US Patent 7289263 Double-pass fiber amplifier

Several examples of double-pass fiber amplifiers including a polarization maintaining (PM) gain-fiber are disclosed. In each example, input and twice-amplified output are separated by an all-fiber, polarization-maintaining polarization splitter combiner. The examples include double-pass fiber amplifiers not including any bulk components and double pass fiber amplifiers including a bulk component or a Faraday rotating mirror located in a position in the amplifier wherein the component is exposed only to radiation amplified on the first pass through the gain-fiber.