Segmented waveguide tapers for low insertion loss, high performance SPE:LiNbO_3 integrated circuits

We present the results of an experimental study of waveguide tapers realized with segmented waveguides in LiNbO_3 substrates using the Soft Proton Exchange (SPE) technique. Measurements show that the tapers can be favorably introduced between the nonlinear or electro-optic part of the components, which requires strong mode confinement to increase efficiency, and the coupling section with a standard optical fiber, which requires low mode confinement, in order to have low coupling losses. These tapers allow almost lossless mode shape transformation with a reduction of the coupling losses up to 0.7 dB, thus proving the practical interest of the approach. As an example, the use of such tapers in a real integrated optical circuit is shown.