The objective of this study is to enhance the power of high-power fiber lasers by designing high-performance fibers and to overcome the challenges associated with the digital design of complex fiber structures. Currently, the optical characteristic parameters of fibers are primarily obtained through experimental measurements or numerical calculations, which are expensive and difficult to accomplish. Therefore, the development of fiber modeling and simulation software for aiding the design is particularly urgent. Existing commercial fiber photonics simulation software typically present issues such as complex operation and non-specialization. In this study, SeeNano, which is a fiber-waveguide structure-design software, was developed. We analyze the cross-sectional structure of multilayer refractive-index fibers from the lateral dimension, establishe various material library models, and optimize the characteristic parameters of the fibers by analyzing their mode, loss, and dispersion characteristics to provide new solutions for enhancing the power of high-performance fibers and high-power fiber lasers.

First, the optical scale of fiber waveguides was considered via mathematical modeling and software development. Initially, a numerical model of the characteristic equation transmission matrix for fibers and other dedicated algorithm models were established to provide a theoretical basis for calculating the fiber mode-field, loss, and dispersion characteristics. Subsequently, based on software engineering, a fiber-waveguide design and simulation software named SeeNano was developed, which features a simple and intuitive graphical user interface with a guided operation flow. It was designed to help users understand the usage of the software promptly and reduce the learning difficulty. Subsequently, the design processes of two cases, i.e., step- and graded-index trench-assisted cases, were introduced, and key characteristic parameters, such as the effective mode-field area, effective mode-field diameter, material dispersion, and waveguide dispersion, were calculated and compared with the results yielded by the commercial software OptiFiber to validate the results. However, the functionality of the software is not yet completed, and the developed features target primarily concentric multilayer refractive-index fibers. Hence, the software functionality must be continuously supplemented and gradually enhanced.

The design of different layers, such as rings (higher refractive index) or grooves (lower refractive index), in the design of novel step- or graded-index multilayer refractive-index fibers has been adopted increasingly in various scenarios to satisfy specific application requirements. This paper introduces the design cases of step- and graded-index trench-assisted fibers. Under different evaluation parameters, the simulation results were compared with those obtained using commercial software OptiFiber. This paper presents comparisons of the mode-field intensity distributions for different fiber structures (Figs. 4 and 7). The effective refractive indices of various modes with eight significant figures match (Tables 2 and 4), and the variations in the mode-field diameter and effective mode area with wavelength show consistent results (Fig. 5). The dispersion curves of material dispersion, waveguide dispersion, and total dispersion as a function of wavelength are similar in most cases (Fig. 8).

This paper introduces the basic functions and case demonstrations of preliminarily developed fiber-waveguide structure design and simulation software, SeeNano. The software provides assistance and guidance in the optimal design of fibers and the selection of fiber parameters, thus enhancing the efficiency of fiber design. The accuracy of the software calculations was verified by comparing simulation results with those obtained using the commercial software OptiFiber. This reduces the difficulty in investigating and designing multilayer refractive-index fibers, reduces the dependence on foreign softwares, and promotes the development of domestic fiber-design softwares. Notably, our research and development team has developed a fiber-laser simulation software named SeeFiberLaser, which begins from the fiber-structure scale and considers the processes of various nonlinear effects, the mode evolution, and the coupling of various physical effects under different time-domain regimes. The software analyzes the effects of fiber device parameters on the laser power, spectrum, and pulse evolution in the longitudinal dimension. The next step is to conduct laser-fiber performance modeling and analysis on the full parameter dimension and multiphysical scale. By continuously improving the basic theory and performing collaborations to develop fibers and fiber-laser software, the associated application requirements shall be satisfied.