Open-source toolbox for photographic characterization of optical propagation.

An alternative method for characterizing optical propagation in waveguide structures based on scattered light imaging is presented and demonstrated for the spectral range of 450-980 nm. Propagation losses as low as 1.40 dB/cm are demonstrated in alumina spiral waveguides. AlGaAs-on-insulator waveguides are measured using a tunable laser and compared to cut-back measurements. On AlGaAs, a one-sigma uncertainty of 1.40 and 2.23 dB/cm for TE and TM polarizations is obtained for repetitions of measurements conducted on the same waveguide, highlighting the approach's reproducibility. An open-source toolbox is introduced, allowing for reliable processing of data and estimation of optical propagation losses.

Continuous-wave second-harmonic generation in the far-UVC pumped by a blue laser diode.

Far-UVC light in the wavelength range of 200-230 nm has attracted renewed interest because of its safety for human exposure and effectiveness in inactivating pathogens. Here we present a compact solid-state far-UVC laser source based on second-harmonic generation (SHG) using a low-cost commercially-available blue laser diode pump. Leveraging the high intensity of light in a nanophotonic waveguide and heterogeneous integration, our approach achieves Cherenkov phase-matching across a bonded interface consisting of a silicon nitride (SiN) waveguide and a beta barium borate (BBO) nonlinear crystal. Through systematic investigations of waveguide dimensions and pump power, we analyze the dependencies of Cherenkov emission angle, conversion efficiency, and output power. Experimental results confirm the feasibility of generating far-UVC, paving the way for mass production in a compact form factor. This solid-state far-UVC laser source shows significant potential for applications in human-safe disinfection, non-line-of-sight free-space communication, and deep-UV Raman spectroscopy.