Modern Optical Networks - Optical Signal Processing by Silicon Photonics - page 24

Copper
wire
braiding

General
copper core

Radio-frequency
electric signal

Insulation

Outer sheath

Coaxial Cable

Light
si gnal

Optical fiber

Core

Core
Light
si gnal

Light
si gnal

Core

Protective
Layer

Outer sheath

Optical- fiber cable

Fig. 3.4 Optical fiber cable

The function of the optical cable may be summarized into four main areas;

• Fiber protection against iber damage and breakage during installation through-
out the life of the fiber.
• Cable strength that may be enhanced by incorporating an appropriate strength
member and by providing the cable a thoroughly designed thick outer sheath.
• Stability in the context of the iber transmission characteristics.
• Identiication and joining of the ibers at joints, within the cable. That is very
significant for cables having large number of optical fibers.

Standard fibers for communication purposes are step-index or graded-index fibers
manufactured nowadays. Graded-index fibers have a core with decreasing refrac-
tive index from the center to the core boundary (Fig. 3.5 ).
These fibers are usually referred to transmission fibers. To increase the trans-
mission capacity and the wavelength range where these fibers are able to be used,
dispersion compensating and active fibers were introduced. Considering the