超声吸收引起的声光偏转器指向偏差研究

Research of pointing deviation of acousto-optic deflector due to ultrasonic attenuation

分别在不考虑晶体超声吸收及考虑超声吸收和超声功率角分布的情况下,建立了声光互作用方程。运用空间傅里叶变换方法推导出衍射光场与入射光场在空频域下的传递函数。仿真结果表明,超声吸收使得衍射光光强峰值位置偏离光束中心,光强不再呈高斯分布,会引起卫星光通信发射端的指向偏差。通过研究超声功率和频率与衍射光光强分布的关系发现,超声功率选取某一数值时可以消除峰值位置偏差,将此功率值定义为最优超声功率Popt。求出声光偏转器整个工作频带内的Popt并进行多项式拟合,得到了最优超声功率与超声频率的关系。按照该多项式关系同步调节超声频率与功率可以补偿超声吸收引起的指向偏差。

Acousto-optic interaction equations were established separately under two situations of without or with the consideration of ultrasonic attention and the angular distribution of ultrasonic power. The transfer function in spatial-frequency domain between the diffracted light and incident light was derived by employing spatial Fourier transform approach. Numerical simulation was performed. The results indicate that due to ultrasonic attenuation, the peak intensity of diffracted light deviates from the center of the beam and the distribution of diffracted light intensity is not Gaussian type any more, which leads to the pointing deviation of transmitting terminal in inter-satellite optical communications. The study of the dependence of the distribution of diffracted light intensity on ultrasonic power and ultrasonic frequency shows that the peak intensity deviation of the diffracted light can be eliminated when a certain value is chosen for the ultrasonic power. This certain value was defined as the optimal ultrasonic power P~. The relation between optimal ultrasonic power and ultrasonic frequency was given by applying a polynomial fitting to various P~ in the whole bandwidth of acousto-optic deflector. The pointing deviation due to ultrasonic attenuation can be compensated by adjusting the ultrasonic frequency and ultrasonic power synchronously according to the expression of polynomial fitting.