Optimization of GRIN lenses coupling system for twin-core fiber interconnection with single core fibers

We aim at a more compact, flexible, and simpler core-to-fiber coupling approach, optimal combinations of two graded refractive index (GRIN) lenses have been demonstrated for the interconnection between a twin-core single-mode fiber and two single-core single-mode fibers. The optimal two-lens combinations achieve an efficient core-to-fiber separating coupling and allow the fibers and lenses to coaxially assemble. Finally, axial deviations and transverse displacements of the components are discussed, and the latter increases the coupling loss more significantly. The gap length between the two lenses is designed to be fine-tuned to compensate for the transverse displacement, and the good linear compensation relationship contributes to the device manufacturing. This approach has potential applications in low coupling loss and low crosstalk devices without sophisticated alignment and adjustment, and enables the channel separating for multicore fibers.