Sumitomo Electric unveils coupled multi-core optical fiber suitable for ultra- long haul transmission

Sumitomo Electric Industries, Ltd. (Osaka, Japan) has developed a new type of coupled multi-core optical fiber suitable for ultra-long-haul transmission, which the company says has set new records for low attenuation*1 and the low spatial mode dispersion*2 in optical fibers for space division multiplexing.

The company maintains that data network traffic in long-haul transmission systems is growing due to the widespread uses of smartphones, data centers, and other applications; and that transmission capacity has been improved with the use of low-loss single-mode fibers. At the same time, to realize such drastic improvements in capacity, space-division multiplexing (SDM) has been intensively studied, and multi-core fiber (MCF) is expected as a next-generation optical fiber that can realize ultra-high-capacity transmission systems.

For its part, Sumitomo Electric has now developed a coupled-core MCF (CC-MCF) including 4 pure-silica cores in the standard 125-µm cladding. The developed fiber has achieved the attenuation of 0.158 dB/km at the wavelength of 1550 nm and the spatial mode dispersion (SMD) of 6.1 ps/√km in the wavelength from 1520 to 1580 nm, both of which are the lowest ever reported in the optical fibers for space division multiplexing, contends the company.

The new product's ultra-low attenuation -- approaching that of the commercial ultra-low-loss single-mode fiber (SMF) -- enables signal transmission with lower noises than previously-reported SDM fibers, and is expected to realize the spatial channel count increase without per-channel capacity degradation. Sumitomo maintains that the SMD of 6.1 ps/√km is one fifth the lowest SMD of previously reported SDM fibers, and thus can reduce the calculation complexity of the multiple-input-multiple-output (MIMO) digital signal processing (DSP)*3 for the crosstalk compensation. Furthermore, the developed CC-MCF with the standard 125-µm-diameter cladding can be cabled with existing cable designs for standard optical fibers, and is expected to have high mechanical reliability equivalent to that of standard optical fiber. Learn more.*1: Attenuation, or (transmission) loss, is the amount of light degraded by scattering and absorption while traveling in an optical fiber. With a lower attenuation, optical signals can be transmitted for a longer distance. The lowest loss of the commercial optical fiber is 0.154 dB/km at 1550 nm, which is realized in the ultra-low-loss single-mode fiber for submarine transmission. The attenuation of the standard single-mode fiber is around 0.185 dB/km. The lowest attenuation of the previously-reported SDM fibers was 0.168 dB/km (averaged over cores).

*2: Spatial mode dispersion (SMD) is the amount of the time spread of the light pulse, induced by the optical path differences between multiple optical paths in an optical fiber. The lower SMD is preferable because the DSP calculation complexity can be reduced.

*3: Multiple-input-multiple-output (MIMO) digital signal processing (DSP) is the digital calculation that can compensate the crosstalk of the MCF and the MMF. Fully mixed signals can be untangled to the original individual signals.