空间相干光通信外差效率及天线像差的影响

空间相干光通信中接收天线像差会使光外差效率下降.对本振光为高斯分布,信号光为爱里斑分布的光外差效率进行了研究,给出了无像差时外差效率的解析表达式.当焦平面上爱里斑半径与本振高斯光束光腰半径之比为1.71时,有最大外差效率81.45%.然后以本振光为理想的高斯光束,信号光受像差的影响,研究了倾斜、离焦、球差、彗差、像散等像差引起的光外差效率损失,给出了存在像差时外差效率的一维积分表达式.研究表明即使在采用离焦校正后,一个波长的球差引起的附加外差效率损失仍可达0.9 dB.因此对于爱里斑位于光轴上的接收天线,在设计时需仔细处理球差的影响.     

空间光通信中发射天线像差对激光传输的影响

空间光通信中发射天线像差会引起远场轴上光强下降.首先分析了无像差的理想发射天线,假设发射光束为高斯光束,在给定发射功率、天线直径时,天线直径与高斯光束直径的最佳比值为1.12,此时远场轴上光强最大.在此基础上分析了像差对远场轴上光强的影响,通过倾斜及离焦补偿,并减小发射光束直径可降低像差的影响.在最优条件下,1/4波长的球差、彗差及像散引起的远场轴上光强的附加损失分别为0.06 dB,0.13 dB及0.31 dB.最后分析了单透镜的像差特性,对于较大直径的发射天线,像差引起的远场轴上光强下降可达10 dB以上.

Abstract：

Aberration of transmitting antenna will decrease the far-field on-axis intensity in space optical communication systems. Aberration-free antenna system is analyzed. By assuming transmitting beam to be Gaussian distribution, and under given optical power and diameter of transmitting antenna, it is proved that the far-field on-axis intensity reaches its maximum when the ratio of the antenna diameter to the Gaussian beam diameter is 1.12. Compared to this maximum intensity, the far-field on-axis intensity loss induced by aberration of transmitting antenna is analyzed. This loss can be reduced by using tilt or defocus adjustment, and decreasing the diameter of transmitted Gaussian beam can also increasing the far-field on-axis intensity. Under optimal conditions, the losses caused by quarter wavelength spherical aberration, coma and astigmatism are 0.06 dB, 0.13 dB and 0.31 dB respectively. Finally, the aberration characteristics of a single lens are analyzed. The decrease of on-axis intensity caused by aberration can reach 10 dB or more for transmitting antenna with a lager diameter.     

基于JAVA的数据库开发与应用研究

随着计算机技术的发展与计算机应用的普及,数据库管理技术逐渐成为当前最为有效的数据管理与处理工具。基于JAVA的数据库开发与应用技术也将成为数据库管理技术的发展趋势。本文着重探讨基于JAVA技术的数据库开发与应用。