We report experiments on a new laser architecture involving phase contrast filtering to coherently combine an array of fiber lasers. We demonstrate that the new technique yields a more stable phase-locking than standard methods using only amplitude filtering. A spectral analysis of the output beams shows that the new scheme generates more resonant frequencies common to the coupled lasers. This property can enhance the combining efficiency when the number of lasers to be coupled is large.
A 2D array of fiber lasers has been passively coupled by a phase-contrast imaging technique in a ring cavity. Efficient coherent operation was demonstrated for 3 × 3, 4 × 4 and finally 4 × 5 ytterbium doped fiber lasers. A phase locking level of 78% was measured with 20 lasers in agreement with simulations. Passive synchronization was stable in time despite the unprotected environment. The measured performances clearly surpass the initial limitation found for passive fiber laser coupling. The improved efficiency and stability are believed to be connected with the contribution of gain to the phase accumulated on a cavity round-trip together with the cavity design.
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