光纖端面的微透鏡在光儲存熱寫入機制中的應用

Abstract

隨著科技發展，人們對軟硬體的要求更加講究，在資料儲存、視聽享受等各方面，不但要求資訊處理的速度要快，更要求資訊儲存的容量要大；因此，具備高密度和高傳輸速率等優點的光碟記錄媒體蓬勃發展。而近來在光資訊儲存的研究，也都是朝著發展更高密度、更快速的光碟系統前進，因此，有人提出表面入射型的飛行讀寫頭來取代傳統基板入射型的讀寫頭，並將高數值孔徑(Numerical Aperture,NA)的物鏡加在表面入射型的飛行讀寫頭上，來縮小光點的尺寸，但是，隨著物鏡NA的提高，物鏡的尺寸與重量也會相對的增加，這對讀取速率、伺服控制等皆有不良的影響，因此，我們提出以單模光纖端面的微透鏡來取代傳統物鏡。 由於考慮到製作過程的簡易，我們採用以融接機在光纖端面接上一小段的矽柱，再以電弧放電加熱，利用表面張力，使得光纖端面形成一個球面透鏡，再者，考慮到透鏡的球面像差，我們在微透鏡的上面加上更細的矽柱，做成曲率更小的透鏡，形成雙曲球面的微透鏡。在結果方面，我們利用球面微透鏡，在波長為660nm時，可得到0.6μm的記號，故微透鏡的等效NA為0.66；而雙曲球面的微透鏡可得到0.5μm的記號，故雙曲球面微透鏡的等效NA為0.8。由於微透鏡的焦距相當的短，在讀寫時，碟片稍有晃動，就會造成微透鏡的損壞，故我們以手動輕輕滑動碟片的方式，來記錄商用碟片，在實驗結果方面，由於熱擴散效應，我們得到約1.8μm的連續記號，故若我們能妥善控制碟片及微透鏡的距離，以實驗中高於50%的耦合效率，這個技術就可以應用在光資訊儲存的領域中了。

Most of commercial optical disks use the substrate-incidence recording which has restrictions in using high numerical aperture objective lens to achieve high recording density. Besides, the objective lens is heavy, thus difficult to further reduce the mass of optical head and improve the seek time. The microlens at the end of single mode fiber is proposed to take the place of the conventional objective lens in thermal writing on both magnetic-optical and phase-change disks for its light weight and handiness. Laser beam is coupled into the single mode fiber with an objective lens, then focus on a disk due to the microlens at the end of single mode fiber. The optical calculation of the microlens suggests that the length of silica rod and the radius of the microlens have to be properly chosen in order to obtain suitable spot size of 0.5μm and working distance of 200μm. Due to the surface tension, we can fabricate a microlens at the end of the fiber by using the arc discharge of fusing machine. The minimum spot sizes of 0.6 and 0.5um of the microlenses at the end of single mode fiber at a 660nm wavelength were demonstrated and the coupling efficiency was 50%. This enables to write continuous marks of 1.8um on commercial disk.