光學調變結構在容積光碟中的應用

Abstract

為了因應電腦、多媒體與網路等科技的發展，更大的記錄容量與高速的資訊存取已成為光資訊儲存技術發展的指標。提升光碟記錄密度的方法可分成兩大類：提升光碟片的面積密度與容積密度。使用較短波長的雷射光源與較大數值孔徑(numerical aperture, NA)的物鏡可提升光碟片的面積密度。除此之外，可在垂直碟面的方向上設置多於一層的記錄面，以倍數提升光碟片的容積密度(volumetric density)，此即為容積光碟技術。本論文中提出光學調變結構(optical switching structure)應用在容積光碟中，使容積光碟中讀出層有高反射及高吸收率，非讀出層有高穿透率，因此可以在不改變雷射光波長及物鏡NA的條件下使容積光碟在各層中的讀寫機制能達到最佳化，如此可以有效的增加每一層光碟記錄容量。

此論文討論光學調變結構應用在重複擦拭型(rewritable type)與寫一次型(write-once type)容積光碟兩方面。論文的第一部分的研究是在於重複擦拭型容積光碟中的記錄層中加入一種光學特性(optical characteristics)對溫度敏感的光學調變結構，使得資料層受到聚焦雷射光照射時及非照射時的光學特性受到精確控制，如此便可提高雷射光使用效率，使得資料層的讀出（或是記錄）特性提昇。

此論文的第二部分討論光學調變結構及透明記錄材料堆疊的容積光碟結構，此光碟結合了寫一次型記錄媒體以及容積光碟兩者優勢，目的在於提昇寫一次型記錄媒體的容量。在此新型光碟中，當雷射光聚焦在光碟記錄層中的其中一層時，光控制層可精確控制在此記錄層的透明記錄材料上溫度變化分佈，造成此透明記錄材料表面高度變化而形成次微米至奈米級記錄信號，如此便可作為高容量多層可記錄式資料儲存媒體。也因為透明記錄材料具有極高的雷射光穿透特性，加上利用光控制層提昇雷射光能量的使用效率，因此在光學讀寫頭僅提供有限雷射光能量的條件下，可以大幅增加光碟中的資料層數目，使得在一基板上的光碟容量得以提昇。此外，此光碟結構亦有製作簡單，相容於現有光學讀取頭架構的優點，故有很廣的應用層面。

Optical data storage industries are continually growing with progress of computer, multimedia, and network markets. In this trend, technologies capable of recording more information thus become increasingly demanded.

The advanced optical storage technologies can be categorized into two groups: one is to increase the areal density of a single-layer optical disk by employing narrow track-pitch, short wavelength laser, and high numerical aperture (NA) objective lens; the other is to multiply the volumetric density of a three-dimensional volumetric optical disk by implementing multiple recording layers along the direction perpendicular to the data surface. The thesis is devoted to increasing the volumetric density by employing optical switching structure in multilayer optical disk.

For reading/recording on a lower targeted recording layer of rewritable type volumetric optical disks, transmitted laser power is decreased by absorption and reflection of the upper layers. Thus, a layer of thermo-chromatic material has been added as an optical switching structure next to the recording layers to modulate the optical characteristics of the recording layers by the diffraction limited laser beam during writing. Experimental results showed that the peak writing power could be reduced by 42% in the disk with an additional optical switching structure. Thus, optical switching structure is promising for rewritable type volumetric recording to optimize the reading/recording performance of the volumetric disk.

A write-once type volumetric optical disk having multiple transparent films with optical switching structure was demonstrated as a recording medium to increase the number of recording layers. In the disk, the optical switching layer was adopted to reduce laser energy decay and increase reading and recording sensitivity. Well-defined marks of about 100 nm in depth can be yielded precisely on the transparent films by a focused laser beam. Writing and reading of a four-layer recordable disk, fabricated by molding and spin bonding techniques, were demonstrated experimentally. Furthermore, by adoption other advanced techniques such as signal processing, parallel accessing, and MOEMS (micro opto-electro-mechanical system) pickup head, the proposed disk is projected to have a capacity over 1 trea-bit.