Conversion Efficiency and Noise in Erbium-Doped Fiber Power Amplifiers

There has been a growing awareness of the importance of Er3+-doped fibers as power amplifiers in many applications including wavelength- and frequency-multiplexed systems as well as distribution systems with large fanouts [1]. This is a consequence of their excellent behavior under highly saturated conditions: immunity to crosstalk and high signal output powers. The characteristics of fiber power amplifiers, however, have not been extensively investigated. Relevant parameters include the operational configuration (forward, backward or bidirectional pumping), the signal and pump wavelength, fiber composition, fiber index and Er3+-doping profile. Due to the high cost of pump lasers and their limited power, the paramount consideration for a power amplifier is efficiency. The signal-to-noise ratio is also of importance, particularly in analog applications such as the AM-VSB systems now favored for video distribution [2], We have investigated both these properties using an accurate numerical model and measured input parameters. The optimum waveguides have been determined for both 980 nm and 1480 nm pumping, and the effects of confined Er3+-doping have also been elucidated.