DESIGN OPTIMIZATION FOR EFFICIENT ERBIUM-DOPED FIBER AMPLIFIERS

The gain and pumping efficiency of aluminosilicate erbium-doped fiber amplifiers (EDFA's) are analyzed as a function of guiding parameters and Er-doping profile for two pump wavelengths of λp = 980 nm and λp = 1.47 μm. Three designs of fiber-amplifier waveguide are considered: a) one with the same mode size as standard 1.5-μm communication fibers (Type 1); b) one with the same mode size as standard 1.5-μm dispersion-shifted fibers (Type 2); and c) one with mode size smaller than those of communication fibers (Type 3). For a 1.47-um pump, fundamental LP01 mode excitation is assumed, while for λp = 980-nm pump, concurrent excitation of LP,, modes is considered. It is shown that excitation of higher order pump modes at 980 nm does not significantly affect the amplifier gain performance. Independently of the Er-doping profile dimensions, the three fiber types have gains in excess of 30 dB with the pump power at 980 nm or 1.47 um in the 20-30-mW range. For Type 3 fiber, 30-dB gains are predicted with a power of 10 mW for either pump. The effect of concentrating the Er3+ doping near the center of the fiber core is shown to increase the amplifier gain coefficients by a factor of 1.5 to 2. The highest gain coefficients achievable with the three types of fiber designs are nearly independent of pump band and signal wavelengths and are: g = 1.25 ± 0.25 dB/mW (Type 1), g = 3.5 ± 0.5 dB/mW (Type 2), and g = 8.25 ± 0.5 dB/mW (Type 3). © 1990 IEEE