9 Simple Rules for Achieving Fiber Polarity

Fiber optics support many of today’s data center, broadcast, AV, industrial and smart building environments.

To keep these critical applications working, the optical signals in a fiber cable must always be transmitted and received on the right port. The ability to maintain proper direction of flow is called polarity. It ensures that the transmitter on one end of a fiber cable can always “talk” to the receiver on the other end of the fiber cable.

Because there are many ways to connect devices using fiber optics, there’s no “right” way to achieve fiber polarity. For example, your fiber project may involve:

• Simplex optics: A single fiber is used to plug things in and establish transmit and receive one one fiber in one direction.
• Duplex optics: Two fibers are used to plug things in and establish transmit on one fiber and receive on the other.
• Parallel optics: Multiple fibers used to establish higher data rates.
• Bidirectional optics: A single fiber is used to both transmit and receive signals in both directions

No matter how your devices are connected, achieving polarity in fiber optics means that the fiber optic link’s transmit signal (Tx) on one end of the channel must match or align with the corresponding receiver (Rx) on the other end.

In duplex fiber applications, which can include workstations and networking hardware, each fiber connects the transmitter on one end to the receiver at the other end to maintain a connection. If polarity is not achieved or maintained, then data stops flowing.

What standards say about fiber polarity

Standards exist today to address fiber polarity:

• ANSI/TIA-568.3-E (Annex C), Optical Fiber Cabling and Components Standard, which outlines serial duplex signal connections and parallel signals connections
• TIA-TSB-5069, Optical Fiber Channel Polarity, which aids in mapping and planning

Solutions (or Methods, as they’re called in TIA standards: Method A, Method B, Method C, etc.) are made up of various components (or Types, as they’re called in TIA standards: Type A, Type B, Type C, etc.), which can be created in different ways. Different Methods to achieve polarity use various component Types.

And while the standards discuss Types of components and Methods of polarity, they don’t explain how components address or impact polarity (they don’t outline factors like fiber positioning and port identification, for example), or how the components themselves interact.

In other words, there’s still work to be done in the standards when it comes to addressing the full spectrum of fiber polarity in the standards.

Achieve fiber polarity on any project

As the number of fiber connections rises to support increasing throughput demands and number of use-case applications, managing fiber polarity becomes even more important to ensure proper connectivity.

Here, we share some of our simple and updated rules for achieving fiber polarity. These rules apply to any fiber project.

1. Avoid changing characteristics on the fly

MPO or MTP connectors that allow installers to select polarity, orientation and/or pinning (we like to call these “unicorn connectors”) in an attempt to be all things to all projects. On the surface, they sound like a very practical solution to address fiber polarity. But they can create more work.

Every time you connect a patch cord at every end, you must go back and verify the correct pinning, orientation and polarity. It’s far from plug and play.

2. Use the right adapters

To maintain mate-ability of connectors that are APC (angled-polish), you must use Type B (aligned keys with a key-up/key-down position) for discrete connectors, such as LCs or SCs, and Type A (unaligned keys with a key-up/key-up position) for MPO connectors.  We recommend that this rule be followed whether you use APC connectors or not.

3. Consider migration paths

When using MPO connectors, be sure they have pinned trunks and unpinned patches, cassettes or array cables to create a future migration path for equipment. QSFP connections are pinned, which will let you use unpinned connectors at both ends of an MPO patch cord.

4. Modified Method A for simplex

For simplex systems, or asymmetrical systems, using modified Method A will be the easiest, most straightforward way to establish fiber polarity. The modifications to Method A include:

• Change the trunks to pinned (rule 3)
• Use A:A cords to keep not only the port but also the fiber number/color on a 1:1 relationship
  
  

5. Modified Method B for duplex

For duplex systems, or symmetrical systems, using a modified Method B will be the easiest, most straightforward way to establish fiber polarity. This approach is not mentioned in the standards. Belden offers it as an augment to the standard, which makes it easier to use and deploy. The modifications to Method B include:

• Change the trunks to pinned (rule 3)
• Change the array adapters to Type A (rule B)
• Remember to invert the port numbering or use a Type A alternate array (that does it for you) to ensure that the port numbering remains a 1:1 relationship
  
  

6. Balance component types

When dealing with atypical systems, such as systems that incorporate both duplex and simplex optics, do what you can to balance out the types of components so that the effect of the component is balanced.

7. Do polarity mapping

If you’re dealing with a complex fiber solution, then polarity mapping is your friend! In a subsequent blog, we’ll discuss the concept of “drawing” or “mapping” polarity, what it means and the value it may (or may not) bring to new fiber projects and existing fiber networks. We’ll also cover the different ways that mapping can be completed.

8. Standardize components

Where practical, use the same components as often as possible to make your job easier by supporting simpler scalability, faster deployment, quicker onboarding and streamlined maintenance. The practice of standardization is one we recommend whenever possible for any data center or network project.

9. It’s okay to be different

You can create different fiber polarity rules for different areas. Just be sure to document everything! That way, everyone will know what to expect.

Learn more about fiber polarity

Fiber polarity isn’t simple or straightforward, but Belden’s team is here to answer your questions and support your fiber projects. We’re also developing a series of webinars focused on fiber polarity, breaking the topic down to help you better understand its relevance and how to manage it.

To learn more about basic fiber polarity rules, you can watch the first webinar in the series at any time.

Related resources:

4 Basic Rules of Fiber Polarity

Polarity Webinar Series: Part 1 - What is Polarity

Fiber Systems Solutions