Research On System And Device For LCOS-based Holographic Video Display

Holographic video display will be the ultimate tool for 3D visualization. The major challenge of current research is that we need a technology breakthrough in the core device, spatial light modulator (SLM). An ideal desired SLM is a kind of high-resolution active devices, whose features go down the wavelength scale of visible light and are capable of complex amplitude modulation. The current developed liquid crystal on silicon (LCOS) benefits from the marriage of LC and CMOS technologies, Combing the holographic diffraction and the physics of liquid crystal photoelectric, it is a good candidate device not only for set up a proof-of-concept holographic display system but also for the development foundation of the final phase modulation device of holographic video display.The developments of holographic video display technology are mainly concentrated on two aspects.On the one hand, the easily achievable SLM devices are employed to investigate the theory, algorithm and architecture of the corresponding holographic imaging system. Similar to other SLM counterpart, e.g., AOM or DMD, the LCOS can modulate either amplitude or phase of an incident light, but not simultaneously. And its pixel feature is one order of magnitude lower than the expected value of light wavelength However, under the guidance of scalar diffractive theory, it is very important to understand how these limitations affect the performance of a holographic imaging system. What’s more, to achieve complex amplitude modulation and further give the design proposal to build the color holographic imaging and multi-plane imaging system based on LCOS. All of the above researches will lay the foundations for future development of holographic video display.On the other hand, based on the perspective idea of upgrading the device, the suitable SLM technology is developed to meet the requirements of diffraction angle, high-resolution, and diffraction efficiency for holographic video display. The performance criteria of SLM devices for 2D display and holographic video displays are quite different. The main problems are that only a small diffraction angle and low resolution could be provided by the current commercial SLMs. There are many challenges to develop the new technology for solving the above problems. Taking the diffraction angle as an example, the pixel pitch of the LCOS shrank to the light wavelength scale is desired, but in that situation, this device is useless because of the very low diffraction efficiency. However, we should note that the LC technologies have amazing resources and versatility. For new applications, many researchers have been attempted to expand the LC capabilities to meet the new demands in performance. Recently, with the development of surface plasma technology, the metasurface, which consists of subwavelength metallic periodic structures, also offers an innovative approach to manipulate the properties of light with its anomalous capabilities. In order to fulfill the requirements of holographic video display, the LCOS technology is employed as the core technology, and we could combine the above physics and engineering area, and set up a comprehensive platform for simulation, experimental and testing on the background of Maxwell’s equations. It will be very helpful to create a big breakthrough in SLM technology.For the purpose of holographic video display, by combining the optics and computational approach, two main contents which surrounding with LCOS-based imaging system and new device design are studied in this thesis. The main research works and contributions of this thesis are outlined as follows:(1) An improved holographic imaging experimental system based on LCOS is proposed. A collimated wave illumination is normally used for the original systems, and the configurations of these systems based on Fresnel reply geometry and Fourier reply geometry are slightly different. In this thesis we present a holographic imaging system using converging spherical wave illumination. Compared to the original system, our system enables fewer optical devices for holographic reconstruction. In addition, through the analysis of the physical characteristic for holographic reconstruction, a universal configuration is proposed for holographic imaging system, which can be used for both Fourier and Fresnel applications, and it is useful to eliminate zero order beam and higher diffraction orders.(2) The state-of-the-art SLM device cannot modulate both amplitude and phase of the incident light field simultaneously. Drawing on complex representation with double-phase method, we have proposed an analytical method to display a complex Fresnel hologram using the phase-only SLM. Two 4f optical systems are employed to synthesize double phase Fresnel holograms (DPFHs) and the programmable blazed phase gratings generated by phase-only SLM are inserted in the Fourier plane. The position-shift of the DPFHs is achieved and finally they are synthesized as a complex Fresnel hologram in the output plane successfully. The phase modulation and programmability of the LCOS are utilized in this method, which could provide a useful flexibility for complex modulation applications.(3) The designs of color holographic imaging system based on either RGB lasers or light-emitting diodes (LEDs) are presented. The basic principles of color holographic imaging are described in this thesis. On account of the sizes of diffractive reconstructed images are corresponding to illumination wavelengths, the original monochrome images are spatially scaled to eliminate the effects arising from the chromatics of the color holographic reconstructions. Meanwhile, the analysis and comparisons of color holographic imaging systems are performed.and the configurations of the systems are set up among four different methods, such as time division multiplexing, space division multiplexing, spatial division and spatial multiplexing. Taking comprehensive consideration on the trade-off between the visual impression of reconstructed image and the complexity of system configuration, the time division multiplexing and spatial division methods have more advantages over other methods.(4) The existing multi-plane holographic imaging method based on Fresnel reply geometry is described. We proposed that the phase of Fresnel phase lens could be added to the generated Fourier phase holograms. The image plane is set in the back focal plane of the Fresnel phase lens. The focal length of programmable Fresnel phase lenses can be changed dynamically to perform multi-plane holographic reconstruction At the different reconstruction distances, several iterated computations are needed by the original method; meanwhile, there is only one iteration need to be performed with our method and the computation time of hologram is reduced.(5) A simulation platform with two commercial softwares, i.e. TechWiz and FDTD Solutions has been performed for LC device in this thesis. Due to the diffraction efficiency is affected by the pixel pitch, the diffractive optical property of LC binary grating with different pixel pitch based on LCOS device is investigated. The utilization of digital blazed grating for improving the diffraction efficiency of LCOS-based holography is investigated in this thesis. To avoid the drawback of reducing diffraction angle and the resolution of display hologram caused by the macro-pixel structure for the period unit of digital blazed grating, we establish a new model of LCOS device. A specially designed gradient metasurface is inserted into the pixel architecture of the LCOS, which offers an innovative approach to manipulate light in subwavelength scale, so the diffraction efficiency of LCOS-based holography could be optimized effectively.