Er3+-doped phosphate glasses for fiber amplifiers with high gain per unit length

The effect of the types of alkaline earth metal ions (Mg2+, Ca2+ and Ba2+) and concentration of Al2O3 and BaO on the refractive index and the effective emission linewidths of the 4I13/2−4I15/2 transition of Er3+ ions in phosphate glasses, 64P2O5 · 12Al2O3 · 3.5(Er2O3+La2O3)·20.5MO (M=Mg,Ca,Ba) and 64P2O5 · 3.5(Er2O3+La2O3) · (21.5 − x)Al2O3 · (11+x)BaO (x=0,3.5,6.5 and 9.5), were investigated. A single mode Er3+ doped phosphate glass fiber with a core diameter of 4 μm was fabricated by the rod-in-tube technique. A new Er3+ doped fiber amplifier is demonstrated pumping with a 980 nm fiber pigtailed-laser diode. A gain per unit length greater than 2 dB/cm is demonstrated, which is the largest gain per unit length for fiber amplifiers to our knowledge.