Figure 1

(a), Schematic of chip-to-chip edge coupling concept between a laser diode and the frequency converter showing the far-UVC generated at an angle above the waveguide core. (b), Waveguide cross-section schematic showing the BBO nonlinear crystal bonded to the SiN waveguide core of width w and thickness h. The Si substrate (not shown in this cross-section) is located below the SiO₂ lower cladding. Geometrical axes \(\hat{x}\), \(\hat{y}\) and \(\hat{z}\) are shown, as well as crystal \(\hat{X}\) axes \(\hat{Y}\), and \(\hat{Z}\) of BBO. Contour lines show the simulated \(\hat{x}\)-polarized electric field profile of the fundamental TE mode at a wavelength of 445 nm. The SiN core guides the mode with a confinement of 58 %, and a significant portion of the evanescent field (26 %) overlaps with the BBO. (c) Scanning electron micrograph showing the BBO crystal directly bonded to the SiN waveguide, with the SiO₂ lower cladding and the Si substrate. Edges of the BBO sample are chamfered for mechanical stability.