From the planning stage to the deployment of an undersea fiber-optic cable, a considerable amount of time, money and resources are invested to ensure the success of the submarine network. A point that is often overlooked during this process, and which can lead to unfortunate delays, is the final acceptance test of the fiber—simply put, it comes down to making sure that the fiber can deliver on the promised and expected bandwidth. This final acceptance test is often ignored since legacy data rates are considered as being extremely challenging to transmit.
With the deployment of 40G/100G, newer and more serious challenges are at hand, and in order to face them, they must be understood and properly prepared for. To do so, there are some critical physical layer tests that must be performed, including dispersion testing, such as chromatic dispersion (CD) and polarization mode dispersion (PMD). Tests that were considered as being of some importance at 10 Gbit/s, have become critical at 40G/100G transmissions.
Once these parameters have been fully qualified and optimized, the system turn-up test must then be performed. These include signal power level and optical signal-to-noise ratio (OSNR) measurements, important in both repeated transoceanic or festoon links. Finally, the network end-to-end level qualification must be done; this is where all the relevant SONET/SDH tests are performed, including tests such as bit error rate (BER).