Abstract
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.
Highlights
Microwave Photonics offers exciting prospects for the realization of future wireless systems for 5G and beyond, operating up to mm-wave and THz carrier frequencies
The situation is even worse in the case of an eigenanalysis, where a larger solution domain leads to more spurious solutions, preventing convergence to a solution
In order to overcome them, a rigorous eigenanalysis electromagnetic simulator based on a finite element scheme is described in this paper, aiming to reveal the electromagnetic characteristics and provide an insightful view of the studied structures
Summary
Microwave Photonics offers exciting prospects for the realization of future wireless systems for 5G and beyond, operating up to mm-wave and THz carrier frequencies. The air interfaces of the RF front-ends in such systems will have to operate in an agile manner to some tens of GHz for cognitive radio applications In this respect, the large bandwidth of optical fiber and the ability to modulate light to several tens of GHz and detect it, as well as the capability of generating THz signals photonically, is of great interest. Even though Maxwell’s equations remain valid at these higher frequencies [7], [12], the extension of microwave simulators to the THz and photonic domains is not straightforward. The main difficulty stems from the operating frequency being three to five orders of magnitude higher than those in microwave structures, in conjunction with the domain discretization in a fraction of the wavelength (at least λ/10, where λ is in the sub-micrometer range).
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