Why you need an OTDR Launch Box

Posted by Gavin On 07 December 2023

Optical time domain reflectometer (OTDR) is a necessary fibre optic testing tool which use light backscattering technologies to analyse the optical fibre performance. It can test the light loss and locate the breaks, splices, and connectors in fibre optic network. However, OTDR has "dead zone" which can affect the testing result if proper measure is not taken. To overcome the limitation of OTDR dead zone, OTDR launch box is being used. This post will introduce OTDR launch box for your reference.

Basic of OTDR Launch Box

OTDR launch box, according to its function and working principle, has a lot of other names, like dead zone box, pulse suppressor, fibre ring, fibre optic launch cable, etc. How can OTDR launch box minimize the effect of OTDR dead zone during fibre optic testing? The following explains the detail.

The dead zone of OTDR, caused by high return level of reflection and affected by the pulse width, might extend hundred meters from the OTDR. Full length of optical fibre is suggested, to use before the optical fibre under test. Thus, the receiver of the OTDR can have enough time to settle. OTDR launch box, which is actually a long spool of optical fibre inserted between the fibre under test and OTDR, can ensure that the OTDR dead zone happens in the OTDR launch box (shown in the following picture). Then, the fibre optic link under test won't be largely affected by the OTDR dead zone.

OTDR Launch Box Usage Guide

The OTDR launch box comes in various packages. The box-design is the most commonly used one with the advantage of durability. It has a long spool of optical fibre with a pigtail on two ends. One of the pigtails is for input, this is used to connect with the OTDR, the other pigtail on the opposite end is for output, which is used to connect with the optical fibre under test. After connecting the input end and output end to the corresponding port, the OTDR launch box can be used to test the attenuation of the fibre link.

The using of OTDR launch boxes seems really easy. However, the handling of them should be careful. If you want to get accurate test result of the fibre link the length of the optical fibre inside the OTDR launch box should be long enough to cover the whole dead zone. OTDR launch box is like fibre optic cables, it has distinct types and one cannot be used in all fibre link test. The following will tell you how to select OTDR launch boxes.

Which OTDR Launch Box Fit Your Applications?

The selection of OTDR launch box is like selecting fibre patch cable. You should consider the fibre type, connector type terminated on pigtails and the polishing type of the connectors. Another important factor should be considered is the length of optical fibre of OTDR launch box as above mentions. The optical fibre of OTDR launch box should be longer than the dead zone. Thus, most fibre OTDR launch box can support hundreds or thousands of meters.

Conclusion

After inserting the OTDR launch box between the OTDR and fibre under test, the affection of the OTDR dead zone can be minimized effectively.

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