1.55 μm Fiber Lasers Using Newly Developed Ce~(3+) and Er~(3+) Codoped Fluoride Glasses

摘要

Er~(3+)-doped fluoride glasses, because of the wide emission spectrum around 1.55μm band, has been investigated as one of the most promising materials for wide-band optical amplifiers and tunable fiber laser sources, which would be of great value in the future optical fiber communication systems.The relavant energy level diagrams of Er~(3+) in fluoride glasses are shown in Fig. 1. For developing a low noise optical device working around 1.55 μm band, instead of the resonance pumping wavelength for the ~4I_(13/2) state, which is the upper state of the 1.55 μm emission, pumping at 980 nm for the ~4I_(11/2) state is much more favourable. However, for Er~(3+) doped fluoride glasses, 980 nm pumping is not suitable for 1.55 μm band operation because the decay of the ~4I_(11/2) state is dominated by the direct radiative relaxation to the ground state. The typical branching ratio from the ~4I_(11/2) state to the ~4I_(13/2) state is about 0.1 to 0.2 for Er~(3+) in fluoride glasses, compared with the value of about 0.90 to 0.95 for Er~(3+) in silica based glasses. This is a limiting factor for developing low noise fluoride optical devices working around 1.55 μm band. Here, by Ce~(3+) codoping, an improvement in the fluorescence characteristics of Er~(3+) in fluoride glasses around 1.55 μm by 980 nm pumping has been demonstrated. Using Ce~(3+):Er+3+-codoped fluoride fiber, fiber lasers operating at 1.55 μm have been realized for the first time by pumping Er~(3+) in fluoride glasses at 980 nm.