Abstract

Sol-gel dipcoating^1,2 is used to apply thin doped SiO₂ layers inside modified chemical vapor deposition (MCVD) preforms for the fabrication of rare-earth-doped fiber amplifiers. In this new process, a MCVD substrate tube is filled with a doped alkoxide sol and is drained at a constant rate, as shown in Fig. 1. Upon collapse, the thin glass layer (≈0.5 µm) derived from gel acts as a negligibly thin diffusion source of dopants. A typical MCVD cladding may be dipcoated with a sol containing both rare-earth ions and index-alternating dopants, such as germanium or aluminum. The entire core is thus derived from sol. Alternatively, a rare-earth-doped coating can be applied over a MCVD core, centering the erbium within the core after preform collapse.

© 1991 Optical Society of America