Patent ID: 6359725
Filing Date: 2002-03-19
Classification: H01S,H04B

Abstract:
A multi-stage optical amplifier, comprising:an optical fiber including at least a first Raman amplifier fiber and a second Raman amplifier fiber, the optical fiber configured to be coupled to at least one signal source that produces at least a signal wavelength &lgr;s and at least two pump sources that collectively produce a pump beam of wavelength &lgr;p, wherein pump wavelength &lgr;p is less than signal wavelength &lgr;s, the first Raman amplifier fiber having an optical noise figure of less than 8 dB and lower noise than the second Raman fiber amplifier, and the second Raman fiber amplifier having a gain level of at least 5 dB; a signal input port coupled to the optical fiber; a signal output port coupled to the optical fiber; a first pump input port, the first Raman amplifier fiber being positioned between the signal input port and the first pump input port and the second Raman amplifier fiber being positioned between the first pump input port and signal output port; a second pump input port coupled to the optical fiber and positioned between the second Raman amplifier fiber and the signal output port; and a first lossy member positioned between the first pump input port and the signal output port, the lossy member being lossy in at least one direction and passage of the pump radiation of wavelength &lgr;p from the second to the first length of amplifier fiber is substantially blocked; and wherein the signal flows in a first direction and the pump beam flows in a reverse direction relative to the first direction.