Improvement of carrier-to-noise ratio in subcarrier multiple access optical networks in the presence of multiple optical beat interference

Summary form only given. Summary form only given. The subcarrier multiple access (SCMA) systems using distributed feedback laser diodes (DFB-LDs) without wavelength control are very suitable for the upstream in passive optical networks (PON) from the point of view of realizing cost-effective and high-performance systems. However, it is well known that optical beat interference (OBI) is one of the serious problems. We have already proposed a method to greatly reduce the OBI which we have named the LSM method. This method employs multiplying the subcarrier signals and an additional signal. We experimentally and theoretically investigated the carrier-to-noise ratio (CNR) characteristics of frequency-modulated (FM) video signals by using the LSM method in the worst case that all of the OBI between any two LDs appeared in the subcarrier band. In this paper, the experimental result shows that the CNR values of the FM video signals can reach the available level by using the LSM method even if three OBIs exist in the subcarrier band, and the theoretical result shows that the acceptable number of OBI increases to ten by using DFB-LDs with an optical linewidth of 100 MHz.