How Dead Zones Affect OTDR Performance

Optical Time Domain Reflecto-meter (OTDR) is one of the most versatile and widely used fiber optic test equipment. It is one of the important fiber optic testers which is commonly used by technicians or installers to certify the performance of new fiber optic links and detect the issues of existing fiber links.

Telecom, video, and data wireless service providers and network operators want to insure that their investments into fiber networks are protected. OTDR helps to test these cables to ensure the installation was properly made and also later helps to troubleshoot problems such as break locations due to dig ups etc.

OTDRs are extremely efficient in gathering data which ultimately create a picture named a “trace” or “signature” that stores a large amount of information for prepared users. It can also be kept as an archive or can be used to verify against a blueprint if a system breakdown occurs.

Fiber optics engineering, commissioning, technical support and FTTx allow the use of OTDRs. They are highly recommended for several sectors such as aviation and defense, electric utility, hardware production, mining, oil and gas as well as transportation. Also, they are mostly used by installers and contractual workers.

There are some specifications of an OTDR which may affect its performance. To understand these specifications, one can get maximum performance from their OTDRs. Dead Zone is one of them.

What is a Dead Zone

Dead zones are important characteristics since they determine OTDR’s ability to detect and measure two closely spaced events on fiber links. In technical terms, the OTDR dead zone is the distance where the OTDR cannot detect any event or artifact on the fiber link.

The Relation Between Dead Zone & OTDRs

It is said that the presence of dead zones is an important drawback for OTDRs, especially in short-haul applications with a large number of fiber optic components. Thus, it is important to minimize the effects of dead zones wherever possible. There is always at least one dead zone in every fiber—where it is connected to the OTDR.

In general, dead zone on the OTDR trace can be divided into event dead zone (EDZ) and the attenuation dead zone (ADZ). The event dead zone is the minimum distance where two consecutive reflective events can be distinguished by the OTDR. On the other hand, the attenuation dead zone is the minimum distance after a reflective event that a reflective event can be measured.

The shortest-possible event dead zone allows the OTDR to detect closely spaced events in the link. For instance, testing fibers in premises networks (particularly in data centers) requires an OTDR with short event dead zones since the patch cords of the fiber link are often very short. If the dead zones are too long, some connectors may be missed and will not be identified by the technicians, which makes it harder to locate a potential problem.

GAOTek OTDRs are intelligent new generation multipurpose instruments which are compact, rugged and field-portable.  They are available in various configurations optimized for different wavelengths.



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