Abstract: A two-stage optical fiber amplifier requiring substantially reduced power comprises a pre-amplifier first-stage operating in the linear region within the small signal limits, and a post-amplifier second-stage operating in a saturated regime providing significant gain compression. The pump power for the pre-amp stage is minimized, and all of the gain compression occurs in the second stage. Minimum pump power and the corresponding amplifier fiber length needed to achieve a predetermined optimum amount of small signal gain required in a given amplifier application may be achieved in variations of the design.

Abstract: Indiscriminately exciting the modes of a multi-mode optical fiber amplifier is avoided by an optical fiber amplifier design in which the excitation of pump modes in the core of a multi-mode fiber is controlled by controlling the pump light launching. The pump light is directed substantially along the center axis of a multi-mode fiber within a predetermined launch angle. Rather than exciting all modes, only lower order modes are affected.