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Abstract

A multi-stage optical amplifier includes an optical fiber with at least a first Raman amplifier fiber and a second Raman amplifier fiber. The optical fiber is configured to be coupled to at least one signal source that produces at least a signal wavelength .lambda..sub.s and at least two pump sources that collectively produce a pump beam of wavelength .lambda..sub.p. Pump wavelength .lambda..sub.p is less than signal wavelength .lambda..sub.s. Signal input, signal output and a first pump input port are each coupled to the optical fiber. The first Raman amplifier fiber is positioned between the signal input port and the pump input port. The second Raman amplifier fiber is positioned between the pump input port and signal output port. A second pump input port is coupled to the optical fiber and positioned between the second Raman amplifier fiber and the signal output port. A first lossy member is positioned between the pump input port and the signal output port. The lossy member is lossy in at least one direction so that passage of the pump radiation of wavelength .lambda..sub.p from the second to the first length of amplifier fiber is substantially blocked. The signal flows in a first direction and the pump beam flows in a reverse direction relative to the first direction.

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First Claim