The effects of germanium doping on the 30-, 1100-, and 1200-cm-1 bands of Si-O-Si were investigated. The Si-O-Si centers, perturbed by the nearby Ge atoms, caused absorptions at largely shifted positions in each band. The oscillator strengths of the 1200-cm-1 absorptions and the peak separations between the 1100-cm-1 absorptions were largely reduced from the corresponding unperturbed ones. Our previously obtained model consistently explains both of the peak energies and the oscillator strengths of these absorptions. The oscillator-strength and peak-separation reduction are both ascribed to the weakening of the anharmonic coupling between the 30- and the 1100-cm-1 impurity modes which causes the 1200-cm-1 band to be their combination band.