| Summary: | 碩士 === 中原大學 === 機械工程研究所 === 92 === Polarizing beam splitter (PBS) is an essential optical component in a projection display with liquid crystal on silicon (LCoS). A large amount of heat was produced in a PBS, because it is usually illuminated by a strong light source. Therefore, the image quality of the projection system is seriously affected and brings a limitation upon the optical performance of the optical system.
In this research, the temperature gradient field of a PBS was controlled and the transmittance spectra of the polarized lights through a PBS were measured. A projection optical system was also developed to study the effects of the PBS stress birefringence caused by the non-uniformity temperature, so that the changes on the image quality such as luminance, contrast ratio and light uniformity can be detected.
The PBS spectra experimental results reveal that the transmittance of the P waves was reduced 2.5% and S waves increased more than 3% when the temperature gradient reached 15℃ in a temperature distribution from 70℃ to 85℃. The projection image quality was also inspected; a contrast ratio of the whole image reducing 15.4% and the corner region of the picture reducing 20-25% was observed. It shows that the temperature gradient seriously affects the efficiency of the projector, such as having a leakage of light in a dark field, non-uniformity of the luminance and degradation of contrast ratio in the projection picture.
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