Issue link: https://www.e-digitaleditions.com/i/1066130
January/February 2019 I 43 FIGURE 6: Shows a cross section of an MPO connector with male (pinned) being plugged into an adapter with a female (unpinned) connector. need a good strategy, keeping in mind to test and verify the configuration. There are similar options and solutions for 12-fiber and 24-fiber systems. Due to the many configuration options available, the design approach should always consider the ease or complexity of testing and validating. POLARITY AND GENDER Along with the advantages of working with MPO-based systems come some challenges. Compared to duplex solutions using single fiber connectors, there are two areas which are significantly different: polarity and gender. In duplex fiber applications, such as 10 Gb, data transmission is over two fibers where each fiber connects the transmitter on one end to the receiver on the other end. The role of polarity is to make sure that this transmit (Tx) to receive (Rx) connection is maintained. To help the industry select and install the right components to maintain proper polarity, TIA-568-C standards recommend the A-B polarity scenario for duplex patch cords—a straight-through connection that maintains the A-B polarity in a duplex channel. Every fiber connector has a key that prevents the fiber from rotating when the connectors are being mated and maintains the correct Tx and Rx position. With MPO connectors, polarity becomes more complicated. TIA recognizes polarity schemes A, B and C, each of which uses different types of MPO cables. There are also proprietary schemes on the market that are not mentioned in the standards. None of these polarity schemes are interchangeable or compatible, so components cannot be mixed and matched from different manufacturers using different polarity schemes and expect it to work. Unlike single fiber connectors, MPO connectors have genders. They are either male (pinned) or female (unpinned) as illustrated in Figure 6. To properly connect them, always plug a pinned MPO into an unpinned connector; this is how the MPO connections maintain proper alignment. All 8, 12, or 24 fibers in the MPO connection need to line up with a sufficient core-to-core connection so that the light can go from one fiber to another without excessive loss. When the connection occurs, it is a physical contact. Without a good, clean, physical connection, the light path will be disrupted and cause reflections and loss. The alignment pins and the alignment holes make it possible to line up all of the fibers and achieve a core-to- core connection so that the light can go from one fiber to another. Never try to connect two male connectors, pinned-to-pinned, as this can damage the pins when attempting to plug them into each other. Even worse is to try and connect two female connectors, unpinned-to- unpinned, because the ferrules (and fiber end faces) can grind against each other and be damaged. With MPO, it is very important to understand what is being connected and whether it is pinned or unpinned. With MPO architectures becoming more prevalent, make sure to check the adapters on the cassettes, patch panels, test equipment, and transceivers to determine whether they are pinned or unpinned. (Quick Tip: Transceivers are always pinned, so make sure to always use an unpinned connector when mating to a transceiver). STANDARDS AND TESTING As discussed, when deploying these new architectures, current standards provide limited guidance, especially when it comes to testing MPOs. Within TIA standards, transmission performance and test requirements are defined in Section 7 of ANSI/TIA-568.3-D, which was last revised in 2015. These standards are based on the corresponding IEC standards 612-80-4.1 and 4.2, allowing for harmonization of the standards.