Emitting a large aperture coherent fiber laser array by a small footprint cascaded internal phase sensing system

Abstract The large aperture coherent fiber laser array (CFLA) holds significant potential for diverse applications, such as optical communication, beam scanning, and energy transmission. In a large aperture CFLA system, precise phase control is of paramount importance; however, it encounters certain challenges. The main difficulty lies in phase detection and the reduction in control bandwidth with an increasing number of combined elements. This paper proposed and experimentally demonstrated a cascaded internal phase sensing technique employing a hybrid optimized algorithm. In the experiment, the entire CFLA had three sub-arrays, each comprising four beamlets. The stochastic parallel gradient descent algorithm was employed to lock the phase of each sub-array, while compensating the phase differences among them using the single-frequency dithering algorithm. Consequently, the complete large aperture CFLA could be directly emitted into free space with locked phases. The average residual phase error was less than ∼ λ /22. Additionally, interference patterns in the far field exhibited approximately 94% visibility with an emitting efficiency of 80%. Since the cascaded internal phase sensing system is compact and separated from the laser emitting system, our technique offers flexibility in designing both beam caliber and arrangement within the CFLA. This work provides practical insights for designing large aperture CFLA systems and achieving effective phase control.