Specifications

4-9

TOKEN RING NETWORK CABLING

Fiber Optic Construction

A ﬁber optic cable is composed of a pair of strands, one used for transmit

and the other for receive. Each strand is composed of a core of glass or

plastic enveloped in a layer of glass or plastic called cladding. The

cladding is further enveloped in multiple layers of plastic or other

materials that provide protection and reinforcement to the core and the

cladding. The refractive index of the cladding is lower than the refractive

index for the core, as indicated in Figure 4-7.

A ﬁber optic cable is classiﬁed by the comparative size of its core to its

cladding. For example, 50/125 cable has a core diameter of 50 microns and

a cladding diameter of 125 microns; 62.5/125 cable has a core diameter of

62.5 microns and a cladding diameter of 125 microns; 100/140 cable has a

core diameter of 100 microns and a cladding diameter of 140 microns.

Figure 4-7. Fiber Optic Cable

Fiber Optic Types

There are two types of ﬁber optic cable:

• Single-mode

• Multimode

Single-Mode

Single-mode ﬁber optic cable is typically used for long-distance

communication. It is characterized by a very small core diameter and a

very wide bandwidth. The long-distance capacity is a function of the

narrowness of the core. Because the narrow core is designed to

accommodate only a single mode, or ray, of concentrated light,

attentuation of the optical signal is minimal, and the signal arrives sharp

and clear at the receiving end.

Glass Cladding Glass Core

5 - 100 microns

125 - 140 microns