Holographic AR display based on the cylindrical holographic optical element for wide viewing zone

We propose a holographic augmented reality (AR) display by using a cylindrical holographic optical element (HOE). The cylindrical HOE is used as a wavelength-selective reflective screen. A three-dimensional (3D) object is not reconstructed on the cylindrical HOE directly, but behind it as a virtual image. Thus, it becomes possible to superimpose the 3D reconstructed image with a real-existent 3D object without physical contact: augmented reality can be achieved. Moreover, in our method, the shape of the HOE is not planar but cylindrical. Thanks to its shape, the viewing zone of our method becomes much wider than that of planar hologram, where the viewing zone is fundamentally limited to only the forward region of the planar hologram. In our method, information of the 3D object to be reconstructed is coded into a conventional planar hologram such as a spatial light modulator (SLM). Then, the wavefront modulated by the planar hologram enters the cylindrical HOE. Because the cylindrical HOE reflects the incident wavefront with a very wide diverging angle, viewers can observe the 3D object from a very wide horizontal range. For this purpose, our method utilizes the reflection on the cylindrical surface. Thus, holograms for modulating the wavefronts have to be designed considering the reflection on the cylindrical HOE properly. In our method, wavefront propagation via the cylindrical HOE is calculated based on the geometric optics. To verify our method, we performed optical experiments, and our holographic AR display was successfully demonstrated.