光學同調斷層掃描(Optical coherence tomography, OCT)，是一種非侵入式及時成像的一種技術，OCT透過麥克森干涉儀技術，利用參考端的反射光與樣品端的背向散射光進行干涉獲得微米等級解析度的影像。目前常見的OCT為自由光學的系統，體積非常龐大，並且頻域OCT(Spectral domain Optical coherence tomography, SD-OCT)系統的架設更是極為困難，所以本論文將藉由絕緣體上覆矽(Silicon-on-insulator, SOI)技術，探討光學元件積體化SD-OCT的應用。
在OCT系統中非常重要的元件為耦合器，耦合器的功能為將光源分成不同比例的光入射至樣品端與參考端，耦合器必須要是對於波長不敏感的並且近似於寬頻光源，然而在矽光子領域中被大家廣泛利用的馬赫詹德方向耦合器(Mach-Zehnder Directional Coupler, MZDC) 其最大平坦度約為 40-nm 波長範圍，MZDC的波長平坦度僅建立在單方向光傳輸的時候，由於晶片型OCT的MZDC必須同時擔任輸出端與接收參考端和樣品端的反射光，若雙向傳輸MZDC為非平坦的訊號會造成OCT影像的訊號雜訊比(Signal Noise Ratio, SNR)較差，我們發現MZDC的雙向訊號可以與陣列波導光柵的功率頻譜進行補償，在有製程誤差的情況下其SNR也會比使用DC的雙向傳輸來的更好，並且其雜訊會與單向傳輸的MZDC相差無幾。
在晶片化SD-OCT系統中，分波多工器(Wavelength Division Multiplexer, WDM)是非常重要的，在自由光學系統中SD-OCT的光柵為閃耀光柵(Blaze grating)，分波為線性且間距非常的小，所以我們決定使用陣列波導光柵(Array waveguide grating, AWG)作為WDM，若AWG要取代閃耀光柵，頻寬必須與光源接近並且通道數要達成一定的數量才能使影像的縱向解析度較高，但越大的頻寬與越多的通道數是非常難以設計的，並且由於SOI的設計其發散角的數值孔徑(Numerical aperture, NA)相當大，無法耦合至性掃描感光耦合元件(Line Charge-coupled Device, Line CCD)，所以將採用多個AWG的組合並結合光偵測器(Photodetector, PD)來取代閃耀光柵加Line CCD。
本論文將會探討AWG的設計對於SD-OCT解析度的影響，並量測AWG+PD晶片化之結果，以及雙向輸出MZDC的波長響應平坦度對於OCT影響與使用DC補償後的效果。

Optical coherence tomography (OCT) is a non-invasive, real-time imaging technique that uses the interferometer technique to obtain micron-level resolution images by interfering reflected light from the reference side with backscattered light from the sample side. Currently, OCT is a free optical system, which is very large and extremely difficult to set up for spectral-domain optical coherence tomography (SD-OCT). In this paper, the application of SD-OCT for the integration of optical components is explored utilizing silicon-on-insulator (SOI) technology.
An essential component in an OCT system is the coupler, which divides the light source into different proportions of light incident on the sample and reference ends. However, the Mach-Zehnder directional coupler (MZDC), widely used in silicon photonics, has a maximum flatness of about a 40-nm wavelength range. The wavelength flatness of the MZDC is only established in the unidirectional direction. Since the MZDC of a chip-based OCT must act as the reflected light at both the output and receive reference and sample end, a non-flat signal in the bidirectional MZDC will result in a poor signal noise ratio (SNR) of the OCT image. We found that the bi-directional signal of MZDC can compensate with the power spectrum of the array waveguide grids, and its SNR is better than the bi-directional transmission using DC in the presence of process error. Its noise is comparable to that of the directional transmission of MZDC.
Wavelength division multiplexer (WDM) is very important in a chip-based SD-OCT system. In a free optical system, the grating of an SD-OCT is a blazed bulk grating, and the wavelength division is linear. Suppose the arrayed waveguide grating (AWG) replaces the bulk grating. The bandwidth must be close to the light source, and a certain number of channels must be achieved to achieve a higher vertical resolution of the image. Still, larger bandwidth and more channel counts are very difficult to design and implement. Also, the numerical aperture (NA) of the SOI design is too large to be coupled to a Line Charge-coupled Device (Line CCD). Moreover, a combination of multiple AWGs and a photodetector (PD) will be integrated instead of a line Charge-coupled Device and blazed bulk grating.
This thesis will examine the AWG effect on SD-OCT resolution and characterize the results of AWG integrated with PD. The impact of wavelength response flatness of bidirectional MZDC on OCT and the impact of using DC compensation will also be further discussed.

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