Abstract

The theory and properties of weakly coupled few-mode fiber (FMF) have been investigated by means of mode power distribution. According to that, a novel weakly coupled FMF with a combined-ring core structure has been proposed. To the best of our knowledge, it is the first time a weakly coupled FMF has realized the goal of supporting six modes and ultra-large minimum effective index difference (min $\mathrm{\Delta }{n}_{\mathrm{eff}}$) of $1.83*{10}^{-3}$ between all neighboring modes. The combined-ring core structure evidently relieves the pressure of modifying $n_{\mathrm{eff}}$ via inserting a single low-index area and a single high-index ring in step-index FMFs. Due to this structure, a weakly coupled FMF design can be realized by the smaller low-index central area (central area radius $d=0.82\mathrm{\mu m}$) and lightly doped high-index ring (the refractive index difference between the ring and the core $\mathrm{\Delta }{n}_2=0.11\%$) compared with former designs. The effective area ($A_{\mathrm{eff}}$) and differential mode delay characteristics of the designed FMF have been optimized. Furthermore, we calculated the bending loss and fiber properties at the C and L bands to prove that our proposed FMF satisfies the requirement of large-capacity mode-division multiplexing optical networking.

© 2019 Optical Society of America

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