• High Power Laser Science and Engineering
  • Vol. 9, Issue 2, 02000e23 (2021)
Xin Zhang1, Shoufei Gao2, Yingying Wang2, Wei Ding2, and Pu Wang1、*
Author Affiliations
  • 1National Center of Laser Technology, Institute of Laser Engineering, Beijing University of Technology, Beijing100124, China
  • 2Institute of Photonics Technology, Jinan University, Guangzhou510632, China
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    High-power fiber lasers have experienced a dramatic development over the last decade. Further increasing the output power needs an upscaling of the fiber mode area, while maintaining a single-mode output. Here, we propose an all-solid anti-resonant fiber (ARF) structure, which ensures single-mode operation in broadband by resonantly coupling higher-order modes into the cladding. A series of fibers with core sizes ranging from 40 to 100 μm are proposed exhibiting maximum mode area exceeding 5000 μm2. Numerical simulations show this resonant coupling scheme provides a higher-order mode (mainly TE01, TM01, and HE21) suppression ratio of more than 20 dB, while keeping the fundamental mode loss lower than 1 dB/m. The proposed structure also exhibits high tolerance for core index depression.

    1 Introduction

    Ultrafast fiber lasers[1] have demonstrated outstanding performance in LIDAR[2], spectroscopy[3], medicine[4] as well as material processing[5] owing to their advantages of good beam quality, compact structure, and easy thermal management. High output power and diffraction-limited beam quality achieved by ultrafast fiber lasers make this technique one of the most remarkable and promising laser technologies existing nowadays. For example, several thousand watts average power[6], up to 26 mJ pulse energy[7], and 22 GW peak power[8] have been reported in recent years. Nevertheless, the progress of power scaling of fiber lasers is currently under challenge. Nonlinear effects[9] and mode instabilities[10] have become two main factors hindering the further development of ultrafast fiber lasers. In general, increasing the mode field area and reducing the power intensity of the core are the most effective strategies to circumvent the nonlinear effects in the optical fiber. However, fibers with large mode area (LMA) usually support multimode propagation which may lead to transverse mode instabilities (TMIs) at high average power. This phenomenon would drastically degrade the emitted beam quality of the fiber laser system.