In today’s data centers, 12-fiber pre-terminated MTP cables are frequently used to establish an optical path between switch tiers. Accomplishing this path in a way that matches the transmit signal (Tx) on one switch port to the corresponding receive signal (Rx) on the other switch port is referred to as polarity. Unlike traditional 2‐fiber configurations LC or SC patch cords, with one send and one receive, since 12-fiber MTP cables have 12 fibers in a connector, the polarity management then becomes more complex. According to TIA standards, there are type-A, type-B and type-C three polarity types MTP cables. Different types polarity cables may have different applications. In this tutorial, we will mainly introduce the type-B polarity MTP cables and its applications.
Type-B Polarity MTP Cable Overview
Often referred to as a 40G MTP cable, the type-B cable is the second standard for polarity, and extremely versatile. This cable assembly can be used to plug directly between your 40G QSFP+ optic transceivers, so it is commonly referred to as a QSFP/QSFP+ cable or Direct Attach 40GBASE-SR4. As you can see in the diagram, this cable has a “flipped” polarity and will result in a Pin 1 to Pin 12 relationship. This is extremely useful because 40G optics utilize parallel optics, meaning instead of alternating Tx and Rx in a duplex pattern, the port will look like the following diagram.
Type-B Polarity MTP Cable
Most 40G optics do not require perfect port symmetry: any Tx can go to any Rx and it will sort it out in the end. This means fiber 12 can interface with fiber 1, because one is Tx and the other is Rx.
Type-B Polarity MTP Cable Types
MTP trunk cable and MTP-LC harness cable are two most common types used in today’s data center. Besides, according to MTP genders, MTP connector is divided into male and female two types. Therefore, in terms of MTP trunk cable, there are female-female, female-male and male-male three types. For MTP-LC harness cable, female MTP-LC harness cable and male MTP-LC harness cable are available.
Type-B Polarity MTP Cable Applications
Since MTP cables have male and female two types, it always requires 1 male and 1 female to mate. The male guide pins fit into the female holes to ensure precise fiber alignment. Attempting to mate two female connectors will result in a seemingly secure connection, but with extremely high loss, and attempting to mate two male connectors will most likely damage one or both connectors due to the guide pins clashing.