Understanding Array Polarity With Parallel Link

The use of pre-terminated fiber assemblies and cassettes is growing, and the deployment of systems with speeds up to and beyond 100G are on the horizon for many users. As a result, the issue of maintaining polarity in parallel fiber-optic links is becoming increasingly important. In the previous posts, we have introduced polarity in point-to-point duplex links which is achieved through what is known as an A-to-B patch cord. In this post, we are going to talk about array polarity with parallel link.

Array Polarity With Parallel Link Overview

Array polarity with parallel link has the corresponding Method A, B and C to establish polarity for parallel signals using an MPO transceiver interface with one row of fibers. For example, 40 Gigabit Ethernet over multimode fiber uses 4 transmit and 4 receive fibers in a 12-fiber array, or 4 lanes at 10Gbps. In order to understand these polarity methods more specifically, we can make a comparison with polarity methods for duplex signals. From the following table, we can easily find out that the breakout MTP cassette and the duplex fiber patch cords in duplex link are replaced with 12-fiber array patch cords that plug directly into the MTP adapter at the patch panel and into the equipment interface in parallel link.

Three Methods for Array Polarity With Parallel Link

Method A

Method A as shown below recognized in 568-C.0 uses Type A backbone on each end connected to a patch panel. On one end of the optical link, a Type A array patch cord is used to connect patch panel, while on the other end, a Type B array patch cord is used to connect patch ports to their respective parallel transceiver ports.

Method B

Also recognized in 568-C.0 uses Type B throughout-Type B array cable, Type B adapters and Type B array patch cords to achieve the whole optical link. More detailed information can be seen in the following image.

Method C

The proposed Method C as shown in the image below is similar to Method A, but it would use Type C trunk cable instead of Type A, and a Type C cross-over patch cord is required at one end and the other end uses Type B patch cable.

Note: An important point to remember is that MPO plugs use alignment pins. For a MPO connection, one plug is pinned and the other plug is unpinned. As MPO transceiver typically has pins, this convention leads to the following implementation on initial build out: 1) Patch cords from transceiver to patch panel are typically unpinned (female) on both ends. 2) Trunk cables are typically pinned (male) on both ends.

As duplex link, there are also three methods for parallel link. However, maintaining array polarity with parallel link is not as simple as it seems. This article can only provide some basic information about the polarity with parallel link. In the following updating, we will talk about more about array polarity system.