雷射脈衝讀取於熱超解析碟片之分析與應用

Abstract

為了持續提升光碟的記錄密度，能夠記錄小於光點大小記號的『熱超解析』方法已使用在下一代的高密度記錄光碟。此種超解析碟片，大都以一熱分佈形成的遮罩層來縮減光點大小，並利用光點中心高熱部分造成材料的非線性變化，開啟一小於繞射光點的孔徑，遂造成超解析效應。 對於這種熱超解析碟片，使用雷射脈衝讀取有著相當的好處，對於孔徑的開啟，孔徑大小的控制，以及功率餘裕等方面上都有較好的表現，並且由模擬以及實驗都可以證明讀出的信號有較好的品質。同時藉著對孔徑開啟的模擬，可以由讀取功率以及記號大小對讀出訊號的關係，確認熱超解析碟片的特徵。 但由模擬及實驗的結果指出，由於脈衝雷射造成光的調變，在信號中造成偵測的困擾。因此提出一個『同步觸發偵測』的方式，利用脈衝讀取法本身的雷射觸發訊號，同步地對量測出的訊號做挑取的動作，由實驗的結果得到，利用此一方法處理得到的訊號品質可以提升約5dB。

In order to improve the recording density of optical disk, the thermal super resolution technology, which can resolve the mark size smaller than optical diffraction limited spot, is used in the high-density optical disks. The thermal super resolution technology utilizes a special mask layer to shade the laser spot. The material of mask layer, which has nonlinear thermal properties, opens an aperture in high temperature area near to the center of the laser spot. Usually, the aperture size is much smaller than the laser spot, thus achieving optical super-resolution. Using laser pulse readout schemes on thermal super resolution disk has several advantages, such as: the better controls of aperture size, the narrower aperture wall width and larger readout power margin, which have been verified by both experiment and simulation. Apertures opening, readout power, mark size and signal quality affect the performance of the super resolution disks. The simulation and experimental results reveal that the light modulation of pulse readout affects the readout signal significantly, as it may confuse the detection channel. A synchronous trigger detection scheme, using the pulse laser trigger signal to pick up the desired signal, is proposed to suppress the adverse effects on light modulation. A 5-dB increase of signal quality by using the detection method experimentally.