MPO Cable and Polarity

Posted byVijay Gupta15/05/20200 Comment(s)

MPO fibre patch cord is a high-density fibre optic transmission jumper which consists of MPO connectors and fibre cables. The MPO connector is built on the MT-style ferrule, designed by NTT. MPO connectors can provide quick and reliable high-performance interconnections up to 4, 12, 24 or more and are usually used with ribbon fibre cables.

MPO connector is about the same size as a SC connector but can accommodate 12 or 24 fibres. Thus, MPO cables provide up to 12 or 24 times the density and offer savings in rack cabling space. MPO connectors has 4-, 8-, 12-, 24-, 36-, 48-, 96-, 144- multi-fibre types, with 12-fiber and 24-fiber arrays being the most used. Nowadays, 12 fibre MPO connector and 24 fibre MPO connector have been broadly deployed into 40G and 100G cabling.

MPO connectors contains several parts such as boot, coupling/housing assembly, ferrule, guide pins, and so on. Because of difference pins types, the MPO connector can be either male or female. The male connector has metal guide pins to ensure fibre alignment when mating while female connector has no pins. These pins make sure that the connector fronts are precisely aligned on contact and that the fibres' end-faces aren’t offset.

MTP/MPO technology, which is of high density, flexibility and reliability with scalable, upgradeable properties, is one of the contributors that lead the migration to 40/100GbE. However, the network designers face another challenge which is how to assure the proper polarity of these array connections using multi-fibre MTP/MPO components from end-to-end. Correct polarity across a fibre network ensures that a transmit signal from any type of active equipment will be directed to receive port of a second piece of active equipment – and vice versa. To ensure the MTP/MPO systems to work with correct polarity, Polarity defines direction of flow, such as the direction of a magnetic field or an electrical current. In fibre optics, it's the A-B-C’s of Fibre Polarity. To properly send data via light signals, a fibre optic link’s transmit signal (Tx) at one end of the cable must match the corresponding receiver (Rx) at the other end.


What Is Polarity?

Keeping the right polarity is essential to the network. A transmit signal from any type of active equipment will be directed to the receive port of a second piece of active equipment and vice versa. Polarity is the term used in the TIA-568 standard to explain how to make sure each transmitter is correctly connected to a receiver on the other end of a multi-fibre cable. Once the component is connected to the wrong polarity, the transmission process will be unable to go on.


MPO/MTP Connector Structure

When discussing about the polarity, MPO/MTP connector is an important component for you to know. An MPO/MTP connector has a key on one side of the connector body. There are two positions of the key — key up or key down. Key up position means that the key sits on top. When the key sits on the bottom, it is the key down position. Moreover, the fibre holes in the connector are numbered in sequence from left to right. Each connector is additionally marked with a white dot on the connector body to designate the side of the connector when it is plugged in. The MPO/MTP connector can be further divided into female connector and male connector. The former has no pins while the latter has two pins on the connector. There is a “key” on the top side of the connector, which has key-up and key-down position. We shall now look into the three methods of mpo for proper polarity


Polarity Types

The three methods for proper polarity defined by TIA 568 standard are named as Method A, Method B and Method C. To match these standards, three type of MPO truck cables with different structures named Type A, Type B and Type C are being used for the three different connectivity methods respectively.

Type A: Type A cable also known as straight cable, is a straight through cable with a key up MPO connector on one end and a key down MPO connector on the opposite end. This makes the fibres at each end of the cable have the same fibre position. For example, the fibre located at position 1 (P1) of the connector on one side will arrive at P1 at the other connector.

Type B: Type B cable (reversed cable) uses key up connector on both ends of the cable. This type of array mating results in an inversion, which means the fibre positions are reversed at each end. The fibre at P1 at one end is mated with fibre at P12 at the opposing end.

Type C: Type C cable (pairs flipped cable) looks like Type A cable with one key up connector and one key down connector on each side. However, in Type C each adjacent pair of fibres at one end are flipped at the other end. For example, the fibre at position 1 on one end is shifted to position 2 at the other end of the cable. The fibre at position 2 at one end is shifted to position 1 at the opposite end etc.


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