Fiber optic testing is necessary in optical installations. Accurate testing result can’t be got without high quality fiber optic testers. And there are various kinds of fiber testers available in the market. Today, this article mainly focuses on introducing several common types of fiber installation tools - testers. When it comes to fiber optic installation and termination, fiber optic testers cannot be ignored. After the cables are installed and terminated, it’s time for testing. But what should be tested with fiber optic testers? Here are some common parameters which need to be tested. Power Measurement: Power in a fiber optic system is like voltage in an electrical circuit. It’s important to have moderate power. Because too little power may not distinguish the signal from noise and too much power can cause errors too. So it’s important to measure power. Loss Testing: Loss testing is the difference value between the power coupled into the cable at the transmitter end and what comes out at the receiver end. In fiber optic system, many things can result in loss such as dirt, connectors and breaks. Optical Return Loss: Optical return loss is the total accumulated light power reflected back to the source from the complete optical span. It includes the back scattering light from the fiber itself and the reflected light from all the joints as well as terminations. Generally, optical return loss is expressed in decibels (dB). And a high level of optical return loss will affect the performance of transmission systems. In addition, some optical testers also can be used for troubleshooting. Having known what should be tested in fiber optic testing. Now it’s time to know something about fiber optic testers. Generally, the common types of fiber optic test instruments are visual fault locator (VFL), OTDR (optical time domain reflectometry), optical power meter, optical multimeter, etc. Following is a brief introduction to the usual types of fiber optic tester.