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.

The transfer matrix approach is used to study the optical characteristics of thermal radiation in a one-dimensional photonic crystal (1DPC) with metamaterial. In this method, every layer within the multilayer structure is associated with its specific transfer matrix. Subsequently, it links the incident beam to the next layer from the previous layer. The proposed structure is composed of three types of materials, namely InSb, ZrO₂, and Teflon, and one type of epsilon-negative (ENG) metamaterial and is organized in accordance with the laws of sequencing. The semiconductor InSb has the capability to adjust bandgaps by utilizing its thermally responsive permittivity, allowing for tunability with temperature changes, while the metamaterial modifies the bandgaps according to its negative permittivity. Using quasi-periodic shows that, in contrast to employing absolute periodic arrangements, it produces more diverse results in modifying the structure’s band-gaps. Using a new sequence arrangement mixed-quasi-periodic (MQP) structure, which is a combination of two quasi periodic structures, provides more freedom of action for modifying the properties of the medium than periodic arrangements do. The ability to control thermal radiation is crucial in a range of optical applications since it is frequently unpolarized and incoherent in both space and time. These configurations allow for the suppression and emission of thermal radiation in a certain frequency range due to their fundamental nature as photonic band-gaps (PBGs). So, we are able to control the thermal radiation by changing the structure arrangement. Here, the We use an indirect method based on the second Kirchoff law for thermal radiation to investigate the emittance of black bodies based on a well-known transfer matrix technique. We can measure the transmission and reflection coefficients with associated transmittance and reflectance, T and R, respectively. Here, the effects of several parameters, including the input beam’s angle, polarization, and period on tailoring the thermal radiation spectrum of the proposed structure, are studied. The results show that in some frequency bands, thermal radiation exceeded the black body limit. There were also good results in terms of complete stop bands for both TE and TM polarization at different incident angles and frequencies. This study produces encouraging results for the creation of Terahertz (THz) filters and selective thermal emitters. The tunability of our media is a crucial factor that influences the efficiency and function of our desired photonic outcome. Therefore, exploiting MQP sequences or arrangements is a promising strategy, as it allows us to rearrange our media more flexibly than quasi-periodic sequences and thus achieve our optimal result.