OVERVIEW

Light emitters are a key element in any fiber optic system. These components convert the electrical signal into a corresponding light signal that can be injected into the fiber. The light emitter is important because it is often one of the most costly elements in the system, and its characteristics often strongly influence the final performance limits of a given fiber optic link.

There are two types of light emitters in widespread use in modern fiber optic systems: laser diodes (LD's) and light-emitting diodes (LED's). Laser diodes may be Fabry-Perot (the name refers to the mirrored surfaces on the ends), distributed feedback (DFB), or more recently vertical cavity surface-emitting laser (VCSEL) types while LED's are usually specified as surface-emitters or edge-emitters. These different classifications will be discussed in detail later in the chapter. All light emitters are complex semiconductors that convert an electrical current into light. The conversion process is fairly efficient in that it creates very little heat compared to the heat generated by incandescent lights. LED's and laser diodes are of interest for fiber optics because of five inherent characteristics:

• Overall small size

• High radiance (i.e., They emit a lot of light in a small area.)

• Small emitting area (The area is comparable to the dimensions of optical fiber cores.)

• Very long life (i.e. They offer high reliability.)

• Can be modulated (turned on and off) at high speeds

LED's and laser diodes are found in a variety of consumer electronics products. LED's are used as visible indicators...