High-power polarization-maintaining LP₁₁-mode fiber laser based on long-period fiber grating for precise welding

An LP₁₁-mode output all-fiber laser was presented, utilizing long-period fiber gratings (LPFGs) and polarization-maintaining optical fiber (PMF). The LPFG was designed and fabricated, achieving a 90.56% efficiency in LP₀₁ to LP₁₁ mode conversion. Furthermore, the transmission stability of LP₁₁-mode in the PMF was also explored, with the spatial mode overlap ratio exceeding 0.95. Ultimately, the high-power polarization-maintaining (PM) fiber laser, capable of the LP₁₁ mode output, was constructed, with the output power of 600 W and the beam quality M² of 2.84. During the process of welding a thick Al-plate, the LP₁₁ fiber laser exhibits a notable 1.88 times greater depth of fusion compared to the commercial single-mode fiber laser, when operating at the laser welding head speed of 100 mm/s. For applications demanding non-circular symmetric high-order modes, this research holds substantial potential for widespread adoption within the field of industrial processing.