MTP®/MPO Polarity

What is MTP®/MPO Polarity?

Fiber polarity refers to the arrangement and alignment of optical fibers in an optical link. In a typical optical link, there are two fibers involved—one for transmitting (TX) and one for receiving (RX). To establish a proper connection, it is crucial to ensure that the TX end of one fiber is matched with the RX end of the other fiber.

MTP®/MPO fiber polarity is reflected in MTP®/MPO connectors, which have multiple fibers arranged in a rectangular array, typically in increments of 12 fibers. Choosing the correct polarization methods in high-density fiber optic systems is important because it determines the correct alignment of transmit and receive fibers between network equipment, such as switches, routers, and servers.

Three Polarization Methods of MTP® Trunk Cable

Type A (Straight-through): In this polarity, the fibers are straight-through, meaning that the transmit (Tx) fibers on one end are connected to the receive (Rx) fibers on the other end. For instance, if a fiber is located at position 1 (P1) of the connector on one side, it will correspondingly align with P1 at the opposite connector. The fiber sequence for a 12-fiber Type A MTP® cable is depicted below:

Type B (Reversed): Type B polarity reverses the positions of the Tx and Rx fibers at one end of the connection. The fiber corresponding to position 1 (P1) at one end is connected to the fiber at position 12 (P12) at the opposite end. The diagram below illustrates the fiber sequences of a 12-fiber Type B cable:

Type C (Pair-flipped): Type C polarity flips the positions of individual fiber pairs, rather than reversing the entire transmit and receive positions. This means that the fiber at position 1 at one end is shifted to position 2 at the opposite end, and the fiber at position 2 at one end is shifted to position 1 at the other end, and so on. The fiber sequence for an MTP®-12 Type C cable is illustrated in the diagram below:

Three Connectivity Methods

Various polarity methods require different types of MTP® trunk cables, but regardless of the method used, duplex patch cables are necessary to establish the fiber circuit. The TIA standard also specifies two types of duplex fiber patch cables terminated with LC or SC connectors, which are employed to achieve an end-to-end fiber duplex connection: A-to-A type patch cable—a cross version and A-to-B type patch cable—a straight-through version.

The following section demonstrates the collaborative utilization of components within the MTP® system to uphold the prescribed polarization connectivity as defined by the TIA standards.

Method A: The connectivity Method A is depicted in the accompanying diagram. It involves utilizing a type-A trunk cable to connect an MTP® module on each end of the link. In Method A, standard A-to-B type duplex patch cables are employed on both sides of the connection.

Method B: In connectivity Method B, the two modules on each side of the link are connected using a Type B trunk cable. It is important to note that the fiber positions in a Type B cable are reversed at each end. As a result, standard A-to-B type duplex patch cables are utilized on both sides to ensure proper connectivity.

Method C: In Method C connectivity, a pair-reversed trunk cable is employed to establish the connection between the MTP® modules on each side of the link. At both ends, standard duplex A-to-B type patch cords are utilized.