Page 310 - Maxwell House

290 Chapter 6

6.3 FIBER OPTIC LINES

6.3.1 Introduction
Fiber optic lines belong to the family of open lines. Nevertheless, we decided to put them in a
separate section not only because of their popularity. They are part of the fiber optics branch of
physics thereby using the different physical principles to guide EM wave energy. The
Encyclopedia Britannica defines the fiber optics as “…the science of transmitting data, voice,
and images by the passage of light through thin, transparent fibers. In telecommunications, fiber
optic technology has virtually replaced copper wire in long-distance telephone lines, and it is
used to link computers within local area networks.” British scientists Charles K. Kao and
George A. Hockham propose to use ultra-pure glass fibers for long-haul and ultra-fast
communication. The Nobel Prize was awarded to Kao for his theoretical work in 2009.
Although the long-haul optical communications supported by a set of bonfires, torches or
searchlights have a long history, but this discovery enormously revolutionized the information
technology and our everyday life. For the first time in the history of our civilization, we gain
the ability not only to send and receive the practically unlimited amount of data anywhere in
the world but do it incredibly fast. The first transatlantic fiber system was deployed in 1988.
Record-low attenuation of 0.1460 dB/km was reported in 2015. It means that the broadband
optical signals can travel 5890 km or 3,660 miles before they need to be amplified and
regenerated. The main disadvantage of fiber optics is that they are more fragile than wire and
are difficult to splice.
The schematic drawing of primary fiber is shown in Figure 6.3.1a and consists of the ultra-pure
high-refractive silica (SiO ) core, the same ultra-pure but lower-refractive silica cladding, and
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one- or multilayer polymer coating or protective jacket. The core diameter ranges from 10 to
600 µm; the cladding thickness is from 125 to 600 µm while the jacket thickness is around 250
- 1040 µm depending on applications. Note that the best performance the fiber lines provide at
a light wavelength from 1500 nm to 1600 nm.

6.3.2 Fiber Optic Line Family

Figure 6.3.1 Optic fiber illustration

Figure 6.3.1 depicts three types of fiber in use:

b) Multimode step-index fiber with core/cladding diameter is 100/140 µm or 62.5/125 µm.
c) Multimode graded-index fiber with core/cladding diameter is 50/125 µm.
d) Single mode step-index fiber with core/cladding diameter is 9/125 µm.