BER Performance of Multimode Fiber Low-Frequency Passbands in Subcarrier Multiplexing Transmission

摘要

Multimode fibers are normally known to have a channel for carrying a signal mainly by their 3-dB modal bandwidth ranging between 200 to 500 MHz-km, depending on the material and structure of the fiber. To use only this 3-dB modal bandwidth, a higher data rate signal cannot be successfully transmitted. Alternatively, it has been shown that the response of the multimode fibers at low-frequency region, defining as the frequency next to the 3-dB modal band, contains many passbands. Additionally, these low-frequency passbands have been shown to be predictable in terms of their peak frequencies; thus, suitable subcarrier frequencies can be obtained and used in SCM system. In this paper, the formula from the previous work for determining the peak frequency of all 6 low-frequency passbands is applied. These 6 passbands and the 3-dB modal band of the multimode fiber are used to convey a high data rate signal. The signal is separated into 7 subcarrier signals and transmitted over these 7 channels using SCM system. The performance of the received signal in terms of the bit-error-rate (BER) is determined and shown. Some modification and adjustment are done in order to improve the performance of the system. It is found that for a multimode fiber with a 200-MHz 3-dB modal bandwidth, a 500-Mbps data rate signal can be successfully transmitted with a BER of lower than 10~(-6). The data rate transmitted over a multimode fiber can be increased 2.5 times comparing to the 3-dB modal bandwidth, without any coding technique applied.