Long-Term Polarization Mode Dispersion Evolution and Accelerated Aging in Old Optical Cables

Today's optical networks are composed of thousands of kilometers of aging optical cables. Many of these cables are located in harsh environments, which contribute to induced birefringence of the fibers and a corresponding increase of polarization mode dispersion (PMD). This letter introduces derived statistics from the longest-known running evaluation of a PMD measuring campaign and an investigation into how higher optical power affects these aging systems. Results indicate strong seasonal dependence of PMD on temperature for an optical cable test bed exposed to atmospheric changes, leading to a 16% increase of a mean PMD value in summer. This fluctuation causes bit error rate limits to be exceeded for 10 and 40 Gbps non-return-to-zero signals, which is a critical issue for applications where high reliability is required. Moreover, due to the high optical power load within old optical infrastructures, a more than 0.15 dB increase of relative loss per year in tested routes, compared with reference routes, has been observed.