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. In one example, light is first passed through a gain fiber in a first polarization direction and then is passed through the gain fiber in a second polarization direction. The light exits the splitter combiner in the first polarization direction.