A high-power ASE source in the 2 μm wavelength band is achieved by using a relatively high-power pump beam that is generated within a fiber laser-based pump source. An optical isolator is included along the pump output path and is critical in maximizing the level of output power in the generated ASE, since without its use the ASE source begins to exhibit self-lasing cavity modes at a relatively low power level. Various embodiments of the present invention are based upon the use of a two-stage (or more) arrangement for generating a high-power ASE output, including an ASE-generating stage for establishing the broadband ASE spectrum and an amplifier stage for increasing the optical power within the ASE spectrum. The amplifier stage itself may include one or more individual amplifying elements in a concatenated arrangement. Optical isolators are included along the signal paths to prevent the type of reflections that would otherwise trigger self lasing.