Design of a Novel Visible Light Bandstop Photonic Crystal Filter Based on Mesoporous SiO₂ Thin Films

Abstract Currently, within the spectral ranges of visible light, ultraviolet radiation, and high-energy X-ray photons, the predominant filtering technology employed is the photonic crystal (PC) passband filter. Nevertheless, these filters exhibit notable limitations, such as a relatively restricted filtering frequency range and intricate fabrication processes. In response to the aforementioned challenges, this paper introduced for the first time the concept of a structurally simple and wideband-stopband filter based on mesoporous SiO₂ thin films, thereby offering a novel solution for relevant domains. The transfer matrix method was used to analyze the impact of different filling ratios and lattice constants on the photonic band gap (PBG) properties of mesoporous SiO₂ thin films. The results showed that, under the optimal filling ratio (r/a = 0.06), narrow PBGs and high transmission could be achieved in the violet (437.54 nm), green (510.46 nm), yellow (583.55 nm), and red (656.35 nm) light bands by adjusting the lattice constant. By extending the range of the horizontal axis for analysis, it was observed that the stopband range of the designed filter had substantially broadened, covering wavelengths above 227.9 nm, 264.8 nm, 303.4 nm, and 340.3 nm, respectively. Consequently, a novel filter with wide bandwidth, narrow bandgap, high reflectivity, and a simplified fabrication process was successfully developed. Additionally, in the X-Z and Y-Z planes, the position and properties of the PBG remained largely unchanged when the incident angle is less than 11.5°. This study not only expands the theoretical research scope of PC materials but also opens new possibilities for their practical applications.