Integrated optical structures obtained by the photoelastic effect

Integrated optical structures can be obtained by tailoring the refraction index in selected regions of a given substrate with electro-optical characteristics. This tailoring can be accomplished, among many techniques, via photoeleastic effect by the induced stress method. One method to induce a stress profile can be devised as, firstly, heating a particular substrate and depositing a film of a second material. Once cooled down to the room temperature, due to the difference of thermal expansions, the substrate and the film are in a state of stress. After removing a stripe from the film, its edges compress the region of substrate below the etched stripe. This compression changes the refraction index due to the photoelastic effect. This technique can be employed to build optical waveguides and modulators in many electro-optical substrates. The spatial profile of stress in such a waveguide is mainly dependent on the difference of thermal expansions, on the film thickness and on the width of stripe removed from the film. We report the development of processes for depositing SiO2 films on LiNbO3 substrates with PECVD technique using TEOS as precursor, which is a popular process used in microelectronics with silicon substrates. Excellent stress induced waveguides with etched channels in the range of 3 to 8 μm of width were obtained. The near field pattern was analyzed and compared favorably with other results from the literature.