The outputs of two fiber lasers have been combined in an external cavity. This proof-of-concept demonstration shows the feasibility of beam combining many (tens to hundreds) fiber gain elements.
C. C. Cook and T. Y. Fan, "Spectral Beam Combining of Yb-doped Fiber Lasers in an External Cavity," in Advanced Solid State Lasers, M. Fejer, H. Injeyan, and U. Keller, eds., Vol. 26 of OSA Trends in Optics and Photonics (Optical Society of America, 1999), paper PD5.