FIBRE OPTIC TESTING
BackFibre Testing
After the cables are installed and terminated, it's time
for testing. For every fiber optic cable plant, you will
need to test for continuity, end-to-end loss and then
troubleshoot the problems. If it's a long outside plant
cable with intermediate splices, you will probably want
to verify the individual splices with an OTDR also,
since that's the only way to make sure that each one is
good. If you are the network user, you will also be
interested in testing power, as power is the
measurement that tells you whether the system is
operating properly.
fiber optics.
Fibre Fault Finding and Testing
Even if you're an experienced installer, make sure you remember these things.1. Have the right tools and test equipment for the job... You will need: Source and power meter, optical loss test set or test kit with proper equipment adapters for the cable plant you are testing. Reference test cables that match the cables to be tested and mating adapters, including hybrids if needed Fiber Tracer or Visual Fault Locator Cleaning materials - lint free cleaning wipes and pure alcohol OTDR and launch cable for outside plant jobs
2. Know how to use your test equipment Before you start, get together all your tools and make sure they are all working properly and you and your installers know how to use them. It's hard to get the job done when you have to call the manufacturer from the job site on your cell phone to ask for help. Try all your equipment in the office before you take it into the field. Use it to test every one of your reference test jumper cables in both directions using the single- ended loss test to make sure they are all good. If your power meter has internal memory to record data be sure you know how to use this also. You can often customize these reports to your specific needs - figure all this out before you go it the field - it could save you time and on installations, time is money.
3. Know the network you're testing... This is an important part of the documentation process we discussed earlier. Make sure you have cable layouts for every fiber you have to test. Prepare a spreadsheet of all the cables and fibers before you go in the field and print a copy for recording your test data. You may record all your test data either by hand or if your meter has a memory feature, it will keep test results in on-board memory that can be printed or transferred to a computer when you return to the office.
Visual Tracing
Continuity checking makes certain the fibers are not broken and to trace a path of a fiber from one end to another through many connections. Use a visible light "fiber optic tracer" or "pocket visual fault locator". It looks like a flashlight or a pen-like instrument with a lightbulb or LED soure that mates to a fiber optic connector. Attach a cable to test to the visual tracer and look at the other end to see the light transmitted through the core of the fiber. If there is no light at the end, go back to intermediate connections to find the bad section of the cable.A good example of how it can save time and money is testing fiber on a reel before you pull it to make sure it hasn't been damaged during shipment. Look for visible signs of damage (like cracked or broken reels, kinks in the cable, etc.) . For testing, visual tracers help also identify the next fiber to be tested for loss with the test kit. When connecting cables at patch panels, use the visual tracer to make sure each connection is the right two fibers. And to make certain the proper fibers are connected to the transmitter and receiver, use the visual tracer in place of the transmitter and your eye instead of the receiver (remember that fiber optic links work in the infrared so you can't see anything anyway.)
Visual Fault Location
A higher power version of the tracer uses a laser that can also find faults. The red laser light is powerful enough to show breaks in fibers or high loss connectors. You can actually see the loss of the bright red light even through many yellow or orange simplex cable jackets except black or gray jackets. You can also use this gadget to optimize mechanical splices or prepolished-splice type fiber optic connectors. In fact- don't even think of doing one of those connectors without one no other method will assure you of high yield with them.Visual Connector Inspection
Fiber optic microscopes are used to inspect connectors to check the quality of the termination procedure and diagnose problems. A well made connector will have a smooth , polished, scratch free finish and the fiber will not show any signs of cracks, chips or areas where the fiber is either protruding from the end of the ferrule or pulling back into it.The magnification for viewing connectors can be 30 to 400 power but it is best to use a medium magnification. The best microscopes allow you to inspect the connector from several angles, either by tilting the connector or having angle illumination to get the best picture of what's going on. Check to make sure the microscope has an easy-to-use adapter to attach the connectors of interest to the microscope.
Measuring power
Power in a fiber optic system is like voltage in an electrical circuit - it's what makes things happen. It's important to have enough power, but not too much. Too little power and the receiver may not be able to distinguish the signal from noise; too much power overloads the receiver and causes errors too.Measuring power requires only a power meter (most come with a screw-on adapter that matches the connector being tested) and a little help from the network electronics to turn on the transmitter. Remember when you measure power, the meter must be set to the proper range (usually dBm, sometimes microwatts, but never "dB" that's a relative power range used only for testing loss.) and the proper wavelengths matching the source being used. Refer to the instructions that come with the test equipment for setup and measurement instructions (and don't wait until you get to the job site to try the equipment)