Phase-locking of multicore fibre laser due to talbot self-reproduction

The multicore fibre laser (MCFL), containing an array of single-mode microcores in a circle inside the pump core, is a promising compact laser source. The problem is to synchronize the radiation of microcores with different propagation constants at a given radiation frequency. The theory of phase-locking of an MCFL with an external mirror and an annular waveguide matched to the multicore fibre and having a length some fraction of the Talbot distance is developed. Collective mode selection appears to occur due to spatial filtering at fractional Talbot distances, while the radiation frequency self-adjusts within the spectral gain range to minimize losses. Parallel coupling between microcores is achieved in the limit of a small fill factor. The maximum number of microcores that can be coupled is found. Good agreement is achieved between the theory and previously published experimental results.