Diffractive optical element and preparation method

A diffractive optical element, configured to:

• receive two-dimensional pattern beams and generate multi-order diffractive beams, wherein the two-dimensional pattern beams are emitted from a structured light projection module, the structured light projection module includes a light source comprising a plurality of sub-light sources irregularly arranged in a two-dimensional array, and the two-dimensional pattern beams correspond to the two-dimensional array;
• and
• project the multi-order diffractive beams to form a speckle pattern on a projection surface, the speckle pattern comprising a plurality of duplicated spot patterns, wherein each of the plurality of duplicated spot patterns comprises diffractive speckles at a same diffraction order, centers of the duplicated spot patterns are respectively placed at positions of diffractive speckles of the diffractive optical element, speckles in each of the plurality of duplicated spot patterns are irregularly arranged, and when the duplicated spot patterns overlap with each other and the duplicated spot patterns satisfy the following formula such that the speckle pattern has a uniform speckle density:
• Mϵ[(1−Δ1)(s/k±n)D/d,(1+Δ2)(s/k±n)D/d],
• where M is an average spacing between every two adjacent diffractive speckles generated by a sub-light source, D is a distance between the diffractive optical element and the projection surface where the speckle pattern is formed, d is a distance between the light source and the diffractive optical element, s is a size of an area formed by the plurality of sub-light sources, n is an average spacing between every two adjacent sub-light sources, both Δ1 and Δ2 are specified error percentages of 20%, and k is a positive integer greater than 1.

A method comprising:

• receiving two-dimensional pattern beams on a diffractive optical element, wherein the two-dimensional pattern beams are emitted from a structured light projection module, the structured light projection module includes a light source comprising a plurality of sub-light sources arranged in a two-dimensional array, and the two-dimensional pattern beams correspond to the two-dimensional array;
• and
• projecting the multi-order diffractive beams to form a speckle pattern on a projection surface, the speckle pattern comprising a plurality of duplicated spot patterns by the diffractive optical element, wherein each of the plurality of duplicated spot patterns comprises diffractive speckles at a same diffraction order, centers of the duplicated spot patterns are respectively placed at positions of diffractive speckles of the diffractive optical element, speckles in each of the plurality of duplicated spot patterns are irregularly arranged, and when the duplicated spot patterns do not overlap with each other and satisfy a first formula or when the duplicated spot patterns overlap with each other and satisfy a second formula, such that the speckle pattern has a uniform speckle density,
• wherein the first formula is:
• Mϵ[(1−Δ1)(s+n)D/d,(1+Δ2)(s+n)D/d],
• where M is an average spacing between every two adjacent diffractive speckles generated by a sub-light source, D is a distance between the diffractive optical element and the projection surface where the speckle pattern is formed, d is a distance between the light source and the diffractive optical element, s is a size of an area formed by the plurality of sub-light sources, n is an average spacing between every two adjacent sub light sources, and both Δ1 and Δ2 are specified error percentages of 20%, and
• wherein the second formula is:
• Mϵ[(1−Δ1)(s/k±n)D/d,(1+Δ2)(s/k±n)D/d],
• where k is a positive integer greater than 1.