OPTICAL MODULATION IN LITHIUM NIOBATE AND BARIUM TITANATE THIN FILMS

Abstract

Electrical to optical signal conversion is an important topic in fiber optic communication systems. Due to its large electro-optic coefficient, bulk lithium niobate (LN) has seen widespread use in commercial optical modulators. In these bulk devices, optical waveguides are created using ion diffusion, resulting in poor refractive index contrast and large device footprint. To reduce the physical device size, we demonstrate a multimode interferometer and a Mach-Zehnder interferometer modulator in z-cut lithium niobate thin film with vertical electrode placements, improving the tuning efficiency. The transverse magnetic optical mode is required to ensure that the polarization aligns with the extraordinary axis of z-cut lithium niobate. We also explore using barium titanate (BTO) thin film as an alternative material for optical modulators by demonstrating a straight waveguide polarization modulator. This work offers an opportunity for z-cut LN and z-cut BTO thin films to serve as platforms of choice for commercial optical modulators.