Low loss sputter coated aluminum nitride waveguides

Photonic integrated circuits (PICs) have experienced an exponential growth in a number of applications, including telecom/datacom, LiDAR, optical sensing/metrology and quantum technology. Most materials and platforms commonly used in integrated photonics, such as silicon-on-insulator (SOI), silicon nitride (Si3N4) and indium phosphide (InP) do not show transmission below ~400 nm, hindering the development of PICs operating in the ultraviolet wavelength range. Furthermore, devices in this wavelength range also require fast modulation and switching in order to enable complex emerging applications. Aluminum nitride (AlN) is a material with a band gap of 6.2 eV, exhibiting a wide transparency window, from the ultraviolet to the mid-infrared. AlN has the capacity to achieve high electro-optic[1], non-linear[2] and piezo-electric[3,4] coefficients, which makes AlN an interesting material for PICs with operation down to the ultraviolet wavelength range. However, high losses have prevented PICs from benefiting from its excellent optical properties. In this work, we present our work on the sputter deposition of low-loss AlN slab waveguides. The optical performance of AlN sputtered slab waveguides after annealing at different temperatures and their relation with the film morphology will be discussed. Preliminary slab propagation losses as low as 1.5 dB/cm at 633 nm of wavelength have been demonstrated.