Omnidirectional photonic bandgaps are a new special type of one-dimensional quasi-photonic crystals that contains semiconductor and dielectric material layers and are investigated here in the Terahertz wave range. The proposed medium is constructed with a special type of layer arrangement, which uses both the Fibonacci sequence as a quasi-periodic sequence and the absolute periodic sequence in a period. As the Terahertz bandgaps of the transmittance spectrum are essential in some devices, the tuning and manipulation of these bandgaps has been of great interest in recent years. One of the best methods of manipulating these bandgaps to reach the desired outcome is by changing their arrangement using different types of quasi-periodic sequences in the structure. The beneficial results of applying these sequences have been clearly observed. So, we propose another new type of arrangement here in order to completely satisfy the changing methods of the photonic crystal structures. According to the results of the current investigation, it has been demonstrated that the proposed arrangement could be used to achieve a wide variety of desirable states. The semiconductor could make the bandgaps tunable via temperature changes through its thermally tunable permittivity. These types of media, which can operate as tunable Terahertz filters and mirrors, offer many promising omnidirectional Terahertz components and devices.

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Although there has been a focus on THz lters so far, there is a signifcant defciency in advancing low-temperature THz lters. According to the needs, we proposed a tunable THz lter that selectively permits the desired incident frequencies to be propagated in relevance with our purpose. The presence of a low-temperature nano superconductor and an undoped semiconductor layers in the proposed structure resulted in a multi-channel THz lter, which could be highly tuned with several parameters such as lattice constants, applied temperature, etc. The achieved transmittance spectra revealed that the emerged transmittance couples and stacks follow exact regulations. Furthermore, the structure exhibited omnidirectional band-gaps for both TE and TM polarized waves. Moreover, the use of a central defect layer gave some transmittance defect modes in the forbidden areas. This structure could be used in some THz devices such as switches, optimized sensors as well as in space industry and telecommunications.

This study investigates the propagating of electromagnetic waves through a one-dimensional quasi-photonic crystal with the transfer matrix method. Our proposed structure consists of two types of double negative metamaterials, organized according to the Thue-Morse sequence law. The results show that changing the structure via quasi-periodic arrangements makes the outcome more varied than applying the absolute periodic arrangement. Given that, our desirable results of interest are more conveniently achieved. The structure completely stops-both s and p polarization at the lower frequencies, for all incidence angles. It also partially stops s and p polarization, at higher frequencies. Moreover, the achieved transmittance spectrum contains several omnidirectional band-gaps, which remain invariant with changes in the incidence angle. The oscillation of the transmittance values also becomes more intense at higher orders of the period number. This study could pave the way for optimizing of photonic crystal circuits, splitters, switches, etc.

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