Recent progress in integrated waveguides based on oxidized porous silicon

In this work we report the latest improvements in integrated optical waveguides based on oxidized porous silicon. Remarkably low propagation loss of 0.2 dB/cm in the visible is demonstrated. Straight waveguides of 1-10 cm long were fabricated in N+-type silicon substrates. Thickness of core region of all fabricated waveguides was of 8 μm while thickness of cladding layer was of 0.8, 1.5, and 2.5 μm. Optical loss in the visible and IR were measured by original method utilizing the 90° vertical bending at the waveguides endings which is a unique property of our waveguides. Significant improvement of the waveguide characteristics was obtained by optimizing the technological process: (a) eliminating the negative effect of swirl defects on uniformity of porous silicon layers; (b) developing the anodization regimes allowing the careful control of the porosity through the porous silicon thickness; (c) using silica mask instead of silicon nitride mask.