BASIC STRUCTURE OF AN OPTICAL
The basic structure of an optical fiber consists of
three parts: the core, the cladding, and the coating or
buffer. The basic structure of an optical fiber is shown
in figure 6-6. The core is a cylindrical rod of dielectric
material. Dielectric material conducts no electricity.
Light propagates mainly along the core of the fiber. The
core is generally made of glass. The core is surrounded
by a layer of material called the cladding. Even though
light will propagate along the fiber core without the
layer of cladding material, the cladding does perform
some necessary functions.
The cladding layer is made of a dielectric material.
Cladding is generally made of glass or plastic and
performs the following functions:
Reduces loss of light from the core into the
Reduces scattering loss at the surface of the core
Protects the fiber from absorbing surface
Adds mechanical strength
For extra protection, the cladding is enclosed in an
additional layer called the coating or buffer.
The coating or buffer is a layer of material used to
protect an optical fiber from physical damage. The
material used for a buffer is a type of plastic. The buffer
is elastic in nature and prevents abrasions. Also, the
buffer prevents the optical fiber from scattering losses
caused by microbends. Microbends occur when an
optical fiber is placed on a rough and distorted surface.
Microbends are discussed later in this chapter.
Optical fibers have small cross-sectional areas.
Without protection, optical fibers are fragile and can be
broken. The optical cable structure protects optical
fibers from environmental damage. Cable structure
includes buffers, strength members, and jackets. Many
factors influence the design of fiber-optic cables. The
cable design relates to the intended application of the
cable. Properly designed optical cables perform the
Protect optical fibers from damage and breakage
during installation and over the lifetime of the fiber.
Provide stable fiber transmission characteristics
compared with uncabled fibers. Stable transmission
includes stable operationin extreme climate conditions.
Maintain the physical integrity of the optical
fiber by reducing the mechanical stresses placed on the
fiber during installation and use. Static fatigue caused
by tension, torsion, compression, and bending can
reduce the lifetime of an optical fiber.
Coatings and buffers protect the optical fiber from
breakage and loss caused by microbends. During the
fiber drawing process, the addition of a primary coating
protects the bare glass from abrasions and other surface
contaminants. For additional protection, manufacturers
add a layer of buffer material. The buffer material
provides additional mechanical protection for the fiber
and helps preserve the inherent strength of the fiber.
Manufacturers use a variety of techniques to
buffer optical fibers. The types of fiber buffers
include tight-buffered, loose-tube, and gel-filled loose-
Figure 6-6.Basic structure of an optical fiber.