Fiber optic polarity is a light signal traveling directionally through a fiber optic cable from one end to the other. In any installation, it is important to ensure that the optical transmitter at one end is connected to the optical receiver at the other. This matching of the transmit signal (Tx) to the receiving equipment (Rx) at both ends of the fiber optic link is called polarity. Fiber Optic Polarity is about making sure that transmit talks to receive.

Fiber optics rely on a bidirectional transmission where the transmitter port on one end connects to the receiver port on the other end. Since fiber optic links require a two-way or duplex connection, there is potential for errors in the installation by connecting transmitter to transmitter or receiver to receiver.

TIA publishes polarity connectivity methods to help installers install and select the right components. Two types of fiber links are outlined in the TIA standard: serial duplex signals connections and parallel signals connections. Two types of duplex fiber patch cords are defined in the TIA standard: (A ‘toward” A) type shown in Figure 1 and (A toward B) type shown in Figure 2. Note: (A toward A) patch cords are not commonly deployed and should be used only when necessary as part of a polarity method. “See ANSI/TIA-568-C.3″.

THE THREE TYPES OF POLARITY

There are three types of MPO trunk cables and connectors to obtain proper MPO polarity:

1. Type A (Straight)

When components are Type A, the fiber identified as 1 (blue, according to the TIA color code) connects to Fiber 1. In other words, 1 goes to 1, also known as Key-up/Key-down. This type applies to adapters, cassettes, and cables.

2. Type B (Crossed)
Fiber 1 goes to Fiber 12 or commonly called Key-up/key-up. This type also applies to adapters, cassettes, and cables.

3. Type C (Cross pairs)
Type C refers to cross pairs, just like with ethernet connections. With Type C, Fiber 1 matches Fiber 2, 2 to 1, 3 to 4, and so on. It only applies to trunk MPO cables.

POLARITY IN MPO

TIA 568 standard specifies three different methods for managing MPO polarity: A, B, and C, each requiring different types of MPO adapters and cables.

Method A

Method A polarity uses straight-through MPO trunks and interconnects cables to map the fibers on both ends of the link. To flip the polarity, an A to B patch cord (LC to LC) at one end must be connected to an A to A cord at the other end. In this method, Fiber 1 arrives at Fiber 2 at the other end of the connection.

Since the fibers at each end have the same position, Method A offers the simplest deployment for multimode channels, easily supporting network scalability for the hyperscale future.

Method B

Method B uses three Type B MPO components or three crosses for the transceiver-transceiver connection. Thus, two A to B patch cords are required on each side of the link. In Method B, the fiber located in Position 1 (Tx) arrives at Position 12 (Rx) at the other end of the link.

Method C

In Method C, two Type A MPO cassettes and one Type C trunk cable are necessary for the system. The polarity flip occurs within the array cable itself. Type C cords use reverse-pair positioning, through crossovers in the array cord, to swap the polarity of pairs of fibers. Thus, each pair of fibers is flipped so the fiber in Position 1 (Tx) arrives at Position 2 (Rx) at the opposite end.

While this method works well for 10 Gbps applications, it does not support parallel eight-fiber 40 and 100 Gbps applications where Positions 1, 2, 3, and 4 of the MPO connection are transmitting and Positions 9, 10, 11, and 12 are receiving.

As a result, Method C is not ideal for migrating your network for the hyperscale.

As fiber optic cables become increasingly popular for transmitting high-speed data, fiber numbers also increase, making their connections more complex. Thus, users should take the time to understand how fiber optics polarity works. Consider the following factors when determining a solution to a polarity problem:

• General Fiber Polarity: Is the polarity straight, crossed, flipped, or other?
• Gender: Are the paired male and female components properly connected?
• Orientation: Is the orientation KeyUp-KeyUp or KeyUp-KeyDown?
• End-Face Alignment: Is it straight or angled?

Multiple applications use array connectivity in the cable plant. Duplex configurations include SFP, SFP+, XFP, SFF, and XENPAK. These duplex connections have simple, consistent transmit-and-receive configurations and they employ A “toward” A cable and A “toward” B patch cords in combination with breakout sets to array adapter types and multiple array trunk configurations.

Installers will buy duplex assemblies and forget to confirm with the supplier if their assemblies are wired straight through or if the pairs were crossed inside the assembly. If the installer purchased all assemblies with the crossed pair that has an even number of assemblies throughout the link, it will cause an error message or may end up damaging the photodiodes in their transceivers.  If the duplex assembly has a clip to hold the two connectors together, the installer could try to manually remove and flip the connectors.  This is time-consuming and could lead to broken fibers.  If the assembly uses a unibody duplex connector (no clips), it may not be possible to retroactively flip the connector pair.  The installer would have to buy another assembly with straight-through wiring which adds costs and time to the installation.

The best way to avoid the problem if you are unsure if a duplex assembly was wired straight through or has crossed pairs is to put a VFL on it.  If the installer was able to flip the connector pair in the field, a VFL: would still be a smart thing to do.  The VFL would verify continuity to make sure the fibers were not accidentally broken during the flip. SENKO has a good tool for this application. Contact Brian Teague Product Manager at SENKO for more information regarding Smart Checker MPO Tester.

SENKO SMART CHECKER MPO TESTER 12 FIBER

Senko Part Number: AFT-G-FC-MPO-02

• < 2 sec testing time
• Verifies the polarity for 12F & 8F MPO assemblies for TIA 568 Method A, B, C
• Verifies continuity of MPO assemblies, patch panels, and cassettes modules
• Works for both SM (angled) & MM (flat) MPO assemblies

If the assembly was wired for crossed pairs, then it would be fine if the link was a single duplex or an odd number of assemblies across the link.  Below is a sketch to illustrate what is happening with even and odd numbers of crossed-pair assemblies.

Understanding fiber polarity and how to connect and maintain a system with absolute certainty is key to a successful installation. The complex part, however, is there is no ‘right’ way to approach fiber polarity as each manufacturer usually provides its own fiber polarity solution.

Consult your supplier as needed TO MAINTAIN

Polarization is NOT to be confused with fiber optic polarity … from (Wikipedia)

In fiber optics, polarization-maintaining optical fiber (PMF or PM fiber) is a single-mode optical fiber in which linearly polarized light if properly launched into the fiber, maintains a linear polarization during propagation, exiting the fiber in a specific linear polarization state; it is little or no cross-coupling of optical power between the two polarization modes. Such fiber is used in special applications where preserving polarization is essential.

This Image is of the cross-section of a polarization-maintaining optical fiber patch cord, taken with an illuminated microscopic viewer called a fiberscope. The two small, eye-like circles are the stress rods and the tiny circle between them is the core. The larger circle surrounding them is the cladding, usually 125 microns in diameter.

AI techniques for improving performance of optical communication systems and networks. The use of AI-based techniques is first studied in applications related to optical transmission, ranging from the characterization and operation of network components to performance monitoring, mitigation of nonlinearities, and quality of transmission estimation.

• In an optical network, there are non-deterministic events taking place, and the lack of full information about the environment is not a rare issue. Therefore, intelligent agents must be able to operate under uncertainty in a robust way. 
• A second key element is the use of decision-making algorithms. 
• The third issue of paramount importance is learning. Learning enables an agent to improve its performance on future tasks due to acquired experience. 

For example, cloud-computing infrastructure, capable of storing the vast amounts of data and possessing the massive amount of computing power required by AI, largely resides in servers. From the Amazon Web Services (AWS) elastic cloud to the Google machine learning infrastructure, almost all of the online tools that have made AI accessible to the entrepreneurial community rely on infrastructure that exists around the Globe. Fostering a culture of innovation and a commitment to research and, most important, nurturing an ecosystem beyond the four walls of the organization are all common to Google’s DeepMind, IBM’s Watson, and Baidu’s Institute of Deep Learning, the most successful AI projects of the past half decade. While it must come as no surprise that Google, IBM, Microsoft, Facebook, and other global technology giants have invested significantly over the decades in machine intelligence. … stay tuned to updates forthcoming! 

… more info

or more of “My World” for more application notes

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