Fiber Optics - Cabletron Systems 100BASE-FX Cabling Manual

Ethernet Media
Category 5 UTP consists of 2 or more pairs of 22 or 24 AWG wire. Category 5 cable
is constructed and insulated such that the maximum attenuation of a 10 MHz
signal in a cable run at the control temperature of 20 C is 65 dB/km. A cable that
has a maximum attenuation higher than 65 dB/km does not meet the Category 5
requirements.

Fiber Optics

Fiber optic cable is a high performance media constructed of glass or plastic that
uses pulses of light as a transmission method. Because fiber optics do not utilize
electrical charges to pass data, they are free of interference due to proximity to
electrical fields. This, combined with the extremely low rate of signal degradation
and dB loss makes fiber optics able to traverse extremely long distances. The
actual maximums are dependent upon the architecture being used, but distances
upwards of 2 kilometers (1.2 miles) are not uncommon.
Glass optical fiber is made up of a glass strand, the core, that allows for the easy
transmission of light, the cladding, a less transmissive glass layer around the core
that helps keep the light within the core, and a plastic buffer that protects the
cable.
There are two basic types of fiber optics, multimode and single mode. The names
come from the types of light used in the transmission process. Multimode fiber
uses inexpensive Light Emitting Diodes (LEDs) that produce light of a single
color. Due to the nature of the LED, the light produced is made up of a number of
differing wavelengths of light, fired outward from the center of the LED. Not all
the rays of light enter the fiber, and those that do often do so at an angle, which
reduces the amount of distance the signal can effectively cover. Single mode fiber
optics use lasers to achieve greater maximum distances. Since light from a laser is
all of the same wavelength, and travels in a coherent ray, the resulting signal
tends to be much clearer at reception than an LED signal under the same
circumstances.
4-14
Cladding
Transmissive Core
Figure 4-7. Fiber Optic Cable Construction (multimode)
PVC Buffer (Jacketing)
1845n07
Cabling Types