These days, Free Space Optics (FSO) has become a prominent mechanism due to its economic nature, broad-bandwidth access technique. The effects of unpredictable weather are difficult to deal. In order to draft the most effective system, Single beam and multiple beam FSO systems are developed which can tackle the atmospheric weather condition's effects on signal. In this dissertation, a practical review on communication channels (FSO) is presented. These channels are used in WDM. It was obtained

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... hat the traditional Wavelength Division Multiplexing (WDM) based FSO system utilized the NRZ encoding method which was less efficient and it was suitable for communication channel which supports 16 transmitters and receivers only. This work is organized to achieve an objective to perform some enhancements in traditional WDM system by replacing NRZ encoding scheme with MDRZ encoding and also the channel size is increased to the32.