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How to Understand the MTP/MPO Polarity of Fiber Cable Right?

(Last Updated On: April 24, 2023)

MTP/MPO with 8 or 12 fibers is typically used in data centers to connect fiber distribution frames in duplex applications or end-to-end parallel fiber applications (such as 40, 100, 200, and 400Gbps) that use 8 fibers for transmission and reception (4 at 25, 50, or 100Gb/s, and 4 at 100Gb/s). When migrating from 10G to 40G/100G, it is essential to understand the polarity and gender of MTP. The correctness of polarity is guaranteed in the optical fiber network to ensure that the transmission signal from any active device is accurately directed to the receiving port of the second active device and vice versa.

In this article:

  • What is Polarity?

  • Polarity Connectivity Examples

  • Commonly Used 12 Core Applications

  • Fiber MTP/MPO Polarity Solution

  • The Rules When Establishing MTP/MPO Polarity Connections

  • Conclusion

What is Polarity?

Polarity is a term used in the TIA-568 standard to explain how to ensure that each transmitter is correctly connected to the receiver at the other end of the multi-fiber cable. Once the component is connected to the wrong polarity, the transfer process cannot continue.

Appropriate polarity ensures that the transmitted signal at one end of the channel matches the corresponding receiver at the other. We need to ensure that multiple optical fibers correspond correctly. All MTP/MPO connectors are equipped with a key and an indicator light (usually a white dot) to indicate the location of the first fiber. The direction of this key is critical to polarity. Three polarity methods are generally available: Polarity A, Polarity B, and Polarity C.

Once you select a way, you must stick with it throughout the channel. Let’s take a closer look.

MPO 01

MTP/MPO Trunk Cable Type A:

Polarity A uses Type A MTP trunk assemblies, a straight-through connection where position 1 at one end of the assembly lines up with position 1 at the other, position 12 lines up with position 12, and so on. To accomplish this, one end of the assembly has the MTP in a key up position, and the other has the MTP in a key down position.

MPO 01 1

MTP/MPO Trunk Cable Type B:

Polarity B uses a B-type trunk cable (key up/ key up) and a B-type patch cable at both ends to establish a corresponding transceiver connection in the entire channel. Because Polarity B always uses the same type of components, including two patch cords at both ends, it is the most recommended method and is the least likely to cause problems when used in the entire data center. If you do not have type A components, you will not risk inserting them into method B channels.

MPO 02 2

MTP/MPO Trunk Cable Type C:

Polarity C is not recommended for parallel optical applications because type C components are cross components, which can flip the pairs in the cable, so that position 1 reaches position 2, position 2 reaches position 1, and 3 to 4, 4 to 3, 5 to 6, 6 to 5, etc. Although this works well for duplex applications where A-B type jumpers are used at both ends, it is still not recommended because you may, need to migrate from duplex to Parallel one day.

MPO 03 2

Polarity Connectivity Examples

The TIA standard also explains that all MTP/MPO polarity methods should use duplex jumpers to complete fiber optic circuits. There are two types of duplex fiber jumper options, A to A connection and A to B connection.

MPO 05 1

Since the goal is to connect the transmit (Tx) signal to the receive (Rx) device, the following table shows the most common combination of components that achieve this.


Applications With Cassettes and MTP/MPO

MPO 07

Commonly Used 12-Fiber Applications

Polarity A cables are used for duplex applications, with standard A-B LC/SC jumpers at one end and A-A LC/SC patch cords at the other end to set the required correct Tx/Rx positions.

Polarity A cables are also used at one end of 40/100 Gig applications to connect the patch panel ports to the corresponding transceiver ports. This setting requires the installation of a B-type MPO patch cord at the other end of the channel.


Polarity B cables are used at both ends of a 40/100 Gig application to connect the patch panel ports to the appropriate ports. This means that both duplex and parallel applications require the same type of patch cord, which is why polarity B is recommended chiefly.

MPO 05 2

Polarity C is used when you need to disconnect the MTP/MPO cable to the duplex LC/SC connector, and you need to connect these connectors to Tx or Rx; use Polarity C. It would be best if you used pair inversion.

Another way to achieve this is to process the inversion on the MTP/MPO switching module at both ends. This method is preferred because you can convert the same cable to parallel optical fiber if necessary.


24-Fiber MTP/MPO Polarity Solution

Some 100G transmission devices use 1 x 24F MTP/MPO ports instead of 2 x 12F ports for sending and receiving. In these cases, a 24F ferrule MTP/MPO connector is required to connect to the device. The other end is usually divided into 12F MTP/MPO connectors connected to the bulkhead adapter and MTP/MPO trunk cable.

The various configuration options are listed below.

MTP/MPO Fiber | Polarity Method A

Type A

MTP/MPO Fiber | Polarity Method B

MPO Type B

MTP/MPO Fiber | Polarity Method C


The Rules When Establishing MTP/MPO Polarity Connections


When the fiber patch cord has different polarity schemes, IT personnel must be conscientious when replacing it on-site. Those who need to learn the polarity or are eager to start and run the equipment may misuse jumpers, affecting optical signal transmission.

The Rule for MTP/MPO Cable and Patch Cord Connection

In the case of A-to-A jumper and A-to-B jumper, there are three general types of arrays (multi-core) optical cable components. Note that the alignment pins on the MTP/MPO connectors are essential for maintaining the correct polarity. Therefore, before using jumpers to connect MTP/MPO fibers, it is necessary to ensure the correct pin positions.

A to B type LC/SC duplex patch cord is a standard crossover that maps the Tx port to the Rx port. By flipping, the polarity of the A to B type jumper is correct. MTP backbone cable type B reverses the fiber position at each end (1 pair 12 and 12 pair 1), and the connector keys are facing up. It is recommended to use this cable connection to maintain the correct MTP/MPO polarity.

Rules for MTP/MPO Cable and Cassette Connection

The selection of the MTP/MPO distribution box also determines the selection of the MTP/MPO cable. You’d better choose an optical fiber distribution box with suitable locating pins so that the MTP/MPO distribution box can perfectly match the MTP/MPO connector at both ends of the MTP/MPO optical fiber cable.

In addition, the back of the adapter installed on the distribution box defines as Method A or Method B to comply with TIA standards.


Network designers use MTP/MPO components to meet the growing demand for higher transmission speeds. One of the biggest problems during this period – polarity can be solved by selecting the correct MTP cable, MTP connector, MTP distribution box, and fiber optic patch cable. Three different polarization methods can be applied to other situations to meet different application needs.

All kinds of duplex patch cables and MPO/MTP patch cables are available for HOLIGHT. For more information, you can contact us at sales@holightoptic.com.

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