Based Electro-optic Effect Of The Polarization Modulation And Detection

The modulation and measurement of polarized light have the important value in the field of optical measurement, especially the object recognization and image application. Recognize the focus target from the complex background is a very important subject in the autoindentify domain. The modulation and detection of polarization are the most newly spring up technology.In the modern technology domain of military, biology, medical, astronomy, geography, oceanography, agricultural, etc., the utilization of polarization light are more and more widely. Think about the application background, the dissertation mainly focused on the study, design and achievement of Liquid-Crystal-Type optical circular polarization modulator, Dual-Liquid-Crystal-Type polarization measurement system, which both used Liquid crystal material, as well as the polarization image analysis system based on PLZT modulator.a). Research on the electric-optical(EO) property of the material and the device technology. This part is an important part of the thesis. In this section, the EO property of many materials was compared and analyzed. Then, two kinds of proper materials were chosen: Liquid crystal and PLZT. A lot of testing was done in order to get the accurate EO properties. Through the testing, two tasks should be accomplished, one of them is studying whether the modulation regular are the same between fact and ideal, so that the difference could be compensated in the application design; the other is searching the modulation law of the work points in the EO proper curve in order that the design should followed. In this part, based on these two materials the experiments of the device were done include the parameter design and proper testing.b). The research of the Liquid-Crystal-Type optical circular polarization modulator(OCPM). In this section, the zero drift of direct current property was utilized for the design and achievement of OCPM. The specialty of this device is the feed-back technology was employed. Utilizing this technology can get the stablecircular polarization state output fast. Based on the EO property, a Liquid crystal device was researched combine with the fabrication technology. According the characteristic of the device the OCPM was designed and achieved. The specialty of the OCPM is adapt to multi-wavelength, stable and fast output and the circular polarization degree reaching to 99.9%. The OCPM was composed of liquid crystal device with optimal parameter design, feed-back control circuit and application software. Its drive voltage is less than 10v, response speed about 25ms. This OPCM has the function that the left-hand and right-hand optical circular polarization work points could be found automatically by the changing wavelength and be fixed.c). The research of the Dual-Liquid-Crystal-Type polarization measurement system. The prime principle of the measurement is identifying the polarization parameters of the incident light from the detected signals through modulating them by Dual-liquid-crystal-modulator (DLCM). In this section a polarization parameter measurement system was designed and achieved with DLCM as the kernel and a signal process system based on DSP chip. The system used two different frequency signals to drive the DLCM. The measurement optical route can be described by Jones matrix. Based on the DLCM, the simulation result and actual measurement result were discussed. All the results were showed that the design was correct, the structure was reasonable and the measurement accurate was high. The experiment has showed that the measurement error of phase retardation is less than 0.17°, error of azimuth angle is less than 0.27° and error of primary axis angle is less than 0.31°. The precision as above can fit the state of polarization parameters measurement acquirements.d). The research of the polarization image analysis system based on PLZT modulator. Based on the research of two projects that mentioned above, this section integrates the technology of one spot polarization modulation and measurement for polarization parameters and to a multi-spot, that is image, polarization modulation and measurement for polarization parameters. Further more, the technology could be used for all state of polarization measurement. In this part, the property of polarized-direction will follow the varying of the electronic field direction wasemployed. Based on this characteristic and the research of EO property, a cross-pole polarization modulator was designed. It has the working mode of multi-phase modulation. Following the research and design, a polarization image analysis system was achieved based on FPGA chip and signal process circuit. The system can send the image signal to the monitor with VGA interface directly. The resolution of image was decided by CCD, and was independent of modulator. According the transmission spectrum of the PLZT was visible and infrared ray, the proper CCD can acquire the different spectrum image. The experiments were showed that the system we achieved with the PLZT modulator as the kernel can obtain the polarization parameter image reliably, and these parameters can manifest the feather of the object more apparent than using the degree of polarization only.