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OTDR testing

Fiber optic link characterization and troubleshooting


Fiber foundation done right with OTDR testing

Fiber is going deeper everywhere as massive rollouts are laying the ground for 5G and IoT in today’s transforming telecom landscape. The promise of tomorrow’s technologies relies on an extremely reliable fiber foundation, whether in data centers, in the field or at customer premises. Verifying the integrity of the fiber optic cables with the right OTDR testing methods has never been more vital to be able to quickly identify and locate faults.

Guidelines for installing or troubleshooting optical fiber links

Getting it right the first time when installing or troubleshooting optical cables means reliable testing equipment and procedures.

For fiber characterization, the testing equipment will need to measure/find the following key parameters:

  • Insertion loss (IL): The loss of signal power expressed in decibels (dB) that results from the presence of an event on a fiber link, such as a splice or a connector. It represents a ratio of the power that comes out of the link over the power that goes in.
  • Optical return loss (ORL): The loss of signal power resulting from the reflection caused at a discontinuity in an optical fiber. It represents a ratio of the power that is reflected over the power that goes in.
  • Optical link length: The distance between the first network connector and the end of a fiber link, including the different events (connectors, fusion splices, macrobends, etc.). Fiber length can be from point-to-point or can be measure going through a splitter all the way to the ONT, depending on the measuring devices used.
  • Fiber-based faults: Any event on an optical link that doesn’t meet the required thresholds to achieve a pass diagnostic for a particular measurement.

These measurements and the fault detection are carried out by using an optical time domain reflectometer, commonly called an OTDR by the industry.


OTDR testing basics

What’s an OTDR?

Used to characterize optical fibers, the OTDR couples a laser and a detector and is based on the principle of reflectometry. The OTDR sends a pulse of laser light into one side of the optical fiber.  As the pulse travels along the fiber, a small portion of the pulse’s energy is reflected to the detector from points along the fiber, such as connectors, multiplexers, splices, splitters and other components on the optical link. An OTDR trace is a graphical representation of power and distance of all elements of the optical fiber. 

Once saved, OTDR results can be used to reference the link for future testing.

When to use an OTDR?

The OTDR is the single piece of test equipment needed to provide the most accurate and complete end-to-end link validation. As opposed to the simple light source and power meter test method, the OTDR can identify and locate any potential faults, macrobends or breaks that could impact network performance.

OTDR testing terminology

Dynamic range: The maximum optical loss an OTDR can analyze from the backscattering level at the OTDR port down to a specific noise level.

Event dead zone: the minimum distance after a Fresnel reflection where an OTDR can detect another event. In other words, it is the minimum length of fiber needed between two reflective events.

Pulse width: the time during which the laser is on. Since time is converted into distance, pulse width has a length.

What to look for in an OTDR?

Reliability and accuracy: best-in-class specifications are vital today to ensure that the fiber foundation can support critical 5G and IoT services. The OTDR is an important investment in ensuring the reliability of fiber optic networks. As such, the OTDR measurements themselves need to be highly reliable and accurate. In today’s evolving telecom backdrop, top-shelf and trusted performance is sure to yield the best return on investment. Low grade OTDRs will come at higher risks and eventually higher costs.

Simplicity and ease of use: Given the complexity involved in OTDR testing, look for automated test processes and results analysis. Smart diagnostics and intuitive visual displays can help field crews up their efficiency with minimal training.

Ruggedness and compact form-factor: With fiber densification, OTDR usage will intensify in the field, in data centers and even near customer premises. Look for ODTRs designed with practicality and ruggedness in mind.

Choosing the right OTDR for your needs

Each application has specific testing requirements. The wide array of options available today can be overwhelming. Consult EXFO’s OTDR and iOLM product category to learn more about our variety of OTDR equipment. Amy, our smart online chabot on the bottom right of your screen, can also help you find your best fit!