Development of Alumina waveguide components for UV spectroscopy

Photonic waveguides operating at ultraviolet (UV) wavelengths can benefit emerging applications as chip-scale quantum computing, label free gas sensing, chemical sensing and biosensing. For example, the on-chip optical absorption measurement at UV wavelengths is a strong candidate for microscale analysis of proteins and nucleic acids, due to their strong optical absorption at short wavelengths. However, the established waveguide platforms based on silicon and silicon nitride can only offer low-loss operation for wavelengths longer than 400 nm. Hence, a novel, low-loss photonics material platform could accommodate an efficient, small form-factor and chip-scale technology for such UV-based applications.

In this project, Al₂O₃ waveguides in SiO₂ cladding are proposed as the basic building block for a UV-compatible, low-loss photonics platform. A first aspect of this project is the design, fabrication and characterization of passive waveguide devices. This concerns components that are required to couple, route and filter UV light, such as grating couplers, edge couplers, single and multimode waveguides, splitters and combiners, wavelength filters, resonators and interferometers. Each component will be characterized on wafer level. Special attention will be given to researching material and phase stability at high optical powers and temperatures.

Next to passive waveguide components, also active waveguide components are required to enable advanced photonic integration circuits. A second aspect of this project is the design and experimental verification of a highly efficient, low-loss photonic switch and modulator.

For UV spectroscopy, a frequency comb is a very interesting source for directly probing atoms or molecules. Although microresonator-based frequency combs have been demonstrated for wavelengths down to 700 nm, the direct comb generation at visible and UV wavelengths is still missing due to the very challenging dispersion engineering. Generation of visible frequency combs have been demonstrated by second-harmonic, third-harmonic, and sum-frequency conversion of a Kerr comb at NIR wavelengths or through supercontinuum generation in Lithium Niobate waveguides.  This project will study the development of a microresonator-based UV frequency comb. Both the non-linear properties of the Al₂O₃ waveguide material itself will be studied, as well as the possibility of integrating  materials with higher optical non-linearity. As the generation of a dissipative cavity soliton requires a delicate balance between the nonlinearity and the dispersion, the different options for dispersion engineering at short wavelengths will be theoretically and experimentally studied.