| Summary: | We present the theoretical study of polarization-maintaining multi-core few-mode fiber (PM MC-FMF) with a cladding diameter of 125 μm, in order to secure the maximum number of independent spatial channels arising in the single fiber. By taking both the inter-core crosstalk (XT) and the intra-core mode coupling into account, we identify that the PM five-core three-mode fiber is able to provide 19 parallel channels without the need of MIMO signal processing. After the numerical optimizations, the inter-core XT of MC-FMF is less than −30 dB/100km, due to the use of trench-assisted heterogeneous core distribution. Meanwhile, the effective refractive index (RI) differences among both spatial modes and polarization modes are more than 8 × 10<sup>−4</sup> and 3.26 × 10<sup>−4</sup> over the C+L band, respectively, due to the introduction of stress and geometric birefringence. Moreover, the cladding diameter of such MC-FMF is the same as that of the standard single-mode fiber (SSMF), leading to a convenient upgrading from the SSMF to the MC-FMF.
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