Design and fabrication of crossed gratings with multiple zero-reference marks for planar encoders

We design and fabricate a new type of crossed gratings with multiple zero-reference marks for planar encoders. The crossed grating together with an indicator can output multiple zero-reference positions along both the x and y directions for 2D displacement measurement. The zero-reference marks are designed on basis of the plane-wave angular spectrum analysis including the diffraction effect. A crossed grating with multiple zero-reference marks was fabricated by holographic exposure and contact ultraviolet exposure. The spacing error of the crossed grating was 0.03 λ ( λ = 632.8 nm) and the average diffraction efficiency of the crossed grating’s four principal nonzero symmetrical orders reached 14%. The measurement repeatability of the zero-reference position was 15.1 nm, while the zero-reference marks only reduced the average diffraction efficiency of the crossed grating by 0.55%.