An Eigenanalysis Study of Tunable THz and Photonic Unbounded Structures Employing Finite Element Method

This work aims at the establishment of a rigorous full-wave eigenmode analysis technique based on a finite element scheme for the study of terahertz (THz) or photonic/optical unbounded structures. This numerical tool follows the last decades' trend to migrate the technological knowledge from microwave to THz and photonic regimes. The performed eigenanalysis offers an insightful view of the studied structures, revealing their characteristics. For the truncation of the infinite solution domain, the first kind absorbing boundary conditions are employed, while the involved spurious modes are eliminated with the incorporation of a tree-cotree splitting formulation. The study focuses on tunable microring resonators supporting leaky-radiating wave propagation and bounded-resonating whispering gallery modes. Tunability is achieved by integrating an electro-optical layer and in turn through the enforcement of an external applied DC electric field. An innovative approach constitutes the numerical determination of the altered dielectric permittivity as a piecewise constant distribution rather than a constant mean value.