All-fiber low-loss connector for accessing both close cores of twin-core fiber

A novel all-fiber connector is proposed for connecting each core of a twin-core fiber (TCF) to a single-core fiber (SCF) core simultaneously and accessing independently the both close cores of the TCF. The connector is mainly composed of two cascaded pieces of collinear four-core fiber (CFCF). The two close optical fields launched from the TCF are separated into two far apart optical fields, so that each optical field could be butt-coupled into one of the cores of one gemini fiber segment, which has two single-mode SCF pigtails. For the simulated example, the center distance of the two optical fields is increased from 16 μm to more than 90 μm, the cross-talk is -37 dB, and the power loss is 0.056 dB. The feasibility of the strategy is partially demonstrated experimentally by fabricating a CFCF by groove & stack & draw method and one gemini fiber segment with pigtails by flame-brushing technology.