Fiber-optic communication systems require a light source to generate the signal that the fiber transmits. LEDs are used in short-distance, low-speed systems due to their broader spectral width and lower cost, while laser diodes are preferred for long-distance, high-speed transmission because. The light from the transmitter is coupled into the fiber with a connector and is transmitted through the fiber optic cable plant. The light from the end of the fiber is coupled to a receiver where a detector converts the light into an electrical signal which is then conditioned properly for use by. The four main types of optical sources are LEDs, Fabry-Perot (FP) lasers, Distributed Feedback (DFB) lasers, and Vertical Cavity Surface-Emitting Lasers (VCSELs). LEDs are tiny semiconductor devices. The basic building blocks of an optical-fibre link are the light source, the fibre and the detector (Figure 1). This isn't an arbitrary choice; it's a calculated engineering decision driven by the physics of silica glass.
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