Scaling of Yb-doped photonic crystal fiber to 200 μm core diameter for high beam quality laser output

The rare earth-doped active fibers not only have ten thousands of square-micron core-area but also deliver a laser with near-diffraction-limited beam quality. However, they have been studied little. In this paper, we design a 200-μm-core-diameter Yb³⁺-doped photonic crystal fiber with a large pitch in the air-hole cladding region. Simulations demonstrate that only fundamental mode (FM) with a mode field area (MFA) of ～28000 μm² can be amplified and propagated at the gain saturation, and the beam quality M² is about 1.5. It is predicted that almost 105 mJ single-pulse energy is available from such a 1.5-meter-length fiber.