Page 345 - Optical Communications Essentials

Source: Optical Communications Essentials

Chapter
20

Manufacturing Issues

A key issue in the successful widespread application of any emerging technol-
ogy is the implementation of cost-efficient component production. Whereas it is
acceptable to use highly expensive custom-made devices for proving that the
technology works, the cost of components must be reduced significantly when
bringing systems into the field. This is especially challenging in optical commu-
nications where new concepts have been appearing rapidly and standards are
not fully mature in many areas. Ways of achieving this include adapting semi-
conductor manufacturing techniques, setting up automation processes, and
devising reliable optoelectronic packaging methods.
This chapter looks at a few of the many issues associated with optical fiber and
component production. First, Sec. 20.1 describes methods for producing optical
fibers. Next, Sec. 20.2 discusses some component design issues, such as integra-
tion of various functions on planar lightwave circuits and athermal package
designs. An important step in manufacturing is the connector and component
polishing process, which is critical for high light coupling efficiency and low optic-
al return loss. Section 20.3 describes some factory automation equipment to
achieve this. Finally, Sec. 20.4 addresses various component packaging issues
such as package designs, bonding of metallized fibers, and hermetic sealing.

20.1. Fiber Fabrication
Modern optical fibers are made of highly pure silica (SiO 2 ) to which certain
impurities, such as germanium or boron, have been added to induce slight
changes in the value of the refractive index. These fibers are produced princi-
pally by what is called a vapor-phase oxidation process. In this method, highly
pure vapors of metal halides (e.g., SiCl 4 and GeCl 4 ) react with oxygen in a high-
temperature environment to form a white powder of SiO 2 particles called soot.
These particles then are collected on the surface of a bulk glass by one of three
different commonly used processes. During or immediately after the collection
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