MPO/MTP polarity problem

MPO/MTP multi-core cables are produced to meet high-density wiring. Especially in the process of migrating from 10G network to 40G/100G network, many network engineers will use MPO/MTP backbone optical cable as the preferred solution. But to ensure the accuracy of the polarity in the MPO/MTP network system, the design of the polarity of the MPO/MTP optical cable is very special. Let's discuss how to correctly maintain the polarity of MPO/MTP.

What is polarity? Generally, an optical link needs two optical fibers to complete the entire transmission process. For example, the optical module includes a receiving end and a transmitting end. When using it, it must be ensured that the receiving end and the transmitting end are in an interconnected state, and the matching between the transmitting end (TX) and the receiving end (Rx) at both ends of the optical fiber link is performed. called polarity. In the traditional wiring system, people usually use connectors such as LC and SC, which can be easily matched, so there is no problem of polarity maintenance. However, for pre-terminated, high-density cabling systems, such as MPO/MTP connection systems, polarity issues must be given high priority.

Before discussing the maintenance of MPO/MTP polarity, let's first get to know the MPO/MTP connector. The MPO connector is a multi-core multi-channel plug-in connector, which consists of a pair of MT sleeves, two guide pins, two shells and an adapter. Its standard feature is to use a standard diameter of 6.4mm x The guide hole and guide pin on the end face of the 2.5mm rectangular ferrule are positioned and centered.

MPO connectors can be used for the connection of 2-12 core fibers side by side, and can be used for simultaneous connection of up to two rows of 24 core fibers. When docking, a spring installed at the end of the ferrule exerts an axial pressure on the ferrule until the outer frame of the connector is locked with the adapter.

There is a male (convex) key on the upper side of the ferrule, which is used to limit the relative position between the connectors when connecting, so as to determine the correct docking sequence of the optical fibers. In addition, MPO connectors are divided into male and female heads. The connector interface is connected by a female plug with a guide pin hole and a male plug with a guide pin and locked in an adapter. Because of its small size, high precision and high density, it is widely used in high-density and high-speed data centers.

MPO/MTP optical link

The three polarity methods stipulated in the TIA568 standard are called method A, method B and method C respectively. In order to meet the TIA568 standard, MPO backbone optical cables are also divided into three types: straight-through, fully crossed and pair crossed, namely, Type A (key up - key down straight through), Type B (key up - key up/key down-key down completely crossover), Type C (key up - key down line pair crossover). The three MPO trunk cables and the three polarity methods will be described in detail below.

Straight-through MPO trunk optical cable: The straight-through MPO trunk optical cable uses a straight-through cable, and the two ends are pre-terminated with an MPO connector with the keyway upward and an MPO connector with the keyway downward. Therefore, the corresponding positions of the optical fibers at both ends of the cable are the same, that is, It is said that the position of the first core hole of the left connector corresponds to the position of the first core hole of the right connector.

Fully crossed MPO trunk optical cable: The fully crossed MPO trunk optical cable uses a reversed cable, and both ends are pre-terminated with MPO connectors with keyways facing upwards. In this cable, the corresponding positions of the optical fibers at both ends of the cable are reversed That is to say, the position of the first core hole of the connector on the left corresponds to the position of the 12th core hole of the right connector.

Line-to-cross MPO trunk cable: The line-to-cross MPO trunk cable is the same as the straight-through MPO trunk cable. The two ends are pre-terminated with keyway-up MPO connectors and keyway-down MPO connectors. However, the line-to-cross MPO trunk In the optical cable, the corresponding positions of the two adjacent optical fibers at one end of the optical cable are opposite to the corresponding positions of the two adjacent optical fibers at the other end, that is to say, the position of the first core hole of the left connector corresponds to the position of the second core hole of the right connector , and the position of the second core hole of the left connector corresponds to the position of the first core hole of the right connector.

Different polarity methods use different kinds of MTP trunk cables. However, all methods utilize duplex patch cords to form fiber optic links. The TIA standard also defines two different types of LC or SC duplex fiber optic jumpers to complete end-to-end duplex connections: A-A (crossover) jumpers and A-B (straight-through) jumpers.

This section describes how to ensure the correctness of the connection polarity of the MPO optical device under the TIA standard.

Type A connection mode: Tx means transmit) reflects the type A connection mode. Type A connection uses straight-through MPO backbone optical cables. In order to ensure the accuracy of the polarity, two jumpers can be used: the left side of the fiber link uses a standard duplex A-B jumper, and the right side uses A-A type Jumper.

Type B connection mode: The type B connection mode uses a fully crossed MPO backbone optical cable. Since the optical fibers at both ends of the fully crossed MPO backbone optical cable correspond to the opposite positions, standard A-B jumpers are used at both ends of the optical fiber link.

Type C connection mode: Type C connection mode uses line-to-cross MPO backbone optical cables, and standard A-B jumpers are used at both ends of the optical fiber link.

The polarity problems faced by network engineers when using MPO/MTP products to meet the growing demand for high-speed transmission can be solved by selecting appropriate MPO optical cables, MPO connectors, MPO conversion module boxes and jumpers. To achieve flexible For a reliable high-density 40/100G transmission solution, you must first choose the desired polarity method, and then select the appropriate MPO/MTP optical device to support this polarity method.