Linear electro-optical analysis model of a lithium niobate thin film modulator with arbitrary crystal axis orientation

Abstract

We propose an improved model for the electro-optic (EO) properties of a thin film lithium niobate (TFLN) Mach-Zehnder (MZ) electro-optic modulator (EOM) with arbitrary crystal axis orientation. We develop an analytical theory based on second-order nonlinear optics to describe the linear EO effect and establish an approximate calculation method with the aid of coupling theory and perturbation theory. By focusing on the optical and microwave electric fields’ dominant components and disregarding minor ones, we simplify the calculation process for the EO coupling coefficient and half-wave voltage length product (V π ⋅L). We achieve a 12% increase in the EO coupling coefficient and a 10% reduction in V π ⋅L by adjusting the crystal axis direction. Our research has significant implications for the design of the TFLN MZ EOM.