Fiber U Self Study

Fiber Optic Testing, Lesson 5: OTDR Testing


Objectives: From this self-study lesson you should learn:
  • What is an OTDR?
  • How is the OTDR used to test a fiber optic cable plant?
  • What can an OTDR test tell you that no other test can?
  • Why is OTDR testing different from insertion loss testing?
  • What are the measurement uncertainties of OTDR tests?

The OTDR is perhaps the most powerful tool for testing fiber optics as well as the least understood and most often improperly used. Because the instrument itself is so complex, simply learning how to operate it takes time, unfortunately leaving little time for most users to really learn how it works and how to interpret test results (called traces or signatures.) At the FOA, the vast majority of questions we receive concern OTDRs and the stories of their misuse are many. Some manufacturers tell customers to just turn it on and push the "test' button and the instrument does everything for you. We know many users who took that advice and many who regretted it: one removed and ruined over $100,000 of cable that was perfectly good and another contractor had to retest over 1000 6-fiber cables.

So it makes good sense to learn how to use this expensive instrument properly. Earlier lessons have shown you how OTDR testing is used to test the cable plant. This lesson will give you much more information on how it works, how to set it up properly and how to interpret test results. Once you finish this lesson, you should be able to use an OTDR properly.

OTDR trace

FOA has a FREE OTDR Simulator you can download and use to practice analyzing OTDR traces. (It's actually the software from a OTDR with many real traces you can analyze in your Windows computer.) There are many traces that show you how the setup of the OTDR affects measurements and many more traces you can analyze.

The course leads you to read online or printed materials (with an emphasis on the online using the FOA Guide), watch FOA YouTube Videos, complete some activities and take the quizzes. Each lesson plan will be self-contained. Lesson plans open in new pages so the course overview page stays open to lead you to the next lesson or you may use the link at the bottom of the page.

Student Assignment

Read the references, watch the videos and take the quizzes (Test Your Knowledge)

FOA YouTube Videos:
FOA Lecture 17: OTDR Testing (How OTDRs work; how they differ from insertion loss testing with a light source and power meter.)
FOA Lecture 18: OTDR Setup (Before you test, you must choose the proper setup, and it can get confusing.)
FOA Lecture 19: OTDR Measurement Uncertainty (No instrument is perfect and it's important to understand the limitations of the instrument before you mistakenly accept results.)

Using An OTDR (hands-on)

Online FOA Reference
FOA Reference Guide to Fiber Optics:
OTDR Testing
(How OTDRs work; how they differ from insertion loss testing with a light source and power meter.)
Frequently Asked Questions about OTDRs
(A FAQ created from  questions users have asked FOA.)
Metrology and Fiber Optics (What are the sources of measurement error in fiber optic measurements?)

Reference Textbook
FOA Reference Guide to Fiber Optics, Chapter 8
FOA Reference Guide to Outside Plant Fiber Optics, Chapter 8 

Extra Credit Reading
Differences In OTDR And Insertion Loss Tests On Multimode Fiber
  (How OTDRs differ from insertion loss testing with a light source and power meter.)

Hands-On Practice
Download the Free FOA OTDR Simulator (You can download a free OTDR simulator with many traces to use for learning about setup and trace analysis.)

Test Your Knowledge
Online Quiz

Next Lesson: #
6, Testing for components, networks and troubleshooting


Table of Contents: The FOA Reference Guide To Fiber Optics

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