Issue link: https://www.e-digitaleditions.com/i/1066130
January/February 2019 I 45 including the core, cladding, adhesive layer and contact zones. With MPO connectors, only two zones matter: the core and the cladding (see Figure 7). Proactive fiber inspection is essential before connecting any fibers. If the end faces are not dirty, then they can be connected. If there is any dirt, clean it and then inspect it again to make sure the cleaning process was effective. A common mistake is cleaning before inspecting the fiber, but there is no point in cleaning something that is already clean, and that fiber end face should not be touched more than necessary. Cleaning MPO connectors can be a challenge. There are specific tools on the market to do it. The one click cleaners have become popular over the last several years. They are easy to use, because they can clean inside of a bulkhead as well as the fiber end face itself. The cleaning tape these devices use is broad enough to go across the entire fiber end face and allows the pins to go on either side of the tape. When considering whether to use wet or dry cleaning methods, note that MPO ferrules are exceedingly prone to static buildup, which means that any kind of dust gravitates right to the fiber end face. A lot of the wet cleaning solutions remove some of the static discharge, which makes it a good idea for MPO connectors. To ensure that the system is free of contamination, both sides of every connection must be clean. Patch cords are easy to access and view compared to the fiber inside the bulkhead, which is frequently overlooked because typically the installer does not have the right tool. However, it is a mistake to skip it. The bulkhead side may only be half of the connection, but it is far more likely to be dirty and problematic. To inspect the patch cord, plug the MPO fiber into the patch cord microscope and scroll through all the fibers to make sure they are all clean. Depending on the number of fibers in the MPO connector, it may be necessary to scroll along both the x and the y axes. A pass/fail analysis of the fibers can be done at the same time; document results as shown in Figure 8. TESTING MPO-BASED SYSTEMS The test equipment will come either pinned or unpinned in its native MPO connectors which dictates some of the testing procedures. The trunk or backbone cable, which can exist between two cassettes, for example, does not always need to be tested. What really needs to be tested are the links and channels. With an MPO system, there may be array cables going to the equipment as part of the initial installation. In that case, testing the channel is more important than testing the link. These factors are important to consider during the network design, so that it can be easily tested and maintained. Earlier, several different architectures were covered that highlighted how flexible MPO-based systems can be. Here is how to test these three common examples (summarized in Figure 9): FIGURE 8: Document test results by downloading them or generating reports. To support higher speeds, different techniques like increased lane rates and more efficient modulation schemes are being used. Above 25Gb/s lane rate, PAM-4 modulation will replace NRZ. This allows for doubling the number of bits per symbol.