We propose an ultra-low inter-core crosstalk (XT) multi-core fiber (MCF) with standard 125-μm cladding. We show the fiber design and fabrication results of an MCF housing four cores with W-shaped index profile; it offers XT of less than -67dB/km over the whole C+L band. This enables us to realize 10,000-km transmission with negligible XT penalty. We also observe a low-loss of 0.17dB/km (average) at a wavelength of 1.55μm and other optical properties compatible with ITU-T G.654.B fiber. We also elucidate its good micro-bend resistance in terms of both the loss and XT to confirm its applicability to high-density optical fiber cables. Finally, we show that the fabricated MCF is feasible along with long-distance transmission by confirming that the XT noise performance corresponds to transmission distances of 10,000km or more.

A PLC based mode multi/demultiplexer based on asymmetric directional coupler has advantages in terms of compactness, mass productivity, low insertion loss, and matured reliability. However, it has relatively large wavelength dependence due to the difference of coupling length. To expand the bandwidth, we have designed two-mode (LP01/LP11a) multi/demultiplexer by wavefront matching method and demonstrated the broadband and low-loss characteristics. This paper reviews the device design by wavefront matching method and investigates the mechanism of its broadband characteristics.