ABSTRACT
A strong interest in erbium-doped ber ampliers (EDFAs) in the late 1980s led to a wide availability of related components and necessary equipment, which spurred initial research in a variety of erbium-doped ber lasers in the early 1990s, including single-frequency ber lasers and multiple-wavelength lasers for potential use as transmitters in telecommunication systems and Q-switched and mode-locked lasers. Most of those ber lasers were core-pumped lasers with powers of less than a few hundred milliwatts. Single-mode diode lasers had maximum power levels of just a few hundred milliwatts then and reached a limit of ∼1 W around the late 1990s. One exception was Er/Yb co-doped ber ampliers, which enabled the use of more powerful solid-state lasers as pumps. In an early demonstration using a pump at 1047 nm from an Nd3+:YLF laser which was in turn pumped by a 3 W AlGaAs diode array, the output power reached 288.4 mW (24.6 dB/m) [1]. The high output powers at 1-2 W were very useful for cable TV networks, which are essentially a distribution system and rely on splitting of a central feed to a large number of households. High power also later became more critical for ber ampliers used in increasingly deployed wavelength-division-multiplexing (WDM) systems in the 1990s, where the large channel counts demanded more powerful ampliers.
