Basic Fiber Optic Communication System
Fiber optics is a medium for carrying information from one point to another in the form of light. Unlike the copper form of transmission, fiber optics is not electrical in nature. A basic fiber optic system consists of a transmitting device that converts an electrical signal into a light signal, an optical fiber cable that carries the light, and a receiver that accepts the light signal and converts it back into an electrical signal. The complexity of a fiber optic system can range from very simple (i.e., local area network) to extremely sophisticated and expensive (i.e., long distance telephone or cable television trunking).
For example, the system shown in Figure 8-1 could be built very inexpensively using a visible LED, plastic fiber, a silicon photo detector, and some simple electronic circuitry. The overall cost could be less than $20. On the other hand, a typical system used for long-distance, high-bandwidth telecommunication that employs wavelength-division multiplexing, erbium-doped fiber amplifiers, external modulation using DFB lasers with temperature compensation, fiber Bragg gratings, and high-speed infrared photo detectors could cost tens or even hundreds of thousands of dollars. The basic question is “how much information is to be sent and how far does it have to go?” With this in mind we will examine the various components that make up a fiber optic communication system and the considerations that must be taken into account in the design of such systems.
