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 Er³⁺: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 power sensitivity 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.