Realization of Mach-Zehnder Modulator with Ultrahigh Extinction Ratio at Maximum Transmission Bias Point

Most of the commercial Mach-Zehnder modulators (MZM) have extinction ratio below 30dB. At maximum transmission bias point, the MZM output contains only even-order optical sidebands along with carrier band, if extinction ratio is very high. However, in practice output also contains spurious odd-order optical sidebands. In this paper, we propose a system for suppressing spurious odd-order optical sidebands in an MZM at maximum transmission bias point. The system is employed using parallel MZMs, electrical phase shifters, optical splitter and optical combiner. The proposed system realizes an MZM with ultrahigh extinction ratio at maximum transmission bias point. The performance of proposed system is better than that of an MZM with extinction ratio of 30dB even at an offset of about +/- 10 degrees in phase shifters.