Reflectogram
The reflectogram — the comprehensive information about connectors, mergings and gaps on all length of an optical line. Actually this graphics image of results of measurement of optical losses in the line. The reflectometer transfers an optical impulse on the mounted optical lines and measures the light particles reflected due to effects of Rayleigh scattering and frenelevsky reflection. The reflectometer displays the disseminated and reflected optical signals as function of length. Comparing an amount of light, reflected in different timepoints, it can define losses to lines and reflection power of the optical cable. Having analyzed the reflectogram, it is possible to measure a deviation and transfer of losses between any two points of a cable line. Besides, specialists can measure the entered losses and reflection power of any optical line. Reflectograms can use also for search of gaps and faults of optical fiber.
Details
Reflectograms have several total characteristics. The majority of reflectograms begin with an input pulse which is result of reflection in reflectometer connection point. After this impulse the reflectogram represents gradually decreasing curve which can be interrupted by deviations. Gradual decrease in a curve is caused by Rayleigh scattering as light moves along each section of the optical cable. This decrease is interrupted by sharp deviations up or down. As the reason of these deviations or spot defects usually serve connectors, mergings or gaps. And at last, the output pulse at the end of the reflectogram is result of the reflection arising on an output edge surface of a cable. It is possible to gain an impression about performance of components of the line and quality of installation, having estimated heterogeneity, represented on the reflectogram. The reflectogram does not cancel need for measurement of the entered losses, but it is used for additional assessment of the first level of work of a fiber line. Testing of the second level allows to confirm that all works and quality of installation conform to project and warranty requirements. For example, the widespread requirement is what losses because of mergings should not exceed 0.3 dB, and losses because of connectors – 0.75 dB. The reflectogram helps to see those moments which are not able to reveal testing of the first level or measurement of length of the line. Full certification of the optical cable of the first and second levels gives the best assessment of an optical cable system and serves owners of network as the proof of quality of installation works. However until now it was hard to seize these opportunities as the equipment necessary for certification of optical lines was more expensive and it was more difficult in operation, than testers for copper lines.
Most of contractors have a team of specialists who accumulated considerable experience of testing of copper cable systems. But the majority or even all of them have no necessary equipment or knowledge for testing of optical lines. And though results of measurement of losses/length and the reflectogram perfectly supplement each other, traditional testers of optical losses and reflectometers are separate devices. Each device costs quite much and has the special user interface. Each of the listed characteristics represents difficulties in equipment of specialists for certification of optical cables. But the most important obstacle is need to study difficult interfaces and to learn to interpret reflectograms.
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