Weakly Coupled Homogeneous 3-Mode 4-Core Fiber With Standard Cladding Diameter

We propose a design concept of a 3-mode 4-core fiber (3M-4CF) with a common depressed (CD) layer and numerically investigated the tradeoff between the optical confinement loss and inter-core crosstalk (XT) for it and three other types of weakly coupled homogeneous 3M-4CFs, i.e., with step index (SI) cores, trench-assisted (TA) cores, and W-shaped (W) cores, with the standard 125-mu m cladding diameter. We reveal that the CD-type 3M-4CF is efficient in suppressing optical confinement loss while maintaining a feasible inter-core XT. We confirm the feasibility of the proposed design concept on the basis of evaluating the optical characteristics for the fabricated CD-type 3M-4CF. We further optimize the design of the CD layer to achieve lower loss. We also show a tradeoff between the micro-bending loss sensitivity and the inter-core XT in our proposed CD structure.