A method for fabricating an optical waveguide crossing structure. The method includes preparing a plate structure including a crossing part array and a guiding part array, each crossing part of the crossing part array being arranged at a gap from a plurality of guiding parts of the guiding part array. The method further includes preparing a waveguide structure including a first waveguide core array, a second waveguide core array and a tank, the tank being formed by removing a crossing region of the first waveguide core array and the second waveguide core array. The method further includes injecting an underfill into the tank. The method further includes depositing the plate structure on the waveguide structure so that the crossing part array and the guiding part array are inserted in the tank. The method further includes curing the underfill.