似噪音脈衝產生超連續光譜源應用於時域及頻域光學同調斷層掃描之研究

Supercontinuum Generated by Noise-Like Pulses for Time-Domain and Spectral-Domain Optical Coherence Tomography

林義倫(Lin, Yi Lun)

指導教授 ： 潘犀靈

國立清華大學/理學院/物理學系/碩士(2015年)

摘要

本論文中，我們設計及架設了光學同調斷層掃描(Optical coherence tomography, OCT)系統。光源為利用似噪音脈衝在單模光纖中產生的超連續光譜(Supercontinuum generation, SC)；中心波長約為1300奈米，頻譜半高全寬可達365奈米。我們將此光源應用於自由空間以及光纖式OCT以估計系統之縱向的解析度。在自由空間的時域OCT中，縱向解析度可達2.3微米與理論解析度2.1微米相當。在自由空間的頻域OCT中，其縱向解析度為2.8微米，理論解析度2.7微米。在全光纖式的頻域OCT中，受限於光纖零組件的頻寬，其縱向解析度為6.4微米，理論解析度5.3微米，訊噪比126.7 dB，約較一般文獻中報導者高20 dB。實驗顯示似噪音脈衝超連續光譜源用於OCT，可有效降低光斑(speckle)，其訊噪比為 41.32 dB，contrast-to-noise ratio (CNR) = 2.86 dB以及equivalent number of looks (ENL) = 3.91. 將此光源經適當長度的色散位移光纖(dispersion-shifted fiber)，可經時域拉伸的方式，形成掃頻光源，縱向掃描速率可高於5MHz，以達到快速掃描的OCT。

關鍵字

似噪音脈衝 ； 光學同調斷層掃描 ； 超連續光譜

並列摘要

In this thesis, we designed and studied a broadband light source for time-domain and spectral-domain optical coherence tomography (TD-OCT, SD-OCT). The supercontinuum (SC) was generated by noise-like pulses from an Yb-doped fiber laser in single mode fiber. The central wavelength of the generated SC is 1300 nm and the full width at half maximum can reach 365 nm. The free space and fiber-based OCT were constructed to examine the performance of the new broadband source. For TD-OCT, the experimentally measured point spread function (PSF) indicates an axial resolution of 2.3 μm as compared to a theoretical resolution of 2.1 μm. For free space SD-OCT, the experimentally measured PSF indicates an axial resolution of 2.8 μm as compared to a theoretical resolution of 2.7 μm. For fiber-based SD-OCT, due to the limited optical bandwidth of fiber components of the OCT system, the experimentally measured PSF indicates an axial resolution of 6.4 μm as compared to a theoretical resolution of 5.3 μm and the signal-to-noise ratio can reach 126.7 dB. Using the noise-like SC light source, speckle in the OCT images can be reduced significantly. In the regions of interest, the speckle signal-to-noise ratio (SNR) = 41.32 dB, contrast-to-noise ratio (CNR) = 2.86 dB and equivalent number of looks (ENL) = 3.91.
In order to achieve real-time OCT, time-stretching technique was applied to generate the swept light source. Making use of dispersion-shifted fiber, we generated the scanning rate higher than 5 MHz from our noise-like SC light source.

並列關鍵字

Noise-like pulse ； optical coherence tomography ； supercontinuum generation

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