Investigation of refractive index and group velocity of metal coated dielectric spherical nanocomposites within both passive and active dielectric cores

This research paper focuses on studying how light behaves in metal-coated dielectric spherical nanocomposites. It investigates different types of light propagation, such as slow, backward, and fast lights. The paper examines the theoretical aspects of these phenomena in composite materials, specifically when spherical nanoinclusions are embedded in either active or passive dielectric cores, or when dielectric-coated metal spherical nanoinclusions are embedded in active or passive dielectric shells. Furthermore, the paper explores the optical properties of the composites at resonant frequencies and explores potential applications of systems that exhibit anomalous dispersion. The numerical observations in the paper discuss the occurrence of slow, backward, and superluminal light pulses in metal-coated dielectric and dielectric-coated metal nanocomposites with spherical nanoinclusions. Additionally, the paper suggests that incorporating gain layers with a negative dielectric function can improve the optical properties of the composite material.