Temperature and Moisture Impact on Polarization Mode Dispersion in Carrier Grade Optical Fibre Links in Kenya

Abstract

In this research work, an investigation was carried out on the impacted environmental factors in Kenya influence Polarization Mode Dispersion (PMD) in an already buried fibre optic cable in the field. A case study was conducted on Liquid Telecom Kenya backbone infrastructure that spans across two main climatic areas. Machakos, located within Northern lowlands with a semi-arid climate, Mau-Summit within Rift Valley and Central highlands were analyzed. A range of data showing change of temperature and relative humidity conditions were obtained alongside PMD tests at different temperature and soil moisture in the field. The results of this work revealed that rise or drop in relative humidity usually does not have immediate influence on PMD but influences temperature that in-turn influences PMD. Relative humidity influence had a negligible impact on PMD in the highlands but had a consistent impact against PMD in semi-arid. A plot of relative humidity against PMD showed an inverse relationship with PMD in semi-arid areas. Comparison between the two tests regions revealed that PMD coefficient recorded in semi-arid region was higher by a factor of 2.6 compared to PMD measured in highlands. 5% of hourly PMD fluctuations in the fibre cable deployed in semi-arid region exceeded industry recommended maximum PMD coefficient of 0.2 𝑝𝑠/𝑘𝑚2. This revealed an outage margin ratio 𝑀𝑇 of 2.13 on 10Gbps links using the cable effectively leading to network outages caused by PMD fluctuations. A 10Gbps link that is safe from PMD induced outages should have minimum outage margin ratio of 3. The results further showed plenty of life-time left in the cable deployed in highland areas because PMD fluctuations never exceeded maximum recommended PMD coefficient. This led to a conclusion that cables stay longer in the filed in deployed in a highland area compared to semi-arid areas. The outage margin ratios for 10Gbps and 100Gbps links were 5.33 and 15.99 respectively. The outcome of this work recommends that Liquid Telecom Kenya should continue carrying out PMD tests alongside replacing high PMD sections in an effort to manage link stability. This being the first PMD analysis on the fibre, routine PMD analysis was recommended in order to track rate of cable aging in highlands because remaining cable life should be determined after routine PMD tests