| Space laser communication is a kind of wireless communication using lasers as an information carrier that has been paid extensive attention over the past half-century because of its large information density,strong electromagnetic compatibility,good confidentiality and small-size.Some countries and regions like the United States,Europe,and Japan have dedicated to research in this field for decades and have made great achievements.China has also paid attention to the research of space laser communication but felled behind since we started late and has made certain progress in recent years.As a key device in space laser communication,the optical antenna is used to transmit and receive laser signal so that the performance of antenna has a strong influence on communication distance,transmission efficiency,stability in the communication process.In this dissertation optical antenna and coupling system has been researched to improve transmission efficiency of optical antenna.The main research contents of the dissertation are shown as follows:(1)Simply introduced working mechanism of semiconductor laser;analyzed theory of transmission and emission characteristics of Gaussian beam which is generated by semiconductor laser.Then a collimating system that consist of two convex lenses with different focal length has been studied to collimate the semiconductor laser beam.(2)Compared with several different types of optical antennas and select reflective antenna as research object for its unique advantages.Cassegrain optical transmitting antenna and receiving antenna system are designed based on vector law of reflection and refraction and accurate 3-D ray tracing of the optical antenna system is calculated.Designed a kind of total reflection film which is made up of photonic crystal.These reflective surfaces of optical antenna can be coated with this film as to improve reflection efficiency.(3)Described a method which is based on vector law of reflection to design off-axis reflective optical antenna with pairs of reflections and a non-conicoid antenna is designed by this method.(4)Designed a Fresnel zone plate with spiral phase that is able to generate dark hollow vortex beam based on diffraction theory and dark hollow beam can be used in Cassegrain antenna to avoided energy loss caused by central obstacle.The relationship between zoon numbers,topological charge and radius of light spot,radius of dark hollow part,ratio of dark hollow part is discussed in detail. |
