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標題: | 以白光二極體為光源之可見光頻域低同調性干涉儀 WLED-Based Low Coherence Interferometry in Visible Wavelength Range |
作者: | Hui-Chuan Cheng 鄭惠全 |
指導教授: | 孫啟光(Chi-Kuang Sun) |
關鍵字: | 低同調性干涉儀,白光二極體,光學同調斷層掃瞄, Low Coherence Interferometry,Light Emitting Diode,Optical Coherence Tomography, |
出版年 : | 2005 |
學位: | 碩士 |
摘要: | 低同調性干涉儀 (Low coherence interferometry) 是光學同調斷層掃瞄術 (Optical coherence tomography) 及光學時域反射儀 (Optical time-domain reflectometry) 的基本架構。由於使用低同調長度或寬頻的光源,使得光學同調斷層掃瞄術及光學時域反射儀可以非侵入式量測材料或生物樣品,並提供高解析度的結構資訊。此外,有分析樣品頻譜能力的低同調性干涉儀亦被發展出來,稱之為傅立葉轉換頻譜儀 (Fourier transform spectroscopy) 及頻譜分析式光學同調斷層掃瞄術 (Spectroscopic optical coherence tomography)。
目前廣泛使用中的低同調性光源主要有利用光子晶體光纖產生寬頻光源,鎖模雷射,…等。而在這些光源之外,我們發現白光二極體由於有極寬的頻寬,極適合拿來當作超高解析度低同調性干涉儀之光源,並可望提供次微米的系統空間解析度。此外,由於白光二極體的可見光頻段是過去未曾被頻譜分析式光學同調斷層掃瞄術拿來用做頻譜分析的波段,而白光二極體的使用,亦提供了新的頻譜分析研究領域。 我們的研究,是目前世界上第一個使用白光二極體作為低同調性干涉儀之光源的案例,亦是第一次有研究團隊利用白光二極體之低同調性干涉儀做可見光頻段頻譜分析的研究。為了提高我們系統之訊雜比,我們自行製作使用於系統中之光纖,並在傳統式低同調性干涉儀系統架構上做部分改良和變動。藉由這些方式,我們可以比以前更快速量得低同調性干涉儀之干涉訊號並取得實驗數據,這項系統的改進對頻譜分析式光學同調斷層掃瞄術的應用非常重要。 我們將報告我們近來的實驗結果以及白光二極體之低同調性干涉儀系統發展情況。我們系統在空氣中可達到一微米的解析度,在氮化鎵半導體中解析度更可高達370奈米。另外我們並以我們的系統來對樣品做頻譜分析,以及討論當頻譜分析時會遇到的問題並提出解決方式。 本論文中,我們做了白光二極體之低同調性干涉儀初期的研究,並證實此系統對於樣品頻譜分析的潛力。基於此系統架構,我們提供了一段過去低同調性干涉儀未曾使用到的可見光頻率範圍,利用此頻率範圍做頻譜分析的研究,相信是未來值得努力的方向。 Low coherence interferometry (LCI) is the basis of optical coherence tomography (OCT) and optical time-domain reflectometry (OTDR). Due to the short temporal coherence length of the light sources (i.e. broadband sources), OCT and OTDR could provide noninvasive morphological cross-sectional information of materials and biological tissues. With broadband light sources, not only high spatial resolution but also spectral information can all be obtained, called Fourier transform spectroscopy (FTS) or spectroscopic OCT (SOCT). There are several kinds of suitable sources used nowadays, such as continuum generation in microstructure optical fibers, low-noise superluminescent diodes, and mode-locked lasers, etc. But we found the nitride based white-light-emitting-diodes (WLEDs) with broadband emission could provide sub-micron spatial resolution in the OCT or OTDR. The visible wavelength range of WLEDs not only enables extremely high axial resolution, but also offers an attractive spectrum region for the applications of SOCT. It was the first time around the world to propose the usage of WLEDs as the light sources in the LCI system. It was also the first time to analyze the spectrum of samples in the visible wavelength range by utilizing WLEDs as light sources. In order to improve the signal-to-noise ratio (SNR), we used taper fibers made by ourselves in the experimental setups to enhance the input optical power. We also had some modifications in the delay arm of traditional LCI system. By means of these modifications, we got the interference trace data more quickly which is significant for the SOCT applications. In this thesis, we reported our recent experimental results and the developments of WLED-based LCI systems. We showed the interference trace of the WLED which we used in the experiments and 1.0 µm FWHM in the air was obtained. The 370nm longitudinal resolution in GaN was achieved with a corresponding 1.0 µm longitudal resolution in the air (refractive index n=2.7 in GaN). We also solved some problems in the spectrum analysis and measured the spectrum profiles of some samples. In conclusion, we had some beginning work on the developments of WLED-based LCI system, and it is very important for the improvements of OCT and OTDR systems. We also showed the great potential for spectrum analysis in the visible wavelength region in the future. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/35237 |
全文授權: | 有償授權 |
顯示於系所單位: | 光電工程學研究所 |
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