With widespread deployment of 40G and 100G networks, high-density MTP/MPO cable solutions are also become more and more popular. Unlike traditional 2‐fiber configurations LC or SC patch cords, with one send and one receive, 40G & 100G Ethernet implementations over multimode fibers use multiple parallel 10G connections that are aggregated. 40G uses four 10G fibers to send and four 10G fibers to receive, while 100G uses ten 10G fibers in each direction. MTP/MPO cable can hold 12 or 24 fibers in a connector, which greatly facilitates the upgrade to 40G and 100G networks. However, since there are so many fibers, the polarity management of the MTP/MPO cable may be a problem.
Structure of MTP/MPO Connectors
Before explaining the polarity, it is important to learn about the structure of MTP/MPO connector first. Each MTP connector has a key on one side of the connector body. When the key sits on top, this is referred to as the key up position. In this orientation, each of the fiber holes in the connector is numbered in sequence from left to right. We will refer to these connector holes as positions, or P1, P2, etc. Each connector is additionally marked with a white dot on the connector body to designate the position 1 side of the connector when it is plugged in.
Structure of MTP/MPO Adapters
Since the MTP connectors can either key up and key down, there are two types of MPO adapters.
- Type A: Key-up to key-down
Here the key is up on one side and down on the other. The two connectors are connected turned 180° in relation to each other.
Both keys are up. The two connectors are connected while in the same position in relation to each other.
Two Polarity of Traditional Duplex Patch Cable
Classic duplex cables are available in a cross-over version (A-to-A) or a straight-through version (A-to-B) and are terminated with LC or SC connectors. Telecommunications Cabling Standard defines the A-B polarity scenario for discrete duplex patch cords, with the premise that transmit (Tx) should always go to receive (Rx) — or “A” should always connect to “B”. Therefore, A-B polarity duplex is very common in applications.
Three Polarity of MTP/MPO Multi-Fiber Cable
Unlike traditional duplex patch cables, there are three polarity for MTP/MPO cables: polarity A, polarity B and polarity C.
Polarity A MTP cables use a key up, key down design. Therefore, as shown in the figure below, the position 1 of one connector is corresponding to the position 1 of another connector. There is no polarity flip. Therefore, when we use polarity A MTP cable for connection, we must use A-B duplex patch cables on one end and A-A duplex patch cables on the other end. Since in this link, Rx1 must connect to Tx1. If we don’t use A-A duplex patch cable, according to the design principle of polarity A MTP cable, fiber 1 may transmit to fiber 1, that is to say Rx1 may transmit to Rx1, which may cause errors.
Polarity B MTP cables use a key up, key up design. Therefore, as shown in the figure below, the position 1 of one connector is corresponding to the position 12 of another connector. Therefore, when we use polarity B MTP cable for connection, we should use a A-B duplex patch cables on both ends. Since the key up to key up design help to flip the polarity, which makes fiber 1 transmit to fiber 12, that is the Rx1 transmits to Tx1.
Like the polarity A MTP cables, polarity C MTP cables also use a key up, key down design. However, within in the cable, there is a fiber cross design, which makes the position 1 of one connector is corresponding to the position 2 of another connector. As shown in the figure below, when we use polarity C MTP cable for connection, we should use a A-B duplex patch cables on both ends. Since the cross fiber design help to flip the polarity, which makes fiber 1 transmit to fiber 2, that is the Rx1 transmits to Tx1.
Different polarity MTP cables may have different connection methods. No matter which type cable you choose, remember its design principle and choose the right cabling infrastructure for your network. FS.COM provides a full range of MTP cables and MTP cassettes, polarity A, B and C are all available.