By propagating beamlets from a periodically placed array of single-mode fiber amplifiers in a large mode-are (LMA) fiber, we find that a self-image of the initial beamlets is formed at certain distances in the LMA fiber. A Talbot mirror fiber device (TMFD) based on this property is proposed for phase-locking of a multi-fiber laser. For this laser system, we investigate how the LMA fiber length variation; the fiber amplifier phase variation, amplitude variation, and displacement affect the self-image qualities and the coupling efficiency.