摻鈰釔鋁石榴石晶體光纖用於光學同調斷層之研究

Abstract

對於光學同調斷層術而言，達成超高縱向解析度的主要光源約有五種：(1)疊接式超螢光發光二極體 (superluminescent diode; SLD)，(2)飛秒雷射 (femto-second laser)，(3)光子晶體光纖連續激發光 (photonic crystal fiber; PCF)，(4)鹵素發光器，(5)增益自發輻射 (amplified spontaneous emission; ASE)。上述前四種高縱向解析光源，因其光譜之非高斯分佈與高光譜雜訊，所以皆有高邊陲雜訊 (side-lobe noise) 的問題，進而導致縱向畫素串音問題。倘若要增進影像品質，則必須要做到近高斯光譜光源。增益自發輻射光源恰可產生近高斯光譜，但是光功率往往相當微弱。因此，使用光波導結構收集增益自發輻射光，即成為其提升光功率之相當重要的利器。 現今本實驗室之開發方向，即利用共抽拉雷射加熱長晶法，生長出雙披覆晶體光纖 (double-clad crystal fiber; DCF) 結構，收集被激發出之增益自發輻射光，進而有效提升近高斯光譜之寬頻光源光功率，增加穿透深度以及訊雜比。實驗室目前已可生長出直徑10微米以下之小纖心雙披覆晶體光纖，提升光源之亮度與橫向空間模態品質。我們利用摻鈰釔鋁石榴石，當作產生寬頻光的生長材料，所產生出之寬頻光，使用於光學同調斷層術上時，擁有1.5微米之縱向解析度。 在此論文中，我們成功將架設出之光學同調斷層系統，使用在魚類角膜與液晶面板上。所觀測出之結構，為傳統之光學同調斷層術，所無法解析出的。在魚類角膜觀測上，發現其基質之三維分布，也同時觀察到角膜隨時間萎縮之現象。另外，此系統在垂直配向液晶面板 (VA-LCD) 之三維掃描上，亦獲得了相當重要的製程缺陷與液晶層厚度資訊，而且此三維資訊，是目前世界上其他技術，所無法觀察到的。 接著，我們更基於此技術與其實驗架構，設計出適用於此架構之原型，預期在未來，能將此原型產品化，進而引入市場。

For optical coherence tomography (OCT), there are about five main light sources to achieve ultrahigh axial resolution: (1) multiplexed superluminescent diode, (2) femto-second laser, (3) photonic crystal fiber (PCF), (4) halogen lamp, (5) amplified spontaneous emission (ASE). For the first four methods, because their spectra are non-Gaussian with high spectral noise, they all have the common problem of high side-lobe noise which will result in axial image pixel crosstalk. In order to improve the image quality, near-Gaussian spectrum is necessary, and the ASE source just has this advantage. But, the optical power is typically very weak. Therefore, using waveguide to collect the ASE light to push up the power is an advantageous solution. Our laboratory used the co-drawing laser-heated pedestal growth method to grow the double-clad crystal fiber (DCF) as a waveguide light source, to effectively collect the ASE light for increasing depth penetration and the signal-to-noise ratio. Until now, we can grow DCF with diameter less than 10 μm, which can improve light source brightness and transversal mode quality. Furthermore, the Ce3+:YAG material was used as the source rod, to grow the DCF structure, which has 1.5-μm axial resolution in air. In this thesis, we successfully applied an OCT system to image the fish cornea and the vertically-aligned liquid crystal display (VA-LCD) panel. The resolved fine structures are not possible by conventional OCT system. For the observation of fish cornea, the 3-dimensional (3-D) stroma population and the atrophic phenomenon with variant time were verified. The defects and the cell gaps of the VA-LCD panel from 3-D OCT reconstruction were also observed and quantized. To our knowledge, this 3-D information can not be obtained by other optical techniques presently disclosed.