利用布拉茲光柵及液晶光學元件達成裸眼式立體顯示器之研究

Abstract

近年來裸眼式立體顯示技術隨著科技蓬勃發展越來越普及化，不管在家用或是公共場合如商店門面都可見到他的應用，然而目前市面上主流的兩種技術還是具備著待解決的問題：視差障壁式（parallax barrier）的低出光效率使得整體亮度過低或是需要高電能來提升亮度；而柱狀透鏡陣列式（lenticular）則有著高交互干擾（crosstalk）及重量較重的缺點。然而在2010年，Chen等人提出以繞射式光學元件－布拉茲光柵層作為立體影像分光元件同時達到高出光效率及輕重量，企圖提供新的裸眼式立體顯示技術的新模型，應用在行動端有著很大的潛力，但由繞射元件帶來的色散效應也降低了影像品質，Chen在後續雖然以製程三種不同週期的布拉茲光柵解決色散效應，卻大大增加了製程的複雜度，並且對於觀賞視域的研究未有太多著墨。 本論文以此為切入點提出了單週期光柵結合鋸齒狀液晶結構的新模型，使用較簡易的製程複雜度解決色散效應，並以電腦模擬8微米週期之布拉茲光柵結合液晶結構，成功顯現消除色散的結果，若以連續式奈米壓印製程（roll-to-roll nanoimprint lithography）量產技術為製程技術的參考，以其最小2微米的製程線寬製作四階（4-level）近似布拉茲光柵結構，在效率上仍可保持著76.4%的出光效率。除此之外，附加的液晶層可藉由電壓調制來調整觀賞距離及視域，以iPad Retina Display®為例可提供38至84公分的觀賞距離範圍。 最後本論文呈現利用擴散片（diffuser）改善觀賞視域（viewing zone），再經由適當的擴散片設計，顯現交互干擾小於0.1此規範限制條件下之立體觀賞視域大小並且統整出擴散片的基本設計概念。

In the recent years, autostereoscopic （AS3D） display has grown increasingly common, in both private settings such as homes, and public settings such as shops and store fronts. However, in the two main types of AS3D systems, namely the parallax barrier method and lenticular method, major undesirable defects exist such as lack of power efficiency for the barrier method, and image crosstalk and heavy weight for the lenticular method. In 2010, Chen et al. proposed an alternative method to achieve AS3D using diffractive optical elements （DOEs）. A blazed grating is adhered directly to the screen surface as the AS3D image splitter, to avoid the efficiency loss posed by the barrier method and strongly decrease the weight, providing a lot of potential on mobile autostereoscopic technology. However, the use of grating introduced chromatic aberration into the system, as the diffracted ray angle is wavelength dependent. Further developments by Chen resulted in a complex panel of blazed grating of three different pitch periods, for the purpose of correcting the chromatic aberration. Besides, there is not much research on the viewing zone of this new structure. Instead of following behind Chen's footstep in increasing the grating complexity, this paper proposes a new AS3D system structure based on a blazed grating of a single period, with the addition of a liquid crystal （LC） refractive element to correct the chromatic aberration. This research simulatedly shows the result of no chromatic aberration and the efficiency as high as 76.4% with the 4-level blazed grating based on a linewidth of 2 μm of a well-known mass production, roll-to-roll nanoimprint lithography (R2RNIL). Furthermore, since the refractive index of the LC can be varied with applied external electric field, the new structure proposed also provides a potential solution to AS3D displays with controllable optimal viewing distance. A viewing distance ranging from 38 cm to 84 cm was achieved by the simulation in iPad Retina Display as our reference model. Finally with the design of the adhered diffuser for the purpose of widening the viewing zone, the viewing zone of the crosstalk below 0.1 was shown successfully and a design rule was deducted.