High extinction ratio characteristics of over 60dB Mach-Zehnder modulator with asymmetric power-splitting Y-branches on X-cut Ti:LiNbO₃

We discuss the performance of Mach-Zehnder modulators with asymmetric power-splitting Y-branches theoretically and confirmed it experimentally. The output characteristics of the modulator depend on the relationship between the power splitting ratios of the front and the back Y-branches. Even if the modulator consists of two asymmetric Y-branches, we can achieve high-extinction-ratio operation, with an additional loss as compared with the ideal case, by tuning the splitting ratio of only one of the two Y-branches. The additional loss, however, is small in many cases because the asymmetry considered here iscaused by fabrication errors.