Off‐Axis Holography with Uniform Illumination via 3D Printed Diffractive Optical Elements

Diffractive optical elements (DOEs) provide a compact and energy-efficient solution to project arbitrary grayscale images onto a distant screen. Unfortunately, they invariably suffer from the zero order spot, which is caused mainly by undiffracted light that travels along the optical axis of an illuminating laser beam. To produce projected images without the bright spot, one can either shift the intended projection off-axis or block the zero order. However, images projected by these methods are occluded by the dark fringes of the diffraction pattern ("shadowing" effect) or increase the complexity of the optical setup. Here, a new type of DOE is introduced with blazed facets to shift the laser power into the off-axis direction. By adding blazed facets onto each phase element of a computer-generated hologram, far-field projections that are free of both the zero order spot and shadowing effects are produced while maintaining a diffraction efficiency as high as 86%. The blazed facets are fabricated by 3D direct laser writing, which enables continuous phase modulation within a single pixel. This concept of sub-pixel level modification of diffractive optical elements can be extended to other applications requiring precise wavefront shaping or detection, such as 3D displays, mixed-reality technology, and optical analog computing.