Researchers at the University of California, Los Angeles, have reported a technique that is based on the separation by implantation of oxygen process that enables the three-dimensional fabrication of waveguide and microcavity structures in silicon. The method promises applications in the development of optical chips, and it may be applied to the manufacture of wavelength division multiplexing filters.Separation by implantation of oxygen involves the selective formation of SiO2 layers in a silicon substrate by exposing the host to a source of oxygen ions and annealing the material at high temperature. In the work, the researchers applied a semitransparent mask made with a thermally grown oxide before the implantation and anneal steps to change the depth of implantation and the subsequent overlayer growth. The technique yielded 286-nm-thick buried rib waveguides with widths of 2 to 12 µm that exhibited optical losses of 3 to 4 dB/cm.