Specialty Optical Fibers Handbook

is not desired during the PCVD deposition process, as this can result in glass

defects (bubbles, etc.). Furthermore, the reaction and deposition of both GeO

2

and SiO

2

is much more efficient than in MCVD, approaching 100%. However,

this leads to a high level of water retention in the glass, which results in higher

optical losses. Typical methods to address the hydroxyl issues include the use of

fluorine-based dopants (C

2

F

6

,SF

6

, etc.), along with the reactants during the

PCVD step [37].

Another advantage—especially for multimode preforms—is that because the

plasma involves no latent heat, it can be traversed very rapidly to produce

hundreds of layers. The resulting deposit, thus, has a very smooth and precise

index profile essential for minimizing intermodal ...