EuroWire November 2024

Technical Article

Multi-core fibre cable development By Don Parris, Pierre Sillard, Adrian Amezcua and Clint Anderson, Prysmian Group; and Rodrigo Amezcua, Juan Carlos and Jose Lopez, University of Central Florida

Abstract In recent years, fibre optic cables with increased optical fibre packing density have become increasingly prevalent because of their ability to maximise limited duct space usage. One promising way to increase the fibre packing density consists of using multi core fibres (MCFs). MCFs are of particular interest because they are easy to connect thanks to now well-mastered fan-in/fan-out (FI/FO) technologies. In this paper, the development and testing are reported for a new 288f ribbon in central tube (RICT) cable containing four-core fibres. 1. Introduction High-density cables have recently received considerable attention because of their ability to meet traffic demand in limited duct spaces, but also because they enable faster, more cost-effective and eco-friendlier installations. One promising way to increase cable density consists of using MCFs or few-mode fibres with standard 125μm cladding diameter [1-4] . In this context, uncoupled MCFs are of particular interest because they are easy to connect thanks to now well-mastered FI/FO technologies and because they are compatible with a reduced coating diameter of 200μm (vs legacy 245μm), thereby further increasing the density [1,2] . In this paper, the development and testing are reported for a new cable containing MCFs. A 288-fibre central tube cable with 24 flexible ribbons was manufactured and tested. Each flexible ribbon contained 12 fibres. All fibres had dual-layer acrylate coating with diameter of 200μm. 23 of the ribbons contained standard single-mode fibres (SMFs); the 24 th ribbon was made using four-core fibres. All of these MCFs were made from the same fibre preform. The cable design was a Prysmian standard design for this fibre count and used all standard materials and dimensions. The cable length was 2,600m. 2. Multi-core fibres Figure 1 shows the cross section of the four-core fibre with a standard 125μm cladding diameter. A trench-assisted step-index

respectively. The crosstalk value was below -50 dB/km at 1,550nm, which is expected for an MCF with a cladding diameter of 125μm and four cores based on trench step-index profiles [3] . FI/FO is based on a tapered fibre device that can be directly spliced to the four-core MCF. FI/FO pairs were spliced to the four core fibre, in which losses below 0.3 dB were achieved. 3. Cable design The cable consisted of the following components: optical 12-fibre ribbons (24), water-swellable tape, buffer tube, strength members, ripcord(s) and cable jacket. This cable had a final outer diameter of about 9.4mm. Figure 2 shows a photo of this 288-fibre ribbon in central tube (RICT) cable.

jacket anti-buckling elements buffer tube water swellable tape

Figure 2: 288-fibre ribbon in central tube (RICT) cable

4. Testing The cable was temperature cycled according to ICEA-744 and the optical attenuation was monitored. Prior to temperature cycling, ten of the fibres in the multi-core flexible ribbon were concatenated so that they could be tested essentially as a single, long MCF. This allowed the use of only two FI/FO assemblies to monitor all cores in these ten MCFs and allowed for bi-directional optical measurements. Figure 3 shows the attenuation profile for one of the four concatenated cores in the MCF. The performance of this core is similar to the other three cores. Here one can see that the average and maximum splice loss was relatively low and that the series of concatenated fibres showed an average attenuation of about 0.285 dB/km.

profile was chosen for the core that allows it to reach low crosstalk values and that can be compliant with both ITU-T recommendations G.652.D and G.657.A2. The average core pitch is 41.4μm. The mode field diameters, cable cut-off wavelengths and chromatic dispersions are compatible with ITU-T recommendation G.652.D. The average attenuations are 0.355 dB/km and 0.197 dB/ km at 1,310nm and 1,550nm,

Figure 1: Four-core fibre cross section

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November 2024