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Performance of linear block code with subcarrier multiplexing system on a multimode fiber using low frequency passbands

Multimode fibers have been shown to not just be able to convey signal at their 3-dB modal bandwidth, which is limited to approximately 200 to 500 MHz-km, but also at the frequency higher than the 3-dB modal bandwidth. At this higher frequency, the magnitude response of the multimode fiber has been analyzed showing that it contains many possible passbands with an average attenuation depending on the number of modes in the fiber. In this work, the passbands at low frequency region; that is, the frequency that is located next to the 3-dB modal bandwidth of the fiber are utilized as sub-channels in transmitting a combined high data rate signal over a multimode fiber. Subcarrier multiplexing technique is used to send a high data rate signal over different low data rate signals. Additionally, a linear block code is adopted in order to overcome the degradation caused by the effect of null in the magnitude response of the fiber. The performance of the system in terms of bit-error-rate is analyzed and the simulated results are given. It is shown that with a (7, 4) linear block code, the average biterror-rate (BER) of lower than 10−8 with a total data rate of 392 Mbps can be obtained. With a total data rate twice the 3-dB modal bandwidth of the fiber, the obtained BER is significantly improved compared to the case of without coding.