High-power filled-aperture coherent beam combining of narrow-linewidth fiber lasers

High-power coherent beam combining (CBC) technology provides a robust solution for overcoming the power limits of single-channel fiber lasers while maintaining excellent beam quality, spectral characteristics, and coherence. In this study, a two-channel filled-aperture CBC experimental platform based on a beam splitter was established. Active phase control was implemented using a multi-dithering algorithm. The initial residual optical path difference was compensated to within 0.5ps by a combination of coarse adjustment via polarization-maintaining (PM) fiber splicing and fine-tuning with a high-precision variable delay line. CBC experiments were performed using 20 GHz narrow-linewidth linearly polarized fiber lasers, achieving a combined output power of 489.2 W with an average closed-loop combining efficiency of 95.4 %. The phase-locking residual error at full-power operation was measured at λ/34. The combined beam exhibited near-diffraction-limited beam quality (Mx2 = 1.21, My2 = 1.32), with nearly negligible spectral broadening.