Voltage Controlled-Bandwidth Electrooptic Push-Pull Mach Zehnder Modulator with Coplanar Electrodes

The desired optical wavelengths of the electro-optic Mach Zehnder Modulator (MZM) is selected. The magnitude of the band-pass wavelengths $(\Delta \lambda)$ is calculated from the −3db rule. The number of the pass wavelength windows increases with the product of the controlled voltage (V) and the modulator length (L). While the width of window decreases and the center of window moves towards higher wavelengths with V. Also the width of window increases with wavelength. For the same modulator output, the product VL becomes constant. The bandwidth evaluation is simplified. Maximum difference between the propagation constants of MZM waveguides is occurred. So, the power transferred between them becomes very weak. And so, the branching angle of the input Y-junction of MZM becomes very small. Propagation constant is calculated by mixing the variation and Maractilli’s methods. The effect of both the electro-optic material and the metal electrodes is studied. LiNbO
3
is the best. The required controlled voltage to make a window at $\lambda=1.30 \mu \mathrm{m}$ is less than at $\lambda=1.55 \mu \mathrm{m}$. The optimum design of the electrodes with respect to the electro-optic waveguides to achieve the required $(\Delta \lambda_{\mathrm{MZM}})$ is done with $50 \Omega$ characteristic inpedance. The bandwidth at any required wavelength is evaluated.