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Titanium-diffused lithium tantalate (Ti:LT) multimode planar waveguide was produced by in-diffusion of titanium thin-film deposited onto a Z-cut congruent LT substrate. Titanium concentration (CTi) in the titanium-diffused layer was profiled by secondary-ion-mass-spectrometry. Modes guided in the waveguide were characterized by prism coupling technique. Refractive index in the waveguide is profiled on the basis of the measured mode indices, and is related to the CTi profile. The results show that both the refractive index and the CTi profiles obey to a Gaussian function. The profiles of titanium-induced extraordinary and ordinary index changes are almost identical, implying that the index change in the Ti:LT waveguide has a small anisotropy and the confinement to the mode field is polarization-insensitive. The ordinary and extraordinary index changes reveal a similar exponential dependence on the CTi with a power index of ∼0.8.

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.

By using focused ion beam (FIB) technique, we have fabricated two air-hole-type triangular-lattice photonic crystals (PhCs) cascaded in a Ti-diffused LiNbO 3 strip waveguide. To ease the problem that the FIB-milled air-holes are not sufficiently deep, which results in that the holes cannot overlap most of optical mode and hence no evident stop-band feature is observed, two measures have been taken: a 0.75-μm-deep shallow trench was milled on the waveguide surface prior to the air-holes, and a scheme of two PhCs cascaded in the same waveguide was adopted. The cascaded two PhCs have the same air-hole array of 15 × 15 with a lattice constant 376.57 nm and an air-hole radius 150 nm. Transmission spectrum of the cascaded PhCs was measured, and a stop-band with a contrast ∼10 dB and a 3 dB bandwidth of ∼200 nm is observed in the spectral region 1.0–1.2 μm, in good agreement with the simulated result. Present work opens up the possibility of implementing desired PhC functions for various photonic applications by cascading multi-PhCs with different structure parameters.

Low-loss gallium(Ga3+)-diffused erbium(Er3+)-doped LiTaO3(Ga:Er:LiTaO3) channel waveguide was fabricated using erbium metal film diffusion followed by photolithographically patterned gallium oxide(Ga2O3) strip diffusion. Secondary ion mass spectrometry analysis shows that Er3+ concentration follows a Gaussian profile, Ga3+ concentration follows a sum of two error functions at the waveguide surface and a Gaussian profile in the depth direction. Optical studies show that the waveguide supports single-mode propagation at 1.5 μm wavelength with a coupling loss