ABSTRACT
In optical wireless communications, the most commonly used light sources are the incoherent light-emitting diodes (LEDs) and the coherent laser diodes (LDs), which are used as the optical transmitters. LEDs are used for short-range, low- to medium-data-rate indoor applications, whereas LDs, which are monochromatic, coherent, high-power, and directional, are mostly employed for high-speed outdoor applications. As for optical receivers in OWC, both PIN photodiodes and avalanche photodiodes (APD) can be used, though the latter are costly but offer higher sensitivity and bandwidth compared to the PIN PDs. This chapter discusses the types of light sources, their structures, and their optical characteristics. The concept of optical direct detection and coherent detection are also covered in this chapter. The chapter also covers a range of noise sources that are encountered in OWC systems as well as the statistics of the optical detection process.
