单极型马赫-曾德尔调制器的互调失真分析

Inter-Modulation Distortion Analysis for Single-Drive Mach-Zehnder Modulator

针对单极型马赫曾德尔电光调制器在Radio over Fiber(RoF)和副载波复用系统中的应用,讨论了输入两路射频信号的情形,给出了电光调制器互调失真的严格通用解析解。该解析解可用于表示任意阶的互调失真项和谐波项。数值结果表明了该解析解的正确性。分析结果表明,调制器的三阶互调失真与调制器偏置相移无关,只与输入射频信号的调制系数有关,并且当外加偏置电压等于调制器的半波电压时,只存在偶数阶的失真项。根据该解析解,可方便地设计模拟光通信系统,精确地预计外调制器的非线性特征,优化系统性能。

For the single-drive Mach-Zehnder electrooptical modulator applied in radio over fiber （RoF） and subcarrier multiplexing systems, the situation for two radio frequency signals inputs is discussed and an exact analytical solution for arbitrary order inter-modulation distortion （IMD） and harmonic terms is derived. The correctness of the analytical solution is approved by numerical results. Analytical results indicate that the third-order IMD is independent of the offset phase shift of the modulator and is only dependent on the modulation index of RF signals. In addition, when the applied offset voltage equals the half-wave voltage of the modulator, there are only even-order distortion terms. With the presented analytical expression, it is convenient to design the analog optical communication systems, precisely predict the nonlinear characteristics of the external modulator and optimize the system＇s performance.