Performance of high-concentration Er/sup 3+/-doped phosphate fiber amplifiers

The performances of high-concentration Er/sup 3+/-doped phosphate fiber amplifiers are reported. The amplifiers are characterized in terms of gain, noise figure, and signal saturation power in a co-propagating pump configuration. A net gain of 21 dB and a gain per unit length 3 dB/cm are achieved in a 71-mm Er/sup 3+/-doped phosphate fiber.