Si-based omnidirectional reflector and transmission filter optimized at a wavelength of 1.55 μm

Omnidirectional (omni-) reflector and transmission filter optimized at a wavelength of 1.55 μm have been realized using Si/SiO2 one-dimensional photonic crystals (1D PCs). Photonic band structures in the PCs with and without a defect layer have been also analyzed. The 1D PCs fabricated have very large omnidirectional photonic band gaps (omni-PBGs), and their measured reflectance spectra are in very good agreement with the calculated results. The omni-PBG in a six-pair Si/SiO2 1D PC (no defect layer, a filling factor η=0.406) exists in a normalized frequency range of 0.223–0.297. Introducing a defect layer generates a defect state in the PBG, and it behaves like electronic impurity levels in the gap with a change in thickness of the defect layer (dD). A six-pair Si/SiO2 1D PC with the structure parameters of η=4.060, dH (Si thickness)=95.3 nm, dL (SiO2 thickness)=234.9 nm, and dD=2.336⋅dH could act as a 1.55 μm-transmission filter for normal incidence light.