EuroWire July 2021

Technical Article

Research on cold-resistant optical cable in alpine regions By Qing Liu, Xindong He, Xianwei Zhao, Zhipeng Ren, Xiaoxu Ma, Fulong Zhang, Shuai Hu, Yifan Ding and Zhongkui Liu, Hengtong Optic-Electric Co Ltd, Suzhou, Jiangsu, China

Abstract Based on the natural geography and climatic conditions of the alpine region, this paper analyses the design basis of the high-cold and temperature-difference area optical cable through theoretical analysis, and discusses the impact of its unique environmental and climatic conditions on the optical cable and the problems encountered in the network engineering laying. The special cable structure and material selection in the alpine region are preliminarily discussed. In view of the cable problems related to low-temperature environments, several methods for reducing the shrinkage of the sheath and the loose tube are discussed, and the transmission performance and mechanical properties in low temperatures are tested so that the optical cable has a stronger mechanical performance against the low temperature. This paper has certain guidance for the design and manufacture of optical cables for use in alpine regions. 1 Preface The fibre optic cable is composed of a silica-coated fibreglass layer, a polymer buffer coating, a PBT sleeve and a special water-blocking jelly (cable jelly). The key points of the product are the selection of materials, cable structure design, cable-forming, and extrusion process control and other technologies. In the low-temperature environment of alpine regions, the defects of optical cable from material selection to optical cable design process parameters and production process technology will be amplified, resulting in material incompatibility of the optical cable, and leading to increased attenuation and “unable to connect”. These faults affect the quality of optical fibre transmission. There are large alpine areas with significant temperature difference between day and night in the north-eastern and north-western regions of China, and most of the regions have relatively long winters. For such areas, conventional fibre optic cable and engineering splicing equipment are selected to complete the deployment of optical networks. In long-term use, some optical cables have problems such as decreased transmission performance and changes in material temperature characteristics, which indirectly or directly affect the communication quality, severely restrict the deployment and normal use of optical communication systems, and become a prominent problem in the field of fibre optic cable R&D and manufacturing. Therefore, the industry urgently needs to focus on researching cold-resistant optical cables in alpine regions; fill gaps in this field as soon as possible; provide reference for operators, communication design units and optical fibre cable manufacturers; improve the quality level and availability of transmission networks; and promote continuous development of communication network construction.

2 Analysis of common faults of optical cable in alpine regions 2.1 Analysis of climate factors in alpine regions The alpine regions in China are usually cold and dry, with varying climates and unclear seasons. The cable laying environment is complex, with various topography such as plateaus, mountains, hills, plains, river valleys, etc. The temperate continental climate is also complex. The effects of temperate continental climate, plateau mountain climate and other climatic environments on optical cable communication mainly include large temperature difference between day and night, cold and dry, long sunshine duration, high solar radiation intensity and high wind speed. These factors influence the communication performance of optical cable from different angles. The specific faults caused are as follows. 2.2 Faults of optical cable in alpine regions Through the environmental analysis above, there are three main problems in the cable faults in cold regions: 1 – Normal operation of the cable under high and low temperatures At present, the most commonly used cable operating temperature range in China is -40 ~ +70°C, while the lowest temperature in most of the low-temperature areas in north-east and north- west China is below -40°C. Under low-temperature conditions, due to the different expansion coefficients between the coating layer, the tube and the optical fibre, the fibre is subjected to axial compression and micro bending, which leads to an increase in attenuation, thereby affecting the transmission of the entire optical communication system. For example, a certain section of the northern part of Heilongjiang Province is laid overhead, most of which is in the mountains, where the terrain is complicated, the temperature difference between day and night is large in winter, and the night-time temperature is lower than -40°C at its coldest. Optical cables often have alarms of OOF at night, and sometimes even a failure of losing signal, resulting in a communication interruption. The fault will be eliminated each time from 9:00 to 10:00 the next day. After the OTDR test, the reason for the poor operation of the systemwas that the temperature was too low, and a low-temperature blockage was formed, which caused the frame to be out of synchronisation in the communication system. After the temperature increased, the cable performance and cable system returned to normal. 2 – Influence of low temperature and large temperature difference on shrinkage of cable material The expansion and contraction of the components inside the cable will cause damage to the cable joint. The optical communication system fault can be classified into the following factors: • The loose tube is retracted into the cable from the cable splice closure, pulling the fibre reserved inside the splice closure to the micro bend to cause an increase in attenuation or breaking • The loose tube extends from the cable into the splice closure, pulling the fibre within the splice closure into a micro bend or a break

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July 2021