In fibre optic transmission, apart from loss, there is another important factor that is often overlooked and that is dispersion. Dispersion is an important factor affecting the performance of fibre optic communication systems.
Optical dispersion is a physical phenomenon caused by the distortion of the transmitted signal due to the different group velocities of the different frequency components or modes of the signal transmitted by the fibre. The so-called group velocity is the transmission speed of light energy in the optical fiber. By optical signal distortion, we generally mean pulse spreading. But what causes the different wavelengths of light to separate from each other? It is the glass! Whether it‘s a prism made of glass or an optical fibre with a fused silica glass core, because glass is a dispersion medium, they all have the ability to bend different wavelengths of light to different angles.
If left unmanaged, this can cause serious problems in network communication systems, especially in fast bit rate applications. 40G systems are more susceptible to dispersion than 10G systems because the signal pulses are more dense at the source. 10G systems can operate up to 100 km trouble-free, whereas 40G systems can operate just a few kilometres without dispersion compensation solutions.
How do dispersion compensation modules reduce dispersion?
A dispersion compensation module (or DCM) is used to compensate for the accumulated dispersion in a single-mode fibre and the dispersion factor is used to characterise the dispersion value. A conventional SMF at 1550nm is approximately + 16 to 17 ps / (nm * km). To properly manage this, the DCM is built using a special type of dispersion compensated fibre inside the module that has a negative dispersion coefficient ranging from -30 to -300 ps/(nm * km).For example, the cumulative dispersion of a 10 km length of fibre would be + 160 to 170 ps / nm, so to compensate for this amount of dispersion, a DCM would be added to the link for a specific and calculated length of fibre to reduce the total dispersion close to 0 ps / (nm * km). Shenzhen HTFuture Technology Co., Ltd. provides high quality dispersion compensators.
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