Study On Viewing Angle Enlargement For Holographic Three-dimensional Image Display

In three-dimensional(3D)image display technology,holographic projection,as a display technology that can reproduce real images,has always been a research hotspot of naked-eye stereo display technology in the world.Holographic projection technology can reproduce exactly the same three-dimensional image with the original object under certain conditions.Viewers can get a real,comfortable experience without wearing any other devices.Spatial light modulation is the key device of holographic imaging.The spatial light modulator can modulate the spatial distribution of light waves,which can meet the requirements of dynamic and real-time imaging.Due to the limitation of pixel size,array size and other performance parameters,the beam deflection angle of spatial light modulator is small,resulting in the narrow field of viewing angle.In order to enlarge the viewing angle of reconstructed 3D image,a beam deflection method for holographic projection is proposed.Based on the time-division multiplexing(TDM)method,multi-view computer-generated holograms(CGHs)are loaded by a spatial light modulator,and projected in sequence to separate the optical path of each viewpoint.Then,the viewing angle of 3D image is enlarged by the beam deflection system.The main research work is as follows:(1)Multi-view CGHs are made to realize angle compensation.With layer-based method,the original 3D object is modeled and sliced into multiple layers of parallel planes.The Fresnel diffraction of each layer is calculated separately and then added up.The 3D computergenerated hologram is obtained by interference of reference light.In order to reduce the amount of computation,a data optimization algorithm is further designed to eliminate redundant parts of obscured data.To realize the angle compensation,the CGHs with different viewpoints are made,and the corresponding phase factors are applied to them to obtain multiview CGHs.(2)With beam deflection method,a holographic projection system for enlarging viewing angle of 3D image is constructed.The multi-view CGHs with different phase factors are loaded into the spatial light modulator,and the beams at different angles are separated by projection in time sequence.To achieve beam deflection and convergence,mirrors and lenses are set according to the light rays.Based on the principle of beam deflection,the decentered lenses group achieves the enlargement of viewing angle in 3D image.Experimental result shows that the beam deflection method can enlarge the viewing angle of 3D image in holographic projection system.The proposed method is compared with the common methods.Compared with the multiple space light modulator system,the single spatial light modulator adopted in this scheme has lower cost.And compared with the mechanical scanning system of the spatial light modulator,the proposed method has a simple system and high operability,without considering the synchronization between machines.The experiment shows that the beam deflection method of enlarging the viewing angle in 3D image display is feasible,and the scheme will show its scientific significance and potential application value in the research of holographic projection.