微奈米光電於光學頭之應用研究Micro; and Nano Optoelectronics in Optical Head Applications

Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/6824

Title:	微奈米光電於光學頭之應用研究Micro;and Nano Optoelectronics in Optical Head Applications
Authors:	王智明;Chih-Ming Wang
Contributors:	光電科學研究所
Keywords:	光儲存;微加工;奈米孔洞;nano-scaled aperture;optical storage;micromachining
Date:	2006-06-24
Issue Date:	2009-09-22 10:29:29 (UTC+8)
Publisher:	國立中央大學圖書館
Abstract:	本論文旨在探討微米及奈米尺度結構之光學特性，也就是所謂的微奈米光學。微光學技術具有將光學系統微型化且降低成本等優點。而奈米光學可利用奈米結構產生一些微光學技術所不能達到的特殊功能。由於微米及奈米光學的功能多樣性，使得該技術於應用領域扮演越來越重的腳色，諸如:偵測器，通訊技術，生物晶片，光儲存等技術。本論文著重於微奈米光學於光學讀取頭之相關應用研究。本文主要內容可分成兩大部分︰在微光學技術部分，我們利用微光學技術，實際製作了一個微型化的光學讀取頭模組。在奈米光學部份，我們探討奈米孔洞的光異常增強特性，並探討其於高密度光儲存技術之應用。在微光學技術方面，吾人利用現有半導體製程技術與微光機電製程技術，製作一系列矽基堆疊式微光學元件，應用於微型化光學讀取頭，使其簡單化、微小化及積體化。本光學讀取頭以三光束法與像散法產生聚焦及循軌誤差訊號，其中包含650nm 雷射二極體、45o矽反射鏡、光柵、全像光學元件與非球面Fresnel lens 等，以自由空間堆疊方式整合各光學元件，以達到將光束聚焦於光碟片上，並產生接近繞射極限的聚焦點，該聚焦點大小約為3μm。此光學讀取頭模組大小約為 10x10x5mm3，總重量約為1.2g。在奈米光學方面，本文旨在探討金屬奈米孔洞的光特性。金屬奈米孔洞早再數十年前以被提出，其近場的光學解析度不受限於繞射極限，其孔徑越小，其空間解析度越高。但傳統繞射理論預測，孔徑越小，其穿透能量亦越低。然而，1998年， Ebbesen 等人於nature上發表，平行光照射次波長2維孔洞陣列金屬薄膜會出現異常的透射增強效應，此效應大大的提高了金屬奈米孔洞的應用可行性。目前研究認為，奈米孔洞的光增強機制大致有以下幾種: 表面消逝波、表面電漿子共振耦合以及狹縫、孔洞波導共振耦合等物理機制。狹縫、孔洞波導共振耦合效應主要受狹縫、孔洞的奈米幾何結構的影響，當其幾何結構滿足近似法布理佩羅共振條件，此時狹縫穿透率可大幅增加，與古典次波長金屬孔洞理論相比，可達到數百倍的穿透光增強效果。本文提出了數種方法來增強奈米狹縫的光穿透效率，以提高奈米孔洞的實際應用可能性。現今的奈米狹縫光增強結構為:數個週期性溝槽環繞著一奈米狹縫。藉由週期性的溝槽產生表面波以提高奈米狹縫之穿透效率。然而此類結構會有一部份的表面波沿著金屬/空氣界面朝狹縫反方向傳遞而無法穿透該狹縫，根據計算延表面散逸的能量由佔總入射能量的14％，為了回收此散逸的能量，我們利用表面波反射鏡形成一個表面波的共振腔，將表面波侷限於共振腔內使傳遞散失的波回收再利用，進而使得穿透效率增強，而表面波反射鏡結構對沿表面傳遞散失能量的的回收率大約是50％。也就是說，藉由表面波反射鏡結構，我們可提升耐米狹縫的穿透率1.5倍。再者，為了得到更高的光能量的利用率，吾人將現今的奈米狹縫光增強結構加以改良，我們將結構改為V型溝槽結構，如圖所示，使其結構類似一般grating coupler結構，藉以增加光場於平行金屬介面之分量，使光利用率提高，根據時域有限元素法的計算結果，將奈米孔洞置於V型溝槽金屬結構中，其穿透率比目前研究的金屬平板結構大6倍以上。This thesis investigates the optics of micro and nano scaled structures, called microoptics and nanooptics. Microoptics and nanooptics continue to advance and diversify due to rising demands for miniaturization, cost reduction, functional integration, and increased performance in optical and photonic systems. Micro- and nano-optics are playing increasing roles in a wide range of applications, including sensors, communications, biomedical, data storage, and other consumer-driven and technology-driven areas. This thesis focuses on the microoptical and nanooptical devices which can be used in optical pickup head system. The main content of this thesis can be separated into two parts: A part of this dissertation presents the realization of a miniaturizing optical head using microoptical and micromachining techniques. Another part of this dissertation presents the near-field properties of a nano aperture which has high potential for optical storage applications. By using the microoptical technology, we have developed a novel stacked silicon-based microoptical system, which is optical-on-axis and transmissible in both visible and infrared ranges. By using this new microoptical system technique, we fabricated a miniaturized optical pickup head module. This optical pickup head consisted of a 650-nm laser diode, a 45o silicon reflector, a grating, a holographic optical element, and some aspherical Fresnel lenses. These optical phase elements fabricated on a SiNx membrane were suspended on Si chips. Each element was then stacked by chip bonding. The integrated optical head had an area of 10x10x5 mm3. The total weight was about 1.25g. The optical performance was successfully characterized. The tracking servo signal pattern on optical disc was measured and a focal spot with an FWHM diameter of 3.1?m was obtained, while the diffraction-limited spot size was 0.7?m. The optical phase elements are made on free-standing SiNx membranes which provide versatile optical functions, such as focusing, splitting, and so on. Since the fabrication process is based on silicon micromachining technology, the optical element is easily integrated with other active and passive devices on a silicon substrate. As mentioned, the other part of this dissertation presents the near-field properties of a nano aperture. The spatial resolution of a small aperture is not limited by diffraction but generally determined by the aperture size, beyond the diffraction limit can be achieved using a nano aperture. Unfortunately, a conventional small aperture has a devastating problem of extremely low transmission. For a small circular aperture, calculations and experiments show that power throughput decays as the fourth power of the aperture size. This low transmission problem greatly hinders the application of a nano aperture for solving significant problems. It has been shown that a large transmission enhancement can be obtained when a nano-scaled slit is surrounded by periodic trenches on the entrance plane of a metallic film. However, until now, the transmission through the nanostructure-surrounded nano-scaled slit is still too low for practical applications. In this thesis, two new methods for further transmission enhancement are proposed: 1. Metallic bumps are used for recycling the surface waves; 2. Tapered substrate is used for propagating constant matching and efficiently exciting surface waves. In this thesis, a very large transmission, 20%, of light through a nano metallic slit bordered by both nano trenches and bumps has been demonstrated theoretically. To the best of our knowledge, this is the first time that a bump structure is proposed for transmission enhancement. The trenches bordering the nano slit are used to excite free-space light into surface waves, while the bumps bordering the trenches are used to confine surface wave leakage. Over 50% of the escaping surface waves can be reclaimed by using a pair of bumps with a reflectivity larger than 99%. As a result, the transmission of a trench-surrounded slit bordered by a pair of bumps can be enhanced 1.5 fold. Furthermore, a nano slit on a tapered metallic substrate was also investigated. By using a 45o tapered structure rather than a traditional metallic plate, a 6-fold transmission enhancement could be achieved, due to the asymmetrical excitation of surface waves and the matching of propagation constants between the surface waves and slit waveguide.
Appears in Collections:	[Graduate Institute of Optics and Photonics] Electronic Thesis & Dissertation

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