Photonic crystal fibers supporting fully separated eigenmodes.

We present two kinds of fully degeneracy-lifted solid-core photonic crystal multi-mode fibers aiming at multiple-input multiple-output-free direct fiber vector eigenmode multiplexing transmission. One of the target fiber structures is able to support 52 fully separated eigenmodes with effective index difference above 1.37×10-4 and confinement loss below 3.28×10-5   dB/km over the whole C+Lband (1530-1625 nm). Specifically, it is suggested that >10-4 effective index separation is sufficient to possess polarization-maintaining properties, while for short-reach stable mode-division multiplexing transmission, the effective index difference >10-3 is highly desired. In particular, the other target fiber structure can further increase effective index separation above 1.10×10-3 among 24 eigenmodes with confinement loss below 6.68×10-4   dB/km over the whole C+L band.