Fiber Optic Wiki

Diagram of OTDR trace with events shown

December 22, 2011

There is a lot of information in an OTDR display. The slope of the fiber trace shows the attenuation coefficient of the fiber and is calibrated in dB/km by the OTDR. In order to measure fiber attenuation, you need a fairly long length of fiber with no distortions on either end from the OTDR resolution or overloading due to large reflections. If the fiber looks nonlinear at either end, especially near a reflective event like a connector, avoid that section when measuring loss.

OTDR Limitations

December 22, 2011

The limited distance resolution of the OTDR makes it very hard to use in a LAN or building environment where cables are usually only a few hundred meters long. The OTDR has a great deal of difficulty resolving features in the short cables of a LAN and is likely to show "ghosts" from reflections at connectors, more often than not simply confusing the user.

Virtual hands-on tutorial on OTDR testing

December 22, 2011

Long Link Testing.Long distance fiber optic links have unique testing needs. Two factors can limit bandwidth on long links, chromatic dispersion and polarization-mode dispersion. These topics are important but complicated, beyone this basic explanation, so there is a complete discussion on the topic and how testing is done in the FOA Online Reference Guide. More on CD and PMD.

Fiber optic network design refers to the specialized processes leading to a successful installation

December 22, 2011

Fiber optic network design refers to the specialized processes leading to a successful installation and operation of a fiber optic network. It includes first determining the type of communication system(s) which will be carried over the network, the geographic layout (premises, campus, outside plant (OSP, etc.), the transmission equipment required and the fiber network over which it will operate. Designing a fiber optic network usually also requires interfacing to other networks which may be connected over copper cabling and wireless.

Clean your connectors and set up your equipment

December 21, 2011

Turn on the source and select the wavelength you want for the loss test. Turn on the meter, select the "dBm" or "dB" range and select the wavelength you want for the loss test. Measure the power at the meter. This is your reference power level for all loss measurements. If your meter has a "zero" function, set this as your "0" reference.

There are two methods that are used to measure loss

December 21, 2011

There are two methods that are used to measure loss, a "patchcord test" which we call "single-ended loss" (TIA FOTP-171) and an "installed cable plant test" we call "double-ended loss" (TIA OFSTP-14 (MM) and OFSTP-7 (SM).) Single-ended loss uses only the launch cable, while double-ended loss uses a receive cable attached to the meter also.

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