Aluminium oxide 1x8 splitter tree for blue light

Aluminium oxide (Al₂O₃) has gained interest in the field of integrated photonics. Al₂O₃ shows low propagation losses, and it is known for its high rare-earth ion solubility. Furthermore, the material has a moderately high refractive index, allowing for design of devices with a small footprint. Another important characteristic of Al₂O₃ is its large band gap (i.e., ~170 nm), compared to materials like InP, SOI and Si₃N₄. The larger band gap results in a transparency window that spans all the way from ultraviolet (UV) wavelengths to the mid-infrared (mid-IR).
In this work, a device is presented that showcases an application of Al₂O₃ at the UV and blue wavelengths. A splitter tree is fabricated from thin Al₂O₃ that supports single mode guiding at these particular wavelengths. Light is evenly split into multiple branches using Y-junctions, to eventually split it into eight output ports. All eight channels are provided with thermal phase shifters. This device can be utilized as an integrated optical phase array (OPA). In this work, the propagation and coupling losses as well as the splitting uniformity of this 1x8 waveguide splitter at 450 nm will be reported.