Experimental evidence for preservation of electro-optic property in titanium-diffused lithium niobate waveguide

Electro-optic (EO) property of titanium-diffused LiNbO3 optical waveguide was studied using prism coupling technique. The EO-effect-induced increment Delta N of effective refractive index (at the wavelength 1311 nm) was measured as a function of externally applied electric field E for TM0 and TM1 modes guided in the titanium -diffused LiNbO3 planar waveguide. By using the linearity between Delta N and E, the EO coefficient r(33) is determined. For reference, the measurement was also performed on a bulk material of congruent LiNbO3, yielding r(33) = 24.9 +/- 0.8 p.m./V, which is in qualitative agreement with that obtained by extrapolating previously reported result to the 1311 nm wavelength, similar to 24 p.m./V, confirming the feasibility of the measurement method. Measurements on the titanium-diffused planar waveguide give r(33) = 25.7 +/- 0.6 p.m./V for the TM0 mode and 25.7 +/- 0.4 p.m./V for the TM1 mode. Both values can be considered as identical within the error, and are the same as that of the bulk material, indicating that the EO property is well preserved in the titanium-diffused LiNbO3 waveguide. The main reason is that the LiNbO3 crystalline phase is well preserved in the titanium-diffused waveguide layer.