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Ti-diffused LiTaO 3 strip waveguide was fabricated by in-diffusion of 8-μm-wide, 100-nm-thick Ti-strip at 1300 °C for 6 h in wet O 2 atmosphere. Its composition, surface morphology, lattice parameter, optical properties and Ti profile characteristics were fully characterized. It is shown that the waveguide is in the congruent composition environment. The waveguide surface caves in ∼70 nm below the crystal surface due to Ti-induced lattice contraction, which is verified by X-ray single-crystal diffraction. Optical characterizations show that the waveguide well supports both TE and TM single-mode propagation at the 1.5 μm wavelength, is polarization-insensitive, and has a loss of 0.4 (0.3) dB/cm for the TM (TE) mode. Secondary ion mass spectrometry analysis shows that the Ti profile follows a sum of two error functions in the width direction and a Gaussian function in the depth direction of the waveguide. [ABSTRACT FROM AUTHOR]

Effects of finite hole depth and non-cylindrical hole shape on stop-band characteristics of photonic crystal formed by air-hole square lattice in Ti-diffused LiNbO 3 strip waveguide were studied theoretically. The study shows that hole depth determines the contrast of stop-band, and the hole radius and conical angle determine the bandgap and location. Cylindrical holes must be sufficiently deep so as to overlap most of waveguide mode and hence obtain a stop-band with high contrast, sharp edge and broad bandgap. Non-cylindrical holes seriously affect the stop-band features. Conical holes cause low contrast and narrow bandgap, and the stop-band shifts with the conical angle. For the cylindrical-conical hybrid holes, the cylindrical portion determines the desired features. Given the difficulty in fabricating high aspect-ratio cylindrical holes, we propose to fabricate the holes at the bottom of a shallow trench, which is introduced into waveguide surface prior to the hole milling. [ABSTRACT FROM AUTHOR]