Page 193 - Introduction to Information Optics

178 3. Communication with Optics

Soot preform

I Matenais
I Gasos
Fig. 3.7. Fiber preform OVD fabrication method.

The typical diameter of the coated fiber is about 250 /mi, although it can be as
large as 900 /im when multiple coatings are used.
The preform is made using several vapor deposition methods. Typical
methods are the outer vapor deposition (OVD) method, as shown in Fig. 3.7,
the modified chemical vapor deposition (MCVD) method, and the vapor-phase
axial deposition (VAD) method. In the OVD method, submicron-sized par-
ticles generated by a flame are deposited on a rotating rod (mandrel). The
mandrel is removed from a soot preform before a sintering process and the soot
preform is dehydrated. The removal of OH (the ion with a combination of
oxygen and hydrogen) is important to lower transmission loss. In the sintering
process, a soot preform changes to a glass preform,

3.2.3.3. Transversal Patterns for Single Mode Fiber

As discussed in the previous sections, the electric field, E z, has a distribution
described by Eq. (3.25). Since the single mode fiber is the most widely used
case, we focus our discussion on the single mode fiber field. This corresponds to
the fundamental mode; i.e., m = 0. Substituting m = 0 into Eq. (3.25), the
normalized transversal distribution of £„ is

J O(KO) '
(3,35)

To make the calculation easier, a simplified empirical formular was developed
for the case of 1.2 < V < 2.4. In this case, the normalized electric field E.(p)