Polarization-maintaining amplifier employing double-clad bow-tie fiber

We report a polarization-maintaining double-clad Yb-doped fiber amplifier employing bow-tie fiber. Borosilicate stress elements were incorporated into the inner cladding of the fiber, yielding a beat length of 5.1 mm at 633 nm. When the fiber was pumped at 975 nm and seeded with linearly polarized light, the polarization extinction ratio was >15 dB , independent of pump power, and the output power was as high as 3.5 W.