High-Efficiency High-Mode-Purity Cylindrical Vector Beam Based on Ring-Core Yb-Doped Fiber

We propose and fabricate a novel ring-core Ytterbium-doped fiber (RCYDF) with a depressed inner core. The experiment demonstrates that the fiber could effectively increase the mode competitiveness of the LP<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> mode while attenuating the fundamental (LP<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub>) mode. Meanwhile, we propose the overlap factor ratio (OFR) to characterize the mode competitiveness of the high-order core (LP<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub>) mode. Based on this fiber, the cylindrical vector beams (CVBs) are generated at 1062.34 nm with a high efficiency of 63.35%. The output of radially polarized (TM<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub>) and azimuthally polarized (TE<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub>) beams are achieved with high-mode-purity of 94.7% and 93.2%, respectively. The CVB fiber laser has great potential application in surface plasmon excitation and laser material processing.