OTDR - Optical Time Domain Reflectometer

Overview OTDR - Optical Time Domain Reflectometer

An Optical Time Domain Reflectometer (OTDR) is an important instrument used by organizations to certify the performance of new fiber optics links and detect problems with existing fiber links.

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Applicable Roles and Jobs

This information is especially helpful if you work in these roles

Network Engineers
Network Cabling Contractors and Installers

Learn About OTDR's

Using an OTDR to Certify New Links

The health of your network depends on the quality of your network infrastructure. This quality begins with complete certificationby contractors or systems integrators that the fiber cabling infrastructure was properly installed. Maintaining a reliable fiber plant is also 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.

Most customers are familiar with Basic Certification - sometimes known as Tier 1 fiber certification – which measures attenuation (insertion loss), length and polarity. This test ensures that the fiber link exhibits less loss than the maximum allowable loss budget for the immediate application. Simple Light Source/ Power Meters or more automated Optical Loss Test Sets can perform this function.

Viewing trace results is simplified with advanced features such as pinch and zoom

Extended or Tier 2 fiber certification supplements Tier 1 testing with the addition of an Optical Time Domain Reflectometer (OTDR) from end to end. An OTDR trace is a graphical signature of a fiber's attenuation along its length which provides insight into the performance of the link components (cable, connectors and splices) and the quality of the installation by examining non-uniformities in the OTDR trace. More advanced units can provide easy to understand Event Maps and loss values for individual components as well as the link. An OTDR trace helps characterize individual events that can often be invisible when conducting only loss/length (tier 1) testing. Only with a complete fiber certification can installers have a complete picture of the fiber installation and network owners have proof of a quality installation.. This fiber test certifies that the workmanship and quality of the installation meets the design and warrantee specifications for current and future applications.

Bi-Directional Testing with an OTDR

Bi-directional testing of fiber links for Tier 2 (OTDR) testing is not only required by industry standards and most manufacturers for warranty, it's also the only way to know the actual overall loss for a link. That's because measuring the loss of fiber connectors and splices, as well as overall link loss, depends on the test direction. Testing a fiber link in one direction can give you different results than testing the same fiber link in the opposite direction.

Because of the significant time and cost involved in testing from both ends, technicians often try to save as much time as possible by testing all links from one end before moving to the other end. Unfortunately this method does not work. To accurately test a fiber link in both directions, the launch and tail cords must remain in their initial measurement positions (even the standards say so) during both tests. But that is simply not possible if you test all the links from one end before moving to the other.

To solve this dilemma, you can test two fibers at the same time and use a loop to connect the two fibers together. This allows the two fibers of a duplex link to be tested in one shot without moving the OTDR to the far end. OTDRs like Fluke Networks’ OptiFiber® Pro feature “SmartLoop” Technology that checks for the presence of the launch, loop and tail fiber when testing a duplex fiber link.

With SmartLoop, technicians can deploy multiple loops at the far end and perform a set of bidirectional tests without ever having to leave the near end--cutting test time by at least 50%.

Detecting Problems Using an OTDR

OTDRs are also used for maintaining fiber plant performance. An OTDR maps the cabling and can illustrate termination quality and location of faults that may hinder network performance. An OTDR allows discovery of issues along the length of a channel that may affect long term reliability. OTDRs characterize features such as attenuation uniformity and attenuation rate, segment length, location and insertion loss of connectors and splices, and other events such as sharp bends that may have been incurred during cable installation or afterwards.

When selecting the right OTDR, network engineers should make sure the tool has certain functionality, such as loss-length certification, channel/event map view, power meter capabilities, an easy-to-use interface, and smart-remote options. In addition, the OTDR needs to provide a reliable means to document the results. Features that make the OTDR easy to operate such as automated setup and Event Map are essential for users who aren’t OTDR experts but need to locate problems fast.

Tools such as the award winning OptiFiber® Pro OTDR provide the ultimate testing and troubleshooting solution to ensure the health of your most critical network cabling. With the OptiFiber Pro OTDR, network engineers have the in-house capability to perform inspection, verification, certification, troubleshooting, and documentation of fiber cabling in a single, easy-to-use OTDR tool.

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