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Maintaining Proper Polarity For MTP / MPO Fiber Links

October 30, 2015

Maintaining Proper Polarity For MTP / MPO Fiber Links

What is polarity?

Polarity is refer to the matching of the transmit signal (Tx) to the receive equipment (Rx) at both ends of the fiber optic link, and its simple object is to provide transmit-to-receive connections across the entire fiber connectivity system in a consistent, standards-based manner.

IA/EIA 568-b-1-7 defines 3 standard methods for maintaining polarity within multi-fiber links. FOCONEC offers standard polarity solutions according to ANSI/TIA-568-B.1-7-2006 standard, which include Method A, Method B & Method C.

How to maintaining polarity?

MTP/MPO factory pre-terminated patch cables with multi-fiber cables(ribbon or trunks) have become the preferred deployment for fiber cabling systems, particularly in data centers. Understanding and maintaining polarity correctly in parallel bi-directional fiber-optic links is becoming increasingly important.

MTP (male) connectors are mated to MTP (female) connectors using an MTP adaptor. Each MTP connector (both male and female) have a key which decides direction of the connector insertion into an adaptor. There are 2 types of MTP adaptors, Key-Up to Key-Up and Key-Up to Key-Down. Method A & C deploy key up to key down adaptors to keep polarity, and Method B use key up to key up adaptor only.

Because A Key-Up to Key Up adaptor will invert all the fibers when two array connectors are connected through the adaptor, i.e. fiber in position 1 (of the 12 fibres) of the first connector will connect to fiber in postion 12 of second mated connector. At every point in a fiber link, the Key-Up to Key-Up adaptor will make the fibers at two sides be flipped and reverse the polarity of the link. Therefore Method B requires more in-depth planning than others to properly identify and manage the circuit inversions.

On the contrary, Key-Up to Key-Down adaptors used in Method A and Method C fiber links are far easier to use when trying to maintain a consistent polartity across a fiber link, make it more easier and flexible to plan, intall, manage and extend the fiber cabling system.

Which Method?

FOCONEC recommends using method A as the most flexible and reliable fiber link in the majority of installations.

Compared to Method C, one A-to- A patch cord required at one end of this fiber link, but it more compatible for bidirectional parallel fiber transmission, this is very important for 40G/100G and future 400G transmission system.

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