Abstract Multicore fiber (MCF) is treated now as a perspective medium for high-power fiber lasers. Here we report on the point-by-point femtosecond (fs) inscription of highly-reflective fiber Bragg grating (FBG) array in all cores of 7-core Yb-doped fibers. By using such complex mirror, we achieved high-power laser generation at a wavelength of 1064 nm in two types of active MCF with different core-to-core distance. At cladding pumping by a 976-nm laser diode of 50 W power, both the MCFs with FBG cavity generate nearly the same output power of up to 33 W, but the laser spectra behave principally different since the generation of the cores is almost independent or strongly coupled in these two cases. To study the effect, we develop analytical model and perform its experimental verification identifying the role of core coupling and FBG characteristics on the generated mode and its spectrum. It is shown that the coupling of the MCF cores leads to the formation of supermodes and their hybridization when reflected from an array of highly-reflective FBGs in a resonator, therefore generation occurs with the same spectrum in all cores, despite the significant difference in the central wavelengths and the shape of the reflection spectra of individual FBGs.

Influence of core coupling on spectral characteristics of 7-core Yb-doped fiber laser with fs-inscribed FBGs