Fig. 1. LTOI substrates and optical waveguides.

a, Schematic of the LTOI wafer-bonding workflow showing hydrogen-ion implantation, bonding, splitting and chemical mechanical polishing (CMP). b, Photograph of the bonded wafer demonstrating uniform and defect-free bonding. c, Thickness map of the LiTaO₃ thin film on the wafer. The x,y axes represent the distance from the wafer centre. d, Atomic force micrograph of the LiTaO₃ thin film surface. Scale bar, 500 nm. e, High-resolution scanning transmission electron-microscopy image of the LiTaO₃–SiO₂ bonding interface. The arrow represents the x-cut crystal orientation. Scale bar, 2 nm. f, Schematic of the fabrication workflow for LTOI optical waveguides, including DLC hard-mask deposition by plasma-enhanced chemical vapour deposition (PECVD) from the methane precursor, DLC dry etching through oxygen plasma, and LiTaO₃ etching by argon ion-beam etching (IBE), followed by redeposition and mask removal. The layers are DLC (black), LiTaO₃ (light blue), SiO₂ (purple) and Si (grey). Spheres show C (black), O (red) and Ar⁺ (green). g, Colourized scanning electron micrograph (SEM) of LTOI microring resonator (blue). Scale bar, 50 μm. h, Colourized SEM of etched LTOI microring and bus waveguide coupling section. Scale bar, 2 μm. i, Colourized SEM of etched LTOI waveguide and sidewall. Scale bar, 2 μm. j, Colourized SEM cross-section of etched LTOI waveguide (blue) on top of SiO₂ bottom cladding (purple). Scale bar, 500 nm.