| Summary: | 碩士 === 國立臺北科技大學 === 光電工程系研究所 === 96 === Liquid-crystal spatial light modulator (LC-SLM) will be used in replace of phase-only diffractive optical elements in our laboratory. It provides a corresponding phase delay to the incident light depending on the external electrical field. The LC-SLM used in our lab is LC-R2500, made by Holoeyes Co., in which the twist angle of liquid crystal is 45° and light operation is in reflective mode.
Before using LC-SLM for the diffraction optical elements, we first measured the amplitude and phase modulation of LC-R2500. We used the Michelson interferometer to produce the interference fringes. By changing the applied voltage of one half the corresponding interference fringes have a certain displacement, which was calculated by a correlation operation. The phase delay of the applied voltage was than obtained as the ratio of the interference displacement to the period of the interference fringes. Because the incident light is different polarized directions might result in different measurement results of the reflectivity and the phase delay, the angle of the polarizer was changed every 10 degrees from -20 to +20 degrees to obtain experiential data to characterize the LC-SLM. The measured characteristic of the phase delay to the gray scale (the applied voltage) are nonlinear, and are used a polynomial of order to fit the measured data. Finally, the phase delays calculated from the polynomial were used in the design of diffractive optical elements which were implemented by LC-R2500.
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