Optical fiber amplifier and coupler

A fiber amplifier comprising

• gain fiber means for amplifying optical signals, and
• fiber optic coupler means having first and second coupler optical fibers, one end of said first coupler fiber being connected to said gain fiber means, the mode field diameter of said first coupler fiber being substantially matched to that of said gain fiber means and being smaller than that of said second coupler fiber, a portion of said coupler fibers being situated in a wavelength dependent light transfer relationship whereby most of the light power of a wavelength .lambda..sub.s couples between said first and second coupler fibers, and most of the light power of a wavelength .lambda..sub.p that is introduced into said first fiber remains in said first coupler fiber.

A wavelength division multiplexer fiber optic coupler of the type in which most of the light power of a wavelength .lambda..sub.p that is introduced into a first coupler fiber remains in that fiber and most of the light power of a wavelength .lambda..sub.s that is introduced into the first coupler fiber couples to a second coupler fiber, said coupler being of the type comprising

• an elongated body of matrix glass having refractive index n.sub.3, said body having two opposed endfaces and a midregion, said fibers extending longitudinally through said elongated body and being fused together along with the midregion of said body, the cores of said fibers being more closely spaced at the central portion of said midregion than at said body endfaces, each of said fibers comprising a core surrounded by a cladding of refractive index less than that of said core but greater than n.sub.3,
• characterized in that the mode field diameter of at least a portion of said first fiber is smaller than that of said second fiber.

A wavelength division multiplexer fiber optic coupler of the type in which most of the light power of a wavelength .lambda..sub.p that is introduced into a first coupler fiber remains in that fiber and most of the light power of a wavelength .lambda..sub.s that is introduced into the first coupler fiber couples to a second coupler fiber, said coupler being of the type comprising at least first and second optical fibers, each having a core and a cladding, said fibers being fused together along a portion of the lengths thereof to form a coupling region,

• characterized in that said first coupler fiber comprises two fiber segments that are fused together end-to-end within said coupling region, and in that the mode field diameter of at least one of the segments of said first fiber is smaller than that of said second fiber.

A wavelength division multiplexer fiber optic coupler comprising

• an elongated body of matrix glass having a refractive index n.sub.3, said body having two opposed endfaces and a midregion, said fibers extending longitudinally through said elongated body and being fused together along with the midregion of said body, the cores of said fibers being more closely spaced at the central portion of said midregion than at said body endfaces, each of said fibers comprising a core surrounded by a cladding of refractive index less than that of said core but greater than n.sub.3,
• characterized in that the mode field diameter of at least a portion of said first fiber is smaller than that of said second fiber.

A wavelength division multiplexer fiber optic coupler comprising at least first and second optical fibers, each having a core and a cladding, said fibers being fused together along a portion of the lengths thereof to form a coupling region, characterized in that said first coupler fiber comprises two fiber segments that are fused together end-to-end within said coupling region, and in that the mode field diameter of at least one of the segments of said first fiber is smaller than that of said second fiber.

A fiber amplifier system comprising

• fiber optic coupler means having first and second coupler optical fibers, the mode field diameter of said first coupler fiber being smaller than that of said second coupler fiber, a portion of said coupler fibers being situated in a wavelength dependent light transfer relationship whereby most of the light power of a wavelength .lambda..sub.s couples between said first and second coupler fibers, and most of the light power of a wavelength .lambda..sub.p that is introduced into said first coupler fiber remains in said first coupler fiber, said first fiber having first and second legs that extend from said coupling region in opposite directions, said second fiber having third and fourth legs that extend from said coupling region in opposite directions, said first and third legs extending from said coupling region in the same direction, said second leg constituting gain fiber means for amplifying optical signals,
• input signal means for introducing light power of wavelength .lambda..sub.s into said third leg, and
• pump source means for introducing pumping light power of wavelength .lambda..sub.p to said first leg.