Fig. 1. X-ray rocking curves from (00.12) reflection of Z-cut HiVac-VPE planar waveguides: (a) logarithmic-type representation of vertical scale and (b) linear-type representation of vertical scale. The waveguides were fabricated with different exchange periods t(h) at T=350°C.

Fig. 2. Extraordinary refractive index profile at λ=633  nm reconstructed by IWKB for planar waveguides fabricated in Z-cut LN by HiVac-VPE at 350°C with different exchange durations. The symbols represent the measured Neff of the propagating modes, except those on the ordinate that represent the raw surface indices calculated by IWKB. Dashed lines are guides for the eye.

Fig. 3. Corrected refractive index profiles at λ=633  nm for planar waveguides fabricated in Z-cut LN by HiVac-VPE at 350°C for different durations. For t=24  h is the raw index profile. The symbols represent the measured Neff of the propagating modes, except those on the ordinate that represent the corrected surface indices. Solid lines are guides for the eye.

Fig. 4. Top: index profiles of Z-cut HiVac-VPE waveguides fabricated for different exchange durations. The symbols represent the measured Neff of the propagating modes, except the IWKB corrected surface indices on the ordinate. The solid lines are the fits obtained by using Eq. (1). Bottom: derivative of the fits. Inset: sub-layers structures of the waveguides. The intensity of the red color suggests the refractive index value in the waveguides.

Fig. 5. SHG profiles and reflected fundamental signal of Z-cut HiVac-VPE waveguides superimposed with index profiles (region in gray color) for (a) t=1  h and (b) t=5  h.

Fig. 6. Near-field imaging of the modes at the output of channel waveguides fabricated at T=350°C for 1 h through the silica mask with openings of (a) 1 μm and (b) 1.5 μm width, respectively.

Fig. 7. Near-field imaging of the modes at the output of channel waveguides fabricated at T=350°C for 1 h through the silica mask with an opening of 2 μm width. (a) Fundamental mode and (b) superior mode + fundamental.

Fig. 8. Far-field picture on a screen of TE-polarized hybrid modes in HiVac-VPE channel waveguide at λ=633  nm for (a) 1 μm width and (b) 1.5 μm width, respectively.