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Understanding Fiber Polarity Method: Which to Choose?

Understanding Fiber Polarity Method: Which to Choose?

40G and 100G are now universally deployed in data centers. As the preferred array-based fiber connector option, the MPO/MTP connector and its cable assemblies are widely used for 40/100G connectivity in high-density data center environments. However, in complex high density cabling, the advantages of MPO/MTP cabling will be lost if you don’t have a proper polarity method. Thus, the TIA 568 standard provides three methods—Method A, B and C, for configuring systems to ensure that proper connections are made. In this blog, these three methods would be described in details which may guide you to select the best method for ensuring polarity across your array-based fiber installation.

Understanding MPO/MTP Basic Structure

Before looking at each method in detail, it is necessary to understand the basic structure of an MPO/MTP connector. As the following picture shows, an MPO/MTP connector contains several parts such as boot, coupling/housing assembly, ferrule, guide pins, and so on. When the MPO/MTP connector is designed with pins, it is called male connector. On the contrary, it is called female connector.

MPO MTP structure

In addition, there is a “key” on one side of the connector body. When the key sits on top, we call that it is the key-up position. In this orientation, each of the fiber holes in the connector is numbered in sequence from left to right. We will refer to these connector holes as positions, or P1, P2, etc. Generally, there is a marker called “white dot” on the side of the connector body that is used to designate the position 1 side of the connector when it is plugged in.

Polarity Method Introduction

The TIA-568-C.0 standard illustrated three array system connectivity methods—Method A, Method B and Method C. This section will introduce them respectively.

Method A
As shown in the picture below, two Method A cassettes with key-up to key-down adapters, a straight-through key-up to key-down MPO trunk cable as well as two patch cables are required in Method A connectivity. The straight-through key-up to key-down MPO trunk cable means that the fiber 1 located in P1 of the connector on the left will arrive at P1 at the other connector. What’s more, it should be noted that the transmit‐receive flip must happen in the patch cables for Method A. In other words, an “A-to-A” patch cable at one end of the connection while an “A-to-B” patch cable at the other end.

Method A

Method B
In Method B, as shown in the following picture, Method B cassettes which employs key-up to key-up adapters are required to link straight-through key-up to key-up MPO trunk cable. With the key up on both ends, the key-up to key-up trunk cable has a different fiber array with Method A type cable. In this type of trunk cable, fiber 1 (Tx) is mated with fiber 12 (Rx), fiber 2 (Rx) is mated with fiber 11 (Tx), and so on. Two straight “A-to-B” patch cables are required at the beginning and end of the link, namely patch cables do not need to be flipped in Method B.

Method B

Method C
Method C uses the same cassettes as Method A, but to link a special key-up to key-down trunk cable. For Method C, each adjacent pair of fibers at one end are flipped at the other end. Notice the swapping of the color positions in the picture below. Fiber channel is completed by utilizing straight “A-to-B” patch cables at the beginning and end of the link. Method C is similar with Method A. The only difference between this method and Method A is that the pair-wise flip occurs in the array cable itself rather than at the patch cables, so that odd-numbered Tx fibers leaving the near-end cassette are in even-numbered Rx positions when they arrive at the remote cassette, e.g. fiber 1 (Tx) is mated with fiber 2 (Rx).

Method C

Which to Choose?

The above section shows us the details of these three methods. The following table summarizes the advantages and disadvantages of them which may guide you to choose a proper one for your network. But, it is very important to know that the method choice should be maintained consistently throughout the installation. Do not mix them throughout the installations.

Method Pros Cons
A One cassette type, easy to produce and purchase Requires pre-configured “A-to-A” patch cables, or field configuration of same
Compatible with many legacy systems
Multiple sources for components
Industry standard
Single-mode and multimode
Standard provides migration path to parallel optics
Ribbon cables can be linked (need male/female connector)
B Single source for components Remote cassette must be flipped and re-labeled
“A-to-B” patch cable only Identification and maintenance of cassettes are different on each end
Industry standard Multimode only
Standard provides migration path to parallel optics Not compatible with legacy systems
Ribbon cables can only be liked using less available (Key Up to Key Up) adapters (need male/female cable)
Fewest vendors
C One cassette type, easy to produce and purchase Less reliable than Method A
Singlemode and multimode Specialized ribbon cable assembly
Industry standard Does not support parallel optics
“A-to-B” patch cable only Not compatible with legacy systems
Less vendor support than Method A
Difficult to extend link

This post introduced three array system connectivity methods and listed their pros and cons that may guide you for polarity selection. In a word, the Method A is polarity flip in A‐to‐A patch cord. The Method B is polarity flip in cassette. And the Method C is flip by pairs. When choosing one of them for your network, the most critical consideration is to select one method and stick with it.

Polarity and MPO Technology in 40/100GbE Transmission (FS.COM)
ANSI/TIA-568-C.0 Standard
Best Practices for Ensuring Polarity of Array-Based Fiber Optic Channels (PANDUIT)

Understanding Fiber Polarity Method: Which to Choose?

Difference Between Fiber trunk, Harness, and Patch Cables

Difference Between Fiber trunk, Harness, and Patch Cables

Pre-terminated fiber cables are considered as a convenient and cost effective solution for today’s fiber optic network, which help save up to 65% installation time. Pre-terminated fiber cables are generally divided into trunk cable, harness cable and patch cable. To many newbies, these classifications often make them confused. Don’t worry, this post will take you easy to understand the difference between them.

Fiber Trunk Cable

Fiber trunk cables are available with today’s required fiber types with MPO/MTP, LC and SC connectors. Trunk cable is generally used for data center infrastructures and backbone applications where cable distances are reasonably predictable and can be easily determined. In a word, it is used as backbone cabling.

trunk cable

Fiber Harness Cable

A fiber harness cable, also called fan-out or breakout cable, is a cable assembly used to break out an MPO/MTP trunk to discrete connectors (such as LC, SC, etc.), in order to feed in to active equipment. The most common configurations of fiber harness cables are 8-fiber MPO/MTP (QSFP+ standard) to 4 duplex LC, 12-fiber MPO/MTP to 6 duplex LC, and 24-fiber MPO/MTP to 12 duplex LC.

harness cable

Fiber Patch Cable

Fiber patch cable, also called fiber patch cord or fiber jumper, is a shorter length fiber cable that is usually used to make connections between a patch panel and active equipment or between two switch ports. According to the connection requirement, there is a variety of connector options for fiber patch cable, such as LC, SC, ST, FC, MPO/MTP, and so on.

patch cable

Do you have a better understanding of these three types of pre-terminated cables after reading the above contents? If not, write down your question in comment for further discussion.

Method B Link With FS.COM MPO/MTP Cassettes

Method B Link With FS.COM MPO/MTP Cassettes

MPO/MTP cassettes are typically designed with 12 or 24-fiber MPO/MTP adapter in the rear panel and breakout to 6 or 12 duplex LC adapters in the front panel. MPO/MTP cassettes provides adaptability for the changing data center environment, offering great advantages, such as cost and space saving, quick to install, simple to manage, and so on. In FS.COM’s MPO/MTP cassettes product line, there are two types of MPO/MTP cassettes used for polarity Method B Link—Type B1 and Type B2. In this post, these two solutions will be presented.

As we know, generally, there are three polarity options for MPO/MTP cable assemblies. Method B is the second polarity method that employs Key-Up to Key-Up adapters to link straight-through Key-Up to Key-Up ribbon cables to fiber cassettes. Method B cassettes are identical to Method A cassettes except that they use Key-Up to Key-Up adapters. Inside the MPO/MTP cassette, from MPO/MTP adapter to LC adapters, there are two kinds of fiber arrange methods. Straght-through 1-1 wiring and Crossover 1-12 wiring, namely Type B1 and Type B2 cassttes offered by FS.COM. The following diagrams shows the Method B Link with Type B1 and Type B2 MPO/MTP Cassettes.

MTP MPO/MTP Cassette Solution – Type B1 Polarity

Type B1 Cassette

MTP MPO/MTP Cassette Solution – Type B2 Polarity

Type B Cassette

FS.COM MPO/MTP Cassettes are equivalent to Panduit, Corning and Levtion optic cassettes, which are more flexibly accommodating for the changing data center environment and specially designed to reduce installation time and cost. For more information, please visit the official website of FS.COM or contact the sales team via

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Choosing the Right Cleaner for Your MPO/MTP Cleaning

Choosing the Right Cleaner for Your MPO/MTP Cleaning

There are various kinds of fiber optic cleaning tools in the market nowadays. In the previous post “Cleaning Tools for Fiber Optic End-face Cleaning” we have presented the importance of cleaning and several kinds of popular tools for fiber optic cleaning in the modern fiber optic systems. MPO/MTP connector and adapter is a multi-fiber assembly that is widely used in today’s parallel and high-density network cabling. Just like other fiber optic connectors and adapters, such as LC, SC, FC, etc., the end-face of the MPO/MTP also requires to keep clean in order to ensure the best optical performance. Since the MPO/MTP is special, there is a specific cleaner for MPO/MTP cleaning when you choose the one-click pen type. Of course, if you just need to clean the MPO/MTP connector, the fiber optic cassette cleaner may be a better choice that it can support cleaning for almost all kinds of fiber optic connectors.

One-Click Cleaner for MPO/MTP

One-click cleaner, as an easy to use fiber cleaning tool, becomes a necessity for both installers as well as fiber optic technicians and troubleshooters. The most commonly used one-click cleaners are 1.25mm cleaner and 2.5mm cleaner, as well as MTP/MPO cleaner. The 1.25mm cleaner is usually used for LC, LC secure keyed and MU connectors cleaning while the 2.5mm cleaner is used to clean SC, ST, FC and E2000 connectors with either UPC or APC polished ferrules. The MTP/MPO cleaner is mainly used for MPO/MTP based connector cleaning. Some MPO/MTP cleaners can also be used to clean both flat polished multimode and 8° angled single-mode MT ferrules.

A common type of one-click cleaner for MPO/MTP is shown in Figure 1. It consists of several parts including the thumb wheel, cleaning head and protective cap.


Figure 1. One-click MPO/MTP Cleaner

One-click MPO/MTP cleaner can be used to clean multimode and single-mode (angled) MPO/MTP connectors, MPO/MTP connectors in adapters, exposed MPO ferrules, and so on. Without the use of alcohol, just a easy one-click operation, it can help user to clean a variety of contaminates on the end-face efficiently. Figure 2 shows the cleaning details of a one-click MPO/MTP cleaner.

cleaning details of a one-click MPO/MTP cleaner

Figure 2. Cleaning Details of One-click MPO/MTP Cleaner

Fiber Optic Cassette Cleaner

Fiber optic cassette cleaner is an ideal choice for fiber connector cleaning. Because it is designed for effective cleaning of almost all fiber optic connectors with an accessible ferrule including LC, MU, SC, FC, ST, MPO/MTP, MTRJ and so on. Fiber optic cassette cleaner uses a densely woven micro-fiber cleaning fabric to remove harmful contaminates off of the ferrule end face. The cleaning tape can be easily replaced with a simple push button shutter operation which greatly help reduce the cost and minimize unwanted dust. Figure 3 shows us the MPO/MTP cleaning with fiber optic cassette cleaner.

MPO/MTP Cleaning With Fiber Optic Cassette Cleaner

Figure 3. MPO/MTP Cleaning With Fiber Optic Cassette Cleaner

Product Recommendation

Recently, FS.COM has launched some special offers of fiber optic cleaners. The prices are very favorable, and with an adequate stock. If you have any requirement on the fiber optic cleaner, such as 1.25mm, 2.5mm and MTP/MPO cleaners or the fiber optic cassette cleaners, it may be good options for you. For more details, I recommend you to visit the promotion page.

Comparison of 40G QSFP+ LR4 and SR4 Optics

Comparison of 40G QSFP+ LR4 and SR4 Optics

At present, for 40GbE, there are several kinds of transmission solutions. People usually use the 4 x 10 GE Breakout cable, 40G QSFP+ module or 40G CFP modules to achieve the 40GbE. Among them, the first two kinds of solutions are most widely used for nowaday 40 Gigabit Ethernet. For aggregation and core native 40 GbE, the 40G QSFP+ module is an ideal choice. There are many different variants of 40G QSFP+ modules which are defined by IEEE 802.3ba to support different applications. 40GBASE-LR4 (40G-QSFP-LR4) and 40GBASE-SR4 (40G-QSFP-SR4) QSFP+ optics are the most commonly used specifications of 40G QSFP+ optics. So, what are the differences between them on the module structure and applications?

The IEEE 802.3ba committee ratified the 40 Gigabit Ethernet standard in June, 2010. Along with the general specification, it defined a number of fiber optic interfaces. These standard interfaces attempted to satisfy a number of different objectives including support for multi-mode fiber and single-mode fiber compatibility. 40BASE-LR4 and 40BASE-SR4 QSFP+ optics both comply the IEEE 802.3ba and QSFP Multisource Agreement (MSA), but for different applications according to their features and parameters. Here are some detailed differences between 40BASE-LR4 and 40BASE-SR4 QSFP+ modules.

  • 40GBASE-LR4 QSFP+ transceivers are most commonly deployed between data-center or IXP sites with single mode fiber.
  • 40GBASE-SR4 QSFP+ transceivers are used in data centers to interconnect two Ethernet switches with 12 lane ribbon OM3/OM4 cables.
Fiber Type and Connector
  • 40GBASE-LR4 QSFP+ transceivers support link lengths of up to 10 kilometers over a standard pair of G.652 single-mode fiber with duplex LC connectors.
  • 40GBASE-SR4 QSFP+ transceivers are generally enable high-bandwidth 40G optical links over 12-fiber parallel fiber terminated with MPO/MTP multifiber connectors.
QSFP+ connectors
Wavelength (nm)
  • 40GBASE-LR4 QSFP+ (Multiplexing and demultiplexing of the four wavelengths are managed within the device): 1271 nm, 1291 nm, 1311 nm, 1331 nm
  • 40GBASE-SR4 QSFP+: 4 x 850 nm
Transmission Distance
    – 10 km on single-mode– 4λ x 10G 1300 nm region
  • 40GBASE-SR4 QSFP+ (parallel optics)
    – 100 m on OM3–10G on 4 fibers per direction
    – 150 m on OM4 –10G on 4 fibers per direction

Obviously, the 40G QSFP LR4 is designed for long transmission used with single-mode fiber while 40G QSFP SR4 is for short distance with OM3/OM4. And “4” here means four lanes. Additionally, they are in different wavelengths and with different connectors. When they used in actual network, they are used different technology.

Ok, the article will be end here as today’s topic is simple. I hope that this post will give you some help and of course due to the limited knowledge of the author, there are some inevitable errors and omissions existing in this paper. Futhermore, if you are very interested in this topic and want to gain more information about it, I suggest you to read the IEEE 802.3ba and QSFP Multisource Agreement (MSA).

Related Recommendation

Fiberstore 40GBASE QSFP+ solution offers customers a wide variety of high-density and low-power 40 Gigabit Ethernet connectivity options for data center, high-performance computing networks, enterprise core and distribution layers, and service provider applications. Recently, Fiberstore has launched a special offer for the 40GBASE-LR4 and 40GBASE-SR4 QSFP+ transceiver modules. There is a large price cut on both of them which can definitely save your budget up to 30% off for the fiber project. In addition, there are also a promotion for MTP patch cables. For more information, please visit the latest news of Fiberstore.