Near-single-mode 3 kW monolithic fiber oscillator based on a longitudinally spindle-shaped Yb-doped fiber
Lingfa Zeng, Xiaoming Xi, Yun Ye, Hanwei Zhang, Xiaolin Wang, Zhiyong Pan, Zefeng Wang, Xiaojun Xu
Abstract
In order to balance the mitigation of transverse mode instability and stimulated Raman scattering effect in the high power fiber lasers, a specially designed Yb-doped fiber, named spindle-shaped Yb-doped fiber, was fabricated with a core/cladding diameter of 20/400 µm at both ends and 30/600 µm in the middle. Based on this fiber, an all-fiber laser oscillator was built and over 3 kW near-single-mode ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:msup> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">M</mml:mi> </mml:mrow> </mml:mrow> <mml:mn>2</mml:mn> </mml:msup> </mml:mrow> </mml:math> factor <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mo>∼</mml:mo> </mml:mrow> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mn>1.3</mml:mn> </mml:mrow> </mml:math> ) laser was achieved with an optical-to-optical conversion efficiency of 78.4%. While operating at the maximum power, the transverse mode instability is well mitigated and the stimulated Raman scattering effect is well suppressed ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mo>></mml:mo> </mml:mrow> <mml:mspace width="negativethinmathspace"/> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mn>34</mml:mn> </mml:mrow> </mml:mrow> <mml:mspace width="thickmathspace"/> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">d</mml:mi> <mml:mi mathvariant="normal">B</mml:mi> </mml:mrow> </mml:mrow> </mml:math> lower than signal laser). Further power scaling is promising by optimizing the structure of the Yb-doped fiber.