Kırılma İndisi Güçlendirilmiş Plazmonik Aygıtlarda Işık Yayılımı

Abstract

The optical properties of metal nanoparticles (MNPs) are primarily determined by localized surface plasmon resonances. In an MNP, the frequency of localized surface plasmons depends on the particle’s size, geometry, and the refractive index of the surrounding local medium. When MNPs are in close proximity, localized hot spots emerge around the nanoparticle, and these plasmonic hot spots play a crucial role, particularly in optical fields. Metal surfaces where plasmonic hot spots occur can lead to the concentration and enhancement of light waves during the journey of light. The formation of plasmonic hot spots is contingent upon the shape and structure of metal surfaces, with smooth and symmetric surfaces facilitating their creation. MNPs can interact with each other through these plasmonic hot spots, resulting in various effects such as polarization, sensitivity, and refractive index changes. The ability to control the refractive index with another (auxiliary) light can revolutionize all photonic technologies. This thesis investigates light propagation in such an environment using both analytical and FDTD (finite difference time domain) methods. This examination goes beyond illustrating light propagation in such photonic devices; it also aims to explore the phenomenon of slow light that can be observed in such a system. The concept of slow light has been previously explored with photonic crystals, relying on deliberately altering the photonic bandgap of these crystals through precise defects. However, these studies are limited by their dependence on photonic crystals, requiring high precision and suffering from low process efficiency due to their irreversible nature. Plasmonic technology offers a more effective solution in this regard. The discussed system not only promises index enhancement but also explores materials with epsilon-near-zero (ENZ) indices, where the index approaches zero. It is possible to achieve both increased index and near-zero index without altering the MNP structure using control light. In this area with limited literature, the data obtained with varying scenarios in this study will serve as a foundation for future research. This study examines the analytical and simulation-based solutions for the changing refractive index due to plasmonic effects in silver nanorods. This allows for the investigation of changing group velocities along with the changing refractive index in the system established with silver nanorods. The consistent and meaningful results obtained from both analytical and simulation-based studies within the scope of the thesis provide a strong basis for future experimental studies. The research demonstrates that all of these effects can be achieved with the assistance of auxiliary light. One surprising and valuable finding is that the control (Ex) source, which would not have a direct impact on the polarization of the signal (Ey) under normal circumstances, induces changes in the signal (Ey). This is due to the indirect influence of the change in polarization at the hot spot, even though the control (Ex) does not contribute to the polarization at the ends of the rod along the y-axis. This simulation first examined the case where the amplitude ratios of the signal and control sources were 1. Subsequently, different amplitude ratios (1, 10, 100, 200) were used, and the system’s response around the hot spot was investigated. In these examinations, a polarization change in the same direction as the signal source, orthogonal to the control, was observed with the varying amplitude of the control source. Under normal circumstances, a change in the amplitude of the control source would not be expected to induce a change in the polarization direction of the signal. However, due to coupling, it was observed that even when the signal source is constant, the changing amplitude of the control contributes to the polarization in the same direction as the signal. The observed anomalous dispersion, ENZ, and other parameters are entirely attributed to this effect. This internally consistent study lays the groundwork for future experimental studies.