The three-dimensional space-division Y-splitter for multicore optical fibers (MCF) is a 3-D device that depends on space-division splitting (SDS) by double-hump graded-index (DHGI) in a rectangular waveguide. It includes multiple single Y-splitters, each one being dedicated to one MCF core. Each Y-splitter layer has three stages, including an expander; a DHGI-SDS; and a separator. The net result of the Y-splitter is that the signal in a single multi-core fiber input has its optical power split 50-50 between two multi-core fiber outputs without an intermediate single-core single-mode fiber (SMF) conversion stage.