Fabrication of sub-wavelength-sized buried structures in silicon with single picosecond pulses from IR-laser system

We demonstrate effective control of the shape and depth of sub-wavelength sized modifications in bulk silicon inscribed by transverse ultrafast single-shot laser pulses of 5 ps at 2.09 μm. A balance of multi-photon absorption and Kerr effect makes it possible to create the modifications with dimensions as small as 0.7 μm × 1.1 μm in the wide range of sub-surface depths. This approach was used for inscription of 9.8-mm long depressed cladding waveguides as a most common 3D structure. Waveguide properties were analyzed at 1.55 μm. The lowest propagation losses and the highest negative refractive index contrast were measured to be 1.8 dB/cm and 2.1 × 10 −3 respectively.