雙光纖探針近場光學頭於儲存系統的應用

Abstract

為了滿足儲存系統對於高效率高精度之近場光源的需求，本論文提出一新穎的雙光纖探針近場光學頭，此近場光學頭包含一個斜切的寫入端以及一個間隙感測端。

斜切的寫入端使用一個次波長C型微孔來產生一個次波長尺寸的近場光點以提高空間解析度。為提高次波長微孔的穿透率，本論文提出了一個創新的複合效應。藉由一特定偏振方向的入射光，照射於一被週期性溝槽所環繞的次波長光波導，或斜向照射於該次波長光波導上，可同時激發表面電漿波與傳播模態。被金屬薄膜所遮蔽之入射光可經由表面電漿波的傳遞，將能量傳遞至光波導的傳播模態，並促使在出射面上表面電漿波的激發。此複合效應可大幅增加次波長微孔的穿透率，模擬數據上顯示，其穿透率可較傳統圓孔高103以上。經由實驗亦證明，此複合效應的存在。遠場的穿透率量測顯示，此複合效應可比單一光波導，增加1.3到1.9倍；近場光強度分佈量測也顯示，出射峰值強度較單一光波導，提高1.6到2.8倍。

由於近場光源包含消散波，所以光學系統與儲存媒體的間隙必須維持在次波長範圍內，通常在100 nm以內。因此藉由引入自混干涉效應，本論文使用一雷射半導體做為間隙感應器。首先我們模擬了雷射感應器的回饋訊號，並根據此訊號設計了一控制器。從實驗結果中得知，當一驅動表面有4.8μm的位移時，此系統之殘留位置誤差低於+/- 1.5 nm；當一旋轉碟片旋轉速度高達1500rpm，並產生16μm的位移時，此系統之殘留位置誤差可控制在+/- 9 nm內。

由於寫入端的高穿透率與感測端的高精度，本論文所提出的雙光纖探針近場光學頭具有高效率、精巧、簡單以及易於與其他系統整合的優勢，將可應用於資料儲存系統。而本論文所提出的複合效應與自混干涉效應，亦開啟了近場光學與近場伺服控制的新方向。

To meet demands of an efficient near-field light source with precisely active gap control in either magnetic or optical storage systems, we demonstrate a novel dual-probe fiber head with gap servo control. The fiber head consists of a straw-shaped writing probe for delivering optical power to the disk surface and a gap sensing probe for detecting the spacing between the probe and the disk surface.

The straw-shaped writing probe utilizes a C-shaped aperture in a metallic film on the end face to yield a near-field subwavelength spot. To break through the theoretic limit on the transmission through subwavelength apertures, we introduce a novel hybrid effect by illuminating the C-shaped aperture surrounded with a corrugated structure or with obliquely incident light. The light obstructed behind the film simultaneously excites surface plasmons waves and couples into propagation modes inside the aperture. The transmission of the straw-shaped writing probe employing the hybrid effect is 103 times higher than that of a conventional fiber probe. Compared to a single C-shaped aperture, the far-field transmission measurement indicates that the hybrid effect results in further enhancement on the power throughput by a factor of 1.3 to 1.9. Near-field intensity distribution also shows that the signal amplitude is increased 1.6 to 2.8 times higher than that of a single C-shaped aperture.

Near-field optical systems increase spatial resolution by employing evanescent waves, so the spacing between the optical device and the medium surface must be maintained within a wavelength, typically less than 100 nm. By employing a self-mixing interferometric effect, a laser diode functions as a position sensor with nano-meter precision. We model and characterize the self-mixing interferometric signal and design a proportional integral controller accordingly. The residual position error is as small as +/- 1.5 nm and +/- 9 nm under an actuated surface with displacement of 4.8 μm and a spinning disk with displacement of 16 μm, respectively.

In addition to high transmission through the straw-shaped writing probe and high precision of the gap sensing probe, the dual-probe system has advantages of compactness, lightness, simplicity, and integration capability. The results that this thesis achieves open a new avenue to near-field transmission and servo control and provide a practical solution for data storage applications.