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Volume 10 Number 3 February 16, 2006


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This Issue's Feature Articles

How to Select an OTDR 

Peter Schweiger, Agilent Technologies, Photonics Measurement Division

How to Choose an OTDR to Test and Troubleshoot LAN Infrastructure 
White Paper By: Harley Lang III, Product Marketing Manager, Fiber Products, Fluke Networks

Product/Service Focus
This issue's focus is Optical Time Domain Reflectometers (OTDRs). You can view and add to our existing list of Test Products/Services, Test Vendors, Test Literature, Test Definitions
What's New in Test
Samsung Regional Manager, Sujin Choi, wins the sponsored iPod drawing at APEX 2006. Try your luck for another drawing of an iPod at the Measurement Science Conference.


  2/15/2006 GÖPEL electronic appoints Test Coach Corporation as Center of Expertise
  2/13/2006 Advantest expands patent fight to Taiwan
  2/13/2006 Agilent Technologies Reports First Quarter 2006 Results
  2/10/2006 Everett Charles Technologies Wins a VISION Award
  2/9/2006 ASE Test Q4 Sales, Earnings Up
  2/3/2006 UCLA develops nanotechnology safety test
  2/1/2006 Agilent and Speedline conduct joint research
  2/1/2006 Cadence income declines 55% despite boost in sales
  2/1/2006 Partners to develop at-speed test
  2/1/2006 President Bush to Help Electronics Industry - Valley’s Lobbying Pays Dividends
  2/1/2006 Win an iPod when you visit Booth at APEX
Conference Articles
  2/7/2006 Engineers still suffering from jitter jitters
Course Descriptions
  2/3/2006 BEST Inc and partners launch lead free training course
Magazine Articles
  2/2/2006 Specsmanship
  2/1/2006 (High-Speed Downlink Packet Access) HSDPA Testing
  2/1/2006 2005 efforts suggest 2006 ATE and DFT trends
  2/1/2006 Analyzing and Troubleshooting Serial Data Buses
  2/1/2006 AOI - Gigabit Ethernet: Coming to a Camera Near You
  2/1/2006 Full-Function DMMs
  2/1/2006 Integrating AOI and Selective Soldering
  2/1/2006 Technology Roadmap Sees Higher Sensitivity to ESD
  2/1/2006 The challenge of multisite test
  2/1/2006 The New EMC Directive - Are You Ready?
  2/1/2006 Wafer-Level High-Power Device Testing
Presentation and Web Seminar Archives
  2/15/2006 NI Joins Test And Measurement Companies To Host PXI Technology And Applications Conference Series
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  2/14/2006 Agilent Technologies introduces first event identification software for digital designers
  2/14/2006 Agilent Technologies N2X multiservices test solution first to offer MEF 14
  2/14/2006 New X-Ray system from phoenix|x-ray
  2/12/2006 Digitaltest announces new boundary scan solution
  2/8/2006 Boundary Scan Platform SCANFLEX meets FireWire
  2/8/2006 Digitaltest Unveils Second Generation Flying Probe Technology
  2/7/2006 ViTechnology unveils bench-top AOI system at APEX
  2/6/2006 Agilent Technologies introduces industry's first jitter tolerance compliance test suite...
  2/6/2006 Agilent Technologies introduces industry's first PCI express multi-lane receiver compliance test suite
  2/6/2006 Agilent Technologies releases industry's first radio equipment test solution for CPRI standard
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  2/6/2006 NI, TI and Spectrum Digital partner in new DSP Starter Kit
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  2/3/2006 KLA-Tencor Unveils Latest eBeam Tool
  2/3/2006 RVSI Inspection Introduces Vision System for Defect Inspection
  2/2/2006 Controller card supports IEEE-488/GPIB in PXI systems
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  2/7/2006 IEEE Approves First Electrical Property Measurement Standard For Carbon Nanotubes
Web postings
  2/1/2006 How to Select an In-Circuit Tester
How to Select an OTDR
Peter Schweiger, Agilent Technologies, Photonics Measurement Division

Optical Time Domain Reflectometer (OTDR) remains a fundamental tool for measuring fiber links, but the product offering has changed as both the available technology and the fiber network under test has changed.

Available products can be grouped into three classes
1. Break locators and fault finders
2. Mainstream Mini-OTDR’s
3. Optical Characterization Platforms

To choose, first evaluate your needs and the skill of the intended users honestly. Questions to ask:

1. Are you Installing or Maintaining fiber?
2. If Maintenance, is finding the location of the fault the main task?
3. If Installation, do you need measure more than loss and length? E.g. Connector quality, dispersion, Optical Return Loss?

For simple maintenance, a simple or low cost OTDR is a good fit. They are easy to use, require the lowest possible investment and some even provide total link loss and optical return loss values.

If you are doing complex installation of high speed networks than you are probably looking for an Optical Characterization Platform. These allow modules, either to be plugged in or better yet snapped on and give the most flexibility, speed and performance.

If you are in between the cases above, welcome to 80% of the users. You need a regular Mini-OTDR based system. There are many products on the market and choosing the best fit requires both a look through the key spec’s, and some hands on time.

What is an Optical Time Domain Reflectometer (OTDR)

 See picture

Figure 1. Simplified Block Diagram and Examples of Events on an OTDR

Figure 1 shows a simplified block diagram and an example of how different “events” appear on an OTDR display or “trace”.  

An OTDR sends pulses of light into a fiber and digitizes the reflected backscatter signal coupled back to its detector. Using the fiber’s refractive index, it converts time into distance over a scale of 100m to beyond 200km. It can measure distance to faults very accurately.  

The need for speed

Whether 100m or 10km long, the increased deployment of fibers needs to be tested in less time with fewer people.

The key specification for an OTDR is dynamic range. It’s the dB difference between the initial power level reflected from the fiber under test and the value equal to the noise floor of the detector, it is specified at the OTDR’s largest pulse width when making a measurement for 3 minutes. 

This figure in dB determines both how far you can measure and how fast an instrument can obtain a clear trace.

Every dB counts. In fact 1db extra dynamic range over another unit can mean an increase in speed and productivity of up to 2X.

Most products on the market are grouped into performance ranges and can be segmented into dynamic range classes of the nearest 5dB.  Table 1outlines the dramatic effect of dynamic range vs. averaging time to acquire a good trace.

Table 1. Dynamic Range vs. Average Time to Acquire a Trace

Link length

Test time

<50 km

100 km

150 km


180 sec





40 sec





10 sec





2 sec





 (See Picture if not clear)

If you are driving hours to measure 2 short fibers, you don’t need to pay the premium for a 45dB OTDR. But if you are installing Metropolitan fiber networks with 864 fibers. The time difference can add up to weeks and a faster OTDR can pay for itself in the very first cable measured. Dynamic range is key, but Ergonomics, storage and other spec’s should influence your decision. 

Table 2. Key Product Specifications and their importance

Dynamic Range

 (See Picture)

Determines range and speed. Serious products range from 30-45db for Single mode (SM) testing, 18-34dB for Multimode (MM) fiber testing.  Compare  products at the same pulsewidth.

Reflection Accuracy.

(See Picture)

Reflections or Reflectances are caused by connectors, mechanical splices, and breaks. High speed networks require small reflectances . Look for a product that measures accurately across a realistic range like 14-60dB with an accuracy of +-2dB.. A great test is to see if an open 100m from the unit reads 14dB.

Loss Accuracy

And linearity

(See Picture)  

Determines total link loss and individual splice loss accuracy. Measuring fusion splices takes high dynamic range and repeatability. Measure a splice a few times and evaluate the instruments repeatability.

Battery Life –hrs

Look for 4+ hours and fast charge times, does the unit indicate actual time remaining or simply display a guess-O-gauge?

Size and Weight

Products exist from 1kg -9kg. In today’s crowded POP’s which unit will fit? The smaller the unit, the lower shipping costs are too. If you want to hold it while measuring and you’ll need a unit <4kg.

Trace storage

What is the internal and optional memory in the product. Does it support flash cards? Do you want a hard drive in an instrument that could be dropped?

User interface

50% of users love touchscreen. 50% prefer reliable keys. Many users? Choose an OTDR with a variety of interfaces. A keyboard input port is a must if you are documenting lots of fibers.


Just enough test or fit for future? Empty frames can cause extra weight and complexity. Inquire if a built in source is an option or standard.

Available Wavelengths

A single wavelength allow fault location, Dual sources can show changes in loss at different wavelengths to detect fiber bending.

Service and Support

Asking what an extended warranty would cost is a great indication of the reliability of a unit and efficiency of the repair organization. Can you get on-site training for your unit?

Consider the whole product and all its supplied accessories and you’ll make a decision that fits your whole process better.

Buy as much dynamic range as you can afford. It makes everything possible.

Whatever you buy. Learn it. Only a small percentage of users actually take advantage of all the time saving features in modern units. Don’t buy a 200hp car and keep it in 1st gear. Read the manual or ask a professional to teach you some driving tip.

How to Choose an OTDR to Test and Troubleshoot LAN Infrastructure

White Paper from Fluke Networks. Contact: Harley Lang III, Product Marketing Manager, Fiber Products

The health of your network depends on the quality of your network infrastructure — maintaining a reliable fiber plant is essential in protecting your business-critical applications. As a network administrator, it is important to understand how to get the best performance from your cabling investment and how to solve problems quickly when they occur. Optical Time Domain Reflectometers (OTDRs) are the tools of choice for troubleshooting and maintaining fiber LAN infrastructure – however choosing the right OTDR for your application can be challenging.

The following whitepaper "How to Choose an OTDR" is Part I of Fluke Network's whitepaper series on Ensuring the Health of Tomorrow’s Fiber LANs. This whitepaper clears up misinformation about OTDR specifications, interpretation, and measurement methods. It describes how LAN OTDRs are different from Telco OTDRs, how to differentiate between manufacturers' specifications, how to develop an understanding of specifications, and how to make informed comparisons between various OTDRs.

Download our insightful whitepaper today at and get all your OTDR questions answered. 

Next Issue's Product/Service Focus
In our next issue of Product/Service Focus we will cover All/Burn-In. You can add or upgrade a listing before the next issue comes out.

If you would like to include an exclusive article on how to best select All/Burn-In, please contact

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