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

Abstract Electro-optic (EO) property of titanium-diffused LiNbO3 optical waveguide was studied using prism coupling technique. The EO-effect-induced increment ΔN 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 ΔN and E, the EO coefficient r33 is determined. For reference, the measurement was also performed on a bulk material of congruent LiNbO3, yielding r33 = 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, ~24 p.m./V, confirming the feasibility of the measurement method. Measurements on the titanium-diffused planar waveguide give r33 = 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.