Impact of Non-Vertical Sidewalls on Bandgap Characteristics of LiNbO3 Photonic Crystals

The formation of slanted sidewalls is an inherent drawback of most available fabrication techniques for thin film lithium niobate (TFLN) devices, especially for miniaturized TFLN photonic crystals (PhCs). We investigate the impact of non-vertical sidewall angles on the band structure characteristics of PhCs based on TFLN, which shows a reduced gap-to-midgap ratio by 50% for a PhC with 60° sidewall angles compared to the one with vertical sidewalls. The gap-to-midgap ratio is compared and optimized for different sidewall angles by changing the main geometrical parameters in TFLN PhCs, with consideration of fabrication feasibility. Furthermore, we have considered the effect of slanted sidewalls on the group index for TFLN photonic crystal waveguides. Our work provides a design guideline for realistic TFLN PhC devices for future large-scale TFLN photonic circuits.