OTDR – Making it Easier to Test Optical Fiber Cabling Faults

Communication networks never go slower, never get simpler, and never stay the same. Likewise, certification testing for fiber-optic cabling has also changed. Various test equipment and enhanced testing regiments are manufactured by many vendors to ensure that cabling can support the new demands placed on networks. Among them, OTDR (shown in the following picture) is a new generation of fiber test equipment, which can make it easier to ensure consistent quality in an optical fiber. I’d like to introduce this new testing tool for you in the following part.

What Is OTDR?

OTDR, also called as optical time domain reflectometer, is an optoelectronic instrument which is basically used to identify and analyze reflective and non-reflective events that cause disturbance in an optical fiber link. OTDR are most effective when testing long cables (more than approximately 250 meters or 800 feet) or cable plants with splices. The data that OTDR produces is typically used to create a picture called as a trace or signature, which can be used for troubleshooting, since it shows where breaks are in fiber, when the trace or signature is compared to installation document. Using OTDR, you can easily confirm the quality of fibers and find where network trouble arises. There are various of OTDR available with different fiber types (like single-mode fiber) and wavelengths (such as 1310 nm, 1550 nm and 1625 nm). The image below shows the working principle of OTDR.

Working Principle of OTDR

OTDR uses the effect of rayleigh scattering and fresnel reflection to measure the characteristics of an optical fiber. In essence, it takes a snapshot of the fiber’s optical characteristics (the trace of length vs returned signal level) by sending high-powered pulse into one end of the fiber and measuring the light scattered back toward the instrument.

As we mentioned above, the trace, which can be analyzed on the spot, printed out immediately for documentation of the system, or saved to a computer for later analysis and comparison, is referred by trained operator to locate the end of the fiber, the location and loss of splices, and the overall loss of the fiber.

What can OTDR Be Used for?

OTDR is widely used in many phases of a fiber system’s life, from the construction, to maintenance, to fault locating and restoration. The following part lists some aspects that it can be utilized:

• Locating fiber cable breaks or cuts. OTDR can be used to predict the distance (in meters from the source) where the optical fiber cable has been disconnected.
• Measuring reflectance or optical return loss (ORL) of connectors and mechanical splices for CATV, SONET, and other analog or high-speed digital systems where reflections must be kept down.
• Identifying dissimilar and mismatched fibers (for example, 50 micron fiber and 62.5 micron fiber) that are connected together affecting the intensity of the light signal.
• Spotting usage of fiber patch cords with a different/incorrect core size that affects signal strength.
• Detecting the gradual or sudden degradation of fiber by making comparisons to previously-documented fiber tests.

Using Tips for OTDR Tester

When using an OTDR, there are a few tips that will make testing easier and more understandable:

• Always using a long launch cable, which allows the OTDR to settle down after the initial pulse and provides a reference cable for testing the first connector on the cable.
• Always start with the OTDR set for the shortest pulse width for best resolution and a range at least twice the length of the cable you are testing.
• Make initial trace and see how you need to change the parameters to get better results.

Conclusion

OTDR is an easier solution to test or identify faults in an installed fiber optic cable network as well as certify new fiber optic cable installation. This text has provided you with some basic information about OTDR tester and tell you several helpful tips for using OTDR tester. Besides OTDR that offered in fiberstore, there are various other types of optical testers, such as VSL (visual fault locator), ADSL tester, optical power meter, and so on. Each tester has unique functions and is used in different applications. If you want to know more information, please visit FS.COM.