All Solid Multistep-Index Core Large Mode Area Single-Mode Fiber

In this paper, a large-mode-area (LMA) single-mode fiber based on multistep-index core structure is proposed. The multistep-index core increases the mode field area (MFA). The trapezoidal refractive ring structure and the trench layer structure ensure the fiber maintains effective single-mode regime. The structure is analyzed using the finite element method (FEM). Numerical results show that the proposed fiber is capable of maintaining effective single-mode regime at a bending radius of 10 cm. The MFA reaches 2578.136 μm² at the wavelength of 2.0 μm. The leakage loss (Loss) is 0.076 dB/m for fundamental mode (FM). The fiber structure also has the potential to develop LMA single-mode fiber with high performance at the wavelength of 1.55 μm. Furthermore, the circular symmetry of the fiber structure makes it insensitive to bending direction. These features indicate the proposed fiber has great potential in the application of the high-power laser system.