基於兆赫波擁有其它電磁頻段所沒有的特殊性質，例如可以直接辨識生物分子和高資料容量運載的能力，所以近年來許多不同層面的應用相繼被開發出來。特別是兆赫波的影像和偵測技術，以及兆赫波通訊元件之開發，都是近期兆赫波科技中最迅速發展的領域之一。由於兆赫波反共振中空波導是目前兆赫波具最低傳輸損耗和彎曲損耗的波導之ㄧ，因此最適合將它應用到兆赫波影像和兆赫波通訊領域。

本論文首先實驗證明一種新型可機械調變之寬頻兆赫波調變器，它係基於一維反共振中空波導，該波導包含一複合式被覆層(cladding)由鋁板與壓克力板構成。透過機械控制鋁板和壓克力板距離，可以動態選擇波導中TE極化的傳輸頻帶，和線性衰減特定頻率之功率。實驗上量測到的最大可調變傳輸頻率為60GHz，約為傳輸頻寬(~116GHz)的 50%；而最大可調變功率比例為20dB。此外，該調變器亦可當作極化濾波器，將TE和TM極化兆赫波分開，其濾波之消光比(extinction ratio)可達到20dB (on-off ratio)。該多功能性整合型波導元件，係直接調變兆赫波訊號，和基於低損耗之兆赫波反共振波導，因此可以免去元件轉換和元件插入損失。

其次，我們利用反共振中空波導實現一光纖掃描式兆赫波內視鏡影像系統，該系統包含一分光鏡、一塑膠反共振中空光纖和一結合光纖之塑膠微透鏡。該新型兆赫波內視鏡系統，不但不需要光纖偶合器，僅使用單一根光纖來傳送入射和從樣品反射回之兆赫波訊號，且亦成功解決過去基於次波長光纖的兆赫波內視鏡高彎曲損耗的問題。該系統具有有接近光學繞射極限之焦點光斑(大小為1.1mm)，大於200的訊噪比(SNR)，以及低波導彎曲損耗(在90ﾟ彎曲時量到的最大反射兆赫波仍有原入射能量之2%)等優點。利用樣品和掃瞄反共振光纖間的干涉現象，我們可以得到樣品折射率分佈與高度分佈的影像，分別成功辨識樣品錠片中的微量物濃度，和矽透鏡之表面曲率。該實驗結果和理論計算相當吻合，對未來應用於活體影像掃描和遙測危險物具有不錯的潛力。

Since terahertz (THz) wave has different properties from other electromagnetic waves, including direct molecular identification capability and high data-delivered capacity, various THz applications have been rapidly developed in recent years, such as THz imaging and sensing and devices for THz telecommunication. THz antiresonant reflecting hollow-core waveguide (THz-ARRHW) has been demonstrated with extremely low propagation loss and low bending loss and enables broadband transmission, which is suitable for THz imaging, remote sensing, and THz communication applications.

In the thesis, we firstly experimentally demonstrated a 1D mechanically tunable frequency and intensity modulator for broadband THz waves based on antiresonant reflecting waveguidance mechanism, and the device is composed of an integrated cladding and a hollow air core. The integrated cladding contains a pair of PMMA slabs and a pair of aluminum (Al) plates outside that. By mechanically control of the spacing of PMMA slab and Al plate, it enables dynamical tuning of transmission band propagating in the THz-ARRHW and linear attenuation of THz power for a specific THz frequency. The measured maximum tunable frequency range is 60GHz which is 50% of transmitted bandwidth (~116GHz), and the measured maximum power attenuated ratio is 20dB at 176GHz. The transmission band shift phenomenon is only observed in TE polarization, but not for TM polarization. Therefore, the waveguide device is also utilized as a polarization filter with an extinction-ratio of 20dB. The multifunctional integrated waveguide device has advantages of direct THz signal modulation avoiding signals transformations and low insertion loss.

In the second part of this thesis, we successfully demonstrated a fiber-scanning THz endoscope imaging system based on a THz-ARRHW, which is composed of a glass-made beamsplitter, a teflon hollow tube, and a micro-lens attached on the output end of tube. The novel THz endoscope not only has a single scanning tube-fiber avoiding the necessity of fiber coupler for both delivering the input THz signals to the sample and collecting the reflective THz signal from the sample to the Golay Cell detector, but also solves the highly bending loss limitation in the subwavelength fiber-based THz endoscope. The reflective imaging system has advantages including with a focus spot of 1.1mm (near the diffraction-limit), a signal-to-noise-ratio greater than 200, and low bending loss since the maximum detectable reflective THz power remains 2% at bending angle of 90 degree. Based on the interference phenomenon occurs between the scanning tube-fiber and sample, we can map out the refractive-index distributions and surface altitudes of an object, which enables us to identify the minute molecular concentrations in the sample pellet and to obtain the lens curvature. The experimental results are well consistent with the theoretical calculations. The demonstrated hollow-tube scanning THz endoscope is promising for future in-vivo biological imaging and remote sensing of explosives.

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