Patent ID: 7286283

Claim:
A method for amplifying light from a source thereof, the light having a first wavelength, the method comprising the steps of: a) coupling the light into an input end of a first optical fiber having a core surrounded by cladding such that the first-wavelength light propagates along said core in a forward direction; b) converting, in a first length of said first optical fiber, at least a portion of the first-wavelength light to light having a second wavelength, different from the first wavelength; c) selectively coupling said second-wavelength light from said core at an output end of said first optical fiber into a second optical fiber in a manner such that coupling of first wavelength light into said second optical fiber is minimized; d) transmitting said second wavelength light along said second optical fiber to an optical amplifier; e) amplifying said second wavelength light in said optical amplifier, said amplification causing second wavelength light to be reflected, and amplified spontaneous emission at said second wavelength be to emitted, propagating in a reverse direction along said second optical fiber back into said core of said first optical fiber; f) selectively coupling at least a portion of said reflected second wavelength light and emitted amplified spontaneous emission out of said core of said first optical fiber, thereby preventing said portion of said reflected second wavelength light and emitted amplified spontaneous emission from reaching the source of the first wavelength light; g) wherein said portion of said second-wavelength light is coupled into said second optical fiber via a wavelength-selective fiber coupler having first and second output arms, said second-wavelength light being coupled into said second optical fiber through said first arm of said wavelength-selective fiber coupler, with residual first-wavelength light being directed out of said first optical fiber via said second arm of said a wavelength-selective fiber coupler, thereby preventing said residual first-wavelength light from reaching the optical amplifier; and h) wherein at least a portion of said reflected second-wavelength light and amplified spontaneous emission is coupled out said core of said first optical fiber via a wavelength-selective device located in said first optical fiber between the light source and the length of said first optical fiber in which first-wavelength light is converted to second wavelength light.