Free-Space Characterization Setup for Low-loss Aluminum Oxide Waveguides at 261 nm

We present a methodology for the characterization of deep-ultraviolet (UV) photonic integrated circuits (UV-PICs) based on polycrystalline Al2O3, operating at a wavelength of 261 nm. The platform enables low-loss propagation in the deep UV, and we demonstrate an image-based analysis pipeline for estimating waveguide attenuation using free-space coupling and scattered-light imaging. The characterization approach combines spatial calibration of the imaging system, background analysis, and controlled exposure conditions to extract the exponential decay of scattered light along the propagation direction. Preliminary measurements suggest propagation losses on the order of 4.6 dB/cm for 600 nm wide waveguides, while narrower waveguides exhibit higher attenuation due to increased scattering and reduced mode confinement. This work primarily documents the experimental setup and analysis methodology used for deep-UV characterization, providing a foundation for further validation and refinement of propagation-loss measurements in integrated photonic devices operating in the deep-ultraviolet regime.