Measuring method for optical nonlinearity of two-dimensional material

A method for measuring nonlinear optical properties of a two-dimensional material comprising graphene, the method comprising:

• providing a plurality of test devices that have different structures and each include an optical waveguide partially loaded with a two-dimensional material, each two-dimensional material having a different length in an optical waveguide axial direction, wherein an overcladding is provided on an entry side and on exit side of the optical waveguide;
• measuring a coincidence rate of a photon pair generated in the optical waveguide after pump light pulse generated by a pump light pulse generation unit has entered the optical waveguide in each of the test devices;
• obtaining a curve of a theoretical-value-based coincidence rate with respect to a length of the two-dimensional material based on at least a duration and a peak power of the pump light pulse, a total length of the optical waveguide, and a length of the loaded two-dimensional material;
• fitting the curve of the theoretical-value-based coincidence rate to an actual-measurement-based coincidence rate corresponding to the different length, comprising
• obtaining a difference between the curve and a plurality of plotted points of the measured coincidence rate for the different length of the two-dimensional material,
• determining a fitting between the curve and the plurality of plotted points;
• when the fitting occurs, determining a nonlinear coefficient γ1 of the optical waveguide and a nonlinear coefficient γ2 of the optical waveguide loaded with the two-dimensional material;
• and
• obtaining a nonlinear refractive index of the two-dimensional material and a nonlinear refractive index of a material of the optical waveguide based on the nonlinear coefficient γ1 and the nonlinear coefficient γ2.