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1-288 cores GYFTY non-metallic Optical Fiber Cable
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Vary from 7 to 14mm
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The additional absorption at either end of the LEDs spectral output may bias the measurements of attenuation on singlemode fiber substantially. Tests from Bellcore showed the effects of sources on measurements of singlemode fiber loss. The LED spectrum covers from the singlemode cutoff wavelength around 1200 nm well into the OH absorption band, while the laser concentrates all its power in an extremely narrow spectral band where the fiber is actually used. Over the range covered by the LED output, the fiber loss varies by 0.2 dB/km, ignoring the OH absorption band. Bellcore tests showed an error of loss caused by the use of the LED of 0.034dB/km.
Even with laser sources, the loss varies substantially according to the wavelength of the source. Again Bellcore tests showed a variation of loss of 0.05 dB/km with source variations of 29 nm (1276 and 1305 nm), within the range of typical sources used in the network. So testing should be done with sources as close to the system wavelength as possible, especially with longer links. (Peters, Bellcore reference).
Modal Effects on Attenuation (This material is duplicated here)
In order to test multimode fiber optic cables accurately and reproducibly, it is necessary to understand modal distribution, mode control and attenuation correction factors. Modal distribution in multimode fiber is very important to measurement reproducibility and accuracy.
What Does Fiber Modal Distribution Look Like ?
Modal distribution in a multimode fiber depends on your source, fiber, and the intermediate "components" such as connectors, couplers and switches, all of which affect the modal distribution of fibers they connect. Typical modal distributions for various fiber optic components are shown here.
In the laboratory, a lensed optical system can be used to fully fill the fiber modes and a "mode filter", usually a mandrel wrap which stresses the fiber and increases loss for the higher order modes, used to simulate EMD conditions. A "mode scrambler", made by fusion splicing a step index fiber in the graded index fiber near the source can also be used to fill all modes equally. If one has a proper optical system, one can control the launch conditions to very specific levels as desired for the measurements being performed.