Takuji Nagashima

Crosstalk variation of multi-core fibre due to fibre bend

It was experimentally and theoretically confirmed for the first time that inter-core crosstalk can be varied more than 20dB depending on bending radius. Simulation results based on coupled-mode equation with equivalent index model are in good agreement with measurement results.

1705-km transmission over coupled-core fibre supporting 6 spatial modes

We present experimental transmission results for a novel 6-core coupled-core fibre with 125 μm cladding diameter. We transmit combined 2-polarization, 6-SDM and 30-WDM channels over a distance of 1705 km, with a spectral-efficiency-distance product of 30690 bit/s/Hz km.

Propagation characteristics of seven-core fiber for spatial and wavelength division multiplexed 10-Gbit/s channels

Propagation characteristics of seven-core fiber were investigated for multiplexed signals of spatial-division and wavelength-division. Effect of chromatic dispersion and inter-core crosstalk were evaluated for 5-km fiber by using 10-Gbit/s channels.

Demonstration of Cladding-Pumped Six-Core Erbium-Doped Fiber Amplifier

We demonstrate cladding-pumped six-core Erbium-doped fiber amplifiers (EDFAs) using two different pump coupling schemes: edge-coupled and side-coupled pumping, where a single multimode laser diode can be applied to pump all cores. Using two in-line cladding-pumped EDFAs at the input and output of a 31-km coupled-six-core fiber, we realized 465-km space-division multiplexing and wavelength division multiplexing transmission in a recirculating loop and achieved a spectral efficiency of 18 bits/s/Hz. Through side-coupled pumping, the cladding-pumped six-core EDFA produced >18-dBm output power per core and had <;6-dB noise figure across the C-band.

6-Mode 19-core fiber for weakly-coupled mode-multiplexed transmission over uncoupled cores

Design and fabrication results of a 6-mode 19-core fiber with the highest relative core multiplicity factor of 30 for weakly-coupled mode-multiplexed uncoupled-core-multiplexed transmission are detailed. Technical challenges for long-haul transmission are also discussed.

Six-Mode 19-Core Fiber With 114 Spatial Modes for Weakly-Coupled Mode-Division-Multiplexed Transmission

This paper describes a six-mode 19-core fiber with 114 spatial modes, which was designed and fabricated for weakly-coupled mode-division-multiplexed (MDM) transmission over uncoupled cores. The 19 identical graded-index cores were packed on a hexagonal lattice with a 62-μm pitch in a ∼318-μm-diameter cladding. The cladding diameter is large, but still mechanically reliable by assuming a 2% proof test and 40-mm minimum fiber bend radius. The inter-core crosstalk is negligibly suppressed and the calculation indicated that a 50-μm core pitch (corresponding to the 266-μm-diameter cladding) is achievable without significant crosstalk degradation. Though the fiber was intended for the weakly-coupled MDM transmission, the differential mode delay (DMD) within a degenerated mode group of LP21 and LP02 modes was not well suppressed. Thus, further DMD suppression within each mode group or splitting the degeneracy of the modes is required to realize multiple-input multiple-output (MIMO) digital signal processing with reduced complexity. Additionally, a numerical investigation revealed that the intra-core inter-modal crosstalk at a butt coupling was induced not only by the misalignment, but also by the refractive index profile mismatch between the butt-coupled cores. Therefore, the tight tolerance on the refractive index profile is important both for DMD control and modal crosstalk suppression.

Transmission over coupled six-core fiber with two in-line cladding-pumped six-core EDFAs

We demonstrate two in-line cladding-pumped 6-core Erbium-doped fiber amplifiers with recirculation loop transmission over 465-km coupled-6-core fiber. Total capacity of 7.2-Tb/s SDM/WDM transmission is achieved with a spectral efficiency of 18-bit/s/Hz.