Study Of Correlater Based On Volume Hologram In LiNbO₃ Doped Fe

With the developing of information and computer technology, the new storage system is needed urgently. Volume storage has become a potential storage means for the merits of high package density, high storage capacity, fast data gransfer rates and short access time. Accordingly, the correlator based on volume hologram is a rising optical pattern recognition technology. Fistly, images for recognition need to be storaged into the refractive crystal with angular multiplexing. All these images serve as template during the later recognition process. Then with the incidence of object light loading the image to be recognized, a sequence of correlation peaks is diffracted, which respond to the image stored. The strength of the correlation peak is proportion to the similarity of image input and that stored. Relative to the conventional target recognition by couputer, the processing progress is parrelelling and time needed has nothing with the number of templates.In our dissertation, hologams are stored in doped LiNbO3. To solve the erasure problem of optical grating stored during the correlation process, we adopt the technology of thermal fixing. Combining the influence of dynamic range and the eficency of thermal fixing, we optimized all the relative parameters and obtain better diffraction efficiency. When the number of images stored as templates is very large, the hologram firstly stored needs a rather long exposure time during the sequential exposure recording. This leads serious light-induced scattering which does great harm to recognition. We introduce batch thermal fixing and study the infulence of inter-batch optical erasure time constant.For real-time recognition with ears of human being as the targets, we take thin crystal as the recording medium. According to the shfiting invariance of defocus volume holographic correlator, we realize the exact subsumption of the inputting real-time image. For the nonreal-time image, we take thick cryastal as the recording medium. Due to the large dymanic range, the number of template stored can be rather large. Without the considering of abberration of image, taking correlation coefficient match plate as the recognition algorithm, 1000 templates were recognized accurately and rapidly in the fourth chapter. For the practicality of volume holographic correlator, we complete a portable correlator system in Chapter 5. In this system, the reference light is convergent beam and reflecitve geometry is adopted. Removing reference light path, we package the laser and information light path and the dimension is about 350×200×70mm3.Furtherly, fractal/space multiplexing is put forward in the fifth chapter. To the voluem holographic correlator, it could improve the storage density and make use of the dynamic range more efficiencly. At last, taking Zn:Fe:Mn:LiNbO3 bar as the recording medium, we store hologarm in a few space with angular multiplexing withour information light path fixed. Thus, with the incidence of information light to be recognized, the parallel correlation with 7500 templates sotred in all the space is realized.