摘要:
分析了大气湍流对采用多抖动法实现的相干合成阵列光束中相位调制信号的影响.文章首先根据广义惠更斯-菲涅耳原理,采用折射率结构函数对大气湍流进行描述,推导了多抖动法相干合成中阵列光束通过大气湍流后相位调制信号的一般表达式.在此基础上进行数值模拟,分析了传输距离、湍流强度、光束阵列占空比和光斑尺寸等因素对相位调制信号的影响.研究发现随着传输距离的增大,相位调制信号强度会先增大后减小,存在一个极大值点;随着湍流强度的增强,相位调制信号强度极大值点的出现距离不断缩短;当光束阵列占空比一定时,随着光斑尺寸的增大,相位调制信号强度极大值点的出现距离不断变长;当光斑尺寸一定时,随着光束阵列占空比的减小,相位调制信号强度极大值点的出现距离不断变长,但其幅值不断减小.文章还比较了平行发射和保形发射两种发射方式对相位调制信号强度的影响,发现通过改变保形发射时的聚焦距离可以改变相位调制信号强度极大值点的出现距离,而且其幅度会大幅提高.最后,从相位调制信号的角度给出了在湍流大气中进行主动锁相相干合成的相关建议,当光束传输距离较近时,采用保形发射形式较好,此时可根据发射系统参数及外界环境条件设置合适的聚焦距离以获得较高的相位调制信号强度,当聚焦距离大于100km时,保形发射与平行发射已无明显区别.
Abstract:
The effect of atmosphere turbulence on phase modulation signal in coherent beam combination with multi-dithering technique is studied. Analytical formulas for the phase modulation signal of beam array propagating in a turbulent atmosphere are derived based on extended Huygens-Fresnel integral. Then the effects of propagation distance, turbulence intensity, filling factor and size of beam array on phase modulation signal are numerically calculated. The results show that with transmission distance increasing, there occurs a maximum of the amplitude of phase modulation signals. With the intensity of atmosphere turbulence increasing, the maximum of amplitude of phase modulation signals will appear in a shorter distance. When fill factor does not change, the distance between the laser source and the maximum of amplitude of phase modulation signals will be increased with of the dimension of laser beam increasing. When the dimension of laser beam does not change, the distance between the laser source and the maximum of amplitude of phase modulation signals will be increased with fill factor decreasing. Finally, the effects of parallel beam array and conformal focused beam array on phase modulation signal are compared, finding that the distance between the laser source and the maximum of amplitude of phase modulation signals can be changed by changing the focusing distance of conformal focused beam array.