Channel waveguides and Mach-Zehnder interferometers were fabricated in LiNbO(3) by annealed proton exchange. The waveguides had a loss of 0.15 dB/cm and a fiber-to-fiber insertion loss of 1.2 dB at 0.8 microm. The measured r(33) electro-optic coefficient of the interferometers was 30 x 10(-12) m/V +/-5%, which agrees well with theory, indicating that there is no degradation in the r(33) coefficient. No variation in insertion loss or switching voltage was observed over 8 months for devices stored at room temperature.
Lithium niobate (LiNbO3 is considered to be the leading electrooptical material for fabrication of active waveguides, modulators, and switches for application in integrated optical circuits. LiNbO3 is a ferroelectric material with a high Curie temperature of 1210°C. This is essential to permit rapid diffusion at high temperature, e.g., >1000°C, without domain reversal. Its high electrooptic coefficient allows modulation at relatively low voltages. Waveguides are fabricated in LiNbO3 by Ti indiffusion around 1000°C, by Li2O outdiffusion, and, more recently, by Li+/H+ ion exchange. We report results of a study on diluted Li+/H+ ion exchange. This process is attractive because it allows control of the index change between 0.003 and 0.1 Furthermore, the fabricated waveguides are polarization selective, have high optical damage resistance, and do not exhibit index instability as is the case with complete Li+/H+ exchange. The variation in both the index of refraction and the diffusion coefficient with composition is very nonlinear. Mechanisms contributing to these nonlinear properties are discussed.
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