OPTICAL SATELLITE COMMUNICATION

Optical satellite communication is defined as communication through the light which carries information between satellites or between satellites and the ground.The optical system consists of the light source, transmitting, receiving and capturing subsystems, it can be concluded that communication signals processed by baseband, encryption and modulation will be sent through optical antennas and received by optical receiving antennas. Finally, the optical impulse modulated signals will be detected and demodulated into the signals that carry the messages, realizing full-duplex optical communication. Additionally, optical satellite communication can be divided into satellite-satellite and satellite-ground optical communication, and intersatellite optical communication is categorized into inter-satellite link (ISL) (containing GSO-GSO, LEO-LEO) and inter-orbit link (IOL) (containing GEO-LEO).High orbit GEO satellite has a wide range of coverage, which makes 3 GEO satellites covering the whole Earth possible. Thus, it is stated that the high orbit GEO optical satellite, acting like the relay satellite of the LEO optical satellite, mainly constructs the connection with the ground optical stations, which eventually produces space-earth integration optical communication network.

Super high-speed data transmission is one of the prior requirements of optical satellite communication. As satellite communication possesses long-distance, approximately 40,000 kilometers per single trip, ground and satellite stations have to produce lasers to obtain emission power high enough to reach other stations. Power loss through the atmosphere, the influence of solar radiation and responsiveness under that wavelength should be taken into consideration during the determination of wavelength. Thus, with all those factors, scientists have determined to study wavelengths of 800nm, 1000nm, and 1500nm, corresponding to the semiconductor lasers, solid lasers and fiber lasers. Additionally, the wavelength of 1550nm, 850nm and 10,000nm is used in ground-satellite links, according to weather and atmospheric turbulence conditions.In conclusion, wavelength determination and design depend on transmission type, transmission environment and service request.

Furthermore, another core technology of optics is optical path design, of which the most vital section is optical antenna design, for the reason that optical signals are sent and received by those antennas in satellite communication links. Nevertheless, traditional optical path design cannot satisfy the miniaturization trend, due to the disadvantages of large volume and heavyweight. Hence, a type of integrated optical antenna was invented, which can be adapted into small laser communication satellites. These antennas were designed on a silicon-oninsulator (SOI) having two different optical couplers (OC).