Understanding Polarity in MPO System

MPO/MTP technology has led to the adoption of 40/100GbE, however on of its challenges is with regards to proper polarity of these array connections.  Maintaining the correct polarity across a fiber network enables signals from any type of active equipment to be  directed to the receive port of a second piece of active equipment – and vice versa. To ensure the MPO/MTP systems work with correct polarity, the TIA 568 standard suggests several methods.

 

MPO Connector

 

First on the list is the MPO connector usually consisting of 12 fibers. 24 fibers, 36 fibers and 72 fibers Each MTP connector has a key on one of the flat side added by the body. When the key sits on the bottom, this is called key down. 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 and is referred as fiber position. The orientation of this key also determines the MPO cable’s polarity.

 

Three Cables for Three Polarization Methods

 

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. In this part, the three different cables will be introduced firstly and then the three connectivity methods.

 

MPO Trunk Cable Type A: Type A cable is 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 fibers at each end of the cable have the same fiber position.

 

The issue of polarity with MPO cables can be easily addressed by selecting the correct type of MPO cables, connectors, cassettes and patch cables. Various polarity settings/methods can be applied  to satisfy the requirements of the 40G environment. 

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