大气激光通信用直锥形光纤发射天线

Tapered fiber transmitting antenna for atmosphere laser communication

提出采用直锥形光纤作为大气激光通信的发射天线,将多模光纤输出的部分相干发散光束变换为准平行光束的方案,既能得到发散角很小的部分相干激光光束,又能保证激光器输出能量的完全传输。采用光线追迹法分析了任意光束从锥形光纤小端面输入、大端面输出的发散角。结果表明,当直锥形光纤长度大于某一特定值时,从小端面输入的入射角小于数值孔径角的所有光线理论上都可以变换为出射角度小于光纤半锥角的光线,因此直锥形光纤可以作为部分相干光源的准直透镜,代替传统的凸透镜,用于改善光束的发散角。对远场光斑进行了数值模拟和实验研究,结果显示:直锥形光纤透镜对朗伯光源的准直光束比传统凸透镜的准直光束发散角小,光斑半径小且均匀性好,证明用此方法可以得到低发散、低空间相干性的光斑。

A transmitting antenna with tapered fiber is proposed to transform the divergence partially coherent light formed by multi-mode fiber to collimate light. This structure can produce a partially coherent light of low divergence and guarantee the output power of laser transfers completely. It is applicable to laser communication in atmosphere. Based on the ray tracing meth- od, the divergence angle of random rays which incidents on the small section of tapered fiber in tapered fiber is analyzed. The propagation property of all the rays incidents on the small section and the angle of incidence less than numerical aperture angle are investigated. The result shows that the emission angle of these rays could be improved to less than the half of the taper angle in theory, if the length of the tapered fiber is larger than some value. For collimation of surface light source, a straight tapered fiber can be used for improving beam angle of divergence instead of traditional lens. According to numerical simulation of far field facula,experimental study is performed. Facula with lower divergence and more uniform distribution of light is obtained by using this method. It is proved that this method is superior to the method of traditional lens.