Expanding Photonic Integrated Circuits (PIC) into the Ultraviolet-C Region: Design and Fabrication of Low Loss SiOx Waveguide

Photonic integrated circuits (PICs) have enabled a large number of applications by using light from the visible to mid-infrared spectrum, but not yet in the ultraviolet-C (UVC, λ = 200 – 280 nm) spectral region. Considering that most of the biomolecules have strong absorption in the UVC, PICs operating in this wavelength range are envisioned to spark new biosensing and biomedical applications. However, the development of PICs in the UVC region is hindered by significant scattering and absorption losses, and limited choices of waveguide materials. Addressing these hurdles, we propose a suspended waveguide design with air-cladding on a silicon substrate. The core of the waveguide is made of thermal silicon oxide. Simulations and optimizations were conducted to identify a single-mode regime at λ = 266 nm. The waveguides were fabricated with a two-step electron beam lithography patterning process. As a result, we achieved propagation losses of 5 dB/cm for single-mode waveguides and 2.4 dB/cm for multi-mode waveguides at λ = 266 nm. Furthermore, we delved into the limiting factors of propagation losses in the UVC region. This work demonstrates on-chip low-loss waveguides in the UVC range for the first time and paves the way for on-chip UVC resonance Raman spectroscopy.