test & inspection equipment
Optical time domain reflectometers (OTDRs) are critical instruments for evaluating optical fiber spans. Like any technology, they are not infallible. As the term ‘reflectometer’ implies, OTDRs work by analyzing optical signals which are reflected (and scattered) back to them. Some people call them “cable radar” because they analyze a reflected signal and not the transmitted signal. Due to this, OTDRs will sometimes generate measurement “artifacts”. One such artifact is a secondary reflection, or an “echo” - often referred to as a GHOST! After reading this article, you won’t be afraid of no ghosts!
Ghosts in the noise
The most common ghosts occur on short spans with a highly reflective open fiber end. In this case, the end of the fiber at distance L1 will generate a high-powered reflection that will arrive back at the OTDR connector. Much of it is received ...
The OTDR is one of the most powerful tools you will purchase to support your fiber network. This article discusses one key but sometimes confusing OTDR specification, Dynamic Range.
The informal definition of Dynamic Range is “how far can my OTDR see?” There are at least two formal definitions of Dynamic Range, the Telcordia definition (the most widely accepted and specified), and IEC definition. Each of these specify the amount of (one way) fiber loss from the initial backscatter (fiber) signature to a given Signal to Noise Ratio (SNR) level on the OTDR trace.
OTDR Dynamic Range Specification (SNR Limit)
IEC 98% Telcordia 50%
The IEC range wil ...