Free Space optics has been emerged as leading communication technology in recent years.. It is an optical communication technology which uses light to propagate the data wirelessly in Free Space. The word "Free Space" exactly means environment, outer space or vacuum. This technology provides high data rate and can handle large amount of information. It uses the Line Of Sight (LOS) path for transmission. In this paper, discussion about various technologies, different gain and loss occurred during the transmission path. Moreover challenges based on modern and real life applications are then described and also some alternatives have been suggested in order to improve them in future.

Inter-satellite communication is a free-space optical technology which is used to establish communication between satellites in space. This work is focused on the transmission of 10 Gbps data over 10,000 km inter-satellite communication link by incorporating orthogonal frequency division multiplexing scheme. The performance of proposed system is evaluated in terms of signal-to-noise ratio, total received power, radio-frequency spectrum and constellation diagrams. KeywordsInter-satellite communication (Is-OWC), Orthogonal frequency division multiplexing (OFDM), Differential phase shift key (DPSK).

Communication has become a utility like electricity and water. With the advancement in the technology, needs of users, services, demands have been increasing day by day. So it requires high bandwidth, higher data rates, and better reliability. So for these reasons optical fibers have been used. Optical communication has advanced from long strands to wireless technology. This has resulted to use the optical communication in space. Inter-Satellite communication is one among them. Large numbers of satellites are revolving around the Earth. So a network is required which can hand-off data from one satellite to another and afterwards to the ground station. Inter-Satellite communication is one of the remarkable technologies. In this paper, inter-satellite optical wireless communication system (Is-OWC) is analyzed using different modulation techniques and formats. Various specifications such as bit error rate, Q factor, and input power are studied.