**2. Fundamental of free space optical 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 Lone of Sight (LOS) communication between the transmitter and receiver as shown in the Fig. (1)[1].

The atmosphere has effects on the laser beam passing through it, so the quality of data received is affected. To reduce this effect, the fundamental system components must be designed to adopt with the weather conditions. This design is mostly related to transmitter and receiver components. In the following subsection, we will tackle discuss the components and the basic system of FSO.

2. Studying the performance of FSO system at wavelengths 780 nm, 850 nm and 1550 nm, beam divergence angle, transmitter and receiver diameter apertures and transmission

The scope of this chapter focuses on studying and analyzing of FSO propagation under weather conditions in Yemen environment for outdoor system. The atmospheric effects divided into two kinds: atmospheric attenuation and atmospheric turbulence. Atmospheric attenuation due to Mie scattering is related to the haze and it is a function of the visibility, and attenuation due to rainfall independent on wavelength. The atmospheric turbulence is

There are three factors which enable us to test the FSO performance as: design, uncontrollable and performance. Design factors are relating to FSO design such as light power, wavelength, receiver and transmitter aperture diameter, link range and detector sensitivity. Uncontrollable elements such as rainfall elements include rainfall rate and raindrop radius, haze element include visibility and turbulence element include refractive index structure. Performance of system was tested during the rainy days and hazy days which can be calculated from the effect of scattering coefficient, atmospheric attenuation and total attenuation. However, the system performance in the clear days can be calculated from

The remainder of this chapter is organized as follow: Discuses briefly the background of FSO. The concept of and the several stages of FSO transceiver are explained briefly. Illustrate the losses of FSO system due to atmosphere channel and geometric losses. Defining the aerosols and visibility and how they effect on FSO system were introduced. Beer's law which describes attenuation of atmospheric channel due to absorption and scattering coefficient was introduced. The atmospheric attenuation types are explained. Stroke's law which describes scattering coefficient due to rainfall was introduced. Geometrical loss and total attenuation are discussed. Represent the analytical study of Yemeni environment. Scattering coefficient and attenuation in hazy days at average and low visibility at three wavelengths (780 nm, 850 nm and 1550 nm) were introduced. The atmospheric attenuation at the lowest visibility conditions was plotted with the link range. Scattering coefficient and atmospheric attenuation in rainy days were plotted once versus rainfall rate and once again versus raindrop radius. Scattering coefficient and atmospheric attenuation to haze in Sana'a, Aden and Taiz cities were calculated. The geometric loss for two commonly used designs of transceivers was evaluated.

FSO is a technique used to convey data carried by a laser beam through the atmosphere. While FSO offers a broadband service, it requires Lone of Sight (LOS) communication

The atmosphere has effects on the laser beam passing through it, so the quality of data received is affected. To reduce this effect, the fundamental system components must be designed to adopt with the weather conditions. This design is mostly related to transmitter and receiver components. In the following subsection, we will tackle discuss the

The conclusion is done based on the overall findings of this work.

**2. Fundamental of free space optical communication** 

between the transmitter and receiver as shown in the Fig. (1)[1].

components and the basic system of FSO.

range.

the effect of variance.

due to variance of refractive index structure.

Fig. 1. Schematic showing FSO Transmitter and Receiver LOS.
