Experimental studies of proton-exchanged lithium niobate waveguides using cinnamic acid

Proton-exchanged planar waveguides in z-cut LiNbO₃ have been fabricated and characterized optically using cinnamic acid as the new proton source. Single-mode waveguides before and after annealing exhibit propagation losses of 0.81 and 0.33 dB/cm, respectively, measured at 0.633 μm wavelength. The diffusion rate is slower than that of the popular benzoic acid. Post-annealing changes the refractive index profile from a truncated-parabolic function to a step function and then a Gaussian-like profile. The effect of annealing on the surface index change and the waveguide depth increase could be accurately modeled by a power-law relationship.