臺灣博碩士論文加值系統

新世代的光儲存系統必定是往高紀錄密度的方向發展，但在縮小紀錄資料點的同時也提高了聚焦的困難度。資料讀取的過程中影響聚焦光點品質的因素很多，例如讀取頭的設計不當、讀取頭中光學元件的缺陷及碟片的傾斜晃動等等，這些因素都會改變聚焦光點的形狀及中心強度。基於此一觀點，本文將利用波動光學的純量繞射理論建構光碟機的數學模型及像差理論來分析聚焦物鏡的像差對聚焦光點的影響，同時我們也將探討碟片傾斜所導致的像差對聚焦伺服訊號(S-Curve)的影響。在模擬的部分我們使用自己的演算法計算光場及光強度再利用MATLAB將模擬結果以圖形的方式呈現，同時以另一套繞射軟體DIFFRACT來作模擬結果的驗證。

Reducing the size of data pattern on optical disk to increase the storage capacity is definitely a direction of development for storage medium. Therefore, high NA (Numerical Aperture) objective lens would be employed to generate tiny spot for the readout process. However, this would make the defocus tolerance rigorous at the same time. Therefore, focusing is still a critical issue in new generation optical storage system.
This thesis is devoted to investigate the effects of imperfect conditions within an optical pickup such as lens aberrations on the spot formation. Besides, the variation of focusing error signal (S-curve) due to the presence of disk tilt aberrations is also studied in this work. Wave optics and aberration theory are introduced in this thesis to calculate the optical field distribution and MATLAB is used to perform our own-developed program codes and plot the simulation results. On the other hand, a commercial software, DIFFRACT, is used to verify our simulation results.

Contents I
List of Figures III
List of Tables Ⅵ
Chapter1 Introduction 1
1.1 Motivation 1
1.2 Framework 2
Chapter2 Optics Theories 3
2.1 Ray optics 3
2.2 Wave optics 6
2.2.1 Elementary waves in wave optics theory 7
2.2.2 Effect of thin lens on incident light wave 9
2.3 Fourier optics 11
2.3.1 Impulse response of free space 11
2.3.2 Fresnel and Fraunhofer approximation for impulse of free
space 13
Chapter3 The Mathematical Model with Aberrations in Optical
Pickup 16
3.1 The aberration-free mathematical model for optical pickup 16
3.2 Aberration theory 23
3.2.1 Introduction 23
3.2.2 Definitions of aberration 23
3.3 Mathematical treatment of aberrations at a lens surface 26
3.4 The expressions for aberration coefficients of a tilted
disk 33
Chapter4 Simulation Results and Discussion 39
4.1 Parameters declaration for our simulation architecture 39
4.2 Investigation of aberrations effect on focus spot quality 45
4.2.1 Spherical aberration 45
4.2.2 Coma aberration 49
4.2.2 Astigmatism aberration 52
4.3 Effect of disk tilt on the variation of focusing error
detection 55
Chapter5 Conclusions and Research Prospects 60
5.1 Conclusion remarks 60
5.2 Research prospects 60
References 62

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