Oxidation effect on optical properties of integrated waveguides based on porous silicon layers at mid-infrared wavelength

Integrated sensors based on guided optical devices can efficiently and selectively detect molecules in the mid-infrared (mid-IR) spectral range, exploiting the vibrational and rotational modes of these molecules at these wavelengths. In this work, a ridge waveguide based on porous silicon (PSi) layers was developed by electrochemical etching followed by a photolithographic process. The ridge waveguide is capable of propagating light in the mid-IR range (3.90–4.35 µm) with optical losses of approximately 10 dB/cm. An oxidation study was performed to stabilize the porous structure and identify the optimal oxidation degree, that allow mid-IR light to propagate in a ridge waveguide based on PSi material for sensing application. The results showed that the ridge waveguide remains capable of propagating light after undergoing partial oxidation at 300 °C and 600 °C (15% and 36% of the oxidation degree respectively) with optical losses of around 30 dB/cm and 60 dB/cm at the wavelength of 4.1 µm, respectively.