Heterogeneous 12-Core 4-LP-Mode Fiber Based on Trench-Assisted Graded-Index Profile

We design a heterogeneous 12-core 4-LP-mode fiber having two different types of cores and trench-assisted graded-index profiles. For the optimum design of the index profiles of these two heterogeneous cores, we first investigate the impacts of various geometric parameters on the effective refractive index of each LP mode, maximum differential modal delay (DMD), and bending losses of the guiding and higher order modes. We then design a heterogeneous 12-core 4-LP mode fiber having a cladding diameter of 242 $\mu {\rm m}$ . The numerical analyses based on the coupled-mode equation show that the inter-core crosstalk levels of the proposed fiber are lower than $-$ 55 dB/km, regardless of modes, as long as the fiber is not bent tightly with a bending radius of $\times$ 10 $-$ 3 $\mu {\rm m}$ $-$ 2 and 42.2, respectively.