Increasing acceptable number of signals in subcarrier multiple access optical networks in the presence of high optical beat interference

This paper theoretically and experimentally demonstrates that our proposed method improves the carrier-to-noise ratio (CNR) of subcarriers and significantly increases the number of acceptable optical signals in subcarrier multiple access (SCMA) systems using distributed feedback laser diodes (DFB-LD´s) with the same center optical frequency. This method reduces optical beat interference by using the multiplied product of the subcarriers and a low-frequency signal. From the experimental results using 1.3 μm DFB-LD´s, the CNR sufficiently satisfies the required level even if the number of optical signals is three. Theoretically, the number of acceptable optical signals increases as LD´s with wider optical line-width or with greater chirp coefficient are used. For example, assuming a laser chirp coefficient of 540 MHz/mA, the maximum number of LD´s that can be used while still meeting the minimal CNR requirement is 12. This number corresponds to 66 optical beat interferences. Thus, this proposed beat-interference reduction technique is very effective in SCMA systems using DFB-LD´s without optical frequency control