Optical Analysis And Experiments Of MEMS-based Grating Light Modulator Array And The Projection Display System

With the development of MEMS technology in recent decades, it has become one import method and power to upgrade the traditional industry and to propel the high technology development. Considering the rapid progress of this new field, it is necessary to carry out the research work on MEMS technology. Carrying out the research work of optical MEMS based light modulator for display has great sense to improve our state technology and competence of display industry. Such work also will propel the development of MEMS technology, especially the optical MEMS technology of our country.Group of the author proposed a novel grating light modulator array, which has been granted the patent, according to the current MEMS development and our own research condition. Dr. Jie, one member of the group, analyzed the optical character of the single grating light modulator, designed and optimized the structure of the grating light modulator. She also discussed the information processing of the grating light modulator in brief. Dr. Zhihai, other member of the group, discussed some key factors of the grating light modulator's fabrication, and analyzed some electrical and mechanical characters of the modulator. Based on their research work, in this dissertation, the author discussed the optical character of the two dimensional grating light modulator array; designed the optical projection system of the grating light modulator; proposed two color projection display methods. The grating light modulator based projection display prototype was set up. With this setup modulated image was achieved. The result verified the feasibility of the grating light modulator for projection display. The author in this dissertation also analyzed the influence of dielectric charging and discharging on grating light modulator, and found the variation of the grating light modulator with the charging and discharging process which improved the MEMS device defection theory. Below lists the research content in detail:1) Optical model of the grating light modulator was optimized with the scalar diffraction theory. The effects of the different arrangement of the upper moveable grating and the bottom reflector mirror on the light modulator were analyzed. The result shows that when the ribbons of the moveable grating are arranged symmetrically along the grating period with the bottom mirror the grating light modulator has best diffraction performance. 2) Optical character of the two dimensional grating light modulator array was discussed systematically. It was found that light diffraction pattern of the grating light modulator array is similar to that of the single grating light modulator. The difference between the diffraction pattern of single grating light modulator and that of the modulator array is that diffraction light distribution of the modulator array has much suborder diffraction light which reflects the spatial information of the different single grating light modulators. Diffraction pattern of the grating light modulator array is the coherent superstition of the diffraction light of each single grating light modulator.3) Digital transform method of signal and system was utlized to analyze the optical character of two dimensional grating light modulator array. The analysis result shows that intensity of the image of the modulator has square cosine distribution when the first order diffraction light is used as the projection light, and the variation period is half of the grating constant number. Surrounding parts of the grating light modulator will degrade modulator's fill factor and the contrast ratio.4) Optical character of the grating light modulator illuminated by extended light source was analyzed with the partially coherent theory. The analyzed result was verified experimentally. Diffraction light pattern of the grating light modulator illuminated by the extended light source is the convolution of diffraction pattern of the modulator illuminated by point light source and the light distribution of the extended light source. The convolution result expands the diffraction pattern and may make different diffraction order light mix together. The mixed light can be separated again with the optical lens.5) Optical projection system of the grating light modulated was discussed. Considering the character of the grating light modulator, one projection system based on the 4F information processing system was proposed. The color projection scheme of the grating light modulator was also discussed. Additionally, character of the grating light modulator illuminated by the light emitting diode was analyzed.6) Projection system based on the micro-fabricated grating light modulator was set up. Diffraction pattern of the grating light modulator illuminated by laser and the light emitting diode respectively were obtained. The results are agreed with the theoretical analysis well. With the projection system setup modulated image was obtained. The result proves the feasibility of the projection system based on the grating light modulator. Color image was also achieved with the projection system under the illumination of red, blue and green laser7) Response character of the grating light modulator was test by the corresponding experimental setup. The result shows that when the frequency of the actuating voltage is not more than 3kHz, the modulator has good responsivity. The experiment setup provides a platform for the analysis of the modulators'mechanical and electrical character.8) Effects of the dielectric charging and discharging on the grating light modulator were analyzed and verified by the experiment. The dielectric charges redistribute the electric filed, and then change the response of the grating light modulator. Moveable grating of the modulator is snapped down at the time of voltage being applied and removed. After the voltage is applied and is removed the moveable grating bounces back if the voltage period is longer than charging and discharging time constant. If the voltage period is much less than charging and discharging time constant grating's displacement gets smaller and smaller with the time going on. Experiment was carried out to verify the theoretical analysis. Experimental result agrees with the theoretical calculation well. The experiment result illustrates the influence of charging and discharging process obviously. One method is proposed to reduce the influence of dielectric charges.