Polarity defines direction of flow, such as the direction of a magnetic field or an electrical current. In fiber optics, it defines the direction that light signals travels through an optical fiber. To properly send data via light signals, a fiber optic link’s transmit signal (Tx) at one end of the cable must match the corresponding receiver (Rx) at the other end.

In duplex fiber applications, such as 10 Gig, data transmission is bidirectional over two fibers where each fiber connects the transmitter on one end and to the receiver on the other end. The role of polarity is to make sure that this connection is maintained.

Polarity in multi-fiber MPO type cables and connectors is more complicated. Industry standards call out three different polarity methods for MPOs—Method A, Method B and Method C. And each method uses different types of MPO cables.