Fast and Controllable Beam Switching in a Pulsed Fiber Laser

In this letter, we demonstrate a fast fiber mode converter in a short piece of special passive fiber. The switching mechanism relies on selective wavelength resonance between the core and a high index surrounding ring in the fiber. Beam switching at 530 kHz from a Gaussian beam shape to an expanded beam with a ring with corresponding M
²
from 1.4 to 3.5 is demonstrated in a modified industrial pulsed fiber laser at power levels in the excess of 15 W.