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

Pulsed laser emission at similar to 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 similar to 1450 nm using most rare-earth-doped silica fibers is inaccessible. Here, we fabricated a bismuth-doped fiber preform with a low concentration of GeO2 (similar to 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 similar to 1 dB/m at 1400 nm and a gain coefficient of similar to 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 similar to 1450 nm with a high pulse energy of 172.62 nJ at a pump power of 155.3 mW. Moreover, wavelength-adjustable NMM from similar to 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 similar to 1406 to 1550 nm, where strong optical absorption by water occurs.