Fabrication of Prism-type Holographic Optical Element for the Application of Small-Form-Factor Optical Pickup Head

本論文提出一反射式稜鏡型全像光學元件(prism-type horographic optical element，PT-HOE)之設計與製作，可應用於高密度微型光學讀寫頭(small-form-factor optical pickup head，SFF-OPH)系統。稜鏡型全像光學元件是將微稜鏡(mricor-prism，MP)的反射功能和全像光學特性結合並製作於微稜鏡之斜面上，不同於以往全像光學元件製作在獨立的平面，並藉由全像光學元件的特性取代分光鏡與圓柱透鏡等之功能，能有效地縮短光路與減少光學系統中元件數目等優點。 在稜鏡型全像光學元件之設計過程中，首先運用光學頭像散聚焦誤差訊號(focusing error signal，FES)偵測法，接著使用光學設計軟體Zemax進行光路模擬，繪出初步的光學頭架構，並以二元光學(binary optics)之概念優化全像光學元件，將模擬完成後的各項係數轉換成二維圖形並製作成光罩。再利用半導體的黃光微影(photolithography)製程技術，將設計完成之全像光學元件圖形製作於半導體基板上，最後並以特殊之晶圓切割方式將基板切割成稜鏡型全像光學元件之外型與尺寸。實驗結果以原子力顯微鏡量測表面形貌週期為2.627um、蝕刻深度為253.28nm，以波長405nm藍光雷射量測元件反射光之零階繞射效率為52.4％、正一階繞射效率為21.6％、負一階繞射效率為21.6％，並架設光路系統模擬物鏡聚焦於碟片時之光斑像散變化，其結果與電腦模擬相近。This thesis proposes the design and production of a prism-type holographic optical element (PT-HOE) capable of being applied to a high density small-form-factor optical pickup head (SFF-OPH) system. Unlike the conventional production of a holographic optical element (HOE) made on an independent plane, the PT-HOE is produced by integrating the reflective function of a micro-prism (MP) with the holographic characteristics on the inclined plane of a prism. Besides, by using the characteristics of the HOE, it could replace the functions of a flat mirror and a cylindrical lens. This is able to effectively shorten the optical path and reduce the number of components in the optical system. During the design process of PT-HOE, the focusing error signal (FES) of astigmatic method was initially used, the using of Zemax light ray tracing software was followed to simulate the optical path for drawing a preliminary optical pickup head structure, and the binary optics concept was then adopted to optimize the holographic optical element. The coefficients obtained from the simulation were converted to a two-dimensional graphic and fabricated into a mask. Further, the semiconductor's photolithography process was used to make the finished HOE graphic onto a semiconductor substrate. Finally, the substrate was cut into the shape and dimensions of PT-HOE by using the special wafer cutting method. The experimental result was measured by using an atomic force microscope. It shows that the period of the surface profile is 2.627um with an etching depth of 253.28nm. A blue laser of wavelength 405nm was employed to measure the diffraction efficiency. The zero-order diffraction efficiency of the component's reflection was found to be 52.4%, the positive first-order reflected light intensity to be 21.6%, and the negative first-order deflected light to be 21.6%. The optical system was then set up to monitor the astigmatic changes of the optical spots for simulating the focusing situations of the objective lens on the disc. This result is consistent with the computer's simulation.摘要 I Abstract II 致謝 IV 目錄 V 圖目錄 VII 表目錄 X 第一章 緒論 1 1-1 導論 1 1-2 文獻回顧 2 1-2-1 繞射光學元件 2 1-2-2 微型光學讀取頭類型 3 1-3 論文架構 8 第二章 相關理論介紹 9 2-1 光學讀取頭基本原理與系統架構 9 2-1-1 光學讀取頭基本原理 9 2-1-2 光學讀取頭基本系統架構及機制 9 2-2 光學頭之聚焦檢測技術 11 2-3 光學頭之循軌檢測技術 14 2-4 光學讀寫頭發展簡介 16 2-5 光柵繞射理論 21 2-5-1 繞射理論概述 21 2-5-2 繞射光柵的應用與分類 25 2-5-3 二階相位光柵之繞射原理 28 第三章 新式微型光學讀取頭系統設計與模擬 32 3-1 前言 32 3-2 物鏡設計 33 3-3 光學系統建立 35 3-3-1 建立去光路系統 36 3-3-2 建立回光路系統 37 3-4 全像光學元件相位多項式設計 38 3-5 全像光學元件設計 44 3-5-1 模擬最佳繞射效率 50 第四章 全像光學元件製作 52 4-1 全像光學元件之製作 52 4-2 微稜鏡之製作 57 4-3 實驗量測 61 4-3-1 繞射效率量測 61 4-3-2 像散光斑量測 64 第五章 結論與未來展望 66 5-1 結論 66 參考文獻 6