Research Of Phase Calculation Problems In Computer Generated Holography

Holography is an important branch of modern optic. It can be used for lights' storage and reproduction. Holography can record all the information of light and reflect the true depth and color of objects. For this reason, it is considered as the most promising technology of the three-dimensional display and has important significance. Classical holography uses interference and diffraction principle of light to record wave amplitude and phase in interference fringe form. The original object is reproduced by the reference light irradiating the interference fringe pattern and diffraction. With the rapid development of computer technology, computer generated holography (CGH) has been appeared in 1965. It combined computer technology with holography together, bringing a new leap forward for the development of holographic display. CGH uses computer coding to make holograms. It doesn't so that complicated in recording by optical devices, while achieving desired virtual hologram production of various objects. These advantages make CGH more promising than optical holography in digital image processing. Because of its unique superiority, CGH has widely used in holography and penetrated into every field of modern scientific research and industrial production in social life. Due to the high frequency of waves, it is difficult to capture all the information of the object wave in actual measurement. We can only get the intensity or amplitude of light field. Phase is difficult to obtain even a direct loss in the acquisition process. However, the phase of light waves contains the depth information about objects. It is essential to reconstruct object wave. For this reason, the research on phase calculation has been widespread concerned in CGH.The paper selected CGH and its' phase calculation problems as research content, researching CGH practical technology by theoretical analysis and experimental verification. The main work done as follows:1. The basic theory of CGH has been introduced. The production methods of CGH, the classification and comparison of CGH has been analyzed.2. The encoding and reproducing method of CGH has been introduced in detail, including the detour phase method, the reference light off-axis correction method, interferometry coding method, etc. It has achieved CGH production and reproduction with computer simulation using these encoding methods. It also discussed the advantages and disadvantages of these methods.3. On the basis of CGH's study, the phase calculation problem has been introduced. To solve it, phase iterative recovery algorithm and transport of intensity equation has been proposed. The principle of the production of pure phase holograms using phase retrieval algorithm and error diffusion algorithm has also been proposed. The effects of reproduced image in different iterations and different iterative algorithms through experimental analysis has been compared.4. Aiming at the study of phase calculation problem in CGH, we propose a double encryption algorithm based on the pure phase hologram. The method has a two-step encryption using random measurement matrix in compressed sensing and random block Arnold transformation model to achieve the security of information transmission. Finally, the encryption methods have been verified by software and hardware experiments respectively using computer simulations and a holographic platform based on silicon liquid crystal spatial light modulator.