Analysis of the Multimode Fiber at Low-Frequency Passband Region

Multimode fibers have been used in communication systems for more than 40 years. The characteristics of such fibers have been investigated and it has shown that not just the 3-dB modal bandwidth of multimode fibers, but the high-frequency passbands can also be used to carry the signal; resulting in an increase of the data rate transmitted by a multimode fiber. However, the low-frequency passbands of multimode fibers have not been studied intensively. In this work, the characteristics of low-frequency passbands of multimode fibers are considered. The peak frequency, the amplitude, and the bandwidth of each possible passband are studied. From the simulation results, it is found that these parameters can be estimated. The approximation formulas for these three important parameters are given. Using the results found, the low-frequency passbands of multimode fibers can be utilized; thus, in comparison to the data rate obtained from the 3-dB modal bandwidth, a higher data rate for transmitting a signal over a multimode fiber can be increased at least 3 folds.