Near-field observations of light confinement in a two dimensional lithium niobate photonic crystal cavity

We report the characterization of a lithium niobate photonic crystal cavity using near field scanning optical microscopy (NSOM) operating in collection scanning mode. The cavity is implemented on an annealed proton exchange waveguide by focused ion beam milling. We observe a confinement of the optical field at the center of the cavity by analyzing the collected light with a probe positioned above the photonic structure. The experimental NSOM results obtained are compared to numerical results obtained by finite difference time domain method. A good agreement is obtained between theoretical and experimental results where a cavity mode appears around λ = 1540 nm.