RESUMO
Bulk materials with a relative electric permittivity ε close to zero exhibit giant Kerr nonlinearities. However, harnessing this response in guided-wave geometries is not straightforward, due to the extreme and counterintuitive properties of such epsilon-near-zero materials. Here we investigate, through rigorous calculations of the nonlinear coefficient, how the remarkable nonlinear properties of such materials can be exploited in several structures, including bulk films, plasmonic nanowires, and metal nanoapertures. We find the largest nonlinear response when the modal area and group velocity are simultaneously minimized, leading to omnidirectional field enhancement. This insight will be key for understanding nonlinear nanophotonic systems with extreme nonlinearities and points to new design paradigms.
RESUMO
The nonlinear coefficient γ is central to the study of cubically nonlinear optical guided-wave structures. It is well understood for lossless waveguides, but less so for lossy systems. A number of methods for calculating γ in lossy systems have been proposed, each resulting in different expressions. Here we identify the most accurate and practical expression for γ. We do so by applying the different expressions γ to air-gold surface plasmon polariton modes in the interband region of gold and compare with a fully numerical iterative method. We thus resolve the outstanding issue of which expression for the nonlinear coefficient to use for lossy waveguides, enabling new insights into the nonlinear response of such systems.
