Engineering Refractive Index Contrast in Thin Film Barium Titanate-on-Insulator

• DOI: 10.1021/acs.nanolett.3c00933
• Publication Date: 2023-08-02T12:38:50Z
• Authors: Yu Cao; Haidong Liang; Hong-Lin Lin; Luo Qi; Ping Yang; Xuanyao Fong; Elhadj Dogheche; Andrew Bettiol; Aaron Danner
• Keywords: Technology; crystallinitycontrol; Materials Science; proton beam irradiation; Condensed Matter; OPTICAL WAVE-GUIDE; [SPI]Engineering Sciences [physics]; refractiveindex; ENHANCEMENT; DIFFUSED LINBO3; Physical; Nanoscience & Nanotechnology; [PHYS]Physics [physics]; Science & Technology; Multidisciplinary; Barium titanate-on-insulator; refractive index; Physics; ELECTROOPTIC MODULATOR; crystallinity control; 620; Chemistry; Physical Sciences; Applied; Science & Technology - Other Topics; metal diffusion

Barium titanate-on-insulator has demonstrated excellent vertical optical confinement, low loss, and strong electro-optic properties. To fabricate a waveguide-based device, a region of higher refractive index must be created to confine a propagating mode, one way of which is through dry etching to form a ridge. However, despite recent progress achieved in etching barium titanate and similar materials, the sidewall and surface roughness resulting from the physical etching typically used limit the achievable ridge depth. This motivates the exploration of etch-free methods to achieve the required index contrast. Here, we introduce three etch-free methods to create a refractive index contrast in barium titanate-on-insulator, including a metal diffusion method, proton beam irradiation method, and crystallinity control method. Notably, molybdenum-diffused barium titanate leads to a large index change of up to 0.17. The methods provided in this work can be further developed to fabricate various on-chip barium titanate optical waveguide-based devices.