Near-hundred-watt all-fiber multicore fiber laser oscillators fabricated by femtosecond direct writing Bragg gratings in a seven-core Yb-doped fiber

We demonstrate the first, to the best of our knowledge, near-hundred-watt, all-fiber, multicore fiber (MCF) laser oscillator, fabricated by femtosecond laser direct writing fiber Bragg gratings (FBGs) in a seven-core Yb-doped fiber. Unlike the traditional point-by-point writing method, our method employs femtosecond laser direct writing of parallel FBG arrays. This method increases the grating area ratio, which enables the fabrication of a grating array within each core of the large-mode-area MCF (core diameter: 14 μm). At the same time, the optimized refractive index modulation significantly enhances the reflectivity of the FBG. A high-power all-fiber oscillator has been constructed to investigate the performance of the multicore FBGs. The multicore fiber oscillator achieves a maximum output power of 92 W, which is, to the best of our knowledge, the highest power of all-fiber oscillators based on FBGs. This work demonstrates the potential application of femtosecond laser direct writing of MCF gratings in high-power MCF lasers.