Optical attenuation in pure and doped fused silica in the ir wavelength region

Infrared absorption spectra of GeO2-, P2O5-, and B2O3-doped fused silica and nondoped fused silica have been obtained in the 3–25-μm wavelength region. It is shown that the intrinsic infrared absorption loss of doped silica fiber increases by several orders of magnitude beyond 1.8–2.0 μm because of the overtone and combination tone vibrations of the SiO4 tetrahedron. The loss spectrum is affected by dopants, especially in the case of B2O3. The lower limit of attenuation in optical fiber is estimated to be about 0.2 dB/km at 1.6 μm.