Patent ID: 7508579

Claim:
Optical apparatus, comprising: an optical fiber amplifier including an all-fiber polarization splitter-combiner having first second, third and fourth ports, 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 first port of the polarization splitter-combiner, exits the first polarization splitter-combiner via the second port thereof and 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, re-enters the first polarization splitter-combiner via the third port thereof following the polarization-rotation, exits the first polarization splitter-combiner via the second port thereof and makes a second pass through the gain fiber in a second polarization-orientation, is polarization-rotated by the polarization rotating arrangement back into the first polarization orientation, enters the first polarization splitter-combiner by the third port thereof and exits the first polarization splitter-combiner via the fourth port thereof.