Optical waveguides for evanescent field sensing

A new fabrication process of ion-exchange waveguides well suited for integrated-sensor applications is presented. The process consists in burying each extremity of the waveguide few microns below the surface while its central region is located at the surface. For a single-mode waveguide at 785 nm, we measured propagation losses of 0.13 dB/cm for the buried portion, 2.80 dB/cm for the surface portion, and losses of 0.40 dB for the transition region. For this structure, we also observed a deformation of the fundamental mode. The proposed method is easy to implement and permits one to control precisely the topography of the elaborated waveguides.