Abstract: Modern technology allows for manufacturing of multicore fibers composed of a number of microcores placed on a circle and doped with Nd$+3$PLU$/ ions. The construction is attractive because of effective absorption of diode laser pump radiation. High-power conditions are easily achievable, and phase coupling between microcore lasers looks very promising for receiving high-brightness radiation from compact fiber lasers. To understand in detail coupling between microcores and evaluate an opportunity to achieve phase-locked operation of the array, a mathematical code describing light propagation in this composed fiber was developed. A numerical code performs direct integration of scalar wave equation in paraxial approximation. Refractive index profile corresponds to N index-guiding microcores. The composite fiber was embedded into square region imitating fiber cladding with lower index. The wave equation was solved using a splitting technique for diffraction/refraction processes on every propagation step. Calculations on the diffraction step were made with help of 2D FFT technique on Cartesian mesh. Numerical accuracy was checked by special tests. Results on simulations of microcore array excitation by injection of a beam into one of microcores will be reported. For realizable in experiments conditions coupling lengths are found. Evolution of far-field patterns for different fiber lengths was studied.!9
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