Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/1864
標題: 光學頭聚焦誤差對雷射反饋雜訊的影響之研究
Study of the laser feedback noise corresponding to the focusing error of optical pickup heads
作者: 許德偉
Shiu, De-Wei
關鍵字: feedback noise;反饋雜訊;focusing servo control;laser diode;optical pickup head;quarter wave plate;relative intensity noise;聚焦伺服控制;雷射二極體;光學讀取頭;四分之一波長片;相對強度雜訊
出版社: 機械工程學系
摘要: 
摘 要
傳統之雷射反饋雜訊量測是以靜態的光學系統架設針對雷射二極體來進行(並非實際光學頭在讀寫碟片之運轉下的方式)。因缺乏回授控制,無法真正量測到光學讀寫頭在實際光碟機內部運作時的雷射雜訊分佈,亦不能提供在各種聚焦誤差與不同碟片轉速情形下的雷射雜訊之相關資訊;因此無法有效地了解光學頭整體讀寫訊號品質的好壞與雷射雜訊間之關係。
本研究結合精密機構設計、光學系統設計、伺服控制設計與光電訊號量測於一體,利用修改商用之光學頭架構作為量測系統之主體,透過以數位訊號處理器(DSP)設計的伺服控制器來驅動致動器(actuator),進行物鏡之聚焦控制,探討雷射雜訊在不同聚焦誤差、碟片轉速與溫度變化下之相對關係。實現以即時性之動態方式量測光學讀寫頭在運轉下之雷射反饋雜訊分佈。
實驗結果發現,當聚焦在光學讀取頭線性區不同位置時,會對雷射反饋雜訊造成不同之影響;溫度變化會影響雜訊之強弱,並且碟片轉速也會造成雜訊之中心頻率改變。此外,本研究也驗證若在光學系統中加入四分之一波長片,確實可降低雷射反饋雜訊,以達到雜訊防治之目的。

Abstract
The conventional measuring system of laser feedback noise was implemented specifically for laser diodes by using a static optical system. (not by a concrete optical head operating under the disk) Without the servo close-loop control, it is impossible to measure the genuine laser noise distribution of a pickup while operating in an optical drive. Furthermore, it is infeasible to obtain the information of laser noise corresponding to the focusing error and rotation speed. Therefore, it is hard to realize the relation between the read-write signal quality and the laser noise of optical heads.
This study was integrated with precision mechanical design, optical system design, servo control design, and opto-electronic signal measurement. With modifying the optical system of a commercial pickup for our main system, the servo controller using a digital signal processor was designed to drive the actuator for the focusing of the objective lens. It provided a dynamic model in real time for measuring the laser feedback noise distribution of a pickup corresponding to the focusing error, rotation speed, and temperature variation under operation.
The experimental results show that the laser feedback noise is responsible to the focusing point within the linear range of an optical pickup head. The noise level is sensitive to the temperature variation and its central frequency is dependent on the disk rotation speed. Besides, this study also verified that the laser feedback noise is reducible by inserting a quarter-wave-plate in the optical system. It is useful for achieving the noise immunity.
URI: http://hdl.handle.net/11455/1864
Appears in Collections:機械工程學系所

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