Highly efficient coupling in lithium niobate photonic wires by the use of a segmented waveguide coupler

The purpose of this article is to show that efficient light coupling in lithium niobate waveguides presenting a strongly confined mode, such as photonic wires, is possible with the use of a periodically segmented waveguide coupler. The coupler consists in an input periodically segmented waveguide whose mode size is adapted to the mode of a standard single-mode fiber coupled to a photonic wire whose mode size is of the same order of the wavelength. The periodic segmentation of the input waveguide allows fulfilling the phase matching condition necessary to achieve an efficient light transfer between these waveguides. The coupling efficiency is typically 5 times higher than the butt-coupled configuration.