單矽晶背投影顯示器中偏振分光器的熱效應研究

The Thermal Effect of PBS in LCoS Projection Display

柯信賓(Hsin-Pin Ko)

指導教授 ： 章明

中原大學/工學院/機械工程研究所/碩士(2004年)

https://doi.org/10.6840/cycu200400186

摘要

偏振分光器(PBS)為單矽晶背投影顯示器(LCoS)中重要的光學元件之一，PBS在高強度的光源照射下會產生大量的熱，因而嚴重影響到投影系統的影像品質，同時也為光機系統帶來了光學效能上的限制。
本研究透過控制PBS的溫度梯度場，量測在熱應力影響下，經過PBS的偏振光之穿透率改變程度，此外並建立一組內含PBS的投影光學系統進行實驗，檢視在上述不均勻溫度分佈下造成的雙折射效應，所影響最後成像畫面的亮度、對比度、均勻度等重要的影像品質變化情形。PBS分光光譜實驗結果顯示在溫度場高低差達15℃時，P光的穿透率下降了2.5%，S光則是上升了3%以上，這樣的變化對投影機的效能影響非常嚴重，從投影影像品質檢驗結果發現，相同溫差下整體對比度衰退了15.4%，而在畫面邊緣的影像對比衰退高達20-25%，上述實驗結果顯示實際投影畫面出現暗場漏光、亮度不均勻及對比下降等情形。

關鍵字

單矽晶投影顯示器 ； 偏振分光器 ； 應力雙折射

並列摘要

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.

並列關鍵字

PBS ； LCoS projector ； stress birefringence

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