The effect of fabrication parameters on a ridge Mach-Zehnder interferometric (MZI) modulator

A study of Mach-Zehnder interferometer (MZI) modulators using unetched and etched Ti:LiNbO/sub 3/ waveguides has been made. A full vectorial finite-element-based mode solver was used, followed by a finite element-based solution of the Laplace equation to calculate the electrooptic effect and, subsequently, the half-wave voltage, V/sub /spl pi// The optical loss due to the metal electrodes was also found using the H-field finite-element method (FEM) incorporating the perturbation method. The microwave effective index, n/sub m/, and the characteristic impedance of the metal electrodes, Z/sub c/, were also found for a number of electrode thicknesses and ridge heights. A semivectorial finite-element beam propagation method (SVFEBPM) was used to estimate the radiation loss for the curved input and output (I/O) waveguides of the MZI. The device characteristics were then studied by making changes to a number of fabrication parameters, of which the two most important were found to be the etch depth of the ridge and the thickness of the SiO/sub 2/ buffer layer.