Wavelength Dependence of Spatial Mode Dispersion in High-Density Randomly Coupled Multi-Core Fiber Cables

We experimentally and numerically investigate the spatial mode dispersion (SMD) characteristics of randomly coupled multi-core fibers (RC-MCFs) in high-density optical cables. Our experimental results show that cabling tends to reduce both the absolute value and the wavelength dependence of SMD, regardless of the number of cores and refractive index profiles of the RC-MCFs. Heat-cycle tests with temperature variations ranging from –30 °C to +70 °C indicate that SMD variations due to temperature changes remain within 1 ps/√km across the S–L band. Numerical simulations using a 2-core model suggest that the wavelength dependence of SMD is correlated with the wavelength dependence of the coupling coefficient at the most frequent bending radius (mode bending radius) in the cable. These results demonstrate that the SMD wavelength dependence of RC-MCF in the high-density cable can be reduced by simultaneously optimizing the core pitch, twist rate, and mode bending radius.