Liquid Crystal Spatial Light Modulator Optical Modulation Characteristic Measurement And Its Application In Optical Image Processing

Liquid crystal spatial light modulator(LCSLM) is the key element in optical information processing, which is especially suitable to be applied in the equipment of the optical pattern recognition. In this thesis, we discuss the optical modulation characteristic of LCSLM and its applications in optics processor such as optical image correlation recognition, amplitude-phase conversion and optical encryption.The amplitude and phase modulation properties are elementary parameters of a SLM. A novel and simple method is proposed to measure experimentally the optical modulation characteristic of LCSLM. A 4f imaging system is introduced in one arm of the Mach-Zehnder interferometer. The under tested LCSLM is placed on the input plane of the 4f system, and the array CCD detector is placed on the output plane of the 4f system, which is used to record the output image or the interferogram produced by the interference between the output image and the reference beam. The amplitude and phase modulation properties can be measured by the intensity, intensity distribution of the output image or by the interference fringes.In the field of the optical pattern recognition, there has been a steadily growing interest in the development of optical correlator by use of SLM A hybrid optical/electronic joint transform correlator (JTC) generally uses a spatial light modulator (SLM) as the input device and a CCD camera as the detector. Both the SLM and the CCD have the grid pixel structure that results in the sampling of the input image and the joint transform power spectrum (JTPS), then the Fourier transformations of the sampled image and JTPS will produce the spatial replica of the JTPS and the correlation signal, respectively. In this paper, the relationships among the structure parameters of the SLM, the CCD, the Fourier transform lens, and the input image are introduced. Some computer simulation results are given, which proved the theoretical analysis. These relationships are important to the configuration and application of JTC.In the last part, firstly, a new approach to the conversion of a given spatial amplitude distribution into a spatially similar phase distribution is proposed, and on the base offormer fundamental idea, we present a security and encryption system. The present method is achieved with an amplitude gray-scale spatial light modulator (SLM) as the image input device and based on double exposure holographic phase-shifting interferometry. Secondly, another new method of amplitude-phase conversion and optical encryption is proposed. This method of amplitude-phase conversion uses an SLM as the image input device and based on a 4/ system, and the encryption system using a configuration of two joined JTC with amplitude SLM. We present the fundamental idea on which the method is based and verify its effectiveness and correctness by series of computer simulation and optical experiment results.