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

Abstract

For Mach-Zehnder modulator (MZM) with ideal extinction ratio, output optical spectrum contains only odd- order optical sidebands at minimum transmission bias point. However, fabrication of the MZMs with very high extinction ratio is not possible yet. Therefore, in practice output of an MZM also contains significant power in even-order optical sidebands at null point. In this paper, system for suppressing even-order optical sidebands at null point is presented. The system is implemented using components such as MZMs, phase shifters, power splitters and optical combiner. The variation of performance for the proposed system with phase offset in phase shifters and extinction ratio difference of parallel MZMs is also analyzed. The performance of proposed system is better than an MZM with an extinction ratio of 30dB for phase offset of ±10° in electrical phase shifters. The system performance is quite tolerant to large phase offset in optical phase shifter.