Calculations of a fibre amplifier with the hexagonal waveguide structure

An ytterbium-doped fibre amplifier with the hexagonal structure containing seven waveguides is simulated by using a numerical program based on the scalar paraxial optics approximation. The influence of the scatter in parameters of active fibre cores on spontaneous phasing discovered earlier is studied numerically for the first time. The critical scatter in the core parameters at which the phase locking of radiation is preserved is found. It is shown that a decrease in the numerical aperture of fibre cores facilitates the stabilisation of phase locking.