I. Introduction
Connecting a multi-core fiber and single mode fibers (SMFs) is one of the core elements to realize transmission systems by the space division multiplexing (SDM) with multi-core fiber (MCF) to expand the transmission capacity [1]. The device is called “fan-in/fan-out device(FI/FO device)” and various development results of FI/FO devices were reported [2]–[7].