EuroWire July 2021

Technical Article

transmission wavelengths of 1,310nm and 1,550nm with OTDR under two large temperature-difference changes (-50°C ~ +70°C, and -60°C ~ +70°C). The temperature is cycled, and each point is tested at a constant temperature for 24 hours. The test results take the absolute value of the change. The specific results are shown in Table 3 . According to the method F1 “Temperature Cycle” in the national standard GB/T 7424.2-2008, the test results show that the additional attenuation at 1,310nm and 1,550nm is lower than 0.01dB/km, which is better than the special requirements in YD/T 901-2018 for allowing additional attenuation of the fibre. 4.2 Environmental performance test analysis For the environmental performance and mechanical properties of the cable, for the bending performance of the cable at low temperature, we use the bending test according to the relevant provisions of GB/T 7424.2-2008. The results show that the test is carried out after freezing at -60°C for 24 hours. The diameter of the cable is bent 15 times. The result shows that the fibre inside the cable is not broken, and the outer sheath is not cracked. Other mechanical performance indicators are shown in Table 4 , and the results all meet the relevant indicators in YD/T 901-2018. 4.3 Test result analysis The cold-resistant optical cable uses low-temperature characteristic fibre gel and low-temperature resistant PBT material. Under the condition of fully satisfying the tensile performance in the cable-forming process, the fibre length in the casing is strictly controlled, and a suitable cable compression window is designed to ensure the temperature difference of the cable after the temperature difference. There is enough free space to avoid the increase in temperature additional loss due to the micro bend loss caused by the low temperature change of the fibre gel. The experimental results show that the additional loss caused by the temperature change of the optical fibre is less than 0.01dB/ km, which effectively guarantees the normal operation of optical communication in alpine regions. The outer sheath of the cable is made of anti-cracking HDPE material, which avoids the breakage of the jacket under temperature ageing, thus ensuring the normal use of the cold-resistant cable and meeting the requirements of the normal operation of the communication network. 5 Conclusion This paper analyses various problems encountered in the practical application of cold-resistant optical cables in alpine regions, and summarises the relevant precautions of cold-resistant optical cables in the selection, design, production and construction of raw materials, which is the performance of optical fibre communication networks in an alpine environment. The protection has important significance, and it also has certain guidance for the construction of optical cable network lines and the prevention and maintenance of faults in other climate and topographic environments in China. 6 Acknowledgements The authors would like to express gratitude to everyone who cooperated in the completion of this paper and manufacture of the product. Thanks to our R&D engineering teams for designing, tracking and testing the samples. n No. 1 2 3 4

Standard requirement

Test results

Test conclusion

Test items

Unit

The fibre should not break and the sheath should be visible

Low- temperature bending performance

The fibre is not broken, the sheath is not cracked

M pa

Qualified

without cracking

Changing rate of tensile strength of sheath before and after ageing Changing rate of elongation at break of sheath before and after ageing

(100 ±2) °C, after 240 h ≤20%

%

15.9% Qualified

(100 ±2) °C, after 240 h ≥300%

%

688% Qualified

Thermal shrinkage

% 100°C, 4 h ≤5%

2%

Qualified

50°C, 96 h Failures/ samples: 0/10

5 Environmental stress cracking number

0/10

Qualified

▲ Table 4: Environmental performance test results of cold-resistant cable

7 References

[1] Chen Bingyan: Design and manufacture of optic fiber and fiber optic cable [M]. Zhejiang University Press, 2016. [2] YD/T839.2-2014: Filling compounds and flooding compounds for telecom- munication cable and optical fiber cable-part 2: Filling compounds for optical fiber. [3] YD/T1118.1-2001: Secondary coating materials used for optical fiber-part 1: Polybutylene terephthalate.

Courtesy of IWCS Cable & Connectivity Symposium, Charlotte, North Carolina, USA.

Hengtong Optic-Electric Co Ltd Suzhou Jiangsu China

liuqing@htgd.com.cn www.htgd.com.cn

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July 2021