Page 347 - Optical Communications Essentials
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Manufacturing Issues
Manufacturing Issues 337
Burner moves back and forth
Burner
Burner
O 2 + metal halide vapors
Glass particles
Rotation Soot preform Bait rod (mandrel)
Figure 20.2. Illustration of the outside vapor-phase oxidation
(OVPO) process.
Figure 20.3. Illustration of the
vapor-phase axial deposition (VAD)
method.
When the deposition process is complete, the mandrel is removed and the
porous tube is vitrified to a clear glass preform. The central hole in the tube pre-
form collapses during the fiber drawing process.
20.1.2. Vapor-phase axial deposition
In the vapor-phase axial deposition (VAD) method, shown in Fig. 20.3, the soot
particles are formed in the same way as in the OVPO process. However, in this
case the particles are deposited on the end of a silica glass rod, which acts as a
seed. A porous glass preform is grown in the axial direction by moving the rod
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