Stable control of the phased fiber laser array under varying beam propagation distance

Phased fiber laser array (PFLA) plays an important role in laser propagation applications. However, in many practical scenarios, the beam propagation distance is constantly changing, which makes the metric propagation delay difficult to obtain, and eventually leads to the divergence of existing control algorithms based on metric optimization. In this paper, the laser ranging technique based on PFLA is introduced to estimate the metric propagation delay in real-time. In addition, an iterative algorithm named dynamically delayed stochastic parallel gradient descent (DD-SPGD) is designed to adapt to the varying metric propagation delay, and ensure the stable control of PFLA. Laser ranging and three channel coherent beam combination experiments based on a 7-unit PFLA were conducted to verify the proposed method. The results show that the laser ranging technique can accurately estimate the metric propagation delay with estimation errors of less than 1%. On this basis, the DD-SPGD algorithm can dynamically adjust the delay parameter (from 0 to 2) and realize stable control of PFLA under different metric propagation delays.