Optical characteristics of a circular photonic crystal (CPC) in the frequency range of 0 to 20 GHz were investigated. The sample was made by alumina rods of 2 mm in radius and 300 mm in length. The alumina rods were arrayed in the form of concentric circles with 6-fold symmetry. The transmission spectra were calculated at various radical distances. When the radical distance was 8 mm, a photonicgap was obtained around 12 GHz. The experimental results were in good agreement with the calculations. Although the lattice positions were shifted from the ones of the CPC, the same transmission spectrum was obtained in the phase-shifted CPC. Phase-shift is a useful means for eliminating translational symmetries that would often appear in the exterior part of a CPC composed of numerous concentric circles. Isotropic photonicgaps were obtained for both a CPC and the phase-shifted CPC.
The relation between the fictive temperature and concentration of electron-trapped centers in Ge-doped silica glass (Ge: SiO2) associated with fourfold coordinated Ge ion (GEC) and GeE' is examined in this study. The fictive temperature of Ge:SiO2, Tf, is determined by monitoring peak positions of 1970 cm-1 and 1870 cm-1 infrared absorption bands. After ArF-laser beam irradiation, ESR spectra of Ge:SiO2 glasses with changing the fictive temperature between 950 and 1250íC were obtained. The concentration of paramagnetic centers increases with increasing Tf. Supposing two kinds of GEC, Ge(1) and Ge(2) depending on the number of nearest-neighbor Ge ions, and GeE' center, ESR spectrum was simulated to estimate the concentration of each paramagnetic center. It has been found that the concentrations of Ge(1) and GeE' increase with increasing Tf, while that of Ge(2) is almost constant.
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