Tm3+/Ho3+ co-doped germanate glass double-clad fiber for broadband emission and lasing above 2 µm
in: Optical Materials Express (2019)
In the paper, 2 µm broadband emission under 796nm laser diode excitation in low phonon energy GeO2-Ga2O3-BaO glass system co-doped with 0.7Tm2O3/(0.07-0.7)Ho2O3 (mol%) and double-clad optical fiber co-doped with 0.7Tm2O3/0.15Ho2O3 (mol%) were investigated. The widest emission band (Tm3+→Ho3+ energy transfer efficiency is 63 %) was obtained for 0.7Tm2O3/0.15Ho2O3 co-doped glass. Optimization of Tm3+/Ho3+ concentration enabled obtaining broadband amplified spontaneous emission (ASE) in double-clad optical fiber with a full width at half maximum (FWHM): 377 nm and 662 nm for 3 dB and 10 dB bandwidth, respectively. ASE spectrum is a result of the superposition of (Tm3+: 3H4 → 3F4) 1.45 µm, (Tm3+: 3F4 → 3H6) 1.8 µm and (Ho3+:5I7 → 5I8) 2 µm emission bands. Hence, highly rare-earth co-doping (790 dB/m – 796 nm pump absorption) and excellent spectroscopic properties of the fabricated germanate glasses and optical fiber become promising for construction compact, broadband ASE sources as well as tunable or dual wavelength fiber lasers.