to-plasmon conversion in hybrid graphene-semiconductor waveguides, predicting the cascading effect in the thirdharmonic generation. Finally, we propose the concept of tunable nonlinear graphene metasurfaces composed of a graphene layer and a planar gold metamaterial. We demonstrate that such hybrid graphene metasurfaces provide strong tunability and dramatic field enhancement, giving rise to the enhanced nonlinear response and high efficiency of the second-harmonic generation.

Chapter 5 summarizes the results and concludes this thesis. Show more