Evanescently coupled fs laser-written type II waveguide array in lithium niobate

We report the realization of an evanescently coupled laser-written type II array in x-cut Lithium niobate. Certain processing parameters allow evanescent fields to extend beyond the regions of damage, while still increasing the index suficiently to guide light. An array consisting of eleven coupled waveguides was fabricated. Coupling was evaluated by observing discrete diffraction patterns of single waveguide excitations at various array sites. Homogeneous coupling was verified within the array, while the outermost guides are slightly detuned due to being formed by just one damage structure.