6.8 W, 3795 nm monolithic all-fiber laser

This study demonstrates, to the best of our knowledge, a record-breaking 6.8 W all-fiber laser operating at 3795 nm. The monolithic resonator integrates a 5-meter-long lightly doped Er^³+:ZrF₄ fiber (1 mol.%) and femtosecond laser direct-written fiber Bragg gratings (FBGs). A slit-assisted beam-shaping technique enabled the fabrication of ultra-low-loss FBG pairs (97% high-reflective, 60% low-reflective at 3795 nm, total insertion loss: 0.2 dB), reducing sensitivity to the laser power before slit modulation during inscription. Notably, we experimentally observed the coexistence of 3795 nm lasing and 2796 nm parasitic lasing and subsequently investigated the conditions enabling simultaneous dual-wavelength operation as well as effective suppression strategies for parasitic oscillations.