新型光學讀寫頭之光路設計暨應用於角度與位移之測定

Optical design of new pickup head and applied in the measurement of tilt angle and displacement

林彥男(Yan-Nan Lin)

指導教授 ： 孫文信 ； 張正陽

國立中央大學/理學院/光電科學研究所/博士(2012年)

摘要

本論文探討新型光學讀寫頭之光路設計暨應用於角度與位移之測定。在本論文的主要的內容分為三個部分：第一部分是單一光電偵測器之複合式光學讀寫頭的光學設計。第二部分是擴束準直鏡之藍光光學讀寫頭的光學設計與應用於角度與位移之測定。第三部分是更進一步的研究關於使用CMOS感測器的DVD光學讀寫頭對於多方位的水平角與傾角之測定。
在本論文的第一部分我們提出單一光電偵測器之複合式光學讀寫頭的光學設計。此複合式光學讀寫頭可以讀取藍光光碟、DVD以及CD碟片的訊號。我們設計此複合式光學讀寫頭使用共光路方式讓三個雷射二極體所發出的雷射光可以遵循同一光軸以達到減少光學元件之目的。此外，我們將三個雷射二極體晶片與一個光電偵測器組裝在一個積體光學裝置(integrated optical unit, IOU)，另外在DVD與CD系統的補償片可與平行四邊形分光鏡(rhomboid beam-splitter prism, RBS prism)做結合。其中閃耀式全像光學元件(blazed holographic optical element, blazed HOE)的設計可以集中光能量至第0階與第1階的繞射光以改善複合式光學讀寫頭的整體光學效率。此複合式光學讀寫頭設計裡的藍光光碟、DVD與CD系統之光學效率分別是5.545 %、 3.889 %以及 3.517 %。在光學效率的模擬結果，本論文所提出的複合式光學讀寫頭之光學效率比三個積體光學裝置的複合式光學讀寫頭還要高，而且此複合式光學讀寫頭的光學元件數目也比較少，有助於縮小複合式光學讀寫頭的體積。
在本論文的第二部分我們提出一個雷射擴束器的藍光光碟讀寫頭可以同時檢測待測面的垂直位移與傾斜角度。為了提高光學效率讓訊號準確可以得到改善，我們使用雷射擴束器讓雷射光的光型從橢圓形轉換成圓形。本研究使用一個四象限光電偵測器去偵測VA, VB, VC, VD四個訊號相對關係，可用來量測待測面的傾斜角度與垂直位移。其檢測訊號是由一個歸一化聚焦誤差訊號與兩個角度訊號所組成。我們所提出雷射擴束器的藍光光碟讀寫頭之光學效率有59.29 %，而市售的光學讀寫頭之學效率卻只有8.08 %。光學讀寫頭擁有較高的光學效率，光電偵測器上的訊號與雜訊就比較容易區分出來。
在本論文的第三部分我們提出一個新穎的檢測方式，利用改良式DVD讀寫頭系統可以同時量測出多方位的方位角以及較小的傾斜角。我們使用一個互補氧化金屬半導體(complementary metal-oxide semiconductor, CMOS)感測器去捕捉影像而且同時分析光型中心位置的微小位移當待測面旋轉一個小傾斜角度去產生一個角度訊號。我們所提出的檢測方法可以判定待測面的方位角從0°到360°，間距為5°；待測面的傾斜角度變化從0°到4.2°，間距為0.3°。模擬結果顯示我們所提出的檢測方法可以辨別待測面多方位的方位角在較小的傾斜角下。最後，我們模擬此檢測系統裡的方位角與傾斜角之解析度分別為4.60°與0.28°。使用較小畫素尺寸的感測器或是縮小聚焦鏡的數值孔徑(NAf)將有助於改善二維角度量測的解析能力。

關鍵字

方位角與傾角檢測差訊號 ； 光學設計 ； 光學讀寫頭 ； 閃耀式全像光學元件 ； 雷射擴束器 ； 聚焦誤差訊號 ； 互補氧化金屬半導體感測器

並列摘要

This thesis investigates the optical design of a new pickup head and its application for the measurements of tilt angle and displacement. The main content of this study can be separated into three parts. Part I describes the optical design for a unitary photo detector and single-path combo optical pickup head. Part II discusses the optical design and evaluation of the optical pickup head with a laser expander for determining tilt angle and displacement. Part III discusses further research related to the evaluation of multi-directional azimuth and tilt angles by a DVD OPH with a CMOS sensor.
In the part I, we presented a compact design for a unitary photo detector and single-path combo optical pickup head (called the combo-OPH) which can be used for Blu-ray Disc (BD), digital versatile disc (DVD) and compact disc (CD) systems. The number of components in the OPH design can be reduced by focusing three discrete wavelength laser beams on a photo detector. The three laser diode chips and a photo detector can be encapsulated within an integrated optical unit (IOU), which is then combined with a compensator and rhomboid beam-splitter prism. The blazed holographic optical elements are designed so as to concentrate the diffracted light power to the 0th-order and the 1st-order and to improve the round-trip efficiency. The simulation results, including the S-curve and optical efficiency, are compared for this combo-OPH with three IOUs. The optical efficiency of the proposed OPH for BD/ DVD/ CD systems as detected by the photo detector are 5.545 %, 3.889 %, and 3.517 %, respectively. Our design results show that the combo-OPH with one IOU performs better than the combo-OPH with three IOUs.
In part II, an optical design is developed for a Blu-ray OPH with a laser expander that can synchronously detect the linear vertical displacement and tilt angle of the test plane. To improve the signal accuracy of the photo detector, a laser expander is used to transform the shape of the laser beam from elliptical to circular. A quadrant photo detector as used to detect the relative relationship between the VA, VB, VC, VD signals, and can be used to measure the tilt angle and displacement at the test plane. Measurement detection and analysis is based on one normalized focusing error signal (NFES) and two angular signals. The optical efficiency of the Blu-ray OPH with laser expander is 59.29 %. The optical efficiency of the currently used commercial OPH is only 8.08 %. The higher optical efficiency of an OPH makes it easier to distinguish between signal and noise at the photo detector.
In part III, we present a new detection method for an improved DVD OPH system capable of measuring multi-directional azimuth and small tilt angles. A complementary metal-oxide semiconductor (CMOS) sensor is used to capture images and analyze the slight shift of the central position of the beam shape when the test plane rotates at a tilt angle to produce an angular signal. The proposed detection method can determine the azimuth angle of the test plane from 0° to 360° at intervals of 5°. The elevation angle measurements vary from 0° to 4.2° at intervals of 0.3°. The simulation results show that the improved DVD pickup head system can recognize multi-directional azimuth angles of the test plane under a small tilt. Finally, we determine that the resolutions for the elevation and azimuth angles in the proposed system are 0.28° and 4.60°, respectively. Using a smaller pixel size for the CMOS sensor or smaller numerical aperture of the focusing lens (NAf) would help to improve the resolution for 2D angular measurement.

並列關鍵字

optical pickup head ； optical design ； blazed holographic optical element ； laser expander ； focusing error signal ； CMOS sensor ； azimuth and elevation angles detecting

參考文獻

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