FTTx Testing: Different Levels for Different Applications

In the past 10 years or so the fiber to the “x” industry, has experienced an extensive boom; generally out-growing the fiber optic industry as a whole. This growth was further spurred on by the Corona Virus pandemic of 2020-22 where many gaps and weaknesses in home & neighborhood networks were exposed due to the large increase in virtual meetings & learning. This led to the allocation of public funds dedicated to the betterment of access to high speed broadband internet. Similar to the 1930s New Deal Era Tennessee Valley Authority bringing electricity to rural Americans in the deep south. Today we look to bring high speed internet to the more rural areas of the U.S.

We had seen even before the pandemic an increased demand for fiber optics when state governments put forth legislation to roll out grants to small telephone companies where high speed internet was lacking. The successes of those initiatives have led one way or another to the current federal infrastructure plan which will bring FTTx to nearly every American within the next several years. Thus it’s an exciting time to be part of the industry, as FTTx applications have a tendency to touch nearly every corner of the market; from enclosures, to cable, to fusion splicers, etc. At the end of all of this is test results. Without that magic four-letter word—PASS, the job isn’t done. But it’s important to note that not all FTTx test applications are equal. There are several different situations a technician may find themselves in; whether it’s installing a new line on an already active FTTx network or performing maintenance work by troubleshooting and testing on an active line or even testing a new network after construction (dark fiber). When installing a new line to a home or other location, first and foremost the technician needs to establish simple continuity of the fiber by using a Visual Fault Locator (VFL).

A VFL is usually a 650nm red colored laser with a range of up to about 3 miles. This low-cost tool will allow the user to confirm two important things: Am I getting light to travel all the way through? If not, where is the light coming out then?

In the industry we refer to this as a “continuity test” which makes sure that the correct fiber has been spliced through and that the fiber is physically sound enough to carry the light all the way to its end. Other tools that are necessary would be a power meter, which can measure the amount of power (dBm) coming into the ONT (Optical Network Terminal) and that it is at the proper level. The final step, if needed would be a basic, smaller handheld OTDR that every tech can have at their disposal. It will record the exact distance from the drop to the house as well as verify that the leg of the splitter is testing at its proper dB loss for its size (i.e. 15-16dB for a 1x32 splitter). Also it would varify that any splices or terminations on the drop cable are producing minimal loss to be within the established loss & power budgets.

When addressing an outage, the testing is a bit more complex. In this scenario, the system is live and will stay active throughout the maintenance testing process. The first thing a technician could use would be a PON Power Meter. This tester will test both the

upstream and downstream signals from the OLT (Optical Line Terminal; downstream) which is from the provider and the ONT (Optical Network Terminal; upstream) at the house. The OLT signal needs to be bridged through the PON PM in order to give the ONT the signal from the OLT it needs to operate. When using an OTDR, one cannot use a standard OTDR, they need to use a PON optimized OTDR that has enough dynamic range to get though higher count splitters like a 1x32, 1x64 and up. To get through a 1x32 splitter you need at least a 36/37dB dynamic range OTDR. For 1x64 you would need a 39/40dB unit. It also needs to have a Live/Filtered test port as the technician will likely be testing into a live signal from the house. This live test port has a special filter that utilizes an out-ofband frequency like 1650nm. This frequency will not interfere with the in-network traffic and filters out the same in-network frequencies from interfering with the OTDR.

Finally, I wouldn’t be doing anyone any favors without mentioning the importance of proper cleaning during all this testing. One-Click cleaners have risen in popularity because they are affordable, convenient, easy to use and overall perform fairly well at cleaning connector tips and the connector tips inside bulkheads. With all the great cleaners out there, you also cannot go wrong with simple alcohol and dry wipes. Be sure to microscope and clean regularly and your testing will be much easier and less time consuming. It seems to be that the sky is the limit for FTTx applications. Now the task at hand will be what has been mentioned and more in the coming years. We hope you look to Fiber Instrument Sales who with almost 40 years of servicing the industry, can help you find the solutions you are looking for when it comes not just to FTTx, but the entire fiber optic industry