The invention relates to optical fiber communications. A multicore optical fiber comprises at least two light-guiding cores made of doped fused silica with refractive indices nc1, nc2, nck, each light-guiding core of the at least two light-guiding cores being surrounded by a respective arbitrarily shaped inner reflecting cladding made of fused silica or doped fused silica with refractive indices nc11, nc12, nclk, which are less than the refractive indices nc1, nc2, nck of respective light-guiding cores; a continuous or intermittent barrier region made of fused silica and having an arbitrary cross-sectional shape, the barrier region being formed in the space between the inner reflecting claddings and an outer cladding of fused silica with refractive index n0, the barrier region having refractive index nb, which is less than the refractive index of each of the inner reflecting claddings; and an external protective coating. In another embodiment the barrier region can be formed of through holes in fused silica or doped fused silica.