Mode-adaptive control of a kilowatt-level large-mode-area fiber laser based on 5×1 photonic lantern

Abstract This study presents high-power mode-selective operation in a large-mode-area (LMA) fiber laser. A spatial mode-adaptive control system incorporating a 5×1 photonic lantern was employed to facilitate mode conversion between the LP 01 and LP 11 modes. The coherence length between the five single-mode arms and the stimulated Brillouin scattering threshold in the amplifier were well balanced by tuning the seed linewidth. In addition, the specific design of the fiber amplifier’s bending radius enabled stable mode-selective output with high mode purity. Consequently, a near-fundamental mode control was achieved in a 42-μm LMA fiber laser, yielding a beam quality M 2 factor of 1.97 at an output power of 1 kW. Subsequently, a stable LP 11 mode laser output with an output power of 219 W and an optical conversion efficiency of 75% was obtained. This research provides a significant technical foundation for the mode-selective operation of high-power LMA fiber lasers.