EuroWire September 2024

Technical Article

original optical attenuation, because the inner space availability within the three divided segments allows cabling of optical fibres with almost zero stress. 4.3 Attenuation variation during cable laying operation Attenuation variation during cable laying operation was evaluated through ITU-T Recommendations G.976 test. Our past study supports that the ITU-T test results are well consistent with attenuation variation during/after field laying operations. [2] All evaluation tests were performed on cable samples and completed with excellent results. Table 2 summarises the test condition of the tensile test with twist restrained. During the tests, optical attenuation was continuously monitored and any variations recorded. The test results are summarised in Table 3 . We obtained excellent results with SC530. Attenuation variation of 200μm diameter optical fibres was small during/after the test.

No.

Item

1

Manufactured cable loss

2

Temperature stability

3

Hydraulic pressure resistance

4

Tensile test with twist restrained

5

Tensile test with torque minimised

6

Mechanical fatigue test

7

Sheave tests

8

Crush resistance

9

Impact resistance

10

Flexure resistance

11

Water ingress tests

Sample length

Approximately 123m

12

Tensile test for fibre itself

Condition of cable end

Twist restrained at both ends

Table 1 : Evaluation test items

Load

NTTS

These points can be achieved by the three-divided steel segment structure design mentioned in section 2 and unique/suitable fibre cabling technology: well-established fibre excess length (fibre slack) control parameters; wide inner space for fibre allocation; and a finely managed process to minimise macro-/micro bending-induced losses and secure the mechanical reliability to obtain the best transmission performance from optical fibres.

1 hour cycle + 2 short time cycles Variation: N/A Residual: ±0.005dB/km

Time

Target

Table 2 : Test condition of tensile with twist restrained

SC530 24-fibre-pair cable

4. Evaluation test 4.1 Evaluation test items

NTTS

60kN

There are three main points to evaluate. The first point is attenuation variation during the cabling process; the second is attenuation variation during the cable laying operation; and the third is mechanical properties after the cabling process. Since the cable structure is based on conventional OCC-SC530, mechanical performance is not changed. 4.2 Attenuation variation during cabling process In 2022, our manufacturing and evaluation test of SC530 with 24 fibre pairs was completed with excellent results. Figure 2 shows optical attenuation variation during the cabling process: attenuation values after copper tubing and LW (PE insulating sheath) process shows small variation from fibre’s

Optical attenuation (variation) Optical attenuation (residual)

±0.000 ~+0.024 dB/km

+0.001 dB/km

Table 3 : Test result of tensile with twist restrained

4.4 Mechanical properties of 200µm fibres after cabling process Thinner coating is assumed to be weaker against external attack (puncture/abrasion resistance) than current 250μm fibre design. In the past, when changing from 400μm to 250μm fibres, we experienced a lot of fibre breaking issues during the cable manufacturing. Engineers struggled to improve the cleanliness of the cable manufacturing process and to improve the surface/material of each fibre path line. We evaluated the tensile strength of 200μm fibres after the cabling process to confirm our cabling process capability and the robustness of the thinner coating. Also, the appearance of fibres was visually inspected with a microscope. The sample fibres were taken from SC530 cable. We confirmed no anomaly in appearance of 200μm fibres and no degradation of tensile strength. The next step in this development is to confirm whether the mechanical properties of fibre change after cable is handled under the expected dynamic tensile conditions, foreseeing for cable laying and recovering operations.

Figure 2 : Attenuation variation during cabling with 24 fibre pairs

62

www.read-eurowire.com

September 2024