Tuning Optical Properties of Cylindrical Nanoinclusions: The Roles of Metal Fraction, Passive and Active Host Matrices

Abstract

The optical behavior of nanostructures is profoundly influenced by their geometry and the properties of the surrounding medium. While spherical nanoparticles have been extensively studied, cylindrical nanoinclusions offer unique anisotropic properties that are advantageous for integrated photonic devices. This work provides a comprehensive theoretical and numerical investigation into tuning the optical properties of cylindrical core-shell nanoinclusions, with a specific focus on the roles of metal fraction and the dielectric nature of passive versus active host matrices. By solving the Laplace equation within the quasistatic approximation (QA), we analyze the local field enhancement (LFE) and optical bistability (OB) for three distinct configurations: metal-coated dielectric cylinders (McDCs), dielectric-coated metal cylinders (DcMCs), and pure metal cylinders. A key finding is that these geometries exhibit fundamentally different resonant behaviors, from dual peaks in metal-coated systems to single peaks in the others. We demonstrate that the metal fraction p is a critical geometric parameter that controls the spectral position and strength of these resonances. Furthermore, the host matrix’s dielectric function, particularly its imaginary part , serves as a powerful material-based tuning knob. Active host matrices with a negative  dramatically amplify the local field and modify OB characteristics by compensating for plasmonic losses. These insights establish clear design principles for optimizing cylindrical nanocomposites for advanced applications in nonlinear optics, all-optical switching, and high-sensitivity nanoscale sensing.