Strain induced optical waveguides in lithium niobate, lithium tantalate, and barium titanate

Publisher Website
Google Scholar
Abstract
Channel waveguides have been produced in LiNbO3, LiTaO3, and BaTiO3 ferroelectric crystals by depositing thick SiO2 films at an elevated temperature and patterning them by reactive ion etching. The static strain resulting from the large thermal expansion mismatch between the substrate and film causes a localized increase in the refractive index via the strain-optic effect. In addition, an electro-optic contribution to the index increase is believed to result from a surface charge distribution which compensates the electric field due to the piezoelectric effect. Single-mode waveguides at a wavelength of 0.633 μm for both polarizations have been produced in x-cut LiNbO3, with losses of 0.8 dB/cm for TE polarization and 0.9 dB/cm for TM polarization. The 11-μm-wide channel waveguides were formed by a z-axis strain induced by a 2.8-μm-thick SiO2 film deposited at 300 °C. Electro-optic modulation was also demonstrated in these waveguides. Guiding for both polarizations was also observed in LiTaO3 and BaTiO3 channel waveguides at 0.83 μm wavelength.