Study Of Gated Imaging Detector Based On Liquid Crystal

With development of the technology, wider dynamic range of imaging detector is requested. In order to make imaging detector can work normally under the hign light (105lx), and the detail reproduction of large contrast image is thought more and more of, especially for some fields which are irradiated under the strong light. Hence, based on the electro-optical of liquid crystal, in this paper, the driver circuit board of commercial liquid crystal display panel is modified and designed that adding FPGA as video image processing module based on the reference design module. Then, a novel partial gated imaging detector based on liquid crystal has been designed, and we have obtained the clear photograph by shooting experiment. The main points of this thesis are as follows:1. A summarize on research status and development of gated imaging detector. Then the optical properties of the liquid crystal material and the structure of twist nematic liquid crystal cell are introduced. The transmission and polarization properties of output light are analyzed by the Jones matrix at last.2. Structure design:According to electro-optical modulated curve of commercial LCD Sony LCX029 and its range of modulated voltage, the reference driver circuit is modified and a video signal process module is added in order to get rid of the DC voltage which is beneficial for the purpose of intensity modulation. It was coupled into the imaging detector that has brought forward partial gated imaging detector as the novel device, built the model and described the working principle. After the driver circuit board was designed, intensity modulation of LCSLM was measured by experiment. Relation between transmittance and grey level are fitted by experiment data which fitting degree is 0.9995. According to the fitting cure, we have obtained the corresponding grey image send to liquid crystal panel that realized light intensity partial gated.3. Theoretical calculation:The relationship between transmittance and wavelength, birefringence index, voltage are derived theoretically. The dispersive of twisted nematic liquid crystal is quantitatively analyzed from the relationship of effective birefringence and transmittance. By the grating spectrometer, the transmissivity of liquid crystal is measured and analyzed with Sony LCX029 TFT-LCD (thin-film-transistor liquid crystal display) in this experiment. It was found that the LCX029 LCD has a low dispersion within the visible light. But dispersion increased along with the gray level. Cat model have been shot by self-made partial gated detector, it is show that dispersive effect can not affected the imaging quality.4. Experimental verification:Photograph of exposal, partial gated by self-made imaging detector, electronic shutter, automatic gain control and aperture are compared. We found that contrast of partial gated image is reduced and prove that the liquid crystal realized partial gated better than traditional whole gated. A clearly license plate with headlights turned on at night is obtained by our prototype.