Troubleshooting Your Optical Fiber Networks

Introduction to OTDR - OTDR does not measure loss, but instead implies it by searching at the backscatter signature on the fiber. It does not measure cable television plant loss that could be correlated to energy budgets.

An OTDR injects a sequence of optical pulses to the fibers below test. It also extracts, from the same end on the fiber, brightness that is scattered back again and reflected back again from points in the fibers in which the index of refraction changes. This working principle works like a radar or sonar, sending out a pulse of brightness from the really effective laser, that is scattered through the glass in the key on the fiber. The intensity on the return pulses is measured and integrated as a function of time, and is plotted as a function on the fibers length Optical coupler .
An OTDR may be employed for estimating the fiber's period and overall attenuation, such as splice and mated-connector losses. It may also be accustomed to locate faults, such as breaks.
The OTDR suffers from many serious uncertainties in measurement and physical limitations. The measurement uncertainties come largely from the variations in backscatter on the fiber CATV Amplifier. The backscatter coefficient is a function on the material properties on the glass in the key as properly as the diameter on the core.
Variations on the fibers components or geometry may cause major modifications in the backscattered light, producing splice or connector measurements uncertain by as much as +/-0.4dB. This has frequently led to confusion by displaying a virtual obtain at a connector, in which the fibers involved have different backscatter coefficients. Connector or splice loss should be measured from both directions and averaged to remove this source of error.
The principle optical components in a simple standard OTDR include a laser, a receiver, a coupler and a front-panel connector.
A laser is pigtailed to a connector on the OTDR through a 3dB optical coupler. This coupler is typically a fused bidirectional equipment but may also be made of discrete optical components.

June 10, 2011

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