Fiber Optic Wiki

What Loss Should You Get When Testing Cables?

December 21, 2011

Before testing, preferable during the design phase, you should calculate a loss budget for the cable plant to be tested to understand the expected measurement results. Besides proviiding reference loss values to test against, it will confirm that the network transmission equipment will work properly on this cable. While it is difficult to generalize, here are some guidelines:

Troubleshooting Hints

December 21, 2011

If you have high loss in a cable, make sure to reverse it and test in the opposite direction using the single-ended method. Since the single ended test only tests the connector on one end, you can isolate a bad connector - it's the one at the launch cable end (mated to the launch cable) on the test when you measure high loss.

OTDR Testing

December 21, 2011

OTDRs are powerful test instruments for fiber optic cable plants, if one understands how to properly set the instrument up for the test and interpret the results. When used by a skillful operator, OTDRs can locate faults, measure cable length and verify splice loss. Within limits, they can also measure the loss of a cable plant. About the only fiber optic parameters they don't measure is optical power at the transmitter or receiver.

Visual Connector Inspection by Microscope

December 20, 2011

Fiber optic inspection microscopes are used to inspect connectors to confirm proper polishing and find faults like scratches, polishing defects and dirt. They can be used both 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.

Optical Power - Power or Loss

December 20, 2011

Practically every measurement in fiber optics refers to optical power measured in dB. The power output of a transmitter or the input to receiver are "absolute" optical power measurements, that is, you measure the actual value of the power. Loss is a "relative" power measurement, the difference between the power coupled into a component like a cable, splice or a connector and the power that is transmitted through it.

Measuring power

December 20, 2011

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.

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