MTP® Brand MPO Polarity Methods vs. Cable Types


MTP® Brand MPO Polarity Methods vs. Cable Types

Methods include the entire link while Type is the polarity of the MPO cable. At some point the link usually will convert the TX to a RX (i.e. LC Pin 1 and Pin 2 will be swapped). In the diagrams below, this is being accomplished in three separate methods.

Method A - creates the swap by having two different configurations of patch cables on each end. On one side the patch cable is pair-flipped, while on the other it is straight through. The cassettes are both straight through and the Type A trunk cable is also straight through (See “Cable Types Diagram”).

Method B - creates the swap by having special “Key-up/Key-up” adapters on the straight through cassettes on each end, and a Type B rollover cable as the trunk.

Method C - creates the swap by having the trunk cable perform the swap using a Type C “Pair-Flipped” trunk cable.

Cable Types Diagram
The MPO/MTP® Type A is considered “straight through” (Pin 1 to Pin 1)
Type B is considered “Reversed”, “Crossed” or “Rollover” (Pin1 to Pin 12)
Type C is considered “Flipped”, “Pair-Flipped”, or “Swapped” (Pin1 to Pin2/Pin2 to Pin1) 

Note: Type A and Type B can be interchanged by removing and reversing the housing on one side of the cable which will switch the cable from a Straight Type A to a Rollover/Reversed/Crossed Type B or vice versa. Type C cannot be changed.

 Understand Multi-fiber connector basics & terminology

  • Differentiate between polarity "Types" & "Methods"
  • Identify and Compare:
    • Type A vs Type B
    • Method A vs Method B
  • Trace a channel in its entirety from transmitter to receiver

Why is this important?

  • Data Center trends
    • Multi-fiber connectors are increasingly popular in Data Centers, Telecom, and many other applications
    • Common to have single-fiber connectors in the same link (e.g. LC's to MTP's back to LC's)
  • Complexity
    • More fiber is just inherently more challenging to keep track of
    • Concatenation of multiple patchcords, trunks, and cassettes
    • Multi-row transceiver modules
  • Equipping yourself with some basic knowledge can enable you to overcome these challenges


Connector vs Ferrule

  • "Ferrule" = Inner component which the fiber ribbon is terminated (i.e. epoxied, cured, polished)
  • "Connector" = Outer component which holds the ferrule and provides a more robust connection

Multi-fiber = Multiple fibers in one connector

  • Fibers are typically bundled in 12-fiber ribbons, with each individual fiber identified by a standard sequence of unique colors (TIA-598-D)
  • Ribbon is typically manufactured in a flat factory ribbon, or as loose individual fibers in a round tube/cable

MPO vs MTP® vs MT

  • MT = Most common multi-fiber ferrule
  • MPO = Most common multi-fiber connector
  • MTP is US Conec's brand of MPO connector
    • Both connectors are intermateable per TIA-604-5-E (FOCIS 5) industry mechanical standard
    • Both available in SMF and MMF variants
    • 12-fiber MTP is most common variant (one row of 12 fibers)
    • 24-fiber MTP increasing in popularity (two rows of 12 fibers)
    • Both available in multiple alternative fiber and row counts

MPO Polarity Industry Standards

  • TIA = Telecommunications Industry Association
    • Leading industry standard providing guidance on MPO polarity
  • Important update:
    • In October 2016, TIA published TIA-568.3-D (i.e. revision D)
    • Rev D adds new guidance on two-row MPO polarity (e.g. 24-fiber)
    • Previously, MPO polarity was spread across two TIA documents (TIA-568-C.3 & TIA-568-C.3-1)
  • Provides guidance on how to:
    • Manufacture individual assemblies (e.g. patchcords, adaptors, trunk cables).
    • Concatenate these assemblies into a proper link (i.e. transmitter channels connect to the receiver channels)

TIA Nomenclature

  • Using consistent terms is critical to avoid confusion.
  • Important Terms:
    • Polarity Types: Individual fiber optic assemblies (i.e. patchcords, adaptors, trunks)
    • Polarity Methods: Concatenation of fiber optics assemblies above

      Note: TIA defines multiple polarity Types and Methods. While both are labelled A, B, & C, we will show how these are two entirely different sets of items.

    • Fiber Number: Sequential number that corresponds to the Blue-Aqua TIA color sequence
    • Position Number (or Fiber Position Number): Sequential number that Hole location on the MPO ferrule

      Note: Typically these numbers are both 1-12, but we will show that the Fiber Number does not always match the Position Number.

    • Top Row: Row of fibers closest to the MPO key
    • Bottom Row: Row of fibers farthest from the MPO key
    • Near End: Connector on left side of TIA drawings
    • Far End: Connector on right side of TIA drawings
    • KeyUP to KeyDOWN: Assembly which the keys of the mated MPO pair are opposed
    • KeyUP to KeyUP: Assembly which the keys of the mated MPO pair are aligned

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