Preparation method for diffractive optical waveguide, diffractive optical waveguide, and imprinting master mold

A preparation method for a diffractive optical waveguide, comprising:

• providing a waveguide substrate;
• forming a graphical imprinting adhesive layer on a surface of the waveguide substrate;
• the graphical imprinting adhesive layer comprises a first graphical imprinting structure and a second graphical imprinting structure;
• the first graphical imprinting structure is formed in a first region of the surface, and the second graphical imprinting structure is formed in a second region of the surface;
• the second graphical imprinting structure has a thickness greater than that of the first graphical imprinting structure;
• performing first-stage etching on the waveguide substrate by using the graphical imprinting adhesive layer as a first mask, so as to form a coupling-in structure on the waveguide substrate in the first region, while the remaining graphical imprinting adhesive layer on the waveguide substrate in the second region maintains a pattern of the second graphical imprinting structure;
• forming a second mask by using the remaining graphical imprinting adhesive layer, and performing a second-stage etching on the waveguide substrate based on the second mask, so as to form a coupling-out structure in the second region;
• wherein the second mask covers the coupling-in structure to protect the coupling-in structure from being etched during the second-stage etching;
• the coupling-in structure and the coupling-out structure differ in structural morphology, and the coupling-out structure has a depth greater than that of the coupling-in structure.