Study of fabrication reproducibility of two-mode optical fibers for mode division multiplexing with MIMO processing

We propose a two-mode optical fiber (TMF) with a low sensitivity of differential modal group delay (DMD) to change of the core radius and the refractive index of the core in the index profile which are major factors for DMD deviation. This was done to achieve high reproducibility of fiber fabrication. The proposed TMF has a graded index (GI) core and a depressed inner cladding, and we optimize structural parameters. We fabricated different kinds of TMFs to confirm the low DMD sensitivity of our proposed fiber. The fabricated TMF showed that the DMD sensitivity to changes in core radius of the TMF was approximately 8 ps/km/μm which is 98% smaller than that of a GI-TMF without a depressed inner cladding.