The Free Space Optics (FSO) uses line-of-sight path beams of light for the optical communication between two points that can send and receive video, voice, and data information through the atmosphere. Free Space Optics links (FSOL) can support communications with high data rate in large unlicensed bandwidths, but the rate of reliability and data are influenced severely by the atmospheric phenomena. This thesis presents a survey of Free Space optical technologies, asserting their deployment in communication systems, furthermore, it deals with the study of the design and characteristics of an experimental indoor FSOL, the optimum design for such systems needs a model that is reliable for atmospheric channels for long-term monitoring of atmospheric turbulence and attenuation in different wavelengths of 526nm, 650nm, and 850nm.
The measurement of atmospheric visibility and the optical path attenuation are based on a theoretical model of an optical communication link propagation in free space. A visibility of (low, medium and High), has been proposed to monitor their effects on system performance evaluation parameters. In theory, it has been found that the power of receiver signal, signal to noise ratio, link margin, and data rate are decreased as a path link increased, whilst it increased as visibility increased through different conditions of attenuation.
The models that available for the relationship between attenuation and visibility due to rain, dust, smoke and fog are evaluated using measured data. This work investigated a theoretical analysis of fog effect on the performance of FSO communication by using modulation techniques of non-return-to-zero - on of keying and return-to-zero in the transmitter, and PIN receiver according to a mathematical model for fog attenuation.
The outdoor FSO communication system mode (Light Pointe Flight Strata 155E 1.25Gbps/850nm Laser Link), are also presented in this thesis. Both attenuation and visibility are measured on a 100m long experimental FSOL operating at (850nm) wavelength that because of its performance is more suitable for an FSO communication system. It also identified the meteorological conditions which that caused particular attenuation events. Available models of the relation between optical attenuation and atmospheric visibility are compared with the measured data. The work has shown that the classical models which widely used in the FSO community are still belittle the optical attenuation at low and medium visibility conditions.