Fiber Polarity Simplified

Fiber Polarity Simplified 

TM 

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Fiber Polarity Simplified 

“Flipped”, “Straight”, “A-to-B” - confused about fiber polarity? 

AMP, AMP NETCONNECT, NETCONNECT, TE Logo, and Tyco Electronics 

are trademarks. 

©Copyright 2009 Tyco Electronics Corporation. All Rights Reserved. 

800-553-0938 

www.ampnetconnect.com 

FIBER POLARITY SIMPLIFIED 

Correct polarity of a few fiber pairs to multiple trunk cables between enclosures can be a bit 

confusing. Fiber adapters are available with six or twelve duplex connections, and depending 

on the enclosure design, the adapters can be mounted in a horizontal or vertical orientation. 

6 Duplex LC Adapters 

This paper explains a few basic concepts following industry standard recommendations to 

help clarify fiber polarity. 

Lets start by reviewing the basic connection between two fiber transceivers. 

Keep those bits flowing............ 

Example Adapter Plates 

12 Duplex LC Adapters 

Simply stated, the polarity of the fiber installation must connect the transmit ports to the 

receive ports of the fiber transceivers to transfer data. 

“Keyways up” 

Tx Rx 

Note the adapter keyways are on top (Keyways up) for both transceivers, and when viewed 

from the front or open port side, the transmit port (Tx) is on the left, and the receive port (Rx) 

is on the right. 

The top view shows the keyways up position with the Tx on the left and Rx on the right when 

viewed from the front or open port side. 

Tx 

Rx 

Top View 

2




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Lets connect the transmit and receive ports with two simplex cable assemblies. 


Rx 

Tx 

Transceiver 1 

With “keyways up” and viewing from the open port side, the Rx is on the right and the Tx on 

the left for both transceivers. 

So when connecting transmit to receive in the above example, there’s a pattern of Right port 

to Left port or Left port to Right port connection with the keyways up and viewed from the 

open port side. 

Instead of Tx to Rx or left port to right port, industry standards uses “A” and “B” indicators to 

maintain polarity throughout the fiber channel. With the adapter “keyways up”, and viewed 

from the open port side, “A” is on the right, and “B” is on the left. 

So lets replace the Rx to Tx with “A” to “B” in a set of fiber adapters. The figure below simulates 

a connection between two fiber enclosures or an enclosure to work area outlet connection. 


“Key up” 

View 

Assembly 1 

Assembly 2 

View 

“Key up” 

B A 

B 

A 

B 

“Key up” 

View 

Note the position of “A” and “B” when viewed from 

the other side of the adapter. 

With the “keyways up” and viewed from the open 

port side, “A” is on the right, and “B” is on the left. 

“Key up” 

View 


Tx 

Rx 

Transceiver 2 


A 

A B 

3

Duplex Patch Cords 

The “Key” is the Key 




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Combining these simplex connector assemblies into a duplex assembly produces an industry 

standard patch cord configured with “A” connecting to “B”. This configuration is commonly 

called “Flipped”. 

AMP NETCONNECT MT-RJ, SC, and LC duplex assemblies are configured per the industry 

standards configuration of A-to-B. 

These patch cords provide the correct polarity for patch panel to equipment and work area 

outlet to equipment connections. 

A 

B 

At this point, we have established that an A-to-B and B-to-A connection must be in place to 

keep the correct transmit to receive path. 

The next important concept to understand is the correct location of A and B as the fiber 

adapter is rotated in various positions. The adapter plates can be installed horizontally or vertically 

or with the port ID’s ascending or descending. Manufacturer’s placement of six vs 

twelve duplex adapters on an adapter plate also changes the orientation of the adapters. 

As previously explained, the “key” to identifying the A and B locations in the adapter is the 

position of the connector keyway. 

For example, the following LC adapters are shown with the correct A and B indicators. 

Note the locations of A and B for the different adapter orientations. 

With the “keyways up” and viewing from the open port side, “A” is on the right, and “B” is on 

the left. 


B A 

B 

A 


LC Duplex Assembly 


B A 

A 

B 


B 

A 

4

Lets Review....... 

B 

2 

A 

B 

1 




A 

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Established that A-to-B and B-to-A connections must be in place to keep the correct transmit 

to receive path. 

“Standard” duplex fiber patch cords are A-B and B-A compliant. 

The location of A and B identifiers in a fiber adapter is relative to the connector keyway. 

The next few sections show the fiber polarity for various adapter to adapter connections. 

Patch Panel Connections 

The following example is a fiber connection between panel adapter plates. 

Note the orientation of the adapter and the A-to-B to B-to-A connections for the fiber pair. 

Rear View Panel 2 

B 

B A 

B A 

Top View 

B 

2 

A 


A B 

A 

B 

1 

A 

5




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The following examples are connections between panels using 6 LC duplex adapter plates. 

View from the open port side and with the keyway up to determine the location of A and B. 

6 5 4 3 2 1 


Horizontal Adapter Plates 

6 5 4 3 2 1 


A 

1 

2 

3 

4 

5 

6 


B 

A 

6 5 4 3 2 1 


1 

2 

3 

4 

5 

6 


A 

Horizontal and Vertical 

Adapter Plates 

Vertical Adapter Plates 

B 

B 

1 

2 

3 

4 

5 

6 


6

Multiple Connections 

RX 

TX 

B 

A 

Polarity Examples 

A B A 

B 




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For multiple connection points, keep A-to-B and B-to-A to maintain the transmit 

to receive path. 

The following examples are backbone connections with 24-fiber cable containing two 12-fiber 

subunits. Each subunit contains 12 color-coded fibers that are grouped in pairs during the 

installation process to form 2-fiber transmission paths. 

The following chart lists the fiber pair color code per industry standard ANSI/TIA-598-C, 

Optical Fiber Cable Color Coding. 

Fiber Color Fiber Number Fiber Pair 

Blue 

Orange 

1 

2 

1 

Green 

Brown 

3 

4 

2 

Slate 

White 

5 

6 

3 

Red 

Black 

7 

8 

4 

Yellow 

Violet 

9 

10 

5 

Rose 

Aqua 

11 

12 

6 

B A B A 

A B A B A B 

Note: An even or odd number of connection points or “hops” does not affect the 

polarity outcome. Keep A-to-B and B-to-A for any number of fiber segments to 

maintain polarity. 

TX 

RX 

7

Patch Panel 2 




B A 

A 

B 

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The first example pairs the fibers for each subunit in the same A and B adapter position. 

Examining the Blue/Orange pair for each 12-fiber subunit in Panel 1, the Blue fibers are in the 

A position, and the Orange fibers are in the B position. With the adapter keys in opposite 

directions within the single plate, the fiber color scheme is reversed for the two 12-fiber subunits. 

When connecting panels together using dual “row” adapter plates, the connection should be 

between adapter rows with the same keyway orientation. See the location of the subunit 

fibers in the adapters shown below. 

When a connection occurs between adapters in the same keyway orientation, the fibers in 

Panel 2 will be color swapped in a reverse-pair position to maintain the A-to-B connection. 

A 

B 

Subunit 2 Fibers 



Rear View of Adapter Plates 

B 

A 

Patch Panel 1 


8

Patch Panel 2 

A 

B 

A 

B 

A 

B 




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This example pairs the fibers for each subunit in the same orientation per the standard twelve 

color code pattern. Examining the Blue/Orange pair for each 12-fiber subunit in Panel 1, the 

Blue fibers for each subunit are in the first position, Orange for the second position, and so 

forth. The results are a consistent color scheme for both “rows” of the adapter plate. 

As mentioned in the previous example, when connecting panels together using dual “row” 

adapter plates, the connection should be between adapter rows with the same keyway orientation. 

See the location of the subunit fibers in the adapters shown below. 

When a connection occurs between adapters in the same keyway orientation, the fibers in 

Panel 2 will be color swapped in a reverse-pair position to maintain the A-to-B connection. 


Rear View of Adapter Plates 

B 

A 

Patch Panel 1 

Subunit 2 Fibers Subunit 1 Fibers Subunit 1 Fibers 

9




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Here is an example of Centralized optical fiber cabling for a fiber-to-the-desk installation. 

Fiber 

Enclosure 

Conclusion 

A B 

B 

Telecommunications 

Room 

Fiber 

Enclosure 

A B 

B 

Equipment Room 

A 

Horizontal Cable 

Backbone Cable 

A 

Patch Cord 

Network 

Equipment 

Telecommunications 

Outlet 

The guidelines presented in this paper follow the recommendations of ANSI/TIA-568-C 

industry standards for reverse-pair polarity. 

The location of A and B identifiers in a fiber adapter is relative to the connector keyway. 

For any number of connection points or orientation of fiber adapters, an A-to-B and B-to-A 

connection will maintain fiber polarity throughout the fiber channel and ensure transmit-toreceive 

connectivity. 

B 

A 

A 

B 

Patch Cord 

Media Converter 

or Fiber NIC 

10

Fiber Polarity Simplified

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