FSO is a line-of-sight technology that uses lasers to provide optical bandwidth connections or FSO is an optical communication technique that propagate the light in free space means air, outer space, vacuum, or something similar to wirelessly transmit data for telecommunication and computer networking. Currently, FSO is capable of up to 2.5 Gbps [1] of data, voice and video communications through the air, allowing optical connectivity without requiring fiberoptic cable or securing spectrum licenses. Operate between the 780-1600 nm wavelengths bands and use O/E and E/O converters. FSO requires light, which can be focused by using either light emitting diodes (LEDs) or lasers (light amplification by stimulated emission of radiation). The use of lasers is a simple concept similar to optical transmissions using fiberoptic cables; the only difference is the transmission media. Light travels through air faster than it does through glass, so it is fair to classify FSO as optical communications at the speed of the light. FSO communication is considered as an alternative to radio relay link line-of sight (LOS) communication systems. This chapter is concentrate on ground-to-ground free-space laser communications. FSO components are contain three stages: transmitter to send of optical radiation through the atmosphere obeys the Beer-Lamberts`s law, free space transmission channel where exist the turbulent eddies (cloud, rain, smoke, gases, temperature variations, fog and aerosol) and receiver to process the received signal. Typical links are between 300 m and 5 km, although longer distances can be deployed such as 8-11 km are possible depending

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Free space optical (FSO) communication is one of the most recently developed modes of wireless communication. FSO is a technique used to convey data carried by a laser beam through the atmosphere. While FSO offers a broadband service, it requires a line of sight communication between the transmitter and receiver. The atmosphere has effects on the laser beam passing through it. For instance, the quality of data received is affected by the scattering and atmospheric turbulence. The atmospheric turbulence is caused by both temporary and special random fluctuations of the refractive index along the optical propagation path. Clear air turbulence impairs the performance of the FSO due to the fluctuation in the intensity of the laser beam. By referring to the two criteria, namely bit error rate (BER) and signal to noise ratio (SNR), this work includes analysis of the effect of atmospheric turbulence on FSO systems in Yemen by using an appropriate model.