Optical waveguides and beam splitters using low-loss aluminum oxide for visible-wavelength photonics applications

Abstract Low-loss visible-light photonic circuits are crucial for high-performance photonic quantum processors. By using aluminum oxide (Al ₂ O ₃ ) for its low visible-light absorption, we achieved waveguides exhibiting an exceptionally low propagation loss (1.39 dB/cm for the transverse electric mode) at red-light wavelengths. Directional coupler beam splitters fabricated using this platform exhibited good controllability of the optical splitting ratios. Furthermore, we fabricated a half beam splitter, which is an essential component of entangled photon generation in quantum optics. These results represent a significant advance towards developing low-loss photonic circuits, paving the way for improved performance in photonic quantum processors.