光學同調斷層掃描 (Optical Coherence Tomography, OCT) 是一種非侵入性、非接觸式的高分辨率成像技術，基於光學干涉理論，從生物組織或非生物組織中接收到背向散射光來產生出干涉訊號，可在不破壞樣品結構的情況下，於短時間內重建出掃描樣品的切面結構影像，其成像深度可達2~3 mm，成像品質可達到10~20 m之解析度，目前廣泛運用於眼科、牙科和心臟外科等醫學方面的研究。
傳統SD-OCT (Spectral Domain - Optical Coherence Tomography) 系統整體結構佔用較大的體積，架構中使用繞射光柵、聚焦透鏡、線性掃描相機 (Line-CCD) 所組成的光譜儀接收OCT干涉訊號。同時此傳統SD-OCT光譜儀均以等波長通道間隔 (Constant λ) 為主，而OCT之傅立葉光學是以波數域 (k-space) 為主，因此造成波長域與波數域之間的非線性關係，使得點擴展函數 (Point Spread Function, PSF) 隨著成像深度的增加而解析度變差，以及靈敏度衰減劇烈等缺點導致深度資訊錯誤，所以在影像資訊上需要透過重新縮放或插值方法進行重新採樣法的訊號處理，使得在波數域中對頻譜進行均勻採樣(constant k)，以呈現出高準確度以及維持高解析度之SD-OCT深度資訊。
本論文藉由絕緣體上覆矽 (Silicon-on-insulator, SOI) 技術作為縮小系統元件體積，設計出等頻率通道間隔 (Constant f) 的階梯光柵 (Echelle Grating) 分波器，由於頻域與波數域之間呈現線性關係，因此不需要透過重新採樣法等訊號處理就可得到高準確度和高解析度的影像品質，經過理論驗證出等頻率通道間隔設計做為分波器可以達成波數域線性採樣頻譜，此頻譜對於OCT系統檢測性能至關重要。論文中以等頻率通道間隔設計的階梯光柵器取代SD-OCT系統中之繞射光柵進行點擴散函數的深度衰減 (Roll-off) 模擬，驗證了等頻率通道間隔 (Constant f) 比等波長通道間隔 (Constant λ) 設計性能最為理想且穩定，其縱向解析度以及靈敏度表現也優於差值法採樣之性能，因此等頻率通道間隔設計可以達到高準確度和高解析度的影像品質。
本論文實驗中，以架設光纖型SD-OCT系統，使用插值方法將干涉訊號進行重新採樣，來探討訊號深度衰減之性能表現。實驗結果為深度1.25 mm的情況下，沒有經過重採樣的情形下，縱向解析度從原本25.76 µm劇烈地增加至79.34 µm，且靈敏度從46.89 dB大幅降低至39.18 dB。經過訊號重新採樣後，18.79 µm的縱向解析度沒有大幅增加，且維持在22.02 µm，其靈敏度由原本47.63 dB些許下降至43.47 dB。實驗上證明了訊號重新採樣之插值方法在深層結構依然可以維持良好的影像品質。
光纖系統為主的SD-OCT量測方面，將分光比10:90矽基馬赫詹德方向耦合器取代光纖耦合器，在光譜儀接收方面使用光學頻譜分析儀 (OSA) 以及線性掃描相機接收同一干涉訊號，實驗結果為兩種光譜儀配置經由訊號處理後的A-SCAN深度資訊皆為一樣，並且比較兩種光譜儀對於縱向解析度以及靈敏度的性能表現。

Optical Coherence Tomography (OCT) is a non-invasive, non-contact, and high-resolution imaging technique using an optical interference theory, which receives backscattered light from biological or non-biological tissues to generate an interferometric signal. The cross-sectional structure of the scanned sample can be constructed within an imaging depth of 2~3 mm and a resolution of 10~20 mm without damaging the sample structure.
The conventional SD-OCT (Spectral Domain - Optical Coherence Tomography) system occupies a large area that uses a spectrometer composed of a diffractive grating, a focusing lens, and a line-scanning camera (Line-CCD) to receive OCT interferometric signals. The conventional SD-OCT spectrometer is based on constant λ channel spacing. In contrast, the Fourier optics of OCT is on k-space, resulting in a non-linear relationship between the wavelength and wavenumber domains, which causes the Point Spread Function (PSF) to decrease in resolution as the imaging depth increases. Therefore, it is necessary to resample the image information by rescaling or interpolating the spectrum sampled with constant k in the wavenumber domain to present the SD-OCT depth information with high accuracy and maintain high resolution.
This thesis uses a silicon-on-insulator (SOI) technology to reduce the size of system components and design an echelle grating spectrometer with equal frequency channel spacing (Constant f). Theoretically, the equal-frequency channel interval design can achieve a linear sampling spectrum in the wavenumber domain, which is essential for the OCT system performance. In this thesis, we replaced the SD-OCT system with an equal-frequency channel interval design with an echelle grating to perform a roll-off simulation of the point spread function. We verified that the equal-frequency channel interval (Constant f) owns the most ideal and stable performance than the equal-wavelength channel interval (Constant λ) design in the longitudinal resolution and sensitivity. Therefore, the equal frequency channel spacing design can achieve high accuracy and high-resolution OCT image quality.
In this thesis, an optical SD-OCT system was set up, and the interferometric signal was resampled by interpolation to investigate the performance of the signal decay in depths. The experimental results show that the longitudinal resolution degrades dramatically from 25.76 µm to 79.34 µm, and the sensitivity decreases significantly from 46.89 dB to 39.18 dB at a depth of 1.25 mm without resampling. After resampling, the longitudinal resolution remains at 22.02 µm, while its sensitivity drops slightly from 47.63 dB to 43.47 dB. The interpolation method of signal resampling experimentally demonstrates good image quality maintenance in deep structures.
The optical coupler was replaced by a 10:90 ratio of silicon-based Mach-Zehnder directional coupler for the optical system-based SD-OCT measurement. The experimental results showed that the A-SCAN depth information after signal processing was the same for both configurations of the optical spectrum analyzer and line CCD in terms of longitudinal resolution and sensitivity.

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