1450 nm High Energy Noisy Multi-Pulse Mode-Locking in Bismuth-Doped Fiber Laser

Pulsed laser emission at ∼1450 nm has a plethora of important applications in medical diagnoses and laser therapy due to the strong absorption by water molecules. However, pulsed fiber laser emission at ∼1450 nm using most rare-earth-doped silica fibers is inaccessible. Here, we fabricated a bismuth-doped fiber preform with a low concentration of GeO
₂
(∼4 to 5 mol.%) through modified chemical vapour deposition method. This fiber preform was drawn into optical fiber through standard fiber drawing technique. This optical fiber was characterized by a peak absorption of ∼1 dB/m at 1400 nm and a gain coefficient of ∼0.5 dB/m at 1430 nm. We incorporate this bismuth-doped fiber into a figure-of-nine laser cavity to generate a noisy multi-pulse mode-locking (NMM) at ∼1450 nm with a high pulse energy of 172.62 nJ at a pump power of 155.3 mW. Moreover, wavelength-adjustable NMM from ∼1430 to 1470 nm was achieved by varying the length of the bismuth-doped fiber from 20 to 60 meters in the laser cavity. This wavelength-adjustable NMM fills the current operation spectral gap from ∼1406 to 1550 nm, where strong optical absorption by water occurs.