Why optical communication links are needed for future satellite constellations

Constellations of satellites in LEO or GSO orbits provide solutions to the communication requirements of future global communication systems. These may employ tens to hundreds of satellites connected to one another using high data rate inter-satellite links (ISL). The options for the implementation of the ISL are to use either microwave, millimetric or optical frequencies. This paper reviews the emerging market for ISLs driven by these future satellite constellations. Comparison with the microwave and millimetric alternatives shows optical technology to be the most attractive solution to achieving the satellite-to-satellite connectivity. A review of how optical ISL terminals operate is given highlighting the critical technologies which are required. Finally, the expected performances for two classes of optical terminals designed for GSO and LEO constellations are presented