Crystalline phase, Ga³⁺ concentration profile, and optical properties of Ga³⁺-diffused lithium tantalate waveguide

Ga³⁺-diffused lithium tantalate (LiTaO₃) strip optical waveguide was fabricated by diffusion (at 950 °C for 1.5 h) of 8-μm wide, 112-nm thick Ga₂O₃-strips photolithographically patterned onto a Z-cut congruent LiTaO₃ substrate. Crystalline phase, composition, optical properties and profile characteristics of Ga³⁺ ions in the waveguide were investigated. We show that the waveguide retains LiTaO₃ crystalline phase and is in congruent composition environment. Optical studies show that the waveguide supports single-mode propagation (at the 1.5 μm wavelength) of not only the extraordinary wave but also the ordinary wave, shows considerable polarization dependence in mode field distribution, and has a loss of 0.2/0.4 dB/cm for the ordinary/extraordinary wave. Secondary ion mass spectrometry analysis shows that the Ga³⁺ profile follows a sum of two error functions (a Gaussian function) in the width (depth) direction of the waveguide.