Study On Fabrication Of SiO₂/TiO₂ Strip Optical Waveguides By Laser Direct Writing

Researches on the materials and arts of fabricating optical waveguides are very important with the rapid development of integrated optics and optical communication systems. Laser direct writing technology overcomes the shortcongings of traditional method on fabricating waveguides basing on photolithography, which shows good virtues of becoming a remarkable technique in manufacturing of optoelectronic parts.In this paper, SiO₂/TiO₂ films were prepared by sol-gel method firstly. Then planar optical waveguides with core layer of SiO₂/TiO₂ film and buffer layer of SiO2 was designed and prepared on Si substrate. The strip optical waveguides were final patterned by laser direct writing of the planar waveguides followed by chemical etching. Moreover, the roughness, surface morphologies, structure and progation loss of the strip optical waveguides were analyzed.The SiO₂/TiO₂ film has lower surface roughness and higher optical transparence. For the SiO₂/TiO₂ planar optical waveguide, the cut-off thickness of the coer layer is 0.29μm and a thickness of SiO2 buffer layer of 6μm is needed at 1550nm on TE0 mode. The propagation loss of planar optical waveguide decreases with increasing thickness of the core layer and the minimum propagation loss is 0.34 dB/cm.In our experiments, laser power and spot size of laser beam are the most two important parameters to affect laser direct writing. There are initial shrinkage threshold and damage threshold during laser direct writing strip optical waveguides on the SiO₂/TiO₂ core film. The difference between the two thresholds increases with the temperature of heat treatment, which is helpful to get strip waveguides with narrower width and good shape. Well patterned strip optical waveguides with a width of 15μm was fabricated using optimized processing and chemical etching parameters. The transect profile of the strip optical waveguide is close to that of the trapezia.The simulation results indicate that the number of mode decreases with the width of the strip waveguide. Single-mod strip waveguides may be gotten for the waveguides with width smaller than 30μm, which is accordant with the experimental results of light propagation. Higher surface roughness, carbon remains, crystallization, and irregular shape of are the main sources to increase the progation loss of the strip optical waveguides. Finally, the cut-back method was used to measure the propagation loss of the strip optical waveguides and the minimum value of 1.77dB/cm in our research was gotten.