Holographic Disc Storage On Photopolymer

Optical Storage has always been a hot topic of industry and academia. The classical bit-oriented optical storage technology developed rapidly, from CD to DVD and Blu-ray Disc, with higher storage density and faster access speed. But it is more and more difficult to increase access speed and storage density only through taking smaller recording spots and utilizing multilayer technology.Volume holographic disk technology has been an important candidate for higher storage density and lower cost of disk. Holographic storage disk systems were widely studied in the world, based on different kinds of photopolymer with good performance. There are three systems developed by Inphase Inc., HDSS project and Optware Inc. respectively, which are nearly commercialized. However, their technologies have not been disclosed. It is our object in this thesis to study and solve some of the key technical problems in holographic storage disk systems on photopolymer.We cooperated with technical institute of physics and chemistry, Chinese Academy of Sciences (IPC_CAS) in developing novel photopolymers for holographic storage. The partner supplied us the photopolymer according to our requirement for it. In our study, the relative strong dark enhancement and uniform post-exposure was detected in the photopolymer that challenged the multiplexing. Thus, one of our topics is the exposure schedule so that the uniform diffraction efficiency can be realized in multiplexing. A previous dynamic model for hologram formation in photopolymer was simplified by us, and three models for writing gratings, dark enhancement and uniform post-exposure, were proposed, respectively,. The analytic expressions were obtained finally. These expressions were utilized to fit the experiment data very well. The important parameters for our novel photopolymer were acquired through fitting curves. Furthermore, the exposure schedule for multiple hologram recording with uniform diffraction efficiency based on UPE model was proposed. It was experimentally demonstrated that, compared with the exposure schedule based on the six-order polynomial method, the UPE model can get more uniform diffraction efficiency. The above description was verified by experiment.To increase the storage density of the holographic disk, we chose the speckle-shift multiplexing method. The disadvantage of speckle-shift multiplexing is that more noise will be introduced to the reconstructed image. Our approach is different from previously reported work. The speckle reference beam was formed by projecting the speckle random phase shifter to the surface of photopolymer through an imaging system with unit magnification. The microstructure of the speckle random phase shifter played an important role on the speckle reference beam. Three speckle random phase shifters with different particle size were fabricated. The experiment results showed that the speckle size generated by the speckle random phase shifter can be controlled by making speckle random phase shifter with different microstructure. In addition, the image quality reconstructed by reference beam with different speckle size was discussed. It was discovered that the larger the speckle size was, the better the image quality was. But this practice also decreased the storage density. So we can reach a compromise between image quality and storage density by adjusting the fabrication scheme of the speckle random phase shifter.In terms of dark enhancement and UPE of photopolymer and the influence of speckle size on shift multiplexing, a scheme was designed to be suitable for speckle-shift multiplexing. To guarantee the storage density as premise, the speckle shift interval was designed to increase the image quality as far as possible, and the fabrication parameters were given. Then, the exposure process in speckle-shift multiplexing was analyzed in detail according to separate regions. The UPE model for calculating the uniform diffraction efficiency was extended to shift multiplexing. An exposure schedule example of uniform diffraction efficiency was obtained from the numerical computation. Finally, it is verified preliminarily by an experiment that speckle-shift multiplexing is feasible through the exposure schedule calculated by our UPE model.