Understanding OTDRs (Optical Time Domain Reflectometers) What You Will Learn In This Basic Self-Study Program: What is an OTDR – optical time domain. 17 Apr Optical time-domain reflectometer (OTDR) is an optoelectronic instrument used to characterize an optical fiber. It can help you understand the. 24 Jan OTDR is a popular fiber optic testing tool which can be used to test the fiber loss, and locate the faults in fiber optic links. However, the OTDR.

Author: Turg Yozshugrel
Country: Turkey
Language: English (Spanish)
Genre: Art
Published (Last): 17 March 2009
Pages: 293
PDF File Size: 2.79 Mb
ePub File Size: 4.7 Mb
ISBN: 730-9-62234-279-7
Downloads: 82874
Price: Free* [*Free Regsitration Required]
Uploader: Grogrel

The FOA Reference For Fiber Optics – OTDRs

A tutorual cable may be used on the far end to allow measurements of the connector on the end of the cable under test also. Connectors and splices are called “events” in OTDR jargon. Later, otdr tutorial can be made between the original trace and a second trace taken if problems arise. Cisco otdr tutorial the early leader in G Ethernet switch port. Other reasons you otdr tutorial want to compare two traces includes: It will simply take longer to acquire each trace.

It can verify splice loss, measure length and find faults. Of course, OTDR traces are otdr tutorial used for troubleshooting, since they can show where breaks are in fiber when otddr are compared to installation documentation. The tutorrial line top represents the attenuation coefficient of the cable in at nmthe green line bottom represents the same cable measured at nm.

It will also read the otdr tutorial between the power levels of the two points where the markers cross the trace and calculate the loss, or difference in the two power levels in dB. There are some calculations involved.

The Introduction of EXFO OTDR

When the markers are selecting the noisy part of the fiber trace, the least squares attenuation 2-pt LSA tool can otdr tutorial applied to calculate the dB loss otdr tutorial the cursors. Futorial fiber, light is scattered in all directions, including some scattered back toward the source as shown here.

Higher attenuation fiber has more attenuation because the glass in it’s core scatters more light. If otdr tutorial tutorkal are identical, such as splicing a broken fiber back together, the backscattering will be the same on both sides of the joint, so the OTDR will measure the actual splice loss. otdr tutorial

OTDRs simply show you where the cables are terminated and confirm the quality of the fibers, connections and splices. You will see this effect in the next section on comparing traces.


The data that the OTDR produces are typically used to create otdr tutorial picture called a “trace” or “signature” that has valuable information for the trained tutorual and can be otdr tutorial for later reference or to check against a otdr tutorial when network trouble arises. The amount of light reflected is determined by the differences in the index of refraction of the two fibers joined, a function of the composition of the glass in the fiber, or any air in the gap between otdr tutorial fibers, common with terminations and mechanical splices.

Many international standards do not allow OTDRs to be used to measure the loss tuforial an installed cable plant. The light scattered back for measurement is not a constant. OTDR is a tutprial fiber optic testing tool which can be otrr to test the fiber loss, and locate the faults otdr tutorial fiber optic links. At any point in time, the light the Otdr tutorial sees is the light scattered from the pulse passing through a region of the fiber.

If powerful optical pulses are inserted into optical fiber, pulse width of the launched optical signal will be increased, which will cause the dead zone at a length of fiber and affect otdr tutorial testing result of OTDR. OTDRs are always used with a launch cable and may use a receive otdr tutorial. In order to measure fiber attenuation, you need a fairly tutoral length of fiber with no distortions on either end from the OTDR resolution or overloading due tugorial large otfr.

All OTDRs offer this feature, where you can copy one trace and paste it on another to compare them. The OTDR looks at the returning signal and calculates loss based on the declining amount of light it sees coming back. Same brand, same quality, same warrenty, why otdr tutorial choose the cheaper one? Back-scattered light and reflected light returns to the OTDR through the fiber and is directed to a sensitive receiver thorugh a coupler in the OTDR front end.

The height of that peak will indicate the amount of reflection at the event, otcr it is so large that it saturates the OTDR receiver. Read more about this: If the first fiber has more attenuation than the one after the connection, the percentage of light from the Ootdr test pulse will go down, so the measured loss on the OTDR will include the actual loss plus a otdr tutorial error caused by the otdr tutorial backscatter level, making the displayed loss greater than it actually is.


To minimize the affection of the OTDR dead zone during fiber optic testing. Using otdr tutorial fiber to overcome OTDR dead zone is the choice in most cases, especially for long optical fiber testing.

Otdr tutorial OTDR will ttutorial the distance difference between the two markers and give the distance. Note how the slope of the curve is much higher in the fiber in this segment?

The OTDR measures distance and loss between the two markers. If you need more resolution, average more with shorter test pulses. If the fiber looks nonlinear at either end, especially near a reflective event like a connector, avoid that section tutoriap otdr tutorial loss.

This is a complicated process involving the baseline of the OTDR, backscatter level and power in the reflected peak. If you look at two different fibers joined together in otdr tutorial Tutoriak, the difference in backscattering from each fiber is a major uttorial of error.

Since otdr tutorial is possible to calibrate the speed of the pulse as otdr tutorial passes down the fiber from the index of refraction of the glass in the core of the fiber, the OTDR can correlate what it sees in backscattered light with an actual location in the fiber.

A real “gainer” – a splice 35 km away in an installed fiber link. OTDRs can take multiple samples of the trace and otdr tutorial the results. To measure splice loss, move the two markers close to otd splice to be measured, having each about the same distance from the center of the splice. Set the pulse width at the shortest width that allows the OTDR to reach the end of the cable plant with a reasonable number of averages.

The using of them is generally the same. Otdr tutorial OTDR uses this “backscattered light” to make measurements along with reflected light from connectors or cleaved fiber ends. tutprial

The launch fiber is actually a length of optical fiber which is long enough to cover the OTDR dead zone to increase the testing accuracy.

Thus it can create a display of the amount of backscattered light at any point in the fiber along its length. The OTDR, however, otdr tutorial a unique optical phenomena otdr tutorial fiber to indirectly measure loss.