| At high altitudes,extreme weather conditions,frequent and variable geological hazards have a significant impact on the communication lines and equipment themselves,as well as their design,construction and operation and maintenance.There have been many problems with the communication facilities in operation on the plateau,which have affected reliable operation of the power communication network.Carrying out the research of plateau power communication support system is an important link to ensure safe and stable operation of power communication network in southwest China.The fiber optic link across the "Tibet-Central" region of China is made up of different types of fiber optic connections,which inevitably includes a large number of fiber optic fusion joints.How to improve the strength of the fusion joint while reducing its loss is an urgent issue to be solved in harsh environments.It is well known that,the ultimate ideal goal of fiber optic fusion splicing is to create an optical fiber fusion joint between two fibers that has both long-term high reliability and relatively low optical loss.However,there are still many problems with splicing performance between different types of optical fibers due to factors such as external environment,fusion tools and differences in fibers themselves.To date,both theoretical studies and experimental reports on the performance of optical fiber fusion splicing under high-altitude harsh conditions are too few and imperfect.The research results in plain areas have been confirmed by engineering practice that they no longer meet the needs of high-altitude areas.For example,fiber optic fusion splicing performance is reduced because the fiber optic fusion splicer work is highly susceptible to high altitude micro-meteorological effects.In addition,excessive splice loss and lower fusion reliability due to low fiber fusion strength in high-altitude environments have all exceeded fiber fusion splice performance budgets.How to solve the problem of poor fiber performance at the fusion joint of high-altitude fiber optic cable is a major issue worthy of study.This thesis has been completed under the financial support of"Research on Key Performance and Technology of Electricity Communication Facilities under Highland Micro-meteorology",a sub-project of the National Major Project of the Tibet-China Networking Project.The fusion splicing process of fiber optic cables in high altitude areas has been addressed,mainly including the study of the influence of fusion current on fiber core expansion and dopant diffusion during the fusion splicing of optical fiber and the research on the modeling of optical fiber fusion performance affected by the high altitude environment.In addition,both the corresponding various simulations and the field fusion experiment verification have been carried out for many times.The main work and innovative achievements of this thesis are as follows:Firstly,the performance of fiber optic fusion splicing in high altitude areas is explored.The discharge effect of the fusion splicer during optical fiber fusion splicing process is studied.The heat transfer characteristics in the fusion region are pondered on.The core expansion problem in the melting zone and the diffusion effect of dopants within the fiber core are analyzed.The effects of fusion current and fusion temperature on fusion time,splice loss and fusion strength are considered.The splice loss model and fusion strength model between different types of optical fibers are established,respectively.The calibration method for improving discharge current of the fusion splicer is given.At the same time,field fusion splicing experiments between different kinds of optical fibers have been carried out in areas with extremely harsh high-altitude environments,obtaining a large number of experimental data.Ultimately,the method is directly applied to the field fusion splicing engineering in high-altitude environment,triumphantly reducing the splice loss by at least 0.013 dB,while enlarging the fusion strength by at least 8.7 kpsi,and meanwhile promoting the success rate and efficiency of fiber fusion splicing,which has certain ref-erence significance for future research on optical fiber fusion splicing under different application scenarios.Secondly,the basic phenomena and theories of fiber optic fusion splice reliability are discussed in high altitude environments.The crack growth characteristics at fusion splicing joint are analyzed.The influence of splicing variables on fusion reliability due to the change of altitude is considered,introducing environmental factors such as temperature,humidity,oxygen content,atmospheric pressure,high wind and gravity.Concurrently,the relationship between inert strength and stress corrosion sensitivity factor of the fusion splice point and the change of altitude is provided.Moreover,the reliability model of optical fiber fusion splicing in high-altitude area is established.A method to improve the reliability of optical fiber fusion splicing in the high-altitude environment is proposed.Furthermore,many sets of field fusion splicing experiments have been conducted at different altitudes.Eventually,the proposed method is directly applied to the optical fibers field splicing projects in high altitude environment,saving construction cost of fiber optic communication link with large span and ultra-long transmission distance at high altitude area,which has certain reference significance for future research on fiber optic splicing reliability in high altitude environment.Thirdly,an exploratory study on fiber splice loss in high altitude environment is conducted.The main reasons of splice loss between two different single-mode optical fibers are analyzed.Then,the influence of the fusion parameters on splice loss during the fusion splicing process is discussed,The influence of fiber mode field diameter mismatch,axial offset,angular tilt and end gap on splice loss caused by high-altitude environment is analyzed in depth,combining effects of temperature,humidity,oxygen content,atmospheric pressure,high wind and gravity.A mathematical model to reduce the splice loss of single-mode fiber fusion splicing under high-altitude environment is established.Meanwhile,the main root causes of the high splice loss in high-altitude environment are sought out.Besides,multiple sets of repeated on-site fusion splicing experiments have been carried out at different altitudes(53m,2980m,4000m,4200m,4300m,5020m,5200m),obtaining a large amount of experimental data.Additionally,several groups of replicated field fusion-splicing experiments have been conducted in the typical "plain"area(53m)and the typical "high altitude" area(4300m),and then the two are compared in depth,which again verify the validity of the model proposed in this dissertation.Ultimately,the proposed method has been applied directly to on-site fiber optic fusion splicing projects in high altitude areas,greatly saving the construction cost and fusion time and achieving good results,which has certain reference value for future research on splice loss and fusion time between different kinds of optical fibers in different environments. |
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