Tunable THz Plasmonic Modes in Indium Antimonide Filled Metallic Cylindrical Thermo-Optical Waveguides

Terahertz (THz) plasmonic tunability is a key requirement for the practical realization of next-generation, ultrafast, and compact plasmonic platforms for sensing, communication, waveguiding, and spectroscopic applications. This study addresses the challenge of weak field confinement commonly observed in metallic plasmonic waveguides by introducing indium antimonide (InSb) as the core material of a cylindrical waveguide operating in the THz regime. Due to its strong THz response and temperature-dependent electronic properties, InSb provides an effective and practically feasible approach for enhancing plasmonic confinement. The effects of temperature variation, along with the influence of core and cladding parameters, on the propagation constant (β), normalized phase velocity (vₚ/c), and effective mode index (neff) are systematically analyzed. Numerical results are presented for dispersion characteristics, propagation bands, attenuation, cut off frequencies, effective mode index, field distributions, and phase velocity in both the insulating (T = 200 K) and metallic (T = 300 K) phases of InSb. Additionally, the impact of waveguide radius and operating temperature on supported plasmonic modes is investigated. The results demonstrate that substantial control over propagation behavior such as plasmonic confinement, propagation band gaps, and optical–acoustic mode hybridization, can be achieved through combined structural engineering and temperature tuning. This reversible tunability enables the realization of temperature-controlled plasmonic waveguides suitable for THz modulators, switches, and sensing devices.