Diffraction-free orbital angular momentum holography

Holography offers significant potential for applications in information storage, encryption, beam-shaping, all-optical artificial intelligence, and three-dimensional displays. However, conventional holograms suffer from rapid image diffraction outside the target plane, resulting in low fidelity and detection challenges. Existing methods for generating diffraction-free beams are typically complex, inefficient, and lack Fourier transform capabilities. We propose a novel approach using an extended depth-of-focus (EDOF) flat lens to create diffraction-free holographic displays. We utilized an inverse-designed extended-depth-of-focus (EDOF) lens that achieves a depth-of-focus of 20 mm (>30,000 <i>λ</i>), which is 14 × greater than that of an equivalent conventional lens. This allows any incident field to be Fourier transformed and remain largely diffraction invariant over an extended depth-of-field, termed the extended spatial-frequency domain (ESFD). We further implement orbital angular momentum (OAM) as an information carrier, demonstrating diffraction-free OAM-encoded holographic images selectable by varying incident OAM modes with topological charges from -8 to 8 on a single device. We experimentally confirm that the diffraction-free OAM beam is able to self-heal in the presence of an occluder. Furthermore, we show that these beams preserve their information content after propagating through 80mm of dense fog, whereas conventional beams completely lose this information due to extreme scattering (attenuation factor of 20×). Our approach shows promising potential for high-security optical encryption, optical tweezers, and advanced optical communication systems.