Understanding Polarity in MPO System

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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.