Optical confinement in TiO2 waveguides fabricated by resist free electron beam lithography

摘要

The performance of TiO2 waveguides fabricated by a novel resist free electron beam lithography technique is reported. The precursor films were first spin coated on substrates followed by patterning and heating under the electron beam. Subsequent dissolution of the pattern in a suitable solvent and annealing leads to the formation of rectangular TiO2 waveguides. Dimensional control of the waveguides is achieved during the lithography step. Phase and morphology studies confirm the high quality of the waveguides. The TiO2 films crystallize in the anatase structure with transmission > 80% and refractive index of 1.95-2.00 in the visible-NIR region. Optical field confinement in the TiO2 waveguides was investigated by orthogonal illumination followed by scanning the waveguide structure with a self-customized optical microscopy system. The optical losses are relatively low as evidenced by the intensity of the light beams propagating through the waveguides. It is further reduced by coupling the light from one waveguide into another waveguide located at close proximity. It is demonstrated that this technique reduces the number of steps while yielding waveguides with performance comparable to any other fabrication technique.