Omnidirectional (omni-) reflector and transmission filter optimized at a wavelength of 1.55 mum 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 eta=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 (d(D)). A six-pair Si/SiO2 1D PC with the structure parameters of eta=4.060, d(H) (Si thickness)=95.3 nm, d(L) (SiO2 thickness)=234.9 nm, and d(D)=2.336.d(H) could act as a 1.55 mum-transmission filter for normal incidence light. (C) 2002 American Institute of Physics. References: 15
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