| With the development of virtual reality technology,artificial intelligence,meta-universe and other new industry,human’s demand for display in the information age is gradually increasing from black and white display to color display,from two dimensional(2D)display to three dimensional(3D)display,from static display to dynamic display.3D display technology can reconstruct 3D effect of real or virtual scenes and meet the visual perception of human eyes,which is widely used in military,education,entertainment,medical treatment,industry,and other aspects.Holographic display technology can simultaneously record phase and amplitude information 3D scene for monocular and binocular depth cues,which is regarded as one of the most ideal and promising 3D display technology.However,there are still many problems in holographic display system,for instance,the refresh rate of optical holographic recording materials is low,the computational efficiency of massive data in computer generated holography is slow,complex amplitude encoding in digital holography is difficult,amplitude and phase information are hard to synchronize in diffraction resconstruction,dynamic holographic display system can only provide low resolution or single color,etc.To achieve the high-quality holographic display effect with true color,dynamic and realtime,this dissertation studies the key technologies of dynamic holographic display in real-time holographic rendering,high quality holographic coding and true color holographic display.The main research contents and innovations of this dissertation include the following three parts:1)Dynamic holographic display method based on ray tracking technologyFor holographic diffraction calculation problem of the point-based method computer-generated holography,if the sampling number of threedimensional objects is increased,the amount of complex light field calculation data at each sampling point of the hologram plane will increase,which affects the computational efficiency seriously.Therefore,the efficient processing between object point data and hologram sampling data is of great significance to improve the efficiency of dynamic holographic display in point-based method.In this dissertation,a method of point-based computer-generated hologram based on ray tracing and parallel computing is analysed.By using Graphics Processing Unit(GPU)parallel computing and ray tracing technology,realistic 3D scenes can be rendered.The combination of point-based method and ray tracing technology is realized,and the generation speed of computer-generated hologram is improved.Howevere,the number of sampling points is inversely proportional to the computing speed in dynamic holographic display based on point-based method.Increasing the resolution of object and hologram will inevitably reduce the hologram computing efficiency.So,this dissertation proposes a computer-generated hologram(CGH)generation method based on ray tracing and parallel layer-based algorithm,which adopts ray tracing technology and GPU parallel rendering.According to the distance between the virtual camera and the object point when the ray hits the threedimensional model,the information of each layer at different angles of the three-dimensional model is directly obtained,and the complex amplitude distribution of the final hologram is obtained by adding sub-holograms of multi layers from different depths.Through the fast Fourier transform algorithm for real-time accelerated calculation of diffraction propagation between hologram plane and object plane,the real-time interactive dynamic display can be realized with 27.8ms per frame.2)High quality holographic display method based on dual spatial light modulator(SLM)Aiming at the problem that the display effect of computer-generated holography is limited by the modulation characteristics of SLM,the independent modulation of the amplitude and phase information cannot be achieved at the same time,and the dynamic display quality is poor.This will seriously affect the data integrity of hologram and introduce error noise,and the dynamic display quality will be poor.According to the characteristics of phase SLM and amplitude SLM,the complex amplitude encoding method is analyzed,and the numerical simulation experiments of double phase encoding method,double amplitude encoding method and cascade multiplication of amplitude phase are carried out,which could effectively improve the display quality of dynamic holography.To effectively utilize the diffraction characteristics of different SLMs,an optimized dual SLMs holographic joint display method based on wavefront frequency decomposition is proposed in this dissertation,and the digital filtering of the image frequency decomposition is realized.The hologram for high-frequency information of the target is loaded by phase SLM,and the hologram for low-frequency information of the target is loaded by amplitude SLM.The amplitude and phase information are increased at the same time.The problem of insufficient frequency processing in other methods is solved.The reconstruction details of the hologram are more complete.The system has improved the quality of dynamic holographic display in different evaluation indicators,including speckle contrast,peak signal-to-noise ratio,and image structure similarity.3)True color dynamic high-resolution holographic display based on angle-controlled lightWhen combining light sources with different wavelengths to achieve true color holographic display,the traditional time division multiplexing method will reduce the dynamic efficiency,the splicing of multiple SLMs will reduce the resolution contribution of sub-holograms,and the different diffraction angles of SLMs for different wavelength will cause chromatic aberration.Using the double beam interference method and holographic printing technology to design holographic optical elements respectively,under the condition of Bragg matching,by adjusting the incident angle of the illumination light source,the angle-controlled light method for different wavelengths can be realized to suppress the chromatic aberration problem.And the color dynamic holographic display quality could be effectively improved.Based on the high refresh rate of digital micromirror devices,the time division multiplexing scheme of the sub-hologram sequence is designed by using the pixel correspondence between the object plane and the hologram plane,and the dynamic holographic reconstruction of the high-resolution object plane is acheived.In this dissertation,the phase SLM is used to load CGH,which is designed and calculated as the light-control element.First,the angle-controlled light hologram of phase SLM is calculated according to the incident angle for the reference light source of three wavelengths and the illumination angle required by the digital micromirror device,and then the color time-sequence sub-hologram are calculated based on the high-resolution information of three-channel object plane.Finally,the color display of the dynamic hologram is performed by changing the time division multiplexing sequence subholograms.High-resolution and dynamic color holographic display system with multi freedom degree of light source is realized. |
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