How does an OTDR work? 

Optical Time Domain Reflectometers, OTDRs, work by injecting optical pulses into the fiber under test and measuring the light that is reflected from various points along the fiber. The reflected light is used to characterize the fiber under test with the strength of the return pulses being integrated against time and plotted as a function of fiber length. By using an OTDR at various points in the network, the feeder and distribution sections of the network can be tested independently. The OTDR can identify and locate each network component and can measure splice loss, connector loss and reflectance along with total end-to-end loss and optical return loss (ORL). The tests must be performed using two wavelengths, enabling detection of bends on the link, which give higher losses at 1550 nm than at 1310 nm.

What are the different EXFO OTDR parameters? 

EXFO OTDRs measure or use these parameters to characterize links: 

• Optical return loss: This shows the amount of power the device reflects compared with the input power. Signal power is lost when a discontinuity causes a reflection. 
• Insertion loss: This parameter measures the lost decibels of signal power from an event along the link. For example, a connector or splice may contribute to power loss. The insertion loss is a ratio of outgoing power to incoming power. 
• Fiber-based faults: These are any events along a link that do not meet diagnostic requirements for a certain measurement. 
• Optical link length: This parameter represents the length between a fiber link’s end and the initial network connector. It includes macrobends, splices, and other events. Different devices may measure a fiber’s length going through a splitter to the ONT or on a point-to-point basis. 

What is QUAD-Mode?

Quad Mode is an OTDR that covers testing of both singlemode and multimode fibers. Both types have two wavelengths which is needed to test a single fiber. With four wavelengths, two in singlemode, and two in multimode, these OTDRs have become known as Quad-Mode OTDRs. 

Do OTDRs have limitations? 

Some challenges, such as dead zones, may be associated with OTDRs. A dead zone is a distance at which the device cannot pick up a second event after a reflection. Connectors are common places for dead zones. Dead-zone issues are normally solved by artificially extending the fiber run by connecting a launch fiber before connecting the OTDR. This “known” piece of fiber is added to the OTDR calculations and is subtracted from measurements internally in the OTDR. 

How do I pick the right OTDR? 

EXFO recommends determining your network application, choosing a form factor, and selecting a technology. Electro Rent partners with EXFO to bring you new and used EXFO OTDR devices. If you need assistance, a representative can help you select a device. These are some points to consider as you look for an EXFO OTDR for sale or rental: 

• Wavelength compatibility: Multimode and single-mode fibers use different wavelengths for testing. Choose a device with a wavelength that is compatible with your network. 
• Dead zones: In an earlier answer, you learned about dead zones. They are critical troubleshooting factors. A lower dead zone improves accuracy. 
• Range and dynamic range: Determine the length of your network, and pick a device with a range that exceeds it. A higher dynamic range facilitates accuracy over greater distances. 
• Portability: Choose a model that meets the demands of your field applications. EXFO offers a variety of compact and portable testing instruments. 
• Ease of use: The device should be easy enough for you or your technicians to operate. EXFO designs its products based on customer feedback. For this reason, they have good ratings for being user-friendly devices. 
• Battery life: A longer battery life minimizes testing interruptions with handheld OTDRs. If you need to minimize downtime, extended battery life is essential. EXFO offers devices with full-day batteries. 
• Buying versus renting: Consider whether you want to buy or rent EXFO OTDR devices. If you are interested in renting, Electro Rent offers fixed monthly payments and affordable rates. 

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