Patent ID: 7289263

Claim:
Optical apparatus, comprising: an optical fiber amplifier including at least a first all-fiber polarization splitter-combiner, a polarization-rotating arrangement, and a polarization maintaining gain-fiber, the amplifier being arranged such that light plane-polarized in a first polarization-orientation enters the amplifier via the polarization splitter-combiner, makes a first pass through the gain fiber in the first polarization-orientation, is polarization rotated by the polarization rotating arrangement into a second polarization-orientation perpendicular to the first polarization-orientation, makes a second pass through the gain fiber in a second polarization-orientation, and exits the amplifier via the polarization splitter-combiner in the second polarization-orientation, and wherein said apparatus further includes a second all-fiber polarization splitter combiner including first second and third ports, wherein the polarization-rotating arrangement is provided by a 90° cross-splice between first ends of first and second polarization maintaining optical fibers with a second end of the first polarization maintaining fiber fiber-coupled to the third port of the second polarization splitter-combiner and a second end of the second polarization maintaining fiber fiber-coupled to the second port of the second polarization splitter-combiner, and, wherein the first-orientation polarized light enters the first polarization splitter-combiner by the first port thereof, exits the first polarization splitter-combiner via the second port thereof, makes the first pass through the gain-fiber, enters the second polarization splitter-combiner via the first port thereof, exits the second polarization splitter-combiner via the second port thereof, is polarization-rotated through 90° by the polarization-rotating arrangement, enters the second polarization splitter-combiner via the third port thereof, exits second polarization splitter-combiner via the first port thereof, makes the second pass through the gain-fiber, re-enters the first polarization splitter-combiner by the second port thereof, and exits the first polarization splitter-combiner via the third port thereof.