應用於高密度光儲存系統讀取信號之模擬

Abstract

隨著對於儲存容量需求的增加，光儲存系統採用較短的波長以及較高的數值孔徑的物鏡，來達成此一目的。但當較高數值孔徑的物鏡被採用時，光的向量繞射特性就應該納入考量。因此，本論文提出了一個結合了「光追跡」與「向量繞射」優點的光學讀取頭模型，不但可以節省計算時間，亦可以達到相當的準確度。 基於先前所提出的光學讀取頭模型，並以DVD+R/RW為例，成功地模擬出其讀取信號(RF signal)、聚焦伺服信號(FES)以及尋軌伺服信號(TES)，並與規格書的標準做比較，以驗證模擬結果的可靠度。此外，本論文也對DVD+R/RW系統，進行公差分析(Tolerance analysis)，其中包含傾斜(Tilt)公差與失焦(Defocus)公差，並與實驗結果作比較，討論公差對於讀出信號及伺服信號的影響。最後，本論文討論了一種在可寫入及可覆寫式系統中常見的現象－饋通現象(Feedthrough)。此現象主要是發生在碟機尋軌時，由於碟片上的溝軌結構(Groove structure)使得聚焦伺服信號會隨著尋軌伺服信號變動的一種干擾(Crosstalk)。此現象會影響聚焦伺服的穩定度，在本論文中會討論其成因以及影響其變化的因素。 可以藉由本論文所提出的光學讀取頭模型的模擬分析，用來在先前設計的步驟當中，發現可能的問題，以期能在發現問題的初步，就能夠找出可能原因，進一步提出解決方案。亦可用於當在碟機系統中發現問題時，將其與以往的模擬結果作比對，以反向推導的方式找出問題可能的原因。

As the coming of the tera-era, the demand for the storage capacity is increasing. It is known that the storage capacity is governed by the ratio of wavelength (λ) of the laser diode and the numerical aperture (NA) of the objective lens. Therefore, the optical data storage system is developed toward a shorter wavelength and a higher NA. When the NA of the objective lens is higher than 0.6, the vector nature of light will play an important role during readout process. The optical model combined the advantages of the ray-tracing and vector diffraction is proposed to achieve a faster calculation and still maintain the reliability. Based on the proposed model, the RF signal and servo signals including the focus error signal (FES) and tracking error signals (TES) are demonstrated and successfully verified with the specification under DVD+R/RW system. Moreover, the tolerance analysis of DVD+R/RW system is accomplished. The tilt and defocus effect are simulated and compared with the experimental results to show how the tolerance affect the readout and servo signals. Finally, this thesis discusses a phenomenon which will happen especially in the recordable and re-writable systems called feedthrough. The feedthrough effect is caused by the groove structures on the recordable disc and lead to a variation in focus error signal with the tracking error signal during track seeking process. The feedthrough effect will deteriorated the performance of the focus servo and the origin and the factors that influence feedthrough are discussed.