The third wireless technology we ll cover in this chapter is optical, which marries optical spectrum technology with wireless transmissions.

An optical wireless system basically is defined as any system that uses modulated light to transmit information in open space or air using a high-powered beam in the optical spectrum. It is also referred to as free space optics (FSO), open air photonics, or infrared broadband. FSO systems use low-powered infrared lasers and a series of lenses and mirrors (known as a telescope) to direct and focus different wavelengths of light towards an optical receiver/telescope. FSO is a line-of-sight technology and the only condition affecting its performance besides obstruction is fog, and to a lesser degree, rain. This is due to the visibility requirements of the technology. Fog presents a larger problem than rain because the small dense water particles deflect the light waves much more than rain does. The technology communicates bi-directionally (that is, it is full duplex) and does not require spectrum licensing. Figure 4.15 represents a common FSO implementation between buildings within a close proximity, which is generally within 1000 feet, depending on visibility conditions and reliability requirements. Some FSO vendors claim data rates in the 10Mbps to 155Mbps range with a maximum distance of 3.75 kilometers, as well as systems in the 1.25 Gbps data rate range with a maximum distance of 350 meters. The optical sector is growing in capability at a rapid rate, so expect these data rates and...