MPO cables, which are typically made with ribbon or micro-distribution cable, make up a substantial share of today’s optical industry. It’s understandable because of the fact that they allow for the high speed transport of optical data in a condensed manner. This is ideal because as one can imagine, space is sold at a premium within the data center environment. In addition to providing many advantages to high-speed networks for their owners and installation technicians, MPO cable assemblies are a no-brainer for higher end bandwidth systems. When it comes down to it, they are primarily used to deliver very large amounts of sensitive data to customers consistently, making them the most reliable form of data transport with high redundancy. With all of these advantages, the 12 and even now 24 fiber MPO-style connectors are more and more becoming the preferred connector within the fiber optic industry.
With this all being said a well known challenge has been to accurately test these cables not only for dB loss but for their “polarity” configuration as well. An MPO cable’s polarity refers to the way the fibers are arranged inside the cable. There are typical polarities used within the industry; “A”, “B”, or “C” polarities. For example, Type-A polarity (straight through) is simple - fiber 1 goes to fiber 1, 2 to 2, 3 to 3 and so on. Type-B polarity (inverted) is laid out for fibers 1 to go to fiber 12, 2 to 11, 3 to 10, and so on. Type-C polarity (twisted pair) is arranged for fiber 1 goes to fiber 2, 2 to 1, 3 to 4, 4 to 3, and so on.
Traditionally, to perform attenuation (loss) testing for MPO cables the user would have to use an MPO to LC breakout cable, use a traditional power meter and test each fiber one at a time through each LC connector. Also, all polarity testing would have to be done manually as well with a visual fault locator or continuity tester. This leads to longer test durations, which means higher labor costs and an overall headache when trying to keep track of what polarity and what fiber number was for which cable.
As MPO cables have increased dramatically in popularity over the last several years. The market has evolved to produce a tester that can accommodate the growing need to test and certify these cables faster and easier. The MPO loss test sets can do all of the core functions that are demanded by the industry: Polarity check, dBm power referencing , “pass/fail” dB loss testing, continuity check, and reporting software that can certify a newly installed MPO cable. This product has cut the testing time down from several minutes to several seconds!
Once you have determined the polarity type, referencing the power meter is done essentially the same way as you would with a traditional power meter/light source set up. Attach your reference cord(s), press the zero/reference button, attach your test cable, select the polarity of the test cable and within about 10 seconds you have your entire MPO cable certified for loss and the passing results can then be stored and are ready to be organized into a report on your PC for you and the customer.
With the ability to save up to thousands of tests and define your own pass/fail thresholds, you have the flexibility to test your MPO cables under just about any situation that you or your customer needs. When it comes to reporting the results, each file slot on the meter contains results for the 12 channels (fibers) and a pass/fail mark is visible so you can easily identify and organize your test results. If you choose, you can export hundreds of files in seconds. Then the PC software program allows you to customize your header information. You can include details such as test location, date/time, operator, company, etc.
The fiber optic industry offers MPO loss test kits for singlemode as well as multimode cables that are of great value to a whole range of fiber optic technicians. The multimode set typically includes the power meter and 850nm light source with appropriate reference cables. If you are testing a large amount of cables for multimode it’s important to make sure that your multimode source is “encircled flux compliant”. Because of the nature of how multimode LED sources launch into a cable, there are other modes of light that exist in the cladding of the fiber for the first few meters which can invalidate the power reference(dBm) . This is traditionally why mandrels have been used for MM testing, however encircled flux compliant sources and/or reference cords are designed to allow for more consistent referencing, thus meaning a lower variation in insertion loss results test after test. As for the Singlemode kits, they can include a 1310nm light or a 1550nm light source. Power meters and light sources can be obtained separately as well.
When it comes to what is expected by customers and clients for MPO testing applications, it’s important to note that it isn’t just insertion loss testing and polarity verification that is needed; there are other tools that are used to maintain and properly certify these types of cables. Because insertion loss is a main concern in testing and most of the loss of the cable is coming from the connectors themselves, MPO inspection probes are gaining in popularity to ensure the MPO end face is clean. This goes hand in hand with the proper cleaning consumables to keep the 12 -24 fiber end faces clean and defect free.
Most MPO test sets today work in conjunction with a MPO capable visual inspection probe with pass/fail software that adheres to the IEC industry standards. This ensures the customer that the cables were inspected and passed when installed and tested. The images can be uploaded into a report in the same fashion as typical single fiber images can be.
As far as cleaning goes, there is a whole range of cleaners one can use. The most effective are the “push-click” style cleaning pens; which can clean both male and female MPO connectors as well as into mating sleeve bulkheads. There are also gel pads that the user will press the connector into and when the connector is removed from the gel pad any debris that was on the connector endface remains in the gel, leaving the endface clean.
Typical MPO test kits would include: MPO power meter, MPO light source(s), reference cords, mating sleeves, A.C. power adapters, reporting software, etc. Separate additional accessories to assist in maintenance: MPO connector push-style cleaner, MPO gender change tool, MPO/LC breakout cable, extra reference cords and mating sleeves.
As you can see the MPO style connector isn’t going anywhere and today the industry offers options that allow technicians to properly verify, test, and certify all aspects of their MPO cable assemblies. Whether it be polarity or continuity verification, insertion loss testing, or end face inspection, the tools exist to confidently certify these assemblies built for high density and high bandwidth applications.
