Optimal Pump Wavelength for Efficient Er sup (3+)-Doped Fiber Amplifiers.

The gain of a highly efficient erbium-doped fiber amplifier was measured when pumped at wavelengths between 1.46micron and 1.51micron. The optimal pump wavelength, lambda (opt) sub p, was determined to be 1.475micron. At this pump wavelength the maximum gain coefficients for signals at 1.531micron and 1.544micron were measured to be 2.3 dB/mW and 2.6dB/mW, respectively. At lambda (opt) sub p high gains were achieved, ranging from 32 dB at pump power P(in) sub p = 20mW up to 40 dB at P(in) sub p = 80 mW. These modest pump powers are within the capabilities of currently available 1.48micron diode lasers. The width about lambda (opt) sub p for 3 dB gain variation exceeded 27 nm for P(in) sub p = 10 mW and 40 nm for P(in) sub p > 20 mW. With this weak dependence on pump wavelength, single longitudinal mode lasers do not have a significant advantage over practical Fabry-Perot multi-mode pump lasers.