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 I-4(13/2) - I-4(15/2) transition of Er3+ ions in phosphate glasses, 64P(2)O(5) . 12AL(2)O(3) . 3.5(Er2O3 + La2O3) . 20.5MO (M = Mg, Ca, Ba) and 63P(2)O(3) . 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 mu m was fabricated by the rod-in-tube technique. A new Er3+ doped Bber 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. (C) 2000 Elsevier Science B.V. All rights reserved.