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標題: | 兆赫波分子影像及偵測應用 Terahertz Molecular Imaging and Sensing Applications |
作者: | Ja-Yu Lu 呂佳諭 |
指導教授: | 孫啟光(Chi-Kuang Sun) |
關鍵字: | 兆赫波,次毫米波,兆赫波影像,兆赫波波導,內視鏡,光纖, Terahertz,submillimeter wave,THz imaging,THz waveguide,endoscope,fiber, |
出版年 : | 2007 |
學位: | 博士 |
摘要: | 利用兆赫波來做影像及偵測是近年來兆赫波科技的主要發展重點,和許多兆赫波的產生和偵測技術的研究發展動力。因為兆赫波具有獨特別於一般電磁波(包含可見光和微波)的特性,例如具有直接辨識分子的能力,利用這些特性可以實現非侵入式、不需外加染劑的分子影像和偵測。因此發展出高靈敏、低損耗以及可以自由彈性控制的兆赫波影像和偵測技術或系統,是近年來許多研究團隊努力結合兆赫波科技這個新興領域和現實各種應用的目標。在此,我們也為此目標提供一些可行性辦法。
本實驗室前人已經發展出具有超高光電轉換效率的兆赫波電光轉換器(THz photonic transmitter),在本論文中我們結合此兆赫波發射器的優點,首次建立一個僅需極低功率驅動之兆赫波分子影像系統,以極低功率(<5mW optical pump, 15V bias)取得高訊雜比(SNR>300)、高解析度、高穿透度(可穿透>3cm之乾燥生物體)之生物分子影像,成功以非侵入式辨識生物體中之分子分佈。我們以鮮花跟乾燥海馬生物樣品作為示範,結果顯示兆赫波可穿透不透明物體,量測到被隱藏的生物之分子影像,直接反應新鮮生物體中的水分子分佈狀況,以及海馬體中的組成蛋白質分子的分佈。 我們也將該具有小體積、高效率的兆赫波發射器和微型生物晶片作平面整合,製作出一種新型微小的兆赫波生物感測晶片。利用該創新之兆赫波生物晶片來偵測微量毒品,可成功將奈米克(~10 nano-gram)等級的安非他命(amphetamine)跟古柯鹼(cocaine)從其他外觀相似的白色粉末中鑑別出來。該偵測屬於近場距離偵測,不需外加兆赫波聚焦系統,即可以完成局部高解析度的分子偵測,對未來實現晶片陣列具有發展潛力。 如何有效地傳輸兆赫波,達成高信雜比的兆赫波影像和偵測系統應用,是另一個大家關注的重點。在本論文中,我們製作了一種空心的微結構光纖來有效傳輸兆赫波。該兆赫波光纖不但具極低損耗、可以寬頻傳輸、傳輸波長可調等優點,並且兆赫波光場可以良好的侷限在微結構光纖的中心空氣缺陷中(hollow air core defect),不受外界干擾地傳輸。我們將從設計、製造和量測頻譜特性等方面來了解該兆赫波微結構光纖,並且說明其傳輸機制。 傳統可見光光纖科技已經發展相當成熟,已經被廣泛的應用到各種活體即時生醫影像或偵測上,例如螢光顯微鏡、內視鏡、外科手術和遙測各種炸藥或毒品等等。兆赫電磁波不但可不需外加任何螢光染劑直接辨識分子影像,並且更具有低雷利散射(Rayleigh scattering)、低光子能量和高穿透深度等特質,使得利用兆赫波來完成生物影像其對生物組織的破壞性會比可見光小許多。因此若能結合光纖跟兆赫波的優點,建立一種光纖掃瞄之兆赫波影像系統,不但能擴大兆赫波的應用範圍如可見光光纖的廣泛應用般,並且能改善目前需要螢光染劑影像系統的缺點。過去本實驗室前人已經發展出低損耗兆赫波次波長塑膠光纖,不同於一般光纖,大部分的兆赫波能量都裸露在次波長光纖之外,因此大大地降低介電吸收損耗,達到一米甚至更長的傳輸距離。在本論文中,我們研究該光纖其影像應用的可行性,先探討次波長光纖在低比例侷限光場(loosely field confinement)狀況下的彎曲損耗、能量傳輸率及頻譜特性,和模態品質(modal spot quality);並且也利用此次波長塑膠光纖,建立了室溫操作之穿透式兆赫波光纖掃描影像系統,直接證明其生物影像之可行性。結果成功取得各種大面積生物體的兆赫波二維影像;顯示該兆赫波次波長塑膠光纖可大面積掃描,得到高訊雜比、高解析度(接近兆赫波繞射極限)的生物影像。最後我們以此穿透式影像系統為基礎,第一個以次波長兆赫波光纖建立了兆赫波內視鏡(THz endoscope),不需聚焦系統而成功取得各種高解析度生物和金屬樣品之兆赫波影像,該影像不但可以二維顯示分子分布,同時亦具有深度解析度顯示出物體表面結構(morphology),特別適用於含水豐富的生物體,克服了傳統穿透式兆赫波影像系統對水氣吸收的限制。 Recently THz imaging and sensing techniques become focusing in THz technology and the main driven force of THz generation and detection. Due to the unique capability of direct molecular identification differed from other EM waves (optical waves and microwaves), it enables noninvasive and label-free molecular imaging and sensing based on THz waves. In order to develop THz imaging and sensing technique or system with high sensitivity, low loss, ease of control and high flexibility for various practical applications, many researchers have made lots effort on it. In this thesis, we provide other alternatives for THz imaging and sensing application. Based on an optoelectronic THz photonic transmitter with ultra high conversion efficiency, we demonstrate a compact THz molecular imaging system with extremely low driven power (<5mW optical pump, 15V bias). Based on the micron-sized photonic transmitter operating at room temperature, an improved signal-to-noise ratio with a reasonable spatial resolution and high penetration depth (>3cm) can be achieved. Biomedical THz imaging has been demonstrated by scanning a dried seahorse and a fresh flower, which were hidden in plastic sample holders and were invisible. Tissue and water distributions of distinct regions of the bio-samples were clearly resolved, showing the high imaging contrasts of the demonstrated system. These results reveal the possibility to construct a compact and high-sensitivity THz imaging system with less than 1-mW optical excitation which is promising in the future clinical application and sensing of hidden objects such as explosives and viruses. By planar integrating a THz micro-source into a glass-substrated microchip within a THz near-field distance, we demonstrate a compact, label-free, noninvasive, and sensitive micro-biosensing system with low-power consumption. The demonstrated THz microchip allows us to locally specify various illicit drug powders with weights on the order of nanograms. Our demonstration shows the possibility to integrate optoelectronic photonic transmitters with the current biochip technology for various biosensing applications, including DNA sequencing, explosive and virus detections, and rapid identification of the static status or even the dynamics of various biomolecules. To efficiently transmit THz waves for achieving THz imaging and sensing with high SNR, is another important issue in THz technology. In this thesis, we develop an air-core microstructure fiber (AMF) for THz transmission. The novel THz-AMF has advantages of with extremely low loss and tunable guiding wavelength by scaling the size of MF. In addition, most THz field is concentrated inside the central hollow air-core and guided without outside interference. We will introduce the design and fabrication of THz-AMF and discuss the waveguiding mechanism. The demonstrated THz-AMF is ideal for various THz applications, including low-dispersion high THz power transmission for nonlinear applications, THz sensing, and THz optical communication for avoiding the interference from surroundings. A THz subwavelength plastic fiber has been previously developed by our labs for low loss waveguiding. Due to most THz field guided outside the fiber core which is different from the traditional optical fiber, resulting in great decrease of dielectric absorption and thus could guide for a long distance (more than one meter). In this thesis, we further explore the feasibility on imaging by using THz subwavelength fiber on which THz wave is loosely guided. We study its bending loss, energy transfer ratio, and modal spot quality. Furthermore, we also construct a compact room-temperature transmitted fiber scanning THz imaging system based on a low-loss subwavelength plastic fiber. Various biological images have been acquired by direct scanning of a THz subwavelength fiber in a large area, and it reveals that the subwavelength plastic fiber enables high SNR imaging with reasonable spatial resolution (close to diffraction limit). Finally, we first ever demonstrate a THz endoscope based on the subwavelength THz fiber, and apply it for imaging of biological specimen and metal pattern without focusing system. The measured images not only reflected the 2D molecular distribution, but revealed the depth variation and thus showed the surface profile or morphology of imaged object. This novel THz endoscope is especially suitable for water-rich biological specimen, because it overcomes the limitation of water absorption which becomes restriction in the conventional transmitted THz imaging system. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/29244 |
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顯示於系所單位: | 光電工程學研究所 |
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