Fabrication of large-aperture and high efficiency Fresnel diffractive membrane optic using a self-aligned method

To reduce the alignment difficulty and achieve high diffraction efficiency, a self-aligned method for fabricating large-aperture multi-level Fresnel membrane optic is proposed. Using this method, the rigorous alignment is avoided during fabrication process and high diffraction efficiency is achieved. A 4-level Fresnel diffractive polyimide membrane optic in 200 mm diameter and 20 μm thickness was manufactured by this method, which exhibits about 63% diffraction efficiency into the +1 order. The thickness variation of the membrane has a RMS of 30 nm.