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1 引言通信技术经历了持续发展 ,携带信息所用频率越来越高。在马可尼的时代只有几百千赫 ,而在光纤系统中使用了激光技术后已达到数百太赫。主要驱动力是可用带宽即传输能力随载波频率成正比增长。在自由空间点对点链接中 ,另一优点开始发挥作用。自由传输电磁波束所能获得的
1 Introduction Communication technology has undergone continuous development and the frequency of carrying information is getting higher and higher. In the Marconi era, only a few hundred kilohertz, and in the optical fiber system using laser technology has reached hundreds of terahertz. The main driving force is the available bandwidth, ie the transmission capacity increases in proportion to the carrier frequency. In free-space point-to-point links, another advantage comes into play. Free transmission of electromagnetic beams available