Polarization-dependent transverse mode selection in an Yb-doped fiber laser

A simple technique for selectively generating the fundamental LP01 and the next higher order donut-shaped LP11 mode with vortex phase front in a cladding-pumped few-moded ytterbium-doped fiber laser is reported. Our approach exploits the difference in polarization behavior of individual transverse modes due to transverse variation of birefringence in a few-mode fiber allowing robust mode discrimination through the use of an appropriately aligned intracavity polarizing element. The laser yielded ∼36  W of output power for both transverse modes with corresponding slope efficiency of 74% with respect to absorbed pump power and a mode purity of 98% for the donut-shaped LP11 mode.