Design And Properties Of Filters Based On One-Dimensional Photonic Crystals

Photonic crystal (PC) is characterized by its photonic bandgap (PBG), where the transport of light or electromagnetic with the frequency falling in the gap is strictly forbidden. The properties of PCs are determined by the photonic band structures (PBS), which rely on the constituent materials (refraction indices) and their spatial structures. PCs are usually composed of two dielectric materials with different refractive indices. Once the constituent materials are chosen, the properties of the PCs are controlled by structure design. Based on the experimentally measured optical constants of the thin films, this work studies the PBS of various structures, and focuses on the relationship between defect structure and the properties of filters based on one-dimensional photonic crystal.Firstly, TiO2 and SiO2 thin films were prepared on glass substrates by RF magnetron sputtering, respectively. The optical constants were determined by the ellipsometry with inversion calculation of the two ellipsometric parameters. The dispersion relationship between thin-film optical constants and wavelength was determined. It was found the inversion calculation of the transmission spectra matched the experimental results, which further verified the simulated results. Those results could provide accurate material optical properties for design of filter structure.Secondly, a defect structure (HL) mL (HL)n of one-dimensional photonic crystal was designed, using TiO2 and Al2O3 as layered constituents. In order to study and optimize the structures of filters, the transfer matrix method was adopted to simulate the optical properties. The results showed that:1) there is a very narrow central transmission window within the photonic band gap; 2) the window position and its width changes while the repetition number of structures aside the defect-layer, the thickness of the defect-layer and the incidence angle are adjusted; 3) when m=19, n=20 and the optical thickness of defect-layer is 387.5nm, the window width can be smaller than O.OOlnm with the window position in 1550nm and the window transmittance almost reaches to 100%.Thirdly, the hetero-structure of (HL)m (κHκL)m was designed again, using the TiO2 and Al2O3 layers as components. The influence of repetition number, thickness, incidence angle of the one-dimensional photonic crystal (HL) m on the photonic band gap position, p-and s-polarized light were investigated. At oblique incidence, a filter allowing p-polarized light to pass, but blocking s-polarized light was designed within the photonic band gap by overlaying the p-polarized energy bands. The structure of these filters contains small number of coatings, and has quasi-rectangular characteristics, which makes them economic and practically applicable.