An optical fiber amplifier employing a prism to optimally couple pump energy into the pump core of a dual clad fiber. The optical fiber amplifier consists of a dual clad fiber having an inner (e.g., signal) core, an outer (e.g., pump) core surrounding the inner core, and a cladding layer at least partially surrounding the outer core. Pump energy can be injected into the outer core through the prism located adjacent to the outer core in order to amplify signals propagating through the inner core.