Patent ID: 6480326
Filing Date: 2002-11-12
Classification: H04B

Abstract:
A system for pumping a transmission fiber of an optical fiber telecommunications span to produce distributed Raman gain in the fiber for amplifying signals being transmitted along the fiber span, comprising:one or more primary pump sources at wavelengths &lgr;p1 . . . &lgr;pi, shorter than pump wavelengths &lgr;f1 . . . &lgr;fk ultimately required to directly produce distributed Raman gain for the signal wavelengths; wherein the wavelengths &lgr;p1 . . . &lgr;pi, of said one or more primary pump sources are shorter than said wavelengths &lgr;f1 . . . &lgr;fk by an amount corresponding to m Raman shifts in said transmission fiber, where m&gE;1; means to provide substantially lower energy at one or more secondary seed wavelengths &lgr;s1 . . . &lgr;sn, where n&gE;1 and &lgr;pisn&lE;&lgr;fk; wherein said means to provide substantially lower energy at one or more of said secondary seed wavelengths comprise reflection means to return, into said transmission fiber, amplified spontaneous Raman scattered radiation, originating in said fiber due to the presence of high power at a wavelength one Raman shift below the particular seed wavelength, and wherein (i) the ensemble of said one or more secondary seed wavelengths &lgr;s1 . . . &lgr;sn includes each ultimately-required wavelength &lgr;fk; and (ii) if m>1, the ensemble of said secondary seed wavelengths &lgr;s1 . . . &lgr;sn includes at least one in the vicinity of each intermediate wavelength &lgr;l, where l=mâˆ’1, mâˆ’2 . . . 1 and denotes the number of Raman shifts in said transmission fiber between said wavelength &lgr;l and the ultimately required wavelengths &lgr;f1 . . . &lgr;fk,; and coupling means to input energy at said one or more primary pump source wavelengths &lgr;p1 . . . &lgr;pi and energy at said one or more secondary seed wavelengths &lgr;s1 . . . &lgr;sn, into said transmission fiber.