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Since these dispersions are independent of each other, they are added to form the total dispersion. Hence, total pulse spreading is give by the formula:
In multimode fibers, polarization mode dispersion is negligible and the formula is given as:
In single-mode fibers, there is no modal dispersion hence the formula becomes:
In the above formula, dispersion is in the unit of time per unit distance (normally nanosecond or picosecond per kilometer) and pulse spreading is in the unit of time (usually nanosecond or picosecond).
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