With the application development of ultrafast lasers in the field of precision processing, how to overcome nonlinear effects and further improve the performance of ultrafast lasers has become a research hotspot. The larger the mode field area of the fiber, the higher its nonlinear threshold [1]. Therefore, using large mode field fibers is one of the most direct and effective ways to overcome nonlinear effects [2–5]. Compared with traditional double-clad fibers, photonic crystal fibers can have many unique optical properties such as single-mode without cutoff, adjustable dispersion, and large mode field area [6, 7], which can overcome many difficulties faced by traditional fiber lasers. Foreign research institutions and companies such as the University of Bath, the University of Jena, and NKT Photonics have conducted a lot of researches on the design, preparation, and application of key technologies of large mode field photonic crystal fibers [8, 9]. In 2000, the Russell group at the University of Bath [10] first achieved laser output in Yb3+ doped photonic crystal fiber. Currently, the maximum core diameter of Yb3+ doped large mode field photonic crystal fiber has reached 135 μm [11]. Chinese companies and institutions such as Wuhan Fenghuo, Huazhong University of Science and Technology, Yanshan University, Tianjin University, Nankai University, 46th Institute of Chinese Electronics, and Shanghai Institute of Optics and Mechanics have successively carried out related researches on large mode field photonic crystal fiber, achieving certain results.