Abstract: 10Gb/s optical quaternary and binary transmission systems are simulated separately with emphasis on the influence of the laser’s side mode on the performance of optical quaternary and binary transmission. It is shown that the influence of the laser’s side mode separation and side mode suppression ratio on the performance of optical quaternary is much greater than that on the performance of optical binary, and the laser’s side mode results in larger penalty in the quaternary system than in the binary system. Therefore it is necessary to avoid using multilevel transmission in the practical optical communication systems.

Key words: optical fiber communication, optical quaternary, dispersion, laser's side mode